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Relation of freshwater plankton productivity to species composition during induced successions Dickman, Michael David 1968

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THE RELATION OF FRESHWATER PLANKTON PRODUCTIVITY TO SPECIES COMPOSITION DURING INDUCED SUCCESSIONS by MICHAEL DAVID DICKMAN B.A., University of California, 1962 M.A., University of Oregon, 1965 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Zoology We accept this thesis as conforming to the requ i red standard THE UNIVERSITY OF BRITISH August 1968 COLUMBIA In presenting this thesis in partial fulfilment of the requirements for an.advanced degree at the University of British Columbia, I agree that the Library, shall make it freely, available for. reference and Study;. I further a g r e e that permission for extensive copying of this thesis for.scholarly purposes may be granted by the Head of my Department or by h.i's representatives. It is understood that copying or pub 1icat ion of this thesis for financial gain shal1 not be a I lowed without my written permission. The Univers , bia Vancouver 8, Canada Department I I ABSTRACT, The species composition, primary productivity and relative abundance of the plankton organisms in Marion Lake, British Columbia were recorded at biweekly intervals for two months following artificial enrichment with nitrate or phosphate or both, of six large wooden enclosures within the lake in four seasons during the year. Enrichment resulted initially in a decrease in diversity and an increase in the productivity of the phytop 1ankton and standing crop of the entire plankton community. These events were col 1ectively termed a "regressive succession" because their "direction" of change was the reverse of that normally encountered in primary and secondary successions. The regressive succession terminated following algal bloom formation, and diversity began to increase slowly while the primary productivity and standing crop of the plankton dropped. This was indicative of the beginning of a secondary succession in which one group of dominant species was replaced by another and then others in turn replaced these. This successional pattern occurred regardless of season, prevailing physical, chemical, or climatological factors. Thus, such a pattern appeared to be a very general one and was disrupted only by the physical removal of the majority of the plankton!c species from the lake resulting from persistent and heavy rains which "flushed" the lake. A statistical analysis of each of the 167 euplankton species observed in the lake was performed using the data from each of the four enrichment series to determine which species responded significantly to artificial enrichment. The individual response patterns were nearly as diverse as the species themselves, however, one of the most common responses was made by very rare species which "bloomed" two to three weeks after nutrient addition. Few primary producers responded to more than one type of nutrient enrichment in any one season which emphasized the importance of Li eb i g 1 s Law of the Minimum. The higher trophic levels, on the other hand, responded more to the increase in standing crop in the different enclosures than to any one particular type of nutrient enrichment. n The Shannon-Weaver formula, H =-f. P. log P., was modified by ! 1 1 changing the definition of P j , that is, the individuals in the ith species divided by the total number in the sample. ' This index was insensitive to changes in the relative abundance of the planktonic species from the higher trophic levels. P. was redefined so that it was less sensitive to number and more sensitive to both relative biomass and relative productivity. This new index of diversity (H ) did not act selectively on the different trophic levels represented in the plankton samples. An understanding of the principles governing community organization and biotic succession should be based on the life history of the individual species comprising the community and not on assumptions about supposed trophic changes. This study indicated that pertinent information about the changes in the structure of a planktonic community could be gained from an analysis of the changes in the relative abundance of each of the species without artificially isolating and culturing these species and without lumping all the organisms into vague trophic categor i es. i V TABLE OF CONTENTS PAGE Abstract ii List of Tables . . vi List of Figures vii Acknowledgements * vi i i 1 ntroduct i on 1 Methods . .... ............ . 5 Experimental Enclosures 5 Enrichment 8 Sampling Procedure 8 Sample Sedimentation 11 Plankton Enumeration .. 13 Taxonomic Identification ............. i \k Bacteria '5 Colorless Plankton 15 Phytopl ankton 15 Zooplankton 16 Counti ng Accuracy .. 16 Re 1 i ab i 1 i ty Code 17 Repeatability 18 Physical Factors 28 Temperature 28 Wind, Light and Precipitation 28 Inlet Discharge 29 Nutrient Analysis ' 32 Primary Productivity 35 Standing Crop 36 V PAGE .' Data Analysis .. . ^ 7 Estimating Cell Volumes and Turnover Rates ........ 38 Results .. .. v-.V.-. • ' 1 + 5 Nutrients ................. ^5 Physical Factors ................. .. .. kG Light 4 6 Wind and Temperature ........... 48 Precipi tation ...................•••'••••••••••••• • .^9 Primary Productivity 53 Standing Crop . 63 Species Composition 63 Changes in Species' Abundance Following Enrichment 65 Species' Enrichment Responses 68 Changes in Relative Abundance of Fungi Following Enrichment ..... • 7© Changes in Relative Abundance of Bacteria Following Enrichment 77 Changes in Relative Abundance of Some Secondary Producers Following Enrichment 77 Diversity Indices 78 D i s ou s s i on . V...... 96 Some Effects of Artificial Enrichment 96 A Model for Plankton Succession 98 Regressive Succession 99 The Role of the Rare Species ..... 1 0 3 Diversity and Primary Productivity 105 Summa ry 108 Literature Cited 1 1 0 mmmmcccxcvii LIST OF TABLES TABLE PAGE I .' Ion- concentrations. 1 n Marion Lake 9 II. Nutrient enrichment concentrations ................... 10 III. Planktonic species of Marion Lake 19 IV. Plankton densities, volumes and relative, turnover , rates kO V.. Primary productivity: three-way analysis of variance in a randomized complete block design VI. Species specific responses to nutrient enrichment .... 69 VI I . Diversity based on relative abundance ... 83 V I I I. Diversity based on relative biomass 85 IX. Diversity based on relative productivity ............. 91 X. Summary of events which occur following nutrient addition 100 LIRE 1 2 3 4, 5 6 7 8 9 10 12 13 14 15 16 17 vii LIST OF FIGURES PAGE Contour map of Marion Lake 6 Photograph of wooden enrichment enclosures 7 Annual pattern of inlet discharge 31 Changes in total dissolved nitrate and phosphate fol1owing nutrient enrichment 34 Annual pattern of daily light intensities ....... .... h~! Annual p a t t e r n of daily temperature maxima and minima near Marion Lake during 1966 and 1967 ............ 50 Primary productivity arid inlet discharge rates .......... 51 Changes in primary productivity following enrichment during the fall and winter series 57 Changes in primary productivity following enrichment during spring ..... 59 Changes in primary productivity following enrichment in the summer series.......................... 60 The annual pattern of primary productivity at Station "A" in Marion Lake ............ 62. Changes in the number of species during succession ...... 67, Significant response patterns to enrichment during the fall enrichment series lb Diversity calculated on the basis of relative abundance (H) in the summer series 82 Diversity calculated on the basis of relative biomass (H.) in the summer series 89 b Diversity calculated on the basis of relative productivity (H^) in the summer series 95 Schematic representation of the changes in plankton standing crop, enriched nutrient concentration and diversity 97 ACKNOWLEDGEMENTS It is a pleasure to express my gratitude to my thesis ad-viser Dr. Ian Efford, Department of Zoology, for allowing me the freedom to learn from my own mistakes whi1e providing the necessary dialogue so that I might profit by them. I wish to thank Dr. P. Larkin for his advice and aid con-cerning statistical treatment of the data as well as A . Fowler, S. Boyer and S. Borden for their assistance in providing suita-ble computer programs for the analysis of the data. My wife, Daryl, gave me the impetus and help necessary to assure the completion of the microscopic enumeration of the plank-ton and the typing of the thesis. C. Behrish and G. Davies pro-vided valuable assistance in the collection of the field data as did K. Tsumura and J. Mathias who also greatly aided in the construction of the experimental enclosures. I am extremely grateful to A . Cattell for his help in con-ducting the nutrient analyses and to Drs. J. Stein and F.J.R. Taylor as well as D. Blinn for their kind assistance in the tax-onomic identification of the phytop1ankton. 1 INTRODUCTION As one stage follows another during the course of a biotic succession there are differences in species composi-tion and productivity of each sere. This sequence of changes follows a particular pattern, the very predictability of which is an indication of the organization which exists within the community. The degree of organization determines the accuracy and generality of the pattern (Hairston, 1959). An understanding of the successional process is essential to an understanding of the organizing factors operating within a com-munity because "communities are not in being; they are the expres-sion of a perpetual stream of matter and energy which passes through the community and which at the same time constitutes it" (Bertalanffy, 1950). The concept of succession concerns the direction of change occurring in time within a community. Do communities tend to de-velop a steady state or homeostatic condition given sufficient time and does a relationship exist between the maturity of a com-munity and its biotic diversity and productivity? These and simi 1ar questions regarding community structure and its relationship to successional maturity might be answered by direct quantitative measures of the changes in primary productivity and species compo-sition which occur during a biotic succession. The f reshwater plankton community was chosen for this study for three major reasons: (1) Successions can be induced arti-ficial ly at any time of the year and the ensuing changes are re-latively rapid, making it an ideal system for experimental manipu-lation; (2) The freshwater plankton community of a small lake is easily sampled; and (3) The planktonic community is relatively independent of other communities for its major sources of energy. The euplank ton constitutes the permanent plankton community of lakes and ponds (Hutch inson, I967, p . 236). Such a community is not just a collection of species but an interacting system in which the fauna and flora are interdependent in many ways. For this reason it is not ,possible to artificially isolate one group from another or from the community as a whole. Results from ex-periments which isolate one species from the rest are often inap-plicable to the natural environment. For this reason changes in abundance of every taxa comprising the p1ankton community. of Marion Lake, regardless of size or taxonomic affiliation, were recorded following artificial enrichment. It was possible to induce plankton successions by adding nitrate or phosphate to large (6000 liters) wooden enclosures. Furthermore, these successions could be induced at any time of year so that it could be determined whether a basic successional pattern existed independently of seasonal' changes or whether it was simply a function of seasonal variation in temperature, light and nutrient concentrations in the water. The concept of biotic succession was first developed by 3 Warming (I896) and Cowles (1899) according to Kershaw (196*0. Early studies of planktonic successions were largely descrip-tive. There were, however, a few early workers concerned with the general nature of the successional pattern who avoided a purely descriptive approach. Allee (1912) investigated the fundamental nature of the successional pattern in several small ponds. The relationship between the physico-chemical environ-ment and its effects on the biota was studied by Kofoid (1903) and Birge and Juday (1922). By the early 1940's a sizable body of information concerning the relationship between phytopiankton periodicity and physico-chemical changes had been published. Hutchinson (1944).noted some of the contradictions and dubious assumptions which had been proposed regarding these "supposed" relationships. Seasonal changes with their accompanying climatological effects were investigated in terms of their role in determining the seasonal pattern of abundance for various algal species by Fritsch and Rich (1913), Eddy (1934), Braarud (1961) and many others. Lucas (1947) was one of the first to stress the impor-tance of water quality (conditioning) and its possible conse-quences to the successional pattern. This concept has been ac-tively investigated by Fogg (1953), Rice (1954), Johnston (1955), Proctor (1957) and Tailing (1962). The relationship between water quality and its suspected effects on particular species, however, is often extremely difficult to demonstrate. Conse-quently, contradictory observations exist as discussed by Raymont (1963). The relationship between productivity and successiori-aT maturity has been investigated by Rodhe (1-9^8) , Klotter (1953), Odum (1956b) Teal (1957) and Fournier (1966). Margalef (1962 and 1967) inves-tigated a great many aspects related to plankton succession in-cluding changes in the pigment structure (1963c) of the popula-tion and the evolutionary consequences of succession (1963a). .His paper on "Certain unifying principles in ecology" (1963b) in^ eludes a careful summary of all the major aspects associated with plankton successions in the sea. Lund (1954), Pat ten (1963) and Hutchi nson (1967) have also reviewed a great number of facets related to this topic. Many other workers- have contributed sub-stantially to the body of knowledge concerning plankton successions. I have only attempted to mention a few of these studies to give an idea of the scope which this field encompasses. Hutchinson (1967, p . 399) states that "the main hypotheses concerning seasonal succession were advanced over 50 years ago. It is therefore perhaps a, 1ittle disconcerting to find that there is still a good deal of doubt about the interpretation of the seasonal changes observed in a particular lake or exhibited by a particular species." The purpose of this study was to inves-tigate the fundamental successional pattern with special atten-tion to changes in primary productivity and species composition in order to determine whether a predictab1e re 1 ationship existed between these two factors during the course of a plankton succession 5 METHODS EXPERIMENTAL ENCLOSURES. To test the effects of nitrate and phosphate addition on plankton productivity and species composition whi1e simulating natural lake conditions I. enclosed several areas in the lake without alteration . to the lake as a whole. Eight areas in the lake were enclosed in 1965 using plywood sheets measuring 3 .05 m on a side and 1.84 m high. The base of the enclosures extended 0.60 m into the lake sediment leaving ] .2k ro exposed above the mud. The mean depth of the water at X and Y (Fig. 1) was 1.0 m. Thus 0.23 m of the enclosure was left exposed above the surface of the lake. Each of the eight enclosures held approximately 6,000 liters when the lake was at its mean height (Fig. 2). During winter the lake level rose above the tops of the enclosures so frequently that they were abandoned and six 100 liter plastic tubs were filled with lake water and 2 cm of lake sediment and placed near the lake's edge. With the exception of the winter series, two blocks of four enclosures each were placed in the lake at X and Y (Fig. 1). This resulted in a mutually orthogonal design as each block of four enclosures contained all the treatments and a control. Prior to chemical enrichment .the enclosures were flushed with lake water using a centrifugal pump. This helped to ensure that conditions in all cages at the start of any enrichment series were as similar as poss i b1e. PREVAILING W I N D S P R I N G O U T L E T INLET Figure 1. A contour map of'. Mai: ion Lake, Br i t i sh Col umb i a wi th i nse ts i nd i cati ng the location of the eight wooden e n d o s u r e s to which nutrients were added to induce plankton successions. n ! FIGURE 2 The four wooden enrichment enclosures at Station "X" in Marion Lake. 8 ENRICHMENT. Hutchinson (1967, p.310) states that "It is commonly be 1ieved that the quantity of phytoplankton that can develop in any water is more likely to be determined by the concentration of combined nitrogen and of phosphorus than by any other factor." Since water analysis showed that these two nutrients were in very low concentrations in Marion Lake (Table I) they were chosen as the two enrichment nutrients most likely to stimulate primary productivity and bloom formation in the plankton. Calcium salts of nitrate and phosphate were chosen because calcium was the most abundant cation in the lake and therefore the least likely to introduce changes in itself. The low temperatures in winter resulted in relatively low solubility of CaHPO^. This resulted in a lower value for dissolved reactive phosphate at the start of the winter series (Fig. 4). The enclosures were enriched only once at the beginning of each series. The enrichment concentrations which were used (Table II) were similar to those used by Fournier (1966) and approximately half the concentration recommended by Chu (19^2) in his Medium # 1 0 . T w o t y p e s of controls were provided: external controls which were located at A and E (Fig. 1) and internal controls consisting of two unenriched enclosures. SAMPLING PROCEDURE. Two liter plankton samples were taken at a depth of one half meter from all enclosures and from lake sites A and E in a Winchester 9 TABLE I. Dissolved ion concentrations in water taken from Marj_on Lake over a four year period. The five water samples were taken from Station "A" at 1/2 meter. All values are given as mg/liter (ppm). Values designated by an asterisk were below the minimal detectable level of the General Testing Laboratories Ltd. (326 Howe St., Vancouver, B.C.). INORGANIC ION 12/3/63 5/11/64 10/30/64 7/10/65 3/14/6 s i o 2 0.2 3.5 1 .3 7.1 1 .3 F e 2 0 3 0.3 0.2 0.2 0.2 < 0 . 