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Some relationships between phytoplankton populations and physical chemical factors in Ladysmith Harbour,… McAllister, Carey Douglas 1956

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SOME RELATIONSHIPS BETWEEN k-hTTOPLANKTOM POPULATIONS AND PHYSICAL-CHEMICAL FACTORS IN LADYSMITH HARBOUR, BRITISH COLUMBIA CARET DOUGLAS MCALLISTER A THESIS SUBMITTED I N P A R T I A L FULFILMENT OF TBI REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS In the Department of ZOOLOGY We accept this thesis as conforming to the standard required from candidates for the degree of MASTER OF ARTS. Members of the Department or Zoology THE UIIYERSITT OF BRITISH COLUMBIA April, 1956 l i ABSTRACT The physical characteristics and distributions in space aad time ©f salinity, temperature and phytoplankton in Lady-smith Harbour are described* It i s shown that water exchange in Inner Ladysmith Harbour i s the result of horizontal mixing and a two-layered circulation. The mean rate of water renew* al in th© Inner Harbour i s calculated to be 32.2. percent of the mean volume per day* It i s shown that four blooms of phytoplankton may occur in Ladysmith Harbour during the grow-ing season, each having characteristic distributions. The distributions of phytoplankton during the f i r s t three blooms are discussed in relation to the physical characteristics and processes in and near Ladysmith Harbour. It is stated that the generic composition of the phytoplankton in Ladysmith Harbour varies in time and space. The rat© of water exchange i s shown to be such that endemic species of diatoms may develop in the Inner Harbour and that under certain conditions apparent endemisfii may occur. It i s shown that both population success** ion and local sequence may be responsible for changes in the generic composition of the phytoplankton with time. Using the mean rate of water exchange and the assumption that renewal of water results entirely from the two-layer circulation, the net rates ofAphytoplankton into Inner Ladysmith Harbour are calculated. It i s shown that variations in the standing i i i crop appear to be more closely related to changes in the rate of advection of phytoplankton than to changes in the rate of removal of cells by zooplankton« The rate of recruitment of phytoplankton by growth i s calculated. It i s computed that recruitment of cells by advection exceeds the recruitment by growth in Inner ladysmith Harbour* i v ACKNOWLEDGMENTS The author wishes to make acknowledgments to Dr. W. Cameron, under whose direction this work was started, for his encouragement and suggestionsj to Dr, R.F. Scagel, under whose direction the thesis was written, for his advice and c r i t i c i s m and f o r data made available by him; to Dr. D.B. Quayle f o r suggesting the problem, f o r his generosity with equipment, time and advice and for making available unpublished data; and to the Provincial Department of Fisheries, under whose employ the f i e l d work leading to this thesis was carried out. He also expresses his gratitude to P a c i f i c Oceanographic Group and i t s members fo r advice and use of equipment, the Department of Transport, Air Services Division for the issuance of unpublished meteorological data, and the Dominion Bureau of Power and Water for freshwater discharge data. V ABSTRACT i i f i B L i ar cyiiT&m» • J*i»*A '>Jt* IPXdi«us& .....«.•»..«».».**.»...«»»........»..*... vxi X . X >1 i AOWA i Ii)!! ....................................... 2 XX. 0 'XJuwU i * wfl <^ f»M Xivi»« T?*c««* d^X& ..»».....*.».«..... 5 km *>'.orpho*etry 9 &* freshwater Oisca&rgo 10 O. J&stributlofi of Salinity ..................... 11 D« Distribution of lenj^ereture .................. 16 £• «®ter Sxehtng® i n ' the Inner K&roouir .......... 2 3 1. lid® 23 2. H*ne*ral Bat«a from Ch*ng«» i n 5©ii:ilty.. 27 3* Circulation •••.••.••**»*...•*•«.•.•.•«• 33 4. Two-lay#jp«i Circulation &£<ch&n&* &et«s 38 a. Continuity of 3alt and folu©@ .... jJH ©. Continuity of Meat end Volusio .... 43 F. wistrioution of *lankton k$ 1. Abundance 4i 2. Cistrifetttian of Goners of rnytoj^lankton. 53 0. Aavection, d r i f t i n g and Growth of i fcytopiauxton in the Inner harbour ......... 60 vi fABLfi Of GU«M*TS (Cont'd) rage 1. Adveetion 60 2. Graslng 61 3. Growth 65 I ? . CONCLUSIONS 70 ¥. u t & u T t m cum .. 75 v i i LIST OF FIGURES Figure Page 1. Ladysmith Harbour: Distribution of depth 1 2. Stuart and Trincomali Channels ........ 4 3« Oceanographic stations i n Ladysmith Harbour .... 6 4* Depths of isohalines, Station I, Ladysmith Harbour, Summer, 1954 ...... . 12 5. Salinity, Ladysmith Harbour, May 3, 1955 14 6. Salinity, Ladysmith Harbour, July 16, 1954 ..... 14 7. Salinity, Ladysmith Harbour, August 27, 1954 .,. 14 g. Temperature, Ladysmith Harbour, May 3, 1955 .... 1& 9. Temperature, Ladysmith Harbour, July 16, 1954 Id 10. Temperature, Ladysmith Harbour, July 24, 1954 1$ 11. Temperature, Inner Ladysmith Harbour, August 4, 1955 20 12* Temperature, Inner Ladysmith Harbour, June 20, 1955 * 20 13. Temperature, Section F. (a) June 21, 1955, Flood Tide 20 (b) July 21, 1955, Ebb Tide 20 14. The Volume of Inner Ladysmith Harbour • .. 26 15 o Sigma-T June 22, 1954 35 16. Sigma-T July 16, 1954 . 35 17. Sigms-T August 5, 1954 35 l i . Sigraa-T December 22, 1954 35a 19. Sigma-T March 17, 1954 • 35a 20. Mean distribution of velocity with depth, May 29-30, 1954 and August 10-11, 1955 35a v i i i LIST OF ?iUUit&3 ( cont'd) Figure Page 21. Salinity, Ladysmith iarbour, July 7, 1954 50 22. Temperature, Ladysmith Harbour, July 7, 1954 ••• 50 23. Concentration of phytoplankton, Ladysmith Haroowr, July 7, 1954 50 24* Moan r e l a t i v e magnitude of standing crop of phytoplankton near l o r l i e r Fas* end im the Ladysmith Harbour Kegion 52 25. Salinity, Ladysmith Harbour-iorlier Pass, .July 2, 1914 .. 52 26. % e*iao»owQ*i. Udyamita Harbour, May 3, 1955 56 27. * Cnaotocoros. Ladysmith Harbour, May 10, 1955.. 56 2*. % etaotowos. Ladysmith Harbour, May 19, 1955.. 56 29. Distribution of Chaetocaroa with depth. Station I j , Hay 18-19, 1§55 3* 30. % Skeletonema. Ladysmith Harbour, June 12, 1954. 5* 31. £ Skeletoned. Ladysmith Harbour, Juno 22, 1954 • 5^ 32. Station X standing crop of plankton • 64 33* Advection and Grasiag of phytoplankton 64 34. Components of total crop of phytoplankton ....... 64 SOME RELATIONSHIPS BETWEEN PLANKTON POPULATIONS AND PHYSICAL-CHEMICAL FACTORS IN LADYSMITH HARBOUR, BRITISH COLUMBIA I, INTRODUCTION Two types of agents may control the abundance, composition and distribution of plankton in a local area* First, local processes, such as grazing, nutrient depletion and regeneration, mixing and heating may act on local plankton populations* Secondly, renewal of the water in the area through circulation or mixing may act on populations directly by adding and re-moving organisms and indirectly by influencing the properties of th© water in the area* Many of the qualitative effects of different types of water movements on the production and distribution of plankton are well known and have been used to account for and predict various marine biological phenomena* An indication of success attained in this field i s the fact that the converse is also true: distributions of marine organisms have been used in deducing physical processes in the sea* However, the possibility of defining quantitative relation-ships between water movements in an area and i t s plankton has received l i t t l e attention* Ketchua (1954) extended his 3 eatuarlne circulation theorem to express the relationship be-tween rates of circulation and distributions of endemic plank-ton populations and summarises the other two attempts at work of this nature {Barlow, 1952, Ketehum e| 1952). In this thesis oceanographic data from Ladysmith Harbour have been used in an attempt to assess the effects of local factors and water exchange on th© distribution and total crop of phytoplankton in Ladysmith Harbour. Ladysmith Harbour i s a small, narrow bay situated on Latitude 49°W. on the east coast of Vancouver Island. In contrast to the typical British Columbia Inlet, i t i s short, about four and one half miles long, shallow, with extensive intertidal flats and apparently less dominated by fresh water inflow. A constriction, approximately at the middle, divides the harbour into a shallow inner portion and a wider and deeper outer bay (fig* 1)« The harbour opens into Stuart Channel, a typical coastal passage separated from Georgia Strait by two chains of islands ( f i g . 2). 5 I I . COLLECTION AND TREATMENT OF DATA Sixty-seven cruises were completed i n and near Ladysmith Harbour between May, 1954 and August, 1955* Six permanent stations were established i n the Harbour ( f i g . 