1 * Mg <0.1 * 0.1 < 0 . 1 * 0.3 0.3 ' P0k <0.1* 0.15 < 0 . 0 5 * < 0.05* 0.02 NO3 0.5 0.1 < 0.1* 0.4 < 0 . 1 * S°3 CI 0.4 0.7 1.7 0.8 < 0.1* 1 .5 2.1 1 .8 1.6 : < 0.5* H 2 C 0 3 3.0 0.5 0.3 0.3 < 0.1* C0 3 Ni 1 Nil Ni 1 Ni 1 Ni 1 K 2 0 <0.4* < 0.3 < 0.5* < 0.5* <o.5* Na 20 3.0 0.7 < 0 . 5 * C 0 .5* ^ 0.5* CaO 2.1 2.6 11.9 7.0 2.7 10 TABLE 11. INITIAL ENRICHMENT CONCENTRATIONS FOLLOWING NUTRIENT ADDITION TO THE ENCLOSURES IN EACH SEASON. ENCLOSURE LOCATION ENCLOSURE VOLUME Fall Series, 1966 4 g. 4 1 3 & 3' 1 & 1 1 2 & 2' A & E Winter Series, 1966-1967 Carboy E Carboys B & D Carboy A Carboys C & F A & E Spring Series, 1967 100 1i ters 1 & 1 1 2 & 2' " 3 & 3' " 4 & 4' A & E Summer Series, 1967 1 & 1 1 6000 1i ters 3 & 3' " 2 & 2' " 4 s 4' A & E CHEMICAL ENRICHMENT TYPE 5900 liters CaHPO Ca(N0 ) 2 Ca(N0_) & CaHPO, 3 2 k Unenriched Control External Control CaHPO 4 Ca(N03)2 •Ca-(N0 ) 2 & CaHPO^ Unenriched Control External Control 7000 liters CaHPO^ Ca(N03)2 Ca(N0 3) 2 & CaHPO^ Unenriched Control External Control CaHPO, Ca(N03)2 Ca(NO ) 2 & CaHPO^ Unenriched Control External Control CONCENTRATION (mg-at/1iter) 0.93 2. 04 2.0k & 0.93 0.0035 & 0.00042 1 0.91 2.00 2.00 & 0.91 0.0027 & 0.00041 1 0.91 2.00 2.00 &.0.9-1 0.0029 & 0.00039 0.90 2.00 2.00 & 0.90 0.0048 & 0.00051 1 1 NO, and PO, respectively, as measured by the method of Strickland and Parsons ( i 9 6 0 ) . bottle three times a week. Each sample was assigned a date-location code number. This number remained with the sample during sedimentation and enumeration. Not until all the samples in any one enrichment series had been enumerated was the sample decoded. This technique was used to ensure against unconscious bias during counting. To determine the selectivity of the Winchester sampler in collecting zooplankton, my samples were compared with those of D. McQueen who used a commercial pump sampler having a discharge rate of 30 liters per minute. One important difference between our two sampling methods was that large diaptomid copepods were more abundant in the pump samples. On the assumption that this resulted from an active avoidance of the Winchester sampler by the diaptomid species a correction factor, f3 = 1.27, was used to adjust the densities of these species collected in the Winchester samples.' SAMPLE SEDIMENTATION. Following the immediate addition of 10 ml of Lugol's I K.I preservative (Ruttner 1953, p.110) the plankton in the samples was sedimented. The Winchester bottles were left undisturbed for three days to allow an adequate sedimentation time for the minute forms (Utermohl, 1931). By carefully introducing a "U" shaped siphon it was possible to remove all but the bottom 1 The quantity of soft bodied rotifers (i.e. Conochi1 us sp.) found in the Winchester samples was significantly higher than the pump sample collection (1000/1 iter vs. 100/-liter). This was probably due to the loss of the smaller soft bodied forms through the diameter pores of the net which was used to concentrate the pump samples. fifth of the water in the sample. The remaining.water,-containing the plankton, was then resedimented. This procedure was repeated until all the plankton from the original 2 liter sample was concentrated into 10 ml. As a result of the repeated sedimentation and siphoning each sample had its plankton content concentrated to about 1/200th of the original sample volume. Due to the disruption of the sedimented material by the introduction of the siphon, the siphonate was examined periodically to determine a correction factor for phytop 1ankton loss during the concentration procedure (OC = 1.098 + 0.045). Thus, if one tenth of the total sedimented volume was found in the siphonate following its resedimentation, OC would equal 1.11. It was also necessary to compare the size distribution of cells in the initial sample and those from the resedimented siphonate. If the two were different it would have been likely that inadequate sedimentation time resulted in the smaller organisms e.g. bacteria, remaining in the siphonate. This did not occur as indicated by a comparison of the size frequency distribution of identical samples which had been allowed to stand for different lengths of time (up to 2 weeks). The presence of organisms in the siphonate appears to result from the disruption of the sedimented material around the glass "U" shaped siphon following its introduction. Because the amount of material lost by this method was relatively constant (1.098 - 0.045) the method proved satisfactory as long as the correction factor o C was used. 13 PLANKTON ENUMERATION: The phytoplankton were enumerated by counting all the organisms in ninety randomly selected microscopic fields, thirty under oil .' immersion (1500X), thirty under high dry (600X) and thirty under medium power (15OX). The smallest organisms were counted under the highest powers and the lower powerers were used for the larger forms. By calculating the ratio of the area counted to the total area of the slide it was possible to estimate the total number of organisms of each species per slide. The actual number per liter was then ^ times the density calculated for that species from the slide ratio times the sample concentration factor (5.0). During enumeration, cells lacking most or all of their protop1 asm were considered to be dead and were not counted. When colonial forms were encountered it was often difficu1t to determine a mean density of cells per colony due to the variability in size and shape of these colonies. Consequently, all the individual cells in the portion of the colony lying within the microscopic field were recorded as separate i nd i v i duals. The zooplankton were counted prior to making the permanent mount. The 16 ml vial containing the 10 ml concentrate from the 2 liter sample was placed under an inverted microscope. By scanning the entire base of the vial all the zooplankton were tallied. The only exception occurred when the phytoplankton was so dense that it prevented the recognition of the zooplankton. In these relatively rare instances the entire contents of the vial was poured into a Sedgewick Rafter counting chamber and the zooplankton counted. Because all the zooplankton concentrated from a 2 liter sample were counted, zooplankton density per liter was one half the number counted. The diaptomid densities were adjusted by multiplying them by the correction factor P as discussed. TAXONOMIC IDENTIFICATION: The problems of becoming competent in the identification of the diverse groups represented in even the smallest community are substantial. These problems are many times more difficult in a large community such as the plankton of an oligotrophic . 1ake be-cause of the large number of species which occur, there,. Over three hundred species from groups as diverse as bacteria and crustacea were present in Marion Lake. Three approaches to the taxonomic problem provided by every synecological study are avai l abl e (Fager , 1963, p . ^17). (1) An arbitrary decision about the types or sizes of species to be examined can be made; this is what the exponents of the study of single species do in an extreme way. (.2) The functions of the organisms in the community can be guessed at and then general energy flow diagrams made.. Unfortunately, each species is usually quite unique and 1umping greatly oversimp1ifies the real system. (3) Each distinct taxon can be identified using num-bers or letters for What appear to be separate species. The dif-ficulty with such an approach lies in an experimenter's inability to communicate his findings about these taxa to others who may be referring to the same taxa with an entirely different set of num-bers or letters. A fourth alternative was adopted in this study: the identification of every taxa encountered with the aid of pub-lished "keys" and the assistance of various specialists in learning the names of the species in each major group. (a) Bacteria. Non-flagellated bacillus or coccoid bacteria can rarely be identified without special staining and culturing techniques. In this study bacteria were distinguished using such obvious criteria as colonial versus solitary and coccoid versus rod-shaped charac-teristics. This method based on gross morphology is discussed by Van Niel and Stanier in Edmondson (1959). Only when flagel1ated forms such as Pseudomonas were observed was it possible to be more precise. (b) Colorless plankton. The aquatic fungi were identified using F.K. Sparrow's key in Edmondson (1959). Fortunately a high degree of host specificity was found to exist in the case of the Phyoomycetes. This greatly assisted in the enumeration and identification of these forms. The colorless flagel1ates and other mastigophora were identified from Skuja (1948) and J.B. Lackey in Edmondson (1959). The Rhiqo-podea were rarely eup1anktonic, most appearing to be transients from the sphagnum. G. Def1andre was used since his key in Edmond-son (1959) has been widely accepted. Dr. D. Francis provided many helpful suggestions in the identification of the Ciliophora. Both Kudo (1954) and L.E. Noland in Edmondson (1959) were used as wel1. (c) Phytop 1ankton. The nomenclature of blue-greens is still in a transitional stage following Drouet and Dai ley's (1956) revision of the coccoid Cyanophyta. Consequently, the names of blue-green algae which have been combined or changed by Drouet and Daily are given in brackets following the older name i.e. Me r i smoped i um (Agmenellum) . Identification was aided by using Huber-Pestalozzi (1938), G.M. Smith ( I 9 5 0 ) and Prescott (1951). The other pigmented phytoplankton taxa were identified using West and West (1904-1912), Huber-Pestalozzi (1941, 1942, 1950, 1955, 1961)/ Patrick and Reimer (1966) and others already mentioned. The assistance from Dr. J. Stein, Mr. D. Blinn and Dr. F.J.R. Taylor in identifying many of the various types of algae in this diverse group gave more reliability to the taxonomic identifications. (d) Zooplankton. Identification was greatly simplified by the work of G. San-dercock and D . McQueen who had previously identified the zooplank-ton in Marion Lake. COUNTING ACCURACY: Vel'Dre (1963) states that at least 1215 specimens of each species or taxa must be tallied in order to obtain estimates de-viating not more than + 5% of the actual value. Because the rela-tive abundance of the different species in a plankton sample varies considerably it was noft possible to count 1215 organisms of the rarer species. For the purposes of this study the criteria of Lund, et. al . (1958) was adopted regarding the rarer species in the sample: "A method which can estimate abundance to an accuracy of + 50% is quite adequate (with respect to the rarer species) and any time spent in making more accurate estimates is largely wasted". As a particular species became more abundant in the water column more of its organisms would be encountered in the samples. Hence the more abundant a particular species became the better the estimates of its abundance. Species occurring at a density below five per liter were too rare to estimate accurately within the confidence range suggested by Lund, e,t. al . (1958) and therefore were not included until they became more abundant than this value. RELIABILITY CODE: Any index of diversity or species composition is biased by the use of conglomerate groups (i.e. taxa termed "unknown") for the simple reason that the larger such a group becomes the lower the apparent diversity becomes. To prevent this from occurring I attempted to identify all taxa regardless of their rarity or phylo genetic position (Table III). This resulted in the following hierarchy: taxa which could not be identified were given the suffix "like" and the genus which they appeared to most resemble was used as the prefix. When I was more certain of the genera but uncertain of the species just the genus is given. The genera followed by "sp." was used for taxa in which I was uncertain of the correct species name. Finally, the genus and species name was used when I was relatively confident of having correctly iden-tified the organism. REPEATABILITY: Once the species list had been made it was necessary to ensure that each taxon would always be called by the same name. This was more important in this study than whether that taxon's name ulti-mately proved correct. To ensure that a high degree of consistency would be met it became necessary to photograph of" draw each new taxon and to include a series of pictures depicting the variability which that form exhibited. This proved an extremely difficult task in the case of the non-thecate, nanno- and microplanktonic forms because of their few identifying characteristics and great variability in size and shape. However, the use of phase contrast microscopy for photography and enumeration greatly assisted the maintenance of the desired level of consistency needed for a meaning-ful comparison of diversity changes in time. A copy of all the photographs is deposited in the file of the Marion Lake Project at the University of British Columbia. T A B L E III A L I S T O F T H E T A X A O B S E R V E D I N T H E P L A N K T O N O F M A R I O N L A K E D U R I N G 1 9 6 5 - 6 7 E u P L A N K T G N S P E C I E S A R E L I S T E D W I T H O U T A N A S T E R I S K . - O N E A S T E R I S K ' D E N O T E S A S P E C I E S A S S O C I A T E D W I T H T H E P E R I P H Y T O N C O M M U N I T Y , * * = O N E A S S O C I A T E D W I T H T H E E P I L I T H I C C O M M U N I T Y , * * * = A N E N D O - O R E P I P H Y T I C S P E C I E S . * * * * A S P E C I E S A S S O C I A T E D W I T H T H E E P I P E L I C C O M M U N I T Y A N D * * * * * I N D I C A T E S A S P E C I E S W H I C H I S M E T A L I M N E T I C < O N E W H I C H S P E N D S C O N S I D E R A B L E T I M E IN T H E P L A N K T O N . C O M M U N I T Y B U T I S I N C A P A B L E O F R E M A I N I N G T H E R E P E R M A N E N T L Y ) . M Y C O P H Y T A A N C Y L I S T E S * * * F U N G A L S P O R E O R M Y C E L I A * * * R H I Z O P H Y D I U M * * * R H U O P H L Y C T I S * * * C L A D O C H Y T R I U M * * * C H Y T R I O M Y C E S * * * S C H I Z O P H Y T A : M A C R O M O N A S M t C R O C O C C U S - L I K E B E G G I A T O A . * V I B R I O E N C A P S U L A T E D B A C T E R I U M E P I P H Y T I C M I C R O C O C C U S * * * T H I O T H R I X - L I K E * * * . P S E U D O M O N A S ... :... .. T H I O C Y S T I S — L I K E * . R H A B D O C H R O M A T I U M B A C T E R I U M * * * C H L O R O B I U M S P I R O C H A E T A M I C R O C H L O R I S - L I K E * * * * C Y A N O P H Y T A A N