3) and were sampled f o r s a l i n i t y , temperature and plankton at intervals ranging from three to ten days i n the summer of 1954* Between September, 1954 and May, 1955 four stations (three of the o r i g i n a l permanent stations and one additional) distributed along the length of the harbour were occupied at intervals of (about a month. In May, 1955 emphasis was shifted from longitudinal sampl-ing of the harbour as a whole to a more intensive study of the Inner Harbour. A grid of stations ( f i g . 3) covering the Harbour was established. P e r i o d i c a l l y the whole grid or selected l a t e r a l sections were sampled for plankton, s a l i n i t y end tempera* ture. I t was found that the length of time necessary to secure a l l three of these types of data on a single cruise was such that changes i n dis t r i b u t i o n due to t i d a l action could be s i g n i f i c a n t . For t h i s reason after May, 1955 each cruise was re s t r i c t e d to securing one or two types of information. Most of the data were collected from a small open inboard-powered boat equipped with a hand windlass and a plankton pump. A t h i r t y - s i x foot launch similarly equipped was used f o r the more extended cruises into Stuart and Trincomali Channels. An Atlas hydrographic bo t t l e , a reversing thermometer and a 200 foot bathythermograph were operated from the hand 7 windless to obtain water samples and temperatures. Plankton samples were taken from subsurface depths through hose one inch in diameter by a rotary pump driven by a power take-off from the inboard engine. In most cases three cubic feet of water measured by a meter were filtered through #20 or ^25 silk or aonel netting, the types of pumps and size of hose generally used in plankton sampling are inefficient in capturing most sooplankton, although excellent for quantitative studies of phytoplankton and some of the smaller and less active soopiankters (Gibbons and Fraser, 1937)The pump used in this study was of low capacity, delivering water at a rate of about one cubic foot per minute. While this does not affect the phytoplankton values, sooplankton concentrations derived from the samples are low. k Chesapeake Bay Institute confined current drag was used to obtain velocity profiles (Pritehard and Burt, 1951). Surface flow patterns were observed with wooden floats as described by T u l l y and Waldichuk (1953). Salinities were determined by Mohr titration. The concentrations of predominant genera of phytoplankton were obtained by identifying and counting the cells in a fraction of each sample in a ruled chamber of known volume and converting these counts to numbers of cells per liter. The volume of the samples analysed ranged from rooo t o j^ 0(j of the original sample. It was found necessary to dilute samples with heavy concentrations of cells in order to facilitate counting. Between 1/20 and 1/5 of the volume of each sample taken at Station X in the summer of 1954 was analysed for the concen-tration of the dominant zooplanktan. Included In this category were copepods, c o p e p o d i d s , s o e a of crab, polychaete larvae, and nauplil of copepods and barnacles. Since the adults of the species of copepods observed were similar in size to the copepodids they were included in the counts of copepodids. Since the distributions of variables in Ladysmith Harbour fluctuate continuously with tide, stations sampled over a period of twenty-four hours were occupied on three occasions. The fact that cruises were mede at various stages of the tide also allows conclusions to be drawn concerning the mean dis-tributions of variables. In addition to data taken during the above program, data secured by other workers and agencies have been used and are listed as follows: (a) Salinity, temperature and plankton from Station I taken at weekly intervals in 1951 and 1952 (D.B. quayle, unpub.). (b) Bata from a series of stations occupied by C.S.A.?. Bhkoli in Stuart Channel and Ladysmith Harbour in May, 1955 (Seagal, 1955). (c) Discharge data for Haslam Creek (Canada Dept. northern Affairs and National Jiesourcea No. 114, 1951-1952, and unpub.). (d) Meteorological data from Cassidy Airport (Can. Dept. Transport, unpublished). (e) Waldichuk M., 1954. unpublished data. 9 I I I . RESULTS AND DISCUSSION *• Morphometry The distribution of depths in the Harbour i s indicated i n Figure 1. About one third of the area of the Inner Harbour l i e s above the aero tide line . Most of this intertidai zone l i e s at the head of the harbour. Two mud flats l i e on the west side of the harbour. Along the east side of the Inner Harbour