A B A E N A S P A N A B A E N A S P . B * P S E U D O A N A B A E N A C H R O O C O C C U S S P . S Y N E C H O C Y S T I S A P H A N O C A P S A S P . ( A N A C Y S T I S . D R O U E T ) M I C R O C Y S T I S ( A N A C Y S T I S , D R 0 U E T ) S Y N E C H O C O C C U S E U C A P S I S — L I K E D A C T Y L O C C O P S I S - L I K E R H A b U O D E R M A ( C O C C O C H L O R I S » S P R E N G E L ) M E R I S M O P E D I U M T E N U I S S I M A < A G M E N E L L U M > D R O U E T ) M E R I S M O P E D I UM P U N C T A T A ( A G M E N E L L U M , D R O U E T ) C O E L O S P H A E R I U M ( G O M P H O S P H A E R I A » D R Q U E T ) G O M P H O S P H A E R I A S P I R U L I N A S P . * ' O S C I L L A T O R I A B O R N E T T I-1 Z u K A L . * O S C I L L A T O R I A L A C U S T R I S ( K L E B ) G E I T L E R N O S T O C S P . * A P H A N I Z O M E N O N F L O S - A Q U A E -•' ( L • ) R A L F S . * C Y L I N D R O S P E R M U M * S T I G O N E M A S P . * G L O E O T R I C H I A S P . * C H L O R O P H Y T A P E D I N O M O N A S - L I K E C H L A M Y D O M O N A S S P . S M A L L C H L A M Y D O M O N A S . S P . ; L A R G E ; _ ;,. . ' . ; C H L O R O G O N I U M E L O N G A T U M D A N G . * G L O E O M O N A S O V A L I S K L E B S . G O N I U M S P . S P H A E R O C Y S T I S G L O E O C Y S T I S G I G A S ( K U T Z ) L A G E R H . N A N N O C H L . O R I S . E L A K A T O T H R I X — L I K E C H L O R O S A R C I N I A - L I K E ' U L O T H R I X : Z O N A T A ( W E 8 E R + M O H R ) K U T Z . * S T I C H O C O C C U S S P . * M I C R O S P O R A * * A P H A N O C H A E T A E S P . * C H A E T O S P H A E R I D I U M S P . * L Y N G b Y A * . \ ' O E D O G O N I U M * B U L 6 0 C H A E T A E S P . * C L A D O P H O R A L I K E * S C H R O D E R I A S P . S E T A C i U M S P . P E D I A S T R U M T E T R A S ( E H R . ) R A L F S . P E D I A S T R U M O B T U S u M L U C K S P E D I A S T R U M 5 P . S O R A S T R U M S P . C O E L A S T R U M S P . C H L A M Y D O M O N A S ( P A L M E L L O I D S T A G E ) * C H L O R O C Q C C U M * O O C Y S T I S P A R V A W E S T + W E S T O O C Y S T I S S O L I T A R I A W I T T R O C K -N E P H R O C Y T I U M N E P H R O C Y T I U M L I M N E T I C U M W E S T + W E S T A N K I S T R Q D E S M U S F A L C A T U S ( C O R D A ) R A L F S . A N K I S T R Q D E S M U S S P I R A L I S ( T U R N E R ) L E M M . A N K I S T R O D E S M U S B R A U N I I ( N A ' E G ) B R U N N T H A L E R C L O S T E R I O P S I S * * * * Q U A D R I G U L A . T E T R A E D R O N S P . S C E N E D E S M U S O B L I Q U U S ( T U R P ) K U T Z . S C E N E D E S M u S D E N T I G U L A T U S ( L A G ) G . M . S M I T H S C E N E D E S M U S A B U N D A N S ( K I R C H N . ) C H O D . S C E N E D E S M U S B I J U G A ( T U R P ) L A G E R H . C R U C I G E N I A I R R E G U L A R I S W I L L E C R U C I G E N T A F E N E S T R A T A S C h M I D L E C R u C I G E N I A Q U A D R A T A M O R R E N M O u G E O T I A S P . * Z Y G N E M A - L I K E * S P I R O G Y R A S P . * M E S O T A E N I U M S P . G O N A T O Z Y G O N S P . * * * * . C L O S T E R I U M M A C I L E N T U M B R E B . * * * . * " C L O S T E R I U M S E T A C I U M E H R . * * * * C L O S T E R I U M A N G U S T A T U M K U T Z . . * * * * C L O S T E R I U M " S P . * * * * C L O S T E R I U M V E N U S K U T Z . * * * * C L O S T E R I U M . P A R V U L U M N A E G . * * * * C L O S T E R I U M D I A N A E E H R . * * * * C L O S T E R I U M C O S T A T U M C O R D A . ' .***'* C L O S T E R I u M T U M I D I U M J O H N S ***•* P t N I u M M A R G A R I T A C E U M ( E H R ) B R E B . **.**• P E N I u M I N C O N S P I C U u M G . S . W E S T P E N I u M C U R T U M B R E B . P L E U R O T A E N I U M T R A B E C U L A ( E H R ) N A G . * * * * D O C I D I U M B A C U L U M B R E B . * * * * T R I P L G C E R A S G R A C I L E B A I L E Y * * * * E u A S T R U M E u A S T R U M E U A S T R U M E U A S T R U M EUASTRUM EUASTRUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM COSMARIUM MICRASTER IAS MICRASTER I AS S P . E L E G A N S ( B R E B ) K U T Z . * * * * B I N A L E T U R P . D U B I U M N A G . *•**'* S P . S M A L L I N T E R M E D I U M C L E V E * * * * H U M I L E ( G A Y ) N O R D S T . Q U I N A R I U M L U N D * * * * A M O E N U M B R E B . * * * * B O T R Y T I S M E N E G H . * * * * P O R T I A N U M A R C H . * * * * O R N A T U M R A L F S . ' * * * * U N D U L A T U M C O R D A * * * * * S P . * * * * * O B S O L E T U M ( H A N T Z S C h ) R E I N S C H . M O N I L I F O R M E ( T U R P ) R A L F S . * * * * G R A N U L A T A B R E B . * * * * P S E U D O P Y R A M I D A T U M L U N D * * * * " T U M I D I U M L U N D * * * * * T I N C T U M R A L F S . C U M I S ( C O R D A ) R A L F S , ... * * * * C U C U M I S ( C O R D A ) R A L F S . M A R G A R I T A C E U M * * * * R A D I A T A H A S S . * * * * * P I N N A T I F I D A ( K U T Z ) R A L F S . * M ' I C R A S T E R I A S C O N F E R T A L U N D * * * * X A N T H i D I UM C R I S T A T U M . B R E B . . * * * * X A N T H I D I U M " A N T I L O P A E U M ( B R E B ) K U T Z . S T A U R A S T R U M C U R V A T U M W . W E S T * * * S T A u R A S T R U M STAURASTRU'M S T A U R A S T R U M S T A U R A S T R U M S T A U R A S T R U M S T A U R A S T R U M S T A U R A S T R U M S T A u R A S T R U M S T A U R A S T R u M S T A U R A S T R U M S T A U R A S T R U M S T A U R A S T R U M S T A U R A S T R U M D U A C E N S E R A L F S * * * * T O H O P E K A L I G E N S E W O L L E : * * * * B R A S I L I E N S E N O R D S T . * * * * A R C T I S C O N ( E H R ) L U N D * * * * M I N N E S O T E N S E W O L L E * * * * G L A D I O S U M T U R N . * * * * S E T I G E R U M C L E V E * * * * B R E V I S P I N U M B R E B . D E J E C T U M B R E B . T R I H A S T I F E R U M G . M . S M I T H * * * P A R A D O X U M M E Y E N G R A C I L E R A L F S . . * * * * • : C R E N U L A T U M ' ( N A G ) D E L P . DO M STAURASTRUM OPHIURA LUND * * * * STAURASTRUM S P . ARTHRODESMUS CONVERGENS EHR. * * * * ARTHRODESMUS INCUS (BREB), HASS. ONYCHONEMA F I L I F O R M I S ROY+BISS SPONDYLOSIUM PLANUM (WOLLE) W . + G . S . W E S T SPONDYLOSIUM PULCHRUM ( B A I L . ) ARCH. * * * * HYALOTHECA S P . DESM.IDIUM SWARTZ11 AG. DESMID IUM BAI LEY I ( R A L F S ) NORDST. BAMBUS INA BORRERI KUTZ . C H R Y S O P H Y T A B O T R Y O C O C C U S B R A U N I I ( K O L . ) K G . * C H R O M U L I N A C H R Y S O C O C C U S S P . C H R Y S A P S I S M A L L G M O N A S S P . S M A L L M A L L O M 0 N A S S P . L A R G E S Y N U R A S P . O C H R O M O N A S u R O G L E N A A M E R I C A N A * C Y C L O N E X I S - L I K E * D I N Q B R Y O N S O C I A L E E H R . D I N O B R Y O N T A B E L L A R I A E ( L E M M ) P A S C H E R *; D I N O B R Y O N S E R T U L A R I A E H R . D I N O B R Y O N : B A V A R I C U M I . M H O F F . ; D I N O B R Y O N C Y L I N D R I C U M I M H O F F . * . D 1 N O b R Y O N U T R I C U L U S S T E I N * L A G Y N I O N S P . * R H I Z O C H R Y S 1 S S P . * C H R Y S O C A P S A ; M E L U i I R A GRANULATA ( E H R ) - R A L F S . * * * * * M E L G S I R A N Y A S S E N S I S O . M U L L . * * * * * M E L O S I R A . L O N G I S P I N A H U S T . * * * * * M E L O S I R A I T A L I C A ( E H R . ) K U T Z . * * * * * M E L O S I R A A M E R I C A N A K G . * * * * * M T L O S I R A S P . * * * * * CYCLOTELLA G L O M E R A T A BACHM. CYCLOTELLA ANTIGUA WM-. SM. * * * * * TLRHSTNOE AMERICANA ( B A I L ) RALFS * • * * * * -TABLLLARIA FENESTKATA ( SYNGB) 'KUTZ. * * * * T A B E L L A R I A F L O C C U L O S A ( R O T H ) K U T Z , T E T R A C Y C L U S L A C U S T R I S R A L F S * * * * S Y N E D R A : A C U S K U T Z . " S Y N E D R A F I L I F O R M I S C L - E U L . S Y N E D R A U L N A ( N I T Z ) E H R . F R A G I L A R I A C R O T O N E N S I S K I T T O N F R A G I L A R I A C O N S T R U E N S ( E H R ) G R U N . F R A G I L A R I A P I N N A T A E H R . . F R A G I L A R I A I N T E R M E D I A G R U N . A S T E R I O N E L L A F O R M O S A H A S S . E U N O T I A M A I O R ( W M . S M ) R A B * * * * S E R R A E H R . * * * * ' S u E C I A A . C L . P R A E R U P T A E H R . * * * * A R C U S E H R . . E L E G A N S O S T R . I N C I S A W M . S M . * * * * P E C T I N A L I S ( 0 . M U L L . ) R A B . F L E X U L O S A B R E B . * * * * C U R V A T A ( K U T Z ) L A G E R S T E R U C A " E H R . M I N U T I S S I MA K U T Z . * * * * * E U N O T I A E U N O T I A E U N O T I A E U N O T I A E U N O T I A E U N O T I A E U N O T I A I I  ( O . . ) R A R . * * * * E U N O T I A E U N O T I A A M P H I C A M P A A C H N A N T H E S C O C C O N E I S N A V I C U L A C O N F E R V A C E A ( K U T Z ) G R U N : . * * * * S I M U L A P A T R . * * * * * R A D I O S A W A L L A C E * M I N I M A G R U N , . * * * * * V I R I D U L A K U T Z , S P - . * * * * * N O T H A W A L L A C E MA I O R ( K U T Z , S T R E P T O R A P H E A C U M I N A T A C L . T E R M I N A T A ( E H R ) P A T R . N O b l L I S E H R . * * * * S P , * * * * P A R V U L A ( R A L F S ) C L - E U L . * * * * S O C I A L I S ( T . C . P A L M ) H U S T . * * * S U B S I O M A T O P H O R A H U S T . * * * * N E I D I U M I R I D I S ( E H R ) C L . * * * * A N O M u E O N E I S F O L L I S ( E H R ) . C L . * * * * A l M O M U E O N E I S S E R I A N S ( B R E B E X K U T Z ) C L . N A V I C U L A N A V I C U L A N A V I C U L A N A V I C U L A N A V I C U L A N A V I C U L A P I N N U L A R I A' P I N N U L A R I A P I N N u L A R I A P I N N u L A R I A P I N N U L A R I A P I N N U L A R I A P I N N U L A R I A P I N N U L A R I A PINNuLARIA * * * * * * * * * * ) R A B * * * * C L . * * * * D I P L O N E I S F I N N I C A ( E H R ) C L . * * * * D I P L O N E I S E L L I P T I C A ( K U T Z ) C L . S T A U R O N E I S P H O E N I C E N T E R O l V ( N I T Z ) E H R . * * * * S T A U K O N E I S F L U M I N E A P A T R . + F R E E S E * * * * F R U S T U L I A R H O M B O I D E S ( E H R ) D E T . * * * * F R u S T U L I A R H O M B O I D E S V A R . C R A S S I N E R V I A B R E B B I S O N I A S P . * * * * G O M P H O N E M A B E R G R E N I I C L . * * * * * G O M P H O N E M A L A N C E O L A T U M A i M O M O N E I S - L I K E * * * * C Y M B E L L A T U R G I D A G R E G O R Y * * * * C Y M B E L L A S P . A M P H O R A S P . A M P H O R A O V A L I S K U T Z . * * * * * . E P I T H E M I A A R G A S ( E H R ) K U T Z . * . * * * . R H O P O L O D I A G I B B A ( E H R ) O . M U L L . * * * * S T E N O P T E R O B I A I N T E R M E D I A ( L E W I S ) S C H M I D T N I T Z S C H I A A M P H I B I A G R U N . N I T Z S C H I A F O N T I C Q L A S U R I R E L L A C A P R O N T B R E B . * * * * S U R I R E L L A R O B U S T A E H R . * * * * S U R I R E L L A S U B C O N T O R T A H U S T . * * * * S U R I R E L L A T E N U I S S I M A * * * * * S U R I R E L L A P A P I L I F E R A H U S T . * * * * S U R I R E L L A D E C I P I E N S O . M U L L . * * * * S U R I R E L L A S P . * * * * E P I P Y X I S U T R I C U L U S E H R . E U G L E N O P H Y T A E U G L E N A L A R G E * * * * EuGLENA SMALL T R A C H E L O M O N A S R H A B D O M Q N A S M I N I M A ( M A T V ) H U B . E R - P E S T . ; ... P Y R R O P H Y T A G L E N O D I N I U M A L B U L U M L U N D G L E N U D I N I U M U L I G I N O S A ( S C H I L L I G . ) WOL< G Y M N O D I N I U M F U S C U M S T E I N G Y M N O D I N I U M U B E R R I M U M ( A L L M . ) K O F O I D G Y M N O D I N I U M S P . S M A L L G O N Y O S T O M U M S P . G L O E U D I N I U M M O N T A N U M K L E B S P E R l D l N I U M P A L U S T R E ( L I N D E M . ) L E F P E R I D I N I U M S P . ( I N C O N S P I C U U M ) ' P E R I D I N I U N L L O M N I C K . i l W O L . P E R I D I N I U M W I L L E I H U I T F . - K A A S . C R Y P T O P H Y T A C H R O O M O N A S ; K A T A B L E P H A R I S - L I K E C R Y P T O M O N A S E R O S A E H R . C R Y P T O M O N A S O V A T A E H R C R Y P T O M O N A S S P . N E P H R O S E L M I S U N P I G M E N T E D P R O T O Z O A ' T H E C A M O E B A * A C T I N O B O L I N A S P . * M A Y O R E L L A V E S P E R T I L I A P E N N A R D . * A R C E L L A S P . * A C T I N O S P H A E R I U M - L I K E A S T R A M O E B A S P . V E J D . O V S K Y ' * * * * E U G L Y P H Y A - L I K E * * * * B I O M Y X A S P . L E I D Y P H R Y G A N E L L A - L I K E * * * * E U G L Y P H A * * * * C H L A M Y D O P H Y R S - L I K E * * * * A C T I N O P H Y R S M O N A S S R . - , . 0 1 C O M O N A S S P . M A C R O M A S T I X S P . S T O K E S ' S T O M A T O . C H O N E S P . P A S C H E R P H Y L L O M I TU 'S S P . S T E I N S T E R R O M O N A S S P . K E N T P A R A M A S T I X S P . S K U J A S T E P H A N O C O D O N L I K E B I C O E C A * * * V A M P Y R E L L A L A T E R I T I A L E I D Y * T R A C H E L O C E R C A * L I O N O T U S * P A R A M E C I U M S P . * U R O S O M A * S P A T H I D I U M * S P I R O S T O M U M ro S T R O D I L I D I U M GYRANS STOKES N A S U L A - L I K E C O L P O D A - L I K E STROMBI D IUM MI NUT I S S I MUM L E E G . STROMBIDIUM DEL I CAT I S S I MUM L E E G . V O R T I C E L L A S P . * . ONYCHODROMUS-L IKE PSEUDOBLEPHARISMA R O T I F E R A CRUSTACEA PLOESOMA SP. , C O N O C H I L O I D E S S P . . TRICHOCERCA S P . * MONOSTYLA S P . * ASCOMQRPHA SP . * POLYARTHRA EURYPTRA W I E R Z E J S K I CONOCHILUS S P . LECANE S P . KERATELLA TAOROCEPHALA* KERATELLA C O C H L E A R I S EHR. S IMOCEPHALUS * EUCYCLOPS * DAPHNTA LONG I S P I N A O . F . MULLER * S I D A C R Y S T A L L I N A O . F . M U L L E R CHYDORUS S P H A E R I C U S O . F . M U L L E R * BOSMINA LONG I R O S T R I S O . F . M U L L E R * C E R I O D A P H N I A S P . POLYPHEMUS P E D I C U L U S L I N N E ALONA S P . ' HOLOPEDIUM GIBBERUM ZADDACH DIAEHANO:S_OMA S P . , STREBLOCERUS S P . * COPEPOD N A U P L I I CYCLOPS B I C U S P I D A T U S THOMASI S . A . F DIAPTOMUS OREGONENSIS L I L L J E B O R G PHYSICAL FACTORS: It Is impossible to determine apriori which of the many physi-cal factors acting on a small lake are likely to affect the pro-ductivity and species composition of its phytoplankton community. For this reason a large number of physical and meteorological fac-tors were recorded during the entire course of this study i.e. per-cent cloud cover, light intensity and duration, air and water temperature, wind direction and speed, underwater light intensities, rainfall, snow and ice depth as well as inlet discharge. The more important of these are described briefly in this portion of the thesis with respect to the method of measurement while the results are given separately in a following section. (a) Temperature. Daily air maximum and minimum temperatures (Fig. 6) were collected by the University of British Columbia Forestry Department at their weather station on Spur 17 located less than two miles from Marion Lake. This and all other data reported here regarding physical factors are on file in the Marion Lake Project Office, Department of Zoology, University of British Columbia. Water temperatures were taken at one half meter at noon near Station E three times a week during the enrichment series and once a week in the period between enrichment series. (b) Wind, light and precipitation. Both wind direction and speed were recorded on a continuous recording anemometer located near the lake. Light duration data were recorded by the University of British Columbia Forestry De-partment on a Campbell-Stokes Continuous Sunshine Recorder which is operated at the Weather Station. Sunlight intensity was recor-ded on a Belfort Recording Pyrheliometer which was placed on a platform above the lake's surface (Fig. 2). I recorded underwater light transmission in the lake on several occassions using a G.M. Submarine Photometer, Model 420 (Efford, 1967). Precipitation was recorded at the Weather Station and lake depth was recorded during each sampling period. (c) Inlet di scharge. Inlet discharge rates are recorded by the Department of Norther Affairs and National Resources, Water Resources Branch, using a Stevens A-35 Water Stage Continuous Recorder on the inlet creek above Marion Lake (Fig. 3). During December and January the water level height recorder froze so that no record was made during that period. The Department converted discharge rates from the North Al1ouette River which is in the same drainage basin as Marion Lake making it possible to estimate inlet discharge for Marion Lake in December and January. 30 ( F i g u r e 3) The annual pattern of inlet discharge into Marion Lake, British Columbia. Values for December and January are estimates based on the discharge data from the North Allouette River of the same drain-age basin. D I S C H A R G E (liters per sec. x 100) co 05 CD 65 W 0 0 - W M -I W CO o CO CO 01 o 32 NUTRIENT ANALYSIS: A one 1 iter sample was taken at one half meter from each en-closure and from A and E in a polyethylene container to be used for nutrient analysis. The samples were analyzed within.half an hour at the lakeside laboratory for nitrate, nitrite, phosphate, bicarbonate and free CO according to the methods described by the American Public Health Association (I965). Total and orthophos-phate were analyzed using the stannous chloride method and "Hach" chemicals. The technique was not sensitive below 0.02 mg/liter total dissolved phosphate. Nitrate and nitrite were analyzed using the Phenoldisulphonic acid method and "Hach" chemicals. This test was sensitive to changes in dissolved nitrate and nitrite above 0.1.0 mg/liter. Nutrients were analyzed three times a week following each sampling period. Thus the field nutrient analyses monitored the loss of the dissolved nutrients from the water column of the enriched enclosures until it dropped below 0.02 or 0.10 P0^-P, N0^-N mg/liter, respectively (Fig. k). Values below this level were determined in the 1aboratory with the aid of A . CattelI using the method of Strickland and Parsons (i960) and a D-U spectrophoto-meter equipped with a 10 cm cuvette. 33 (Figure 4) Total dissolved nitrate nitrogen and phosphate phosphorus concen-trations within the experimental enclosures following nutrient enrichment in each of the four seasons ©f the year* Vertical lines represent 95% confi cence limits about the mean (N = 8). The absence of a confidence limit indicates that the nutrient concentration Was below the minimum value detectable Using "Hach" chemical Si 200 ISO 100' 050 0-1 250 200 FALL NOj-N 150 u o 43 •H ^ 1 0 0 -U O ft Q50-i -fcrt^—» — ; —• •• •—i—| j ,T"'" r-'V'T i ,— . WINTER o w ft bo 150 too Q50 tso-100 0.50 SPRING SUMMER 0 2 4 6 8 10 12 14 .16 18 20 22 24 26 28 30 32 34 3d 38 40 42 • A Y S F O L L O W I N G E N R I C H M E N T 35 PRIMARY PRODUCTIVITY: The increase in abundance of the phytoplankton resulting from the addition of new individuals to the population can only rarely be used as a measure of that community's productivity because si-multaneously a continuous depletion of the population is occurring and it is extremely difficult to assess this quantitatively. Con-sequently, the rate at which a mixed assemblage of algal species incorporate carbon is used as an index of their productivity. In order to measure production using this method a pair of 300 ml B.O.D. bottles were filled at 1/2 m in each of the enclosures and external control locations three times a week during the enrichment series. In addition a 300 ml B.O.D. "dark" bottle was included for each pf the three treatment types and external control. Four microcurries of Carbon-14 were added to each of the bottles as described by Goldman (1963) and the samples incubated at one half meter at Station E. The bottles were kept in black cloth bags or inside a covered box from the time the original sample was with-drawn to the time that incubation began. The samples were incubated from 10 A.M. to 2 P.M. and then placed in a light-tight box to stop primary production. Next a known fraction of the bottle was (R) filtered through an H.A. Millipore ' 0.45 micron pore diameter filter at 38 cm Hg,(15 lbs.per sq. in.) pressure. Following fil-tration the filters were numbered and dried in a desiccator and 14 sent to the International Agency for the Determination of C in Denmark. 36 STANDING CROP: Two methods of estimating plankton standing crop or biomass were used in this study. The first and probably least reliable method according to Ruttner (1953, p . 1 A3) consisted of measuring the height of the sedimented plankton in the 16 ml vials in which they were stored. This method makes no allowances for differences in compaction between differently shaped organisms nor does it distinguish between tripton and plankton. The justification for employing such a method was that estimates of relative standing crop based on the height of the sedimented column within the 16 ml vials compared very closely (correlation coefficient of 0.7*+ with 39 degrees of freedom) with estimates based on total plankton counts. The second method was used to check the reliability of the first. Forty plankton samples were chosen arbitrarily, ten in each season, and the plankton counted. When these independent estimates of plankton standing crop were used to test the relia-bility of the sediment height method the latter was found sufficient-ly reliable for the purposes of this thesis. Consequently, the sediment height method of estimating plankton standing crop was used throughout this study. There appear to be two reasons why this method was Marion Lake: 1) Over 90% of the phytoplankton in this lake are spherical nannoplankters and dif-ferences in compaction with similarly shaped cells is unlikely to substantially alter the height of the sedimented column. 2) The amount of tripton in the water does not appear to alter dras-37 tically during the year inside the wooden enclosures and tubs. DATA ANALYSIS: In presenting the results of the primary productivity series it was possible to minimize the effects of the external factors such as light and temperature by subtracting the mean primary pro-ductivity values of the unenriched enclosures (internal controls) from those of the enriched enclosures. Because the enrichment ex-periments were designed to evaluate the relative importance of the three enrichment regimes (NO3, PO^ and N C y P O ^ ) on primary pro-ductivity such a procedure is applicable. Thus in the figures of phytoplankton primary productivity the internal control values were subtracted from each of the other enrichment types for each sampling date. The control corrected values Were then log trans-formed to facilitate plotting. A single asterisk is used in this thesis to designate an "F" value which when tested against the "F" table was found sig-nificant at the 0.05 level of probabi1ity whi1e a double asterisk indicates significance at the 0.01 level. All the raw data taken from Marion Lake such as plankton a-bundance at each station, nutrient concentrations and physical factors, etc., were punched on I.B.M. cards and analyzed using the I.B.M. 7044 computer. The raw data which comprises over 1000 pages of computer print-out is 38 stored in the Marion Lake Project File in the Department of Zoology at the University of British Columbia. It was not feasible to con-sider the presentation of the raw data. On a number of occasions missing data resulted from the ac-cidental loss of the plankton samples taken from the lake. Al-though these missing values occurred very infrequently a method of estimating them was necessitated by many of the computer pro-grams used in the data analysis of this study. Two methods of estimating missing values were employed. Originally all values were estimated using the method described by Steele and Torie (i960) for the calculation of missing values for a randomized complete block design. These values were compared with those of the repli-cate sample and the two were found to agree very closely. Thus the replicate values were used in subsequent estimates and one degree of freedom subtracted for each estimate. When both repli-cates were missing the more time consuming technique of missing data estimation by covariance described by Steele and Torie (i960, p . 32k) was used. Throughout this study numerical estimates of a species' den-sity were not rounded off in order to avoid accumulating rounding errors in the various computer programs in which the data was used. The computer output presented in this thesis, however, is only accurate, to three significant places. ESTIMATING CELL VOLUMES AND TURNOVER RATES: The volumetric contribution of each species to the total plankton volume of the sample was calculated as described by Kutkuhn (1958). Organisms were measured with the ocular micrometer 39 to determine length, width and height. These measures were used to estimate the organism's volume by choosing an appropriately shaped spheroid and using its formula to calculate the volume in cubic microns of the organism in question. Thus Chiamydomonas sp. small was measured in over 25 separate, samples and its mean volume calculated from the formula for an ellipsoid. The mean volume estimates for each species are listed in Column C of Table IV. Estimates of the relative biomass and the relative abundance of the different species in the samples were used in calculating various indices of diversity for each of the samples. The use of these diversity indices is described later in the thesis. The calculation of diversity based upon relative productivity prompted the estimation of mean "turnover rate" of the different planktonic species found in the lake. The turnover rate was estimated from two types of information: 1) the length of time each species was observed in the lake and 2) the mean rate of reproduction of that species. The first factor was determined directiy from my data of bimonthly plankton samples during all of 1966 and 1967. This data is summarized in the first column of Table IV for each of the eu-planktonic species in the lake. The second factor was determined from data given in the literature i.e. Edmondson ( i 9 6 0 ) , Cushing (1959, Verduin (1959) and Tailing ( 1 9 6 2 ) , etc. There are numerous errors introduced by estimates of a particular species' growth rate from values in the 1iterature of related but different species. The estimates of turnover rate given in Column D of Table IV serve only as rough approximations of the actual values. - T A B L E • I V T H E R E L A T I V E A B U N D A N C E I S G I V E N . F O R E A C H O F T H E S E A S O . M S O F T H E Y E A R T H E F I R S T C O L U M N O F N U M B E R S R E P R E S E N T S F A L L , T H E N E X T W I N T E R . E T C - . • . R E L A T I V E A B U N D A N C E R E D O R D E D O N A S C A L E F R O M : 0: T O 5 * H E R E 0 I IN U I C A T E S N O O R G A N I S M S O B S E R V E D I N A N Y O F T H E S A M P L E S T A K E N I N T H A T S LASO I S W H I L E 5 I N D I C A T E S T H A T A L L T H E S A M P L E S T A K E N I N . T H A T S E A S O N C O N T A I N E D O N E O R M O R E O R G A N I S M S O F T H A T S P E C I E S . T H E . M E A N D E N S I T Y I S G I V E N I N N U M D E R P E R L I T E R A N D T H E M E A N V O L U M E I S G I V E N I N C U B I C M I C R O N S . T U R N O V E R C O E F F I C I E N T S A R E I N R E L A T I V E . U N I T S * 1 = O N E R E P R O D u C T I V E C Y C L E P E R Y E A R . S E A S O N A L A B U N D A N C E S P E C I E S N A M E . M E A N M E A N T U R N O V E R D E N S I T Y V O L . C 6 E F F I C I E N T M Y C O P H Y T A , 3021 FUNGAL.SPORE OR MYCELIA .' 3 060 : 175 2 00 1012 RHIZOPHLYCT is - 19555 . 18 200 0001 CLADOCHYTRIUM 0 10 200 1002 ANCYLISTES / "-. - ' - 5480 5 200 1001 -RHIZOPHYDIUM .' 9580 3 200 . . ..  .. oooi CHYTRIOMYCES 10734 5 200 SCHIZOPHYTA 4335 E P I P H Y T I C MICROCOCCUS 8535600 1 300: 0010 ENCAPSULATED BACTERIUM 4448300 8 300 0001 BACTERIUM 2049600 "1 300 425 5 CHLOROBIUM •'-.....- 3 02230 6 300 1000 T H I O T H R I X - L I K E 945750 4 300 3134 RHABDOCHROMAT IUM ' : .970750 2 300 4234 PS.EUDOMONAS 451690 3 300 4335 MICROCOCCUS-L IKE 26484000 1 300 5344 BEGG I ATOA 994275 8 200 1000 MACROMONAS 0 805 100 1120 V I B R I O 21461 10 300 1000 S P I R O C H A E T A 2125300 4 300 C Y A N O P H Y T A 0010 RHABDGDERIMA(COCCOCHLORIS>SPRENGEL) . ,64091 5 175 .- 4025, MICROCYSTIS , ( ANACYST I CA » DROUET ) . .. . .3.0000 1: 250 . .: 0010 SYNECHOCYST15 .149710 45 250 1000 SYNECHOCOC'CUS 25583 268 100 - .4020 C f l R O O C O C C o o o P . , , 3 3 7480 382 250 ' 12 54 C O E L U b p H A E R I . u M ( G O M P H O S P H A E * I A 6 5315 14 25 0 2 0 1 4 ' MER I SMOP ED I UM PONCTA T A•( AGMENELLUM > DR.OU E T ) - 2 0 0 5 ME RI SMOP E D1 UM . T EN UI S S IM A ( AGME N E L LU M ? DROU E'T ) .41-2 5 APHAMOCAPSA SPO(ANACYSTIS?DROUET) : ; 1012' GLOEOCAP.SA-LI KE - , -V-" ' V " . - - : -- 1 0 0 0 " E U C A P S I S - L I K E ",''" : -0001 60MPH0SPHAERIA 1 0 0 1 O S C I L L A T O R I A LACUSTRIS ( K L E B ) GE ITLER 2012 PSEUDOANABAENA "CHTOR 0 P"HVTA • : - . 1015 PEDINOMONAS -L IKE 5135 CHLAMYDOMONAS SP E 0033 GL0E0M0NAS OVAL I S 0010 GONIUM SP 0 4-3-4,-5 - s-p HAER 0 CY S T I S 1004 GLOEOCYSTIS GIGAS 2 2 1 1 NANNQCHLORIS SMALL tARG'E-KLEBS, (KUTZ) LAGERHO 0 0 0 1 C H L O R O S A R C I N I A - L I K E 4013 SCHRODERIA SP 0 _30'24~"S"E""T"ACI U"M""S"P O - -1 0 0 1 PEDIASTRUM TETRAS (EHR ® ) RALFS 0 1003 PEDIASTRUM SP« CDCFCS 0010 SORASTRUM SP S 4015 OOCYST IS PARVA WEST+WEST 1012 00CY"STTS "SOL I "TAR IA "WITT ROCK 3043 ANKISTRODESMUS S P I R A L I S LEMMO 4 0 1 4 ANKISTRODESMUS FALCATUS 4034 SPQNDYLOSIUM PLANUM (WOLLE) W0+GOSCWEST 4025 SCENEDESMUSDENTICULATUS SMITH -LOOL- SCENEDE-SMUS BIUUGA ( TURP) "LAGERHO 3 0 0 1 SCENEDESMUS OBLIQUUS (TURP) KUTZ,, 0010 SCENEDESMUS ABUNDANS (KIRCHNO.) 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PASCHER ACTINOPHYRS A C T I N O S P H A E R I U M - E I K E N A S U L A - L I K E C O L P O O A - L I K E STROMBIDIUM M I N U T I S S I M U M L E E G . STROMBIDIUM DEL I CAT I S S I MUM L E E G . S T R O B I L I D IUM GYRANS STOKES GONYQSTOMUM S P . SP I RO-STOMUM ONYCHODROMUS-LIKE POLYARTHRA EURYPTRA W I E R Z E J S K I KERATELLA C O C H L E A R I S E H R . PI_-EE-SOMA S P . LECANE S P . CONOCHILUS S P . POLYPHEMUS P E D I C U L U S L I N N E H O L O P E D I U M G I B B E R U M ZADDACH DAPHNIA LONG I S P I N A O . F . MULLER ALONA S P . COPEPOD- NAUPLI I S I DA C R Y S T A L L I N A O . F . M U L L E R DIAPTOMUS OREGONENSIS L I L L J E B O R G 26752 280 150 5513 279 150 111410 167- 150 253350 263 150 517610 500 150 1930 704 100 4469 8000 100 3578 179595 75 39581 5450 75 3664 3984 75 7770 4181 75 2696 8294 75 1681 67324 150 592 56-547 75 3UU 67421 60 135 35 60 32 38 60 0 - 5 ••• 60 2 30 60 157 21 60 2 9 00 0 10 23 155 10 0 569 10 0 105 10 3 31 10 3 3 00 0 .10 6 56300 2 45 RESULTS NUTRIENTS: The addition of phosphate or nitrate singly or in combination to the enclosures resulted in an immediate increase in the concentration of these dissolved nutrients in the water column. With the exception of the winter series, these augmented nutrient concentrations returned to their pre-enrichment levels within two weeks following ferti1ization (Fig. 4 ) . This rapid loss of dissolved inorganic nitrate and phosphate from the water column has been observed by many workers as discussed by Hutchison ( 1 9 6 7 ) . During winter, however, the dissolved reactive nitrate, and to a lesser extent phosphate, remained in the water column at a relatively high concentration for a much longer period of time (Fig. 4). As was previously stated, the winter series was conducted in 100 liter tubs instead of the wooden enclosures which were used for the other enrichment series. An important difference between the tubs and the enclosures was the conspicuous absence of periphyton from the former. Consequently, the tubs with their 1imi ted mud substrate (2 cm in depth) and absence of periphyton would have a reduced demand for the added nutrients. Nutrient concentrations in the lake as a whole were very low. The specific conductivity range of six to ten micro ohms corrected to 20° C is only slightly higher than the specific conducti-vi ty found in rain water. The nitrate and phosphate concentrations in the lake were so low that they could only be measured by using a special cuvette with a 10 cm optical path in the D-U spectrophotometer and the sensitive technique described by Strickland and Parsons (-I960)'. Total d i ssol ved (reactive) nitrate and phosphate concentrations (microgram- at. per liter, NO^-N and PO^-P) were lowest at the inlet (0.266 + 0.014 and 0.055 + 0.007, respectively). - They were nearly as low at the spring (0.416 and 0.082, respectively) while they were highest in the shallow portions of the lake where lake water renewal from the inlet in slowest (0.0872 and 0.116, respectively) for the two nutrients. The standard deviations in the latter cases were similar to those given for the inlet. Recent reports by Rigler (1968) indicate that it may be impossible to measure orthophosphate in lake water. PHYSICAL FACTORS: a) Light.. In fall the average light intensity during the four hour incubation period (10 A.M. to 2 P.M.) was 0.32 g-cal/cm 2 per m j n . A mean light duration of 5.4 hours was recorded during the fall enrichment series. Light intensities below 0.02 g-cal/cm per m I n. did not register on the continuous daylight