the rocky shore drops sharply. From the west, the bottom slopes gradually, changing from a mixture of mud and gravel to a soft organic ooze at the zero tide level. The deepest pert of the Inner Bay l i e s along the eastern shore. Mean depths In the Inner Harbour range from three to 35 feet in the channel and in the Outer Bay from 35 to about 130 feet. The constriction between the two parts of the bay i s about 600 feet across. The narrow channel formed by this constrict-ion i s deepest at the western side and shallows rapidly toward the east shore forming a modified s i l l . The difference in depth between the two parts of the harbour may have effects on the distribution of plankton due to restriction of the depth of the euphotic zone, lack of a deep reservoir of nutrients and the greater ratio of surface area to volume in the Inner Harbour. The latter suggests that the relative concentrations of sessile and bottom f i l t e r feeders and fixed plants will be higher in the Inner Bay. 10 Unless the Increased concentration of filter feeders is offset fey the effect of the shallow depths in excluding such planktonie grasers as the more abundant copepods, phytoplankton in this harbour may experience a gradient of grazing* the greater relative concentration of plants per unit volume in the Inner Harbour suggests that phytoplankton will meet increased competition for nutrients there. However, the difference in the ratio of surface area to volume may result in higher relative concentrations of becteris In the Inner Harbour. If this is the ease, the rate of regeneration of nutrients there could be higher, perhaps offsetting the effect on phytoplankton of competition for nutrients. The fact that such regeneration would occur within the suphotIc zone would add to the importance of the nutrient turnover. *• Freshwater gr^na^e fhe drainage area of the whole harbour is 39.6 square miles and that of the Inner Harbour is 20.4 square miles. The average annual rainfall is about 37 inches, giving a mean annual dis-charge of fresh water into the Inner Bay of about 5.5 at 10^  cubic meters. This would form a layer 1.5 meters thick on the Inner Bay. M© single stream dominates the drainage. Three major streams, tar© in the Inner Bay and one larger one in the Outer Harbour discharge from the west shore. Small crooks, seepage and direct runoff contribute the rest of the fresh-water drainage. While none of the streams entering Ladysaith Harbour are 11 metered, discharge figures are available for Haslam Creek in an adjacent watershed about five miles northwest of Ladysmith (Water Resources Pub, 114), The drainage area of Haslam Creek i s about 27 square miles, comparable to that of the Inner Harbour. These discharge figures indicate peaks of flow in November, February and April-May. The November and February maxima occur during periods of heavy rainfall and may be separated by a time when precipitation i s being stored as snow i n the watershed. The melting of this stored runoff may result in the spring peak discharge, C Distribution of Salinity Surface salinities ranging from 13 o/oo to 29 o/oo have been observed at Station I in Ladysmith Harbour (Quayle, un-published data). Subsurface salinities may exceed 29.5 o/oo, but are not known to reach 30 o/oo. Typically three major s a l -i n i t y minima occur each year. Two are associated with the autumn and winter peaks of freshwater discharge. The third occurs in midsummer when drainage has an almost negligible effect on salinity. Cruises into Stuart, Trineomali and Northumberland Channels indicate that the summer salinity minima result from intrusions of Georgia Strait water, diluted by the Fraser River spring freshet, into the Stuart-Trlncomali Channels system. Several such intrusions may occur in a summer, with increases in salinity between them ( f i g . 