recorder. Consequently, periods of heavy rain or cloud cover which"occurred during the daylight hours did not register on the recorder. Thus the reported light duration values only refer to light above a certain threshold. During fall, both light duration and light intensity are decreasing. The compensation depth (1% of the surface light intensity) is never exceeded in Marion Lake due to its shallowness (2.2 m mean depth) and high transparency. The latter can be attributed to the low plankton standing crop and the absence of significant concentrations of colloidal or particulate material in the water column of the lake. In winter surface light intensities dropped to 0.10 g-cal/cm^ per (Fig. 5) with a mean daily duration of 3.3 hours. By spring the mean <D CL « E £ CO 0 1 CD 1.2 1.0 0.8 0.6 _ 0.4 0.2 0.0 Figure 5. Annual pattern of daily light intensities recorded between the hours of 10 a.m. to 2 p.m. at Marion Lake. All values are rounded to the nearest JUNE AUG OCT DEC FEB APR JUNE AUG 1966 1967 '4 24 light intensities had increased to 0.42 g-cal/cm per m i n. with a 4.8 hr. mean daylight duration period. Summer 1ight intensities were high, mean intensity was 0.78 g-cal/cm per min. and mean l ight duration was 10.1 hrs. b) Wind and Temperature Wind serves mainly to increase the amount of turbulence in the lake. Strong wind blowing along the entire length of the lake increases turbidity by stirring the lake to the bottom (Chand1er,1944). Since the compensation depth is never reached due to the shallowness of the lake circulating phytop1ankton do not spend any time in uni11uminated water as a consequence of wind mixing. During much of the year the prevailing southerly winds reach 2-5 m/sec. in the late afternoon. In winter the formation of a thin ice cover over the lake's surface prevents wind mixing. This results in the typical temperature inversion profile described by Rodhe (1948). Temperatures immediately below the ice of 1°C rise to nearly 4°C near the bottom of the lake. In the part of the lake (channel) where there is an appreciable current from inlet to outlet, however, an inversion is rarely detectable. Water temperatures remained low (about 5°C)until mid-spring although the ice had cleared by the end of February. It was not until late summer that stratifi-cation of the lake in terms of its temperature profile occurred. The ensuing thermocline lacked stability and strong winds were capable of destroying it even when the temperature of the epilimnion was at its annual maximum (26 - 28°C maximum recorded). During fall the 49 thermoclIne disappeared entirely and the lake became holomictic. Wide fluctuations in the daily ambient temperatures (Fig. 6) were damped only slightly by the shallow layer of water within the lake. Consequently, the lake temperature at 1/2 m remained within a few degrees of the ambient air temperature. (c) Precipitation. The annual rainfall of 240 cm (94 inches) near Marion Lake provides considerable runoff to its small (6.5 sq. km) and steep drainage basin. During heavy rains the water level in the lake rises more than a meter in twenty-four hours. If the rain persists a volume of water equivalent to that of the lake itself enters the lake in 2.3 days (Efford, 1967). Thus a high rate of Water renewal or flushing persists through much of the year in Marion Lake (Fig. 3). There is good evidence that a high flushing rate results in lowered primary productivity in the phytoplankton of this lake (Figs. 8, 9 and 10). On days with high inlet discharge (i.e. those with high rates of flushing) primary productivity in the lake was low. Thirty-two primary productivity values from days having a light 2 intensity of 0.5 + 0.05 g-cal/cm /min. were chosen from over 132 because of their nearly identical light intensities. Primary productivity was plotted against inlet discharge on these days (F'S- 7). A correlation coefficient of 0.57 with 31 degrees of freedom was significant at the 0.01 level of probability. A multiple regression of light (Xj) and discharge rate (X^) against the dependent variable (Y), primary productivity, resulted in the following equation: Y = 0.17 + 2.21 X. - 0.002 X Thus primary Figure 6 . Annual pattern of daily JUNE 1966 1967 Figure 7- Primary productivity and inlet discharge on days having similar light intensities (0.5 1* 0.05 g-cal/cm"-per hr.). The correlation coefficient of 0.57 with 66 degrees of freedom was significant at the 0.05 level of probability. Primary productivity values were plotted on a logarithmic scale to facilitate graphing • • P B Q D U E T I V I T V ( m g . c / m 3 per hr] A T C O N S T A N T . L IGHT 3 productivity increased an average of 2.21 mg carbon/m per hour 2 for each g-cal/cm per min. of light while it decreased 0.002 3 mg-C/m per hour for each 1iter/second increase in flushing. Both factors had a significant effect on primary productivity (P <0.05; N = 132). 53 PRIMARY PRODUCTIVITY: Within the scope of this study it was necessary to determine three major factors regarding changes in primary productivity following enrichment: 1. Did nutrient enrichment have different effects on primary productivity at different times in the year? 2. How did the different nutrients used in the enrichment series ' affect primary productivity? 3. Did the different levels of primary productivity in the lake at the time of e n r i c h m e n t influence the trends in primary productivity within the enriched enclosures in the different seasons of the year? To answer the first question, a three-way analysis of variance with randomized complete blocks as described by Steele and Torie (1958) was used as the basis of a computer program to analyze the data. Table V lists the results of this analysis. During each of the four seasons there was a significant (P < . 0 1 ) treatment effect. There was also a highly significant "time-treatment" interaction whiich was interpreted to mean that the serial samples taken during each enrichment series may not have been independent. The resulting lack of independence ip, the repeated samples may have resulted in sequence or carry-over effects of the type described in the section on species composition analysis. Consequently, a second type of analysis was employed which did not make the assumption of repeated sample independence. Fisher (1963) developed a method of trend • analysis which is discussed later in this paper. Using his technique of polynomial trend analysis to analyze the primary productivity data cpl1ected from the enriched enclosures in the four seasons resulted in the following conclusions. With the exception of the fall nitrate and the nitrate-phosphate treatments which were probably affected by flushing of their enclosures, all other enriched enclosures gave a positive significant ( P < 05) response to PRIMARY PRODUCTIVITY: THREE-WAY ANALYSIS OF 54 VARIANCE IN A RANDOMIZED BLOCK DESIGN TABLE V FALL 1966 E F 1 SUM OF SQUARES 1S4H SQUARE F 1. Time 10 0.08616 08.616 131.90 * * 2. Treatment 3 0.15860 52.867 809.31 if* 3. Block (N&S) 1 0.00008 00.083 1.28 4. 1 X 2 30 0.13735 04.57S 70.09 5. 1 X 3 10 0.00313 OQ.33^ • 4.80 * 6. 2 1 3 3 0.00045 00..U9. 2.28 7. 152X3 30 0.00148 00.049 0.76 Error 88. 0.0,0575 . 00.065 : Total 175 0.39300 WINTER T966-67 DF SUK OF/ SQTLIR3S MEAN SQUARE - F 1. Time 4 0.09189 • 22.973 101.40 * * 2. Treatment 3 0.10321 34.403 151.85 * * 3. Block (2T&S) 1 0.00006 00.063 0.28 4. 1 X 2 12 0.32401 .' 27.001 . 119.18 * * 5. 1 X $ 4 0.00165 00.413 1.83 6. 2 X 3 3 0.0CC31 00 ..104 0.46 7. 1X2X3 12 0.00389 00.325 1.43 Error 40 0.00906 00.226 Total 79 0.53410 v SPRING .1967 DF STJl'I OF SQUARES' : .MEAN SQUARE F 1. Tine ' 12 1.34130 111.770 105.31 * * 2. Treatment 3 3.98840 1329.510 1252.62 * * 3.- Block (ii&S) 1 0,00104: 1.044 0.98 4. 1 X 2 36 2.510C0 ; 69.721 65.69 * * 5. 1 X 3 12 0.00868 0.723 0.68 6. 2 X 3 3 0.0014-8 : 0.492 . 0.46 7. 1X2X3 36 0.00545 • 0.151 0.14 Error 104 0.11038 1.061 Total 207 7.86730 SUI1ISR 1967 DF SI3M OF SQUARES MEAN SQUARE 1 -2. 3. 4. 5. 6. 7. Time , Treatment Block (N&S) 1 X 2 1 X 3 2 X 3 1X2X3 Error Total 17 3 1 51 17 •3 51 144 287 13.06000. 13.34502 0.04384 13.72512 0.26898 0.17199 0.36972 0.98562 41.08365 762.239 4448.317 43.844 269.134 15.823 57.329 V.249 6.844 112.24 649.90 0.41 39.32 '0.31 0.38 0.59 3 1. All Sum of Squares values are tines 10 55 nutrient addition. Thus the cubic polynomial equation of best fit for the control enclosures was significantly different from the same for the various enriched enclosures at all times in the year with the two exceptions which were mentioned. The second question regarding primary productivity, whether different enrichment nutrients affect primary productivity differ-ently, was a more complex one. To answer it the results of each of the four enrichment series were dealt with separately. Enriching the water within the enclosures resulted in significant increases in the primary productivity of the phytoplankton in all but two (fall series) of the enriched enclosures. During the fall series the calcium phosphate enriched enclo-sures responded most rapidly giving the highest primary produc-tivity values for that series (Fig. 8 ) . On four separate occasions during this series high inlet discharge resulting from heavy rains (indicated by arrows in Figs. 8 , 9 and 10) may have partially flushed the w o o d e n enclosures by spilling over their tops. If this did occur t h e n different enclosures may have received different amounts of lake water as their tops were not all equally distant from the surface of the lake as some had settled slightly further into the mud than others. This may explain why the nitrate and nitrate-phosphate enriched enclosures did not respond signifi-cantly to enrichment in this series. Furthermore, no blooms oc-curred in any of the enclosures. This may be an indication that the lake level was rising above the enclosure tops and partially flushing the algal standing crop before it had sufficient time to reach b l o o m concentrations. Zooplankton abundace inside and outside the enclosures was not significantly different so that it seems unlikely that grazing could account.for the low standing Figure 8 . Changes in primary productivity following enrichment during the fall and winter series. The primary productivity of the control (unenriched) enclosures was subtracted from the enriched enclosure values to give "control corrected" values for this and the succeeding two figures. Vertical arrows in these figures represent days with high rainfall. Days in which algal blooms were first noted are indicated by a rectangle (NO^), oval (PO^) and hexagon (NO^-PO^). Vertical lines in this and the succeeding two figures represent 95% confidence limits (N = k). Points without vertical lines were not significantly different from the control means. 57 SEPT OCT crop inside the enriched enclosures. The results of the winter series indicated that even with the very low water temperatures (2° C) and light intensities (0.02 2 g-cal/cm /m,i n under the ice) which prevailed during this series, primary productivity within the ice covered tubs increased five-fold above that in the lake during this season. The Calcium ni-trate enriched carboys yielded the highest primary productivity values for the winter series (Fig. 8). On 6 March an algal bloom was observed in the nitrate enriched enclosures as indicated by the rectangle in Figure 8. No other blooms occurred. Rain water more than replaced the two liter samples which were removed three times a week from the tubs. Thus, as in fall, water renewal in the enriched enclosures may have retarded "bloom" formation. During the spring series the combined nitrate-phosphate en-richment was more effective in augmenting primary productivity than either of the two nutrients administered separately (Fig. 9). In this series as in both the summer and winter series the nitrate enrichment was the single most effective nutrient in in-creasing phytoplankton primary productivity. Summer differed from the spring enrichment series only in magnitude. The phosphate-nitrate enrichment was again the most effective regime for augmenting primary productivity. In summer^ primary productivity was over two times higher than at any other time in the year. The highest primary production value ever re-corded in Marion Lake, 49 mg C/rrr/hr. (a control corrected value 3 of 43 mg C/m /hr., Figure 10) occurred in the summer enrichment series in the nitrate-phosphate enriched enclosure. . E \ c > h > h G • • • CE D. > EC < E CL • w h G III cr cr • G _i 0 II I-z 0 G 24 22 20 18 16 14 12 10 S P R I N G S E R I E S 1967 - 2 -26 28 30 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 1 3 APRIL M A Y J U N E Fi gure 9 Changes in primary productivity following enrichment during spring. Figure 10. Changes in primary productivety following enrichment in the summer series. I N T E R N A L C O N T R O L C O R R E C T E D P R I M A R Y P R O D U C T I V I T Y <mg c/m 3 per hr) 61 The third question, how did seasonal differences affect the enrichment series in terms of their primary productivity, can be answered by comparing the trends in primary productivity in each season from inside the enclosures (Figs. 8, 9 and 10) with those from the lake as a whole (Fig. 11). At the start of any enrichment series the enclosures were completely "flushed" with lake water so that primary productivity inside and outside the enclosures was nearly identical. Thus during fal1 ?primary productivity inside and outside the enclosures was the same at the start of that season's enrichment series but within three weeks the phytop 1ankton productivity in the lake decreased while primary productivity inside the enriched enclosures 1 nearly doubled. In winter, while primary productivity in the lake remained low, productivity inside the enriched tubs increased until a heavy and persistent rain in mid-March resulted in considerable overflow from the tubs forcing the termination of the winter series. In spring, primary productivity in Marion Lake began to slowly increase (Fig. 11). This trend was greatly enhanced inside the enclosures. Even the unenriched enclosures increased significantly above the primary productivity of the lake as a whole. The reasons for this are discussed in the section on zooplankton responses. in summer, primary productivity within the lake as a whole and in the enclosures was higher than at any other time of the year. High temperatures and light intensities combined with a low flushing rate contribute to this annual peak in primary productivity in the lake. During this season as much as 5 mg of carbon is fixed per m^ Per hour. Inside the enriched enclosures primary productivity may be as much as 10 times higher indicating the importance of both nutrients and "flushing" to the level of P R I M A R Y P R O D U C T I V I T Y C m g C / m 3 per hr] primary productivity in this oligotrophic lake. STANDING CROP: Changes in standing crop and primary productivity were closely \ • • correlated (r = 0.89; 1 & 89 D.F.; p < 0.01). Thus an increase, in standing crop results in an increase in primary productivity within the 1ake In nearly al1 cases, increases in primary productivity, when they persisted, resulted in algal blooms. Bloom concentrations of phytoplankton within the enriched enclosures is indicated by a hexagon (nitrate-phosphate enriched), oval (phosphate enriched), and rectangle (n.itrate enriched) in Figures 8, 9 and 10. Standing crop, as in the case of primary productivity, was related to the inlet discharge rate. An increase in the inlet discharge resulted in a.dilution of the total algal standing crop in the piankton. SPECIES COMPOSITION: How does nutrient enrichment affect the species composition of the phytoplankton? To answer this question quantitatively it was necessary to employ trend analyses using orthogonal polynomials (Fisher, 1963). When a nutrient is added to. an enclosure the ensuing changes in species composition must be compared with those which occurred within the unenriched enclosures to determine which of the changes were a response to ferti1ization and which were not. The density of a particular species within an enclosure on a particular day influences the density of that species on successive days. There-fore the samples drawn from any one enclosure were not independent in time. These sequence or carry-over effects are an indication of a lack of independence in the repeated samples. Randomizing or counterbalancing such carry-over effects only serves to con-found them with the treatment effects (Edwards, i960). Consequently, the use of polynomials in recognizing significant differences in trends was used in place of