4). In late f a l l and early summer salinities above the halo-12. FIGURE 4 DEPTHS OF ISOHALINES ( S % o ) , STN- I , LADYSMITH HARBOUR , SUMMER, 1984 13 eline tend to increase to seaward. In midsummer when d i l u t i o n i s occuring t h i s gradient i s reversed and s a l i n i t i e s decrease to seaward. In la t e summer and early f e l l the gradients above the halocline may be variable. At the l a t t e r times change In s a l i n i t y along the harbour may be n e g l i g i b l e , or s a l i n i t i e s at Station II i n the Outer Harbour may be either higher or lower than at Station I or Station I I I , Longitudinal s a l i n i t y gradients below the halocline are usually smaller than those above. At times the gradient below the halocline i s the same as the upper gradient and at times i t i s opposite i n d i r e c t i o n , fhe longitudinal gradients are t y p i c a l l y small - less a.lonc| the lenqVW of the Ko-rbour thaa one part per thousand,. However, s a l i n i t y data from Station I i n the winter of 1951 reveal very strong v e r t i c a l gradients of s a l i n i t y i n the upper three feet. I f wind mix-ing i n the more exposed Outer Harbour could break down this structure, then large horizontal gradients might develop i n winter. Such gradients were not observed i n this study since surfaee s a l i n i t i e s were not observed during the f i r s t year. However, the winter cruises do Indicate that the v e r t i c a l gradients of s a l i n i t y are much stronger i n the Inner Harbour than just off the harbour, suggesting that wind mixing may act as suggested, t y p i c a l longitudinal s a l i n i t y sections i n the harbour are shown i n Figures 5, © and 7, Tv-a-m^ ense s a l i n i t y gradients i n both Inner and Outer 20 4 0 STATION I SALINITY (%o LADYSMITH HARBOUR , MAY 3, 1955 SPRING, FRESH WATER DRAINAGE-FIGURE 20 DEPTH [FEET) 40 SALINITY (%<>: LADYSMITH HARBOU JULY 16,1954 MIDSUMMER, DILUTION FROM SEAWARD FIGURE 6 20 40 26 5 2 70 SALINITY (%o> LADYSMITH HARBOUR , AUGUST 2 7, 195 4 LATE SUMMER, GRADIENTS VARIABLE • FIGURE 7 280 r. 15 0-CTOS5 t h e w i d t h Harbours ar© usually of th© order of 0.1 - 0.2 o/oo and are always less than 0.5 o/oo in the spring and summer, the only periods when lateral salinity gradients were observed. The lateral gradients are variable but a tendency to lower sal* initios on the west side i s observed, except when dilution from seaward i s occuring. Sometimes the lateral gradients reverse below the halocline* Observations made at six stations (ED 1.5. ED 3.5* H 4, H 1, K 1, K 4) occupied by three vessels over a period of twenty-four hours on May 10-19, 1955 indicate that salinities above and below the halocline tend to vary with tidal height* Salinities in the Outer Harbour tended to increase on flood tides and decrease on ebb tides. The fact that the reverse was true at the pair of stations in the Inner Harbour could be due to the movement of relatively dilute water off the mouth of Holland Creek (f i g . 1) Into the Inner Bay on the flood tide. The halocline in the Outer Harbour showed a ten-dency to a steady decrease in depth rather than any marked tidal fluctuations. The range of variation of salinity with tide was about 0.1 • 0.6 o/oo. The average excursion of the intersection of isohalines with the surface on ebb or flood tides wes about one half a mile. Since cruises in the f i r s t two patterns of stations required a maximum of about three hours, the maximum distortion in longitudinal plots of salinity due to tidal variation during the cruise should be about one quarter of a mile. Since the maximum distortion amounts to less than one eighth of the 16 length, of the harbour, i t i s neglected. Observations made at a station occupied for twenty-four hours on May £9-30, 1954 i n the constriction forming the . entrance to the Inner Harbour indicate that the extremes of s a l i n i t y at t h i s location occur at times of maximum t i d a l current rather than at the extremes of t i d a l height. This could r e s u l t from th® bottom configuration i n the Gap which may impede water flow except at maximum current speeds. However, l a t e r a l temperature sections across the constriction indicate strong and characteristic distortion i n the con-figuration of isotherms f o r both ebb and flood tides ( f i g . 13). Since the twenty-four hour station was situated to th® east of the middle of th® Gap, the change i n s a l i n i t y may be an ef f e c t of the di s t o r t i o n rather than a true indication of the average s a l i n i t y of th® water moving through the constric t i o n . ®» D i s t r i b u t i o n o f Temperature Maximum surface temperatures of about 7 5 ° F occur i n August and minima of about 3<*9F i n February. Temperature maxima and minima generally coincide with s a l i n i t y minima. This may result partly from the coincidence of radiation and s a l i n i t y cycles and partly from the s t a b i l i t y at s a l i n i t y minima which usually occur with strong v e r t i c a l gradients. Inner Ladysmith Harbour has a source and