the customary analysis of variance. The temporal variation in the abundance of a particular species in any of the three treatment types was divided into cubic trend components by applying orthogonal polynomials (Fisher, 1963). An "F" test of each coefficient of the polynomial was made by di-viding the trend coefficient (P) by the error of the estimate (E) and squaring the quotient (P/E) . The number of degrees of free-dom equals 1/n - (m - 1), where n = the number of observations used in the equation and m = the number of independent variables (3 in a cubic polynomial such as the one used in this analysis). Computations were performed on an I.B.M. 70Mt computer using the "L.Q..F." subroutine prepared for the University of British Columbia computing center by A . Fowler. A full description of the program is available •from the University of British Columbia Computer Science Department. Those species which produced a pattern (time trend), that was significantly different from the one produced in the control en-closures were listed in Table IV. These species increased (or decreased, indicated by a minus sign) in the enriched enclosure at a significantly greater rate than they did in the unenriched (control) enclosures. CHANGES IN SPECIES ABUNDANCE FOLLOWING ENRICHMENT: The number of different kinds of species does not drop sharply following enrichment. Instead it remains the same or may even increase slightly (Fig. 12). Even during an algal bloom two to three weeks after fertilization there are still nearly the same number of species in the water column as existed before the enrich-ment. The relative abundance of some species, on the other hand, has changed markedly. A few species increase in relative abun-dance dramat i cal 1 y fol 1 owi ng ferti l'i zati on • whi le the majority of the species become relatively less common in the samples taken from the enriched enclosures. It appears, therefore, that the addition of nitrate or phosphate to the water column does not enhance the productivity of the majority of the species which occurred there prior to enrichment. This is not surprising as these species were growing in water having extremely low nutrient concentrations and were presumable adapted to this environment. Changing the environment by nutrient addition is more likely to favor a new group of species which are "adapted" to the new nutrient condi-tions. The interesting observation made in this study was that the original species, for the most part, continue to reproduce in the fertilized enclosures and they only become less abundant relative to the species which "bloom", hence community diversity drops not because the original species have become rare but because a few species have become extremely abundant. (Figure 12) Changes in the number of species counted in a one-fifth liter sedimented sample during the summer enrichment series. The triangle represents the value from the north enclosures and the circle the south. All but the control enclosures were en-riched on 11 July 1967. The following three figures employ the same symbols. 6 5 4 3 2 1 7 1 61 5C 4 C 3C 20 10 7 0 60 5 0 4 0 3 0 20 10 7 0 60 5 0 4 0 3 0 20 10 60 5 0 4 0 3 0 20 10 67 Summer Series Nitrate & Phosphate Internal Control External Control 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 6 . 3 0 1 T H 11 , 3 15 17 19 z T ~ 2 3 J uly A u g . SPECIES' ENRICHMENT RESPONSES: Two questions were asked regarding the response pattern following enrichment of each euplankton species; 1. when after enrichment did a species respond (if at all), and 2. to what nutrient(s) did it respond. A significant response to nutrient addition could be either positive or negative, the latter is indicated by a - sign following the species' name in Table VI. An example of a significant negative response to enrichment was provided by the ciliate Strombidium delicati ssimum whose density decreased in all but the nitrate-phosphate enriched enclosures during the fall series (Fig. 13). A species which occurred at a low density prior to enrichment (rare species) required about two weeks to reach bloom concentrations. The density of the algal species, Crucigenia, was plotted as an example of the positive response pattern of a rare species (Fig. 13). For the first eighteen days following nitrate addition this species was so rare that it was not recorded in the samples, then suddenly it became the most abundant algal species in the nitrate enriched enclosures. A species which occurs at a density of one cell per liter and which doubles via fission once every twelve hours will reach a density of 134 million cells per liter in two weeks time if it suffers no mortality This number is high enough to allow for a sizable mortality factor and still result in bloom concentrations (defined by Lackey (194-9) as 500 i n d i v i d u a l s per liter) within two to three weeks. Brook (1958) reported that bloom formation occurred about two weeks after his TABLE VI. SPECIES WHICH RESPONDED SIGNIFICANTLY TO NUTRIENT ENRICHMENT SPECIES NAME Schlzophyta Beggiatoa 11 Micrococcus-like u Pseudomonas Rhabdochromatlum Cyanophyta Coelosphaerium M Microcystis Chroococcus sp. Chlorophyta Scenedesmus denticulatus ii II Anklstrodesinus spiralis Pediastrum tetras Nephrocytium Elakatothrlx-lilce Chlamydomonas sp. large Pedlrvomonas-like RESPONSE + + + + + + + + + + + + + SEASON Fall Winter Spring Summer Summer Winter Summer Spring Summer Fall Fall Fall Fall Summer Spring Summer Summer Summer Summer Summer TREATMENT" •N, P N+P P N N+P P P N+P N+P P N P N+P N Na N+P N+P N N+P N3 N+P N WHEN THE RESPONSE OCCURRED IN THE SERIES Mid Mid Mid Late Early Mid Mid Late Late Late Late Late Early Early Throughout Throughout Mid Early Mid Early SPECIES NAME RESPONSE Chrysophyta Chrysapsis + + Ochromonas + Dinobryon sertularia Ehr. Dinobryon bavaricum Qyclotella glomerata + Frustulia rhomboides + Synedra filiform!s + n ti Navlcula minima Euglenophyta Trachelomonas n Cryptophyta Cryptomonas erosa + Cryptomonas ovata + Unpigmented protozoa Sterromonas sp. + Strobilldium gyrans + 11 M Strorabidium delicatisslmum + 1 WHEN THE RESPONSE OCCURRED IN SEASON TREATMENT THE SERIES Summer Summer Summer Spring Pall Summer Pall Pall Spring Summer Summer P N+P All P N N P N, N+P N, N+P N P Early Late Mid Late Mid Early Late Throughout Throughout Throughout Mid Pall Summer N N+P Late Mid Spring Summer All P Mid Throughout Summer Fall Spring Fall Fall N+P N+P N+P N P Throughout Throughout Early Early Early SPECIES NAME RESPONSE Crustacea Ceriodaphnia sp. + Sida crystallina + M 11 + SEASON TREATMENT WHEN THE RESPONSE OCCURRED IN THE SERIES Summer Pall Summer N+P N+P N+P Throughout Mid Late 1 N P N+P All Ca(N03)2 CaHP0^4H20 Ca(N03)2 and CaHPO^'^O N, P and N+P 72 enrichment of several Scottish Lochs. It is possible, therefore that the lag of two weeks following enrichment prior to bloom formation is the time required for a rare species to respond (growing exponentially) to the effect of fertilization. The two week lag or delayed response is only a lag in the eyes of the observer, the species, presumably, is reacting immediately to the added nutrient but is in such low density that it is not noticed by the observer unti1 a week or more of exponential growth has elapsed. This so-called delayed response by a rare species was the most common pattern observed in this study. It is possible, however, that such a delay was real, i.e. a species which was just below the density threshold of detection may have "waited" a week or two following fertilization to respond. It was impossible to distinguish between these two alternatives from the data obtained in this study. The diatom species, Frustulia rhomboides, is an example of a species which was not rare at the time of enrichment and therefore it was possible to determine whether or not it was responding immediately after enrichment. At the time of enrichment it was at a relatively high density, however, its concentration in the phosphate enriched enclosure was initially only 8 cells per liter above its concentration in the unenriched enclosure (Fig. 13). This is to be expected since both enclosures had just been flushed with lake water. Six days later, however, its concentration in the phosphate enriched enclosure was over 700 cells per liter above that of the control enclosure's. In such cases it is likely that the species is responding directly to the (Figure 13) Significant response patterns to enrichment during the fall enrichment series. The density of the particular species in the control enclosures was subtracted from its density in the enriched enclosures and the logarithm of the difference plotted against time for each sampling period. Missing data is indi-cated by a gap in the plotted line. ENRICHED - CONTROL ENCLOSURE DENSITY (log o x n o . p e r l i ter) N I T R A T E PHOSPHAT E u « p u * b tx o bi o ® PHOSPHATE & N I T R A T E o w rt-© 0 H» H ere B ft o* p H» H« & 0 nutrient itself and not to some secondary effect of the added nutrient. A delayed response from a species whose initial concentration was above the detectable threshold could be interpreted as tempory inhibition by the nutrient or as a response to some secondary effect of the nutrient. Again it would be impossible to distinguish between these two alternatives from the data gathered in this study. Regarding the second question, to what nutrient(s) did a particular species respond, in general, an algal species rarely responded to more than one type of enrichment at any one time. Thus a species whose growth was limited from insufficient dissolved nitrate would be unlikely to respond positively to phosphate enrichment which is consistent with Liebig's Law of the Minimum. In a few cases, however, an algal species did respond in all the enriched enclosures simultaneously as in the case of Ochromonas (Table VI). It is possible that different biochemical "races" of this species could have been responding in the different enclosures or alternatively, Ochromonas may have been reacting to some secondary factor which was produced in the differently enriched.enclosures or it may even have been feeding hetero-trophically. It is only possible to indicate that further study of this species under similar conditions might result in some very interesting observations. A final alternative should also be mentioned, perhaps Ochromonas did not increase its density at all in the enriched enclosures but instead, dropped in density in the unenriched enclosures for one reason or another. The polynomial trend analysis which was used to determine significant response patterns would not have been able to distinguish between these two alternatives. This study was designed to enable the detection of the ge patterns of community change which occur during an induced suc-cession and to determine which of the many planktonic species in this lake were responding significantly to nutrient enrich-ment. In order to find an explanation for the diverse response patterns indicated by this study a different type of approach would have been required. Hopefully, team efforts in which both approaches are conducted simultaneously and information from one used in the other will become more common in the fu-ture. CHANGES IN THE RELATIVE ABUNDANCE OF FUNGI FOLLOWING ENRICHMENT The incidence of fungal infection of planktonic species in Marion Lake was very low. Epipelic diatoms such as Pinnu-laria sp. and desmids (i.e. Cosmarium sp.) appeared to have the highest infection rate. These species were only encoun-tered in the plankton samples following periods of major tur-bulence caused by high winds. Consequently, quantitative es-timates of fungal infection of the epipelic and meroplanktonic species was not possible. Fungal infection of euplankton species was very low (ap-proximately 3% of any one diatom or desmid species). The speci which produced the first algal bloom after fertilization were generally very small (i.e. Chrysapsis) and the incidence of fungal infection of these species was nearly nil. Following this bloom, however, larger species increase in their rela-tive abundance and some of these species may show signs of 77 fungal infection, especially toward the end of their maxima. It appears that these species are more suseptible to fungal infection at this time rather than that fungal infection causes their decline in density. CHANGES IN RELATIVE ABUNDANCE OF BACTERIA FOLLOWING ENRICHMENT: Bacteria, with only one exception, did not respond imme-diately to enrichment (Table VI). Because nearly all the bac-terial species which resulted in a significant response pattern were present in appreciable numbers prior to enrichment, the de-layed response which was typical of the bacterial species was not delayed because they were rare opportunist species. Con-sequently, it appeared that the bacteria were giving a secon-dary response to the artificial enrichment and were not re-acting directly to the added nutrients; otherwise their re-sponse would not have been a delayed one. This may mean that the bacteria required some substance produced by the earlier respon-ding algal species. It appeared more likely, however, that the increase in the detrital component in the water column which was observed during bloom formation may have provided both the sur-face area and the "food" source necessary for rapid bacterial reproduction. CHANGES IN RELATIVE ABUNDANCE OF SOME SECONDARY PRODUCERS FOLLOWING ENRICHMENT: Zooplankton and ciliate predation appears to be the major factor contributing to the sharp drop in relative abundance of the bloom species which appeared in the wooden enclosures following enrichment. Many ciliates (i.e. StrobiIidium and Strombidium, colonial rotifers such as Conochilus and small cladocera) increased dramatically in all the enriched enclosures They also increased in the unenriched enclosures, however, as these also had higher phytoplankton densities than the external controls (A and E). Consequently, statistical trend analyses which compared changes in abundance between the unenriched and enriched enclosures failed to show significant differences in the majority of cases. Had the external controls been used for comparison with the enriched enclosures significant differ-ences between nearly all the ciliates, rotifers and small cladocera would probably have been found. Unfortunately, such a comparison would not be justified because the external control were different in many ways from the enriched enclosures, while the internal controls differed only in one respect (i.e. they were not enriched). It soon became evident in this study that simply enclosing a portion of the water column in Marion Lake either by removing 5 or 10 liters in a polyethylene container or constructing wooden enclosures resulted in significant increases of the phytoplankton standing crop within the isolated water column. It appears, therefore, that lake water renewal (flushing) was a principle factor in contributing to the low phytoplankton standing crop in Marion Lake s DIVERSITY INDICES: The purpose of this thesis was to determine whether the species composition and primary productivity of a freshwater plankton community changes in any predictable pattern following nutrient enrichment. In order to determine whether such a pattern existed in the collected data it was necessary to con-dense the information recorded from each of the samples. Con-sequently, the relative abundance and the number of species in each sample was summarized by calculating the sample's index of diversity. "Numbers expressing the relationship between the number of species and their relative abundance in a biotic community are called indices of diversity" (Odum, et. al., 1960). These indices are sensitive to two factors as already indicated: (1) the total number of species per sample and (2) the relative abundance of the individuals of each species in the sample. The Shannnon-Weaver formula, - P. log. P (Shannon 1 ' ' and Weaver, 1963), was used in this study as a means of cal-culating diversity because it necessitated only a minimal nun>-ber of assumptions about the distribution of the parent popu-lation (Pielou, 1966). In order to express the changes in relative abundance of the various planktonic species following enrichment an in-dex of diversity (H) was used. This index was used by Margalef (1958) and is based on the relative abundance of each species within the sample. The diversity index (H) of each sample was calculated by determining the probability (P.) of finding a particular species in the sample. Thus in a sample of 100 individuals, 10 of which are Pediastrum sp. and 90 of which are Pseudomonas, the probab i1i ty (P ) • of f i nd i ng Ped i astrum sp. is 10/100 or 0.10. By taking the logarithm of 0.10 and mul-tiplying its logged value times itself (0.10) the partial di-versity contribution (P. log„ P.) of Pediastrum sp. in that particular sample was calculated. By adding the partial diver-sity contributions of each species occurring in the .sample together P. 1og z P.), the total sample diversity (H) was determined. The bacteria of any one species in a.particular sample were commonly ten to a hundred times more abundant than the commonest algal species. Consequently, the index of diversity (H) was very heavily weighted in favor of the bacterial frac-tion present in these samples. I have termed this effect "swamping" because the high bacterial density made the index of diversity (H) insensitive to changes in relative abundance of the rarer and larger non-bacterial species. Thus, when diversity (H) was plotted against time following artificial enrichment the resulting line was essentially flat (Fig. W ) . In order to remedy this situation an index of diversity which was less sensitive to shear number and more sensitive to rela-tive biomass was developed by multiplying a species' mean volume times its sample density. This resulted in a new index of diversity (H^) . When diversity (H b) was calculated for the plankton samples taken during this study the enormous biomass of the zooplankton in these samples again "swamped" the index so that changes in the relative biomass of the smaller species were not significant (Table VIII). The zooplankton, which were generally the rarest species in these samples had. such a large individual biomass that they were the dominant species in terms of relative biomass (Table VIII). This is what would be expected •from the inverted Eltonian pyramid of biomass. During bloom formation the number of rotifers and cladocera 81 (Figure \b) Diversity calculated on the basis of relative abundance (H) using the data of the summer enrichment series. No signifi-cant differences between the control and enriched enclosure trendsQusing the method of polynomial trend analysi s) occurred. The triangles represent samples taken from the north enclo-sures and the circles are replicate samples taken from the south enclosures. 