sink of heat i n addition to the usual ones of oceanographic and meteorological o r i g i n i n the extensive area of i n t e r t i d a l f l a t s . Th© large 17 intertidsl zone w i l l g ain or lose heat during low tide periods according to the conditions prevailing. When the flats are submerged during high tides the gain or loss of heat w i l l be passed on to the water. This phenomenon, coupled with the effect of the shore configuration in restricting water exchange and wind mixing, may be reflected in the temperature dis-tributions. In addition, the shallow depths eliminate the possibility of modification of temperatures resulting from mixing with deep water. In spring, summer and early f a l l temperatures above the thermocline tend to decrease, sometimes Irregularly, toward the mouth of th® harbour {figs. S, 9, 10, 11, 12). Temperature gradients in the thermocline are sometimes strong. Below the thermocline the gradients may be similar or opposite to those above the thermocline. Temperatures in the Inner Harbour tend to decrease from head to mouth and from west to east in spring and summer. This may result from the fact that the intertidal f l a t s , sources o f heat in spring and summer, l i e at the end and side opposite to the source of colder water. At times the distribu-tions of temperature as indicated by extensive use of the bathythermograph are quite irregular within th© net gradient ( f i g . 1 2 ) . This Irregularity may result partly from the effect of the constriction mentioned on page 16 • In long-itudinal plots of the distribution of temperature taken by bathythermograph on the flood tide, isotherms rise sharply STATION X l b XT H E DILUTION FROM SEAWARD FIGURE 9 FIGURE 10 19 over the "semi-sill" in the constriction and follow the bottom down closely inside the s i l l (fig. 12). During large tidal rises relatively cold water from the greater depths of the Outer Harbour may be forced in over the s i l l , and be unable to move out on the following ebb tide. This effect may be enhanced by the existence of a two-layer system of circulation i n which cold water tends to flow inward along the bottom. The distribution of the intertidal sources of heat and mixing resulting from a jet stream through the Gap on flood tides may also contribute to the sometimes irregular distribution of temperature* Characteristic transverse distributions of temperature for both flood and ebb tides were observed in the Gap (fig* 13)* The transverse gradients are typically strong with temperatures in the upper sone decreasing from west to east on the flood tide and from east to west on the ebb* Toward the bottom the gradients tend to reverse. These characteristic distributions may be a combined result of the constriction and a two-layer system of circulation* Variations i n temperatures at the six stations occupied for twenty-four hours on May 16-19, 1955 were more irregular than variations in salinity. The temperature changes differed at each of the three sections and, except for stations % and H^, the stations i n each pair exhibited differences in the change of temperature with tide* Of the six stations only ED3.5 8 1 1 ( 1 K4» t h e inner and outermost on the west side of the Harbour revealed regular FIGURE 13 21 variation in temperature with tidal height. At station paired with ED35-but on the east side of the inner Bay, shallow layers of warm water were observed at both lower low water periods, as might be expected. However, Isotherms below a depth of ten feet showed l i t t l e change in depth, other than to appear slightly shallower at low water after the small ebb tide. This effect could be attributed to the movement of the upper water out over the relatively immobile deeper water on this small tide. At Stations % and H4 in the Outer Harbour surface temperatures tended to vary directly with tidal height. Below a depth of about twenty feet th© changes in temperature at these two stations were simitar.:., showing an increase on the small ebb, a marked decrease on the small flood and virtually no change on the large flood and large tides. The temperatures at Intermediate depths showed a steady decrease at Station H^, the eastern station, and paralleled the deeper temperature changes at Station H^. As already mentioned, temperatures at Station K^ , the western station at the mouth of the Outer Harbour, varied directly with tidal height. Temperatures below a depth of about ten feet at Station Ki, across