3 2 1 3 2 1 3 2 1 3 2 1 3 2 1 82 Summer Series Nitrate & P h o s p h a t e o £ O , P h o s p h a t e o N i t r a t e O A E x t e r n a l C o n t r o l i i i r-—i i i i T - f i i i n r~ i i i ~ i i i i—i i 1 0 1 2 U 1 6 1 8 2 0 2 2 2 4 2 6 2 8 3 0 1 3 5 7 9 11 1 3 1 5 1 7 1 9 2 1 2 3 2 5 J u l y Aug. SPECIES NAME Chromatium-1ike * Crucigenia irregularis Wille Pseudomonas-1ike « Chrysapsis sp. * Ch1amydomonas sp. small * Monas sp. Ochromonas sp. « Pedinomonas sp. Chiamydomonas sp. large Chromulina sp. Gymnodinium sp. small Merismopediurn punctata Meyen Coelosphaerium sp. Cryptomonas erosa Ehr. Microcystis sp. Chroococcus sp. Mallomonas sp. small El akatothr i.x-1 i ke Quadrigula sp. Ankistrodesmus falcatus (Corda) Ralfs. Cyclotella glomerata Bachm. Oocyst is parva West + West Strombidium delicatissimum Leeg. Scenedesmus denticulatus (Lag) G.M. Smith Fragilaria pinnata Ehr. Dinobryon bavaricum Imhoff. Oocystis solitaria Wittrock Synedra filiform is Cl-EuL Cryptomonas ovata Ehr, Gymnodinium sp.' large Colpoda-1i ke TABLE VIII NUMBER/LITER 632000 379000 379000 253000 253000 126000 126000 126000 126000 126000 126000 85800 15000 12000 9000 8580 5150 3600 3430 3430 2570 2400 1720 1200 900 858 858 858 858 300 300 PARTIAL DIVERSITY CONTRIBUTION 0.484 0.390 0.390 0.312 0.312 0.201 0.201 0.201 0.201 0.201 0.201 0.154 0.040 0.034 0.027 0.025 0.017 0.012 0.012 0.012 0.009 0.009 0.007 0.005 0.004 0.004 0.004 0.004 0.004 0.001 0.001 ACCUMULATED PARTIAL DIVERSITY 0.484 0.873 1 .260 1 .570 1.880 2.080 2.290 2.490 2.690 2.890 3.090 3.240 3.280 3.320 3.340 3.370 3.380 3.400 3.410 3.420 3.430 3.430 3.440 3.440 3.450 3.450 3.460 3.460 3.460 3.470 3.470 SPECIES NAME Glenodinium albulum Lund Arthrodesmus incus (Breb) Hass. Oicomonas sp. Keratella cochlear is Ehr. Polyarthra euryptra Wierzejski Conoch i1 us sp. Diaptomus oregonensis Lilljeborg Cyclops bicuspidatus thomasi S.A. Forbes Ceriodaphnia sp Sida crystallina O.F. Muller Polyphemus pedicuius Linne TOTALS NUMBER/LITER PARTIAL DIVERSITY CONTRIBUTION ACCUMULATED PARTIAL DIVERSITY 300 0.001 3.470 300 0.001 3.470 300 0.001 3.^80 30 .001 3.480 10 .001 3.480 6 .001 3.480 5 .001 3.480 4 .001 3.480 1 .001 3.480 1 .001 3.480 1 .001 3.480 2830000 3.48 = H TABLE VIII SPECIES NAME BIOMASS/LITER Diaptomus oregonensis Li11jeborg ** 2815.00 Gymnodinium sp. small 804.66 Cyclops bicuspidatus thomasi S.A. Forbes ** 498.80 Crucigenia irregularis Wille 63.55 Polyphemus pediculus Linne ** 45.00 Chromulina sp. 33.85 Monas sp. 33.22 Chiamydomonas sp. large 27.78 Gymnodinium sp. large 19.64 Chrysapsis sp. * 16.42 Chiamydomonas sp. small * 16.42 Si da crystal 1ina O.F. Muller ** 15.00 Keratella cochlear is Ehr. ** 11.40 Strombidium delicatissimum Leeg. 7.17 Cryptomonas erosa Ehr. 6.09 Dinobryon bavaricum Imhoff, 4.04 Mallomonas sp. small 3.62 Polyarthra euryptra Wierzejski ** 3.50 Quadrigula sp. 3.45 Chroococcus sp. * 3.28 Ochromonas sp. " 3.16 Pedinomonas-1ike 3.16 Fragilaria pinnata Ehr. 1.77 Colpoda-like 1.64 Ceriodaphnia sp. ** 1.38 Chromatium-1ike * 1.26 Conochilus sp. ** 1.26 Pseudomonas-1ike * 1.14 PARTIAL DIVERSITY ACCUMULATED CONTRIBUTION BY BI0MASS DIVERSITY 0.418 0.418 0.446 0.864 0.354 1.218 0.088 1.306 0.067 1.373 0.053 1.426 0.053 1.479 0.046 1.525 0.034 1.559 0,030 1.589 0.030 1.618 0.030 1.646 0.022 1.667 0.015 1.683 0.013 I.696 0.009 1.705 0.008 1.713 0.008 1.722 0.008 1.730 0.008 1.738 0.007 ' 1.745 0.007 1.752 0.004 1.757 0.004 1.761 0.004 I.765 0.003 1.768 0.003 1.771 0.003 1.774 SPECIES NAME BIOMASS/LITER Cryptomonas ovata Ehr. . 1.01 Elakatothr ix-1i ke 0.65 Synedra filiformis Cl-Eul. 0.65 Ankistrodesmus falcatus (Corda) Ralfs. 0.65 Oicomonas sp. 0.65 Arthrodesmus incus (Brab) Hass. 0.64 Oocyst is parva West + West 0.60 Glenodinium albulum Lund 0.53 Cyclotella glomerata Bachm. 0.52 Scenedesmus denticulatus (Lag) G.M. Smith 0.42 Mer i smoped i urn punctata Meyen <> 0.34 Oocystis solitaria Wittrock 0.32 Coelosphaerium sp. .* 0.21 Microcystis sp. * 0.09 H, = 1.80 TOTALS b 4453.97 1 6 B iomass/ Ii ter x 10 PARTIAL DIVERSITY ACCUMULATED CONTRIBUTION BY BIOMASS DIVERSITY 0.003 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.001 0.001 0.001 0.001 0.001 .777 .779 .781 .783 .785 .786 .788 .790 .791 .792 .793 .794 .795 .796 1 .796 87 increased, especially Ceriodaphnia and Sida crystal 1i na (Table VI). This increase in density of only a few zooplankton species was nevertheless very substantial when calculated in terms of relative biomass. Consequently, the index of diversity (H^) suddenly dropped as an algal bloom began (Fig. 1 j.) . Because this index was so insensitive to changes in relative abundance of the smaller species, however, it did not adequately repre-sent the total community and therefore an index which was sen-sitive to changes in relative abundance of all the species irrespective of their size or biomass was sought. The index of diversity based on relative productivity (Hp) was sensitive to changes in community structure following enrichment and was adopted for use in this study. Consequently statements about species diversity are based on H calculated P diversity. The index of diversity (H ) is similar to the P index developed by Margalef (1958) which calculated diversity on the basis of relative abundance (H) . Both indices use the m formula, diversity = - < P . log P . However, P. is defined i i 2 i i differently in each case, Margalef defines P as the "pro-i bability of finding the It'1 species". This is equal to n/N where n is the number of individuals of species "I" in the sample and N is the total number of individuals in the sample. Defining diversity in this way resulted in a very uneven repre-sentation of the different trophic levels found in the Marion Lake samples. Thus the zooplankton (designated with a double asterisk in Table VII) do not make a significant contribution to the diversity index. All species below the line in Tables VII, VIII, and IX fail to contribute significantly to the total diver-(Figure 15) Diversity calculated on the basis of relative biomass (H ) using b the data of the summer enrichment series. Significant differences in all the enriched enclosures were calculated using the method of polynomial trend analysis of Fisher (1963). Summer Series 89 Nitrate & Phosphae X) X 03 « (0 E o bo 0) > ffl CD OC c o "O 0) CO ro m o > Q Internal Control External Contro l "i—r -1—i—r-1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8 3 0 July "T i i—i—r—i—i 9 1 1 1 3 1 5 1 7 1 9 2 1 2 3 2 5 Aug. sity of that sample. Because it was shown (Fig. 14) that the index of diversity (H) failed to reflect changes in species composition during induced succession, the index H was adopted P in its place. The index of diversity, H , which is based on the re-lative productivity of each species,^ was calculated in the following manner: H = - " p log 2 P.. P. is defined as P j 1 i i p/P where p is the productivity of species I in the sample and P is the total productivity of the sample. Productivity is defined here as the product of a species' mean sample density and biomass times its annual turnover rate. Thus Diaptomus oregonens i s with one egg batch per year was assigned a turn-over coefficient of one (Table IV). This, times its mean vol-ume (560,000,000 cubic microns) and sample density (i.e. 5 per liter as in Table VII), gives it a productivity value (p) of 9 2.8 x 10 units. By summing the p values for each species in the sample the total productivity (P) was determined and p/P or P. was then calculated for each species in the sample (Table IX). The pseudomonad bacterium 1isted in the same table (Row 19) was present in the plankton for 94 days of the year reproducing by fission roughly twice a day in that period. Hence it was given a turnover coefficient of 200 (188 rounded to the appropriate number of significant figures). This times its mean volume (4.5 cubic microns) and sample density (378,900 per liter) gives it a productivity value (p) of 341 x 1 0 6 . The relative productivity contribution (P. log 2 P.) for each species is then calculated and the species are ranked in order of their relative productivity contribution. The partial diversity TABLE IX RELATIVE SPECIES NAME PRODUCTIVITY/LITER Gymnodinium sp. small 60300 Crucigenia irregularis Wille 6370 Chiamydomonas sp. large 4170 Chromulina sp. 3380 Diaptanus oregonensis Lilljeborg ** 2820 Chiamydomonas sp. small * 2460 Monas sp. 1660 Chrysapsis sp. * 1640 Gymnodinium sp. large 1470 Chroococcus sp. * 655 Cyclops bicuspidatus thomasi S.A. Forbes ** 498 Pedinomonas-1 ike 473 Polyphemus pedicuius Linne A * 450 Cryptomonas erosa Ehr. 434 D i nobryon bava r i cum 1mhoff. 404 Chromatium-1ike 378 Mallomonas sp. small 361 Quadrigula sp. 344 Pseudomonas-1ike * 341 Ochromonas sp. * 315 Strombidium delicatissimum Leeg. 304 Keratella cochlearis Ehr. A * 285 Sida crystal 1ina O.Fi Muller AA 150 Polyarthra euryptra Wierzejski A * 96 Fragilaria pinnata Ehr. 88 Cryptomonas ovata Ehr. 75 Colpoda~li ke 68 Merismopedium punctata Meyen « 68 Elakatothrix-1ike 64 Ankistrodesmus falcatus (Corda) Ralfs. 6k Arthrodesmus incus (Breb) Hass. 63 01 cyst is parva West+West 60 PARTIAL DIVERSITY CONTRIBUTION ACCUMULATED PARTIAL DIVERSITY 0.391 0.269 0.204 0.177 0.156 0.141 0.1 06 0.105 0.097 0.051 0.041 0.039 0.038 0.037 0.035 0.033 0.032 0.031 0.030 0.028 0.028 0.026 0.015 0.010 0.009 0.008 0.008 0.007 0.007 0.007 0.007 0.007 0.390 0.660 0.864 1 .040 1 .190 1 .340 1.440 1.550 1.650 1.700 1.740 1.780 1.820 1 .850 1 .890 1 .920 1 .950 1 .980 2.010 2.040 2.070 2.100 2.110 2.120 2.130 2.140 2.150 2.160 2.160 2.170 2.180 2.180 RELATIVE , PARTIAL DIVERSITY ACCUMULATED SPECIES NAME PRODUCTIVITY/LITER x 10 CONTRIBUTION PARTIAL DIVERSITY Scenedesmus denticulatus (Lag) G„M. Smith Coelosphaeriurn sp. Glenodinium albulm Lund Synedra filiformis Cl-Eul. Oocystis solitaria Wittrock Oicomonas sp. Conochilus sp, Cyclotella glomerata Bachm. Ceriodaphnia sp. Microcystis sp. TOTALS 42 0.005 2.190 42 0.005 2.190 39 0.005 2.200 32 0.004 2.200 32 0.004 2.210 32 0.004 2.210 31 0.004 2.220 25 0.003 2.220 13 0.002 2.220 2 0.001 2.220 90600 Hp = 2.22 values listed In Column 2 of Table IX were calculated by mul-tiplying P. log^ P. by minus one. Summing the partial diver-sity contributions of each species in the sample gives. H^ = 2.22. This procedure was followed for each of the 300 samples taken in the four enrichment series. The results of the summer series are summarized by Figure 16. Samples withdrawn from the enclosure at the time of enrich-ment had relatively high diversity (H^). Within a week this diversity dropped to less than half its initial value. After another week or two diversity began to increase in a series of "ups and downs" which culminated in a diversity which was over two times higher than the preenrichment level'(Fig. 16). This same trend was noted in the other three enrichment series. Thus it appears typical for the successional series which oc-curred following enrichment in Marion Lake. 94 (Figure 16) Diversity calculated on the basis of relative productivity (H ). P Significant differences between all of the enriched enclosures and the control enclosure trends were recorded (P £ 0.05) using the method of polynomial trend analysis (Fisher, 1963). Summer S e r i e s 95 0 . 5 -0 . 3 -0.1 -"i T r—i i—r—i—i—i—r—i—r 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8 3 0 1 I I I I I 1 ! 1 I I 1 3 1 5 1 7 1 9 2 1 2 3 2 5 July Aug. DISCUSSION SOME EFFECTS OF ARTIFICIAL ENRICHMENT: The addition of one or more nutrients to a lake in which these nutrients were previously sparse may initially inhibit phytoplankton productivity (Fournier, 1967) or may result in a relatively rapid increase in the relative abundance and pri-mary productivity of a few species (Brook, 1958). In either case the added (inducing) nutrient(s) soon returns to its pre-enrichment concentration. A schematic representation of the major changes in standing crop, nutrient concentration and community diversity plotted against time is presented in Figure 16. The initial drop in diversity is a result of the marked increase of one or two species following nutrient enrichment. The point of lowest diversity is roughly correlated with the point of highest total algal density. This dense standing crop of phytop 1ankton is usually'associated with a bloom which is formed by one or more of the dominant algal species. Following the bloom .diversity increases as one group of species is replaced by another, diversity.rises during the transition phase then levels off as the new group of species becomes dominant then increases again as this group is replaced by yet another. This gives rise to a step wise increase in diversity following bloom formation (Fig. 16). This study was not continued for a long enough period of time to determine whether a so-called "climax" or "mature" Figure 17. A schematic representation of the changes in plankton standing crop, enriched nutrient concentration, and diversity following an artificially DAYS F O L L O W I N G ENRICHMENT community is ever reached and maintained. Brook (1958) con-tinued monitoring the changes in the species composition of the phytoplankton for 18 months after his artificial enrichment at which time one group of species was still replacing another. Possibly a true "climax" is never reached in the lacustrine environment as environmental conditions there rarely remain constant for any length of time. Furthermore, planktonic species do not appear capable of altering their lacustrine environment to the extent which terrestrial plants demonstrate. A MODEL FOR PLANKTON SUCCESSION: Ramon Margalef (1958), Odum, et. al. (I960), Cooke (1967), Beyers (1963) as well as a number of others maintain that suc-cession has a direction; that succession progresses from a state of low complexity (heterogeneity) to one of increased complexity and stability. According to the above sources, succession in the plank-tonic community leads to a mature (older) community with the following characteristics: 1. A community composed of relatively long-1ived species. 2. Such species are well adapted to their particular en-environment and 3 . are isolated in small breeding communities having re-latively few adaptations for dispersal. k . Due to the increased isolation of small units of the population the frequency of homozygosity is high and there is a resulting limitation of genetic re-assort-ment. 5. The relative rate of reproduction of these species is low. It appears that the more efficient or special-ized a particular species becomes the slower its par-ticular growth rate. 6 . Competition is shifted from intra- to interspecific forms. 7. Organisms are efficient in using the available nutrients and growth factors resulting in little of these substances accumulating in the abiotic environment. 8 . As a result of these factors a steady state exists between the organism and its environment. The conclusions reached above about the outcome of planktonic successions were largely supported in my study (in situations where comparisons could be made). The results of my study are summarized ih TABLEX,' 0 n l Y minor differences exist between the above and Table X. For instance, in this study "bloom" conditions always appeared to be associated with the lowest diversity and highest standing crop and productivity ? and therefore blooms would be indicative of communities with low "maturity" in Margalef's sense of the word. Margalef (1963b), however, refers to a dinof1agellate "bloom" as indicative of a fairly mature successional community. Thus it is not clear where blooms exist on the successional maturity scale. Since all blooms are a result of major oscillations in abundance and since most have a relatively low diversity it is unfortunate that they would not all share a similar position of low maturity in successional terms. REGRESSIVE SUCCESSION: The effects which nutrient addition had on the species composition, standing crop and primary productivity of the plankton within the enclosures in Marion Lake has led to the following generalizations. At the time of fertilization a community of organisms TABLE X . A LIST OF THE MAJOR SEQUENTIAL E V E N T S W H I C H OCCUR FOLLOV/ING INDUCED BLOOM FORMATION IN MARION LAKE. The observed event (i.e. nutrient depletion) is recorded in the left hand column and the hypothesized consequences of the observed changes are listed in the center and right hand columns. SEQUENTIAL EVENTS FOLLOWING "BLOOM" FORMATION • \ DIRECT CONSEQUENCES "STEADY STATE" RESULT D i ssolved nutr i ents removed from the water column. Selection for more efficient and less "leaky" nutrient con-sumers. Species with larger si^e. lower R and lower P/B . • o Dissolved nitrates become scarce. More species with a high carot-enoid to chlorophyll ratio (Yentch and Vacarro, 1958). These species reproduce slower, hence R n approaches Environmental accumulation of cells, i.e. h i gh s tand i ng crop Increased zooplankton survival resulting in increased grazing pressure. •'. Selection for inedible forms having spines or toxins with resulting increased biotic • di versi ty. Food gathering mechanisms become more specialized. ; More kinds of organisms, high d i vers i ty (H^). Increased food-chain stabi1i ty (MacArthur,' 1955) . R = intr i ns i c -rate of i ncrease ; P / B = ( m 9 Carbon f ixed/mVhr)/(mg Carbon stand i ng crop) . R n = community respiration rate; P n = community productivity. 101 exists together in the plankton. The addition of nitrate or phosphate to this community does not immediately alter the abundance of most of these species. One or two of the rarer species, however, often respond dramatically to enrichment by greatly increasing their density in the enriched'enclosures. (Abundant species may also respond in a similar manner as well.) Consequently, the total number of species in samples taken fol-lowing enrichment remains fairly constant or may even increase (Fig. 11). As the added nutrient concentration returns to its pre-enrichment level (Fig. b) different species come to dominate (in terms of their relative productivity) the plankton community of the enriched enclosures. By this time, approximately two and a half weeks after fertilization, the dissolved nutrient concen-tration of the added nutrient within the enriched enclosure has returned to its pre-enrichment level. At this point the plankton diversity begins to increase. According to the foregoing description it appears that the enrichment of a freshwater phytoplankton community results in a succession composed of two opposed stages. The first stage is characterized by a successive reduction of diversity often culminating in a bloom in which a few species dominate the community in terms of their relative productivity of- abundance. This type of succession is termed a "regressive succession" because its "direction" of change is the reverse of that normally en-countered in primary and secondary successions. Regressive suc-cessions are induced by the alteration of any factors which upset the dynamic equilibrium which exists between the community members and their environment. For example, a regressive suc-cession was induced by the systematic removal of the star fish, 102 Pisaster ochraceous, from the intertidal community (Paine, 1966). P i saster removal resulted in the increase in the relative abun-dance of the barnacles in these areas and this eventually re-sulted in the barnacles crowding out nearly every other inter-tidal species, a situation comparable to a "bloom". The initial addition of nutrients or pollutants to the phytoplankton results in the same phenomenon i.e. one or two species bloom and consequently dominate the community in terms of their relative productivity. The regressive succession is terminated by the establishment of a new dynamic equi1ibriurn between the bloom forming species and the factors which caused the disruption of the initial equilibrium. The regressive suc-cession, however, is usually very temporary because the fac-tors which were initially responsible for inducing the succession are alleviated by the very biotic response which they initiate. Thus as the new species uti1ize the added nutrients or pollu-tants the concentration of these substances in the water column drops until it returns to the pre-enrichment level (barring further additions). This then results in a secondary succession (phase two) which re-establishes the original dynamic equili-brium with its higher biotic diversity. In summary, the alteration of the planktonic environment by natural causes such as upwelling or vernal mixing or even man-incuded factors such as those classified as pol1utants, results in a regressive succession which usually culminates in an algal bloom and is characterized by a trend toward decreased diversity and increased primary productivity of the planktonic commun i ty. THE ROLE OF THE RARE SPECIES: The great majority of the 167 eupiankton species observed in Marion Lake (Table IV) were very rare. It is important to distinguish between two different types of rare species. Odum, et. al. (i960) describes a rare species which is a "special-ist" in the sense that Limbaugh's (1961) "cleaner shrimp" were specialists. Such species are adapted to a particular type of activity within their community. A human analogy of this type of specialist species would be a doctor's doctor. Odum describes a hierarchy in which the rare species are those which are furthest removed from what he terms the "basic occupation" of their particular community. Thus a doctor's doctor would be a relatively rare individual because his "functional distance" from the basic occupations of his community (i.e. logging) would be relatively large. The grocer, on the other hand, deals directly with the loggers and would be closer, in Odum's sense, to the basic industry. Therefore, one would expect to find more grocers than doctor's doctors in such a community. A second type of rare species has been described by Hutch-inson (1951) as an "opportunist" species and differs from the above type of rare species in two important ways: (1) Unlike the- specialist species which reproduce quite slowly and are long-lived, the less specialized opportunist species are ca-pable of extremely rapid reproduction under favorable condi-tions and (2) Theyoften exist in very low numbers in a semi-or totally dormant condition. Thus the opportunist species takes no active part in its community (when rare) until con-ditions favor its reproduction. 1 ok These two types of species may be valuable indicators of the amount of organization existing within any particular community. In communities where "opportunist" species-are abundant relative to the number of "specialist" species it is likely that a low degree of community organization exists. When the reverse is true a community with a high level of or-ganization as described by Odum, et. al. (I960) exists. In Marion Lake, which might be termed "unstable" as a result of its frequent and irregular "flushings" resulting from high inlet discharge, the plankton community rarely appears to have time to even approach a stage of successional maturity of the nature described for various other lakes (lund, 1965)-It appears that before sufficient time has occurred for any substantial organization to take place high inlet discharge removes the majority of the plankton population via the outlet and alters physical and chemical factors in the water column sufficiently to induce a regressive succession. This fact is reflected by the species composition of the plankton in Marion Lake where over 90% of the plankton are spherical nannoplankters i.e. small species of Chiamydomonas and Merismopedia. According to Margalef (1967) such species are indicative of a low degree of successional maturity and hence low community organization. Furthermore, a large number of "opportunist" species are present in the lake. The evidence for this is that addition of a par-ticular nutrient in any one season results in the increase of one or more previously rare species ("opportunists"). The species which respond to nitrate addition at the start of the enrichment series are replaced by species which respond later in the successional series. The opportunist species which 105 respond to nitrate in the fall series are different from those which respond to phosphate or nitrate-phosphate combination in that season. Moreover, different rare species respond to the same nutrient at different times in the y e a r . Consequently, a large number of opportunist species appear to be potentially available, existing either in some resting form in the sediment or in the water column at very low densities so that they are rarely detected until conditons favoring.their reproduction occur. A good example of such a species is Elakatothrix which has never been recorded from the plankton of Marion Lake with the exception of the nitrate-phosphate enriched enclosure where it occurred at a very high density (100,000 per liter). Therefore, the plankton and sediments of Marion Lake appear to abound in various kinds of "opportunist" species while "specialist" species, as described by Odum, e t . a l . (I960), do not contribut substantially to the plankton com-munity of this lake. It may be possible to use the ratio of the number of op-portunist species to the number of specialist species as an indication of the degree of organization or maturity which exists in the plankton of a particular lake at any specified time. As the number of specialist species increases and the number of opportunists drops the level of community organi-zation would be 1ikely to rise. DIVERSITY AND PRIMARY PRODUCTIVITY: Following artificial enrichment diversity decreases (Fig. 15) and primary productivity increases (Figs. 8 , 9 and 10). This relationship appears to general for lacustrine 106 environments (Yount, 1956). Thus, the more eutrophic or pro-ductive a particular lake, the lower its plankton diversity is likely to b e . This observation is contradictory to statements made by Connell and Orias (1960) which claim that increased productivity results in increased diversity. A possible explanation of this contradiction may lie in a consideration of the time factor. It is possible that many eutrophic lacustrine environments exhibiting low diversity and high algal productivity have not maintained their high productivity for sufficient time to allow the more "specialized" species the necessary time to displace the type of species described by MacArthur and Levins (1964) as a "Jack-of-al1 -trades". The latter, although less specialized, is capable of rapid colonization and, furthermore, should persist as long as certain similarities between the different resources which they utilize exist (MacArthur and Levins, 1964). Consequently, it may take fairly stable conditions and a good deal of time before the "Jack-of-al1-trade" species can be replaced by a more specialized form(s). Evidence from the paleological studies of Frey ( i960) and Goulden (1964) indicates that periods of sustained (on a geological time scale) high productivity were correlated with high cladoceran diversity. Studies by Stockner (1967) of the diatoms in sediment cores from Lake Washington, on the other hand, indicated a significant inverse correlation between dia-tom diversity and density. T h l s , however, was only evident in the top (surface) layers of the core samples. Thus it appears that insufficient time had elapsed following the tem-porary eutrophication of Lake Washington after World V/ar I 107 for the fauna and flora of the plankton to attain a high diver-sity. The immediate result of eutrophication is the reduction of biotic diversity and the augmentation of primary and secondary productivity. When a sustained level of high productivity is maintained for a century or more it is possible that the biotic diversity of that area will increase. Whether such an increase would result in a concomitant decrease in the total productivity of the system is not known. The advantages of studying the planktonic community were in-dicated in the introduction to this paper. The major advantage was the rapidity in which the species of the plankton community progress toward successional maturity making it an ideal community for successional studies. It is significant that a popu1 ation capable of rapid succession is prevented from reaching successional maturity largely as a result of insufficient time i.e. .conditions change before sufficient time for the organizational processes necessary for successional maturity can occur. According to the discussion of the relationship between pro-ductivity and diversity it appears that one must know both the general level of production as well as the length of time in which that level was maintained before accurate predictions concerning biotic diversity can be made from product!vity measures. 108 SUMMARY 1. The results of biweekly measurements of primary productivity, dissolved nitrate and phosphate concentrations, plahkton standing crop and species composition following artificial enrichment of six wooden enclosures in Marion Lake indicated that plankton succession follows a predictable pattern. 2. This successional pattern was repeated regardless of season and prevailing physical conditions every time the enclosed plankton community was artificially enriched. 3. These successions were terminated by heavy and persistent rains which removed the majority of the plankton from the lake by flushing them out of the enclosures and lake and into the outlet stream. k . The plankton successions (induced by artificial enrichment) occurred in two phases. The first phase, termed a "regressive succession" was indicated by a decrease in diversity (H p) of the planktonic community following an increase in relative product!vity a few phytoplankton species. Concomitantly, primary productivity and standing crop in^ creased while the dissolved nitrate and/or phosphate concentrations in the water dropped. A decline in denity of the species forming the algal blooms signaled the end of the regressive succession. The second phase, which was similar to a terrestrial secondary succession, was indicated by an increase in plankton diversity and a corresponding decrease in standing crop and primary productivity. 109 5 . Three hundred and forty-two taxa were identified from Marion Lake plankton samples, one hundred and sixty-seven of which were euplankton species. Many of the rarer taxa appeared to be what Hutchinson (1951) termed "opportunist" species, and the majority of these were extremely specific in their physico-chemical require-ments. Different opportunist species responded at different times in the year and at different times in any one season to identi-cally enriched enclosures. 6. It appears that a relationship exists between biotic diversity and temporal stability. Planktonic communities which have main-tained a high level of productivity over a substantial period of geological time have high diversity. 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