the Harbour from K4, varied inversely with tidal height. Above ten feet, at Station Ki a decrease i n temperature occured on the f i r s t flood tide and a slow increase in temperature continued from the f i r s t high water period until occupation of the stations 22 was terminated* The complexity of these variations of temperature with t i d e could be due to simple distributions of temperature and complicated patterns of flow, to complicated distributions of temperature and simple flow patterns or to intermediates be-tween these two alternatives. The rel a t i v e regularity of the vari a t i o n i n s a l i n i t i e s suggests that the distrib u t i o n of temperature rather than flow patterns may be responsible for the complex variation of temperature with t i d e . Some temp-erature sections from the Outer Harbour reveal complex d i s -tributions indicating that t h i s may be the case. The station occupied f o r twenty-four hours i n the Gap indicates that temperatures varied in much the same way as s a l i n i t i e s . Extremes occurred at times of maximum eurrent speed rather than at high and low-tide periods* On august 10-11, 1955 a station was occupied f o r twenty-four hours at position CD*5 i n the grid of stations covering the Inner Harbour ( f i g * 3 ) » Bathythermograph casts and observations of v e l o c i t i e s at eight depths were made at i n t e r -vals of one hour for the twenty-four hour period. At high and low tides and halfway between high and low tides bathy-thermograph casts were made at four stations across Section CD. In general maximum temperatures occurred at low tide® and minimum temperatures at high ti d e s . The maximum change i n temperature of about 4°F took place at a depth of 12 feet on th* large flood tide between lower low water and high water. The depths of the isotherms did not change smoothly, but with many small irregular fluctuation® which wer© greatest in. the lower region of th® thermocline. These fluetuation® may indicate turbulence or be an effect of the ©onstrietion. Saeh of the eight observations on the transverse distribution of teafieratur© indicated that teaperatures above the theraoclin® increased toward the west side ©f the harbour. I© distinctive variations in the lateral distributions ©f temperature with tide were observed other than a general increase aad decrease of temperature. ioagitudiaal temperature gradients in the Inner Harbour vary from 2F* to about 7F° along its length. For th© whole harbour, the longitudinal gradient may exceed 10F*. Vertical temperature gradients from less than 2f* t© ©ver i a r * in 25 feet have been observed in the Inner lay. Transverse gradients of up to 2 4"across the width of th® laaer Barbeur may occur. E* y&ter. l&sihengs in. .the Inner .Marbffiir 1. Tide fa© volumes of water aad percent changes in th© volume of the Inner larbeor due t® tidal action are discussed since they may give an indication ©f the rat© of water exchange and the magnitude of the r©l® tbat tide plays ia water renewal ia th® Inner Bay. Th® volume ©f water contained by th® Inner Bay was obtained 24 by taking the areas enclosed by successive depth contours ( U . S . Hydrographic Office Chart Mo, 2564), multiplying by the appropriate depth increment aad summing the volumes so obtained. The In t e r t i d a l area, being of l i t t l e interest to mariners i s not contoured on the hydrographic charts. Since i t was necessary to know the di s t r i b u t i o n of i n t e r t i d a l depth contours i n order t o calculate changes i n volume due to tide & r i s e of six feet was assumed between the s«ro tide level and intersection of the mudflats with the approximately v e r t i c a l shoreline. The slope between the aero and six foot l e v e l s was- assumed to be such that the three foot contour divided the area between them i n h a l f . The volume of water beneath different depths i s presented i n figure 14, Table 1 indicates the percent changes i n volume occurlng an various range® of ebb t i d e . Mean tide level i n ladysmith Harbour i s about $ feet and th© mean t i d a l range i s about 7 feet giving a mean volume of shout 16.4 x 10 cubic meters with a range of 4 4,2 x 10 m, • 3.5 x 10^ m^ . Thus snout 3 7 percent of the smm high tide volume of the Inner Say Is involved in each tide or about 7 0 percent/day. The sum of mean area of the two small passes into Burleith Arm i s about 5 percent of the cross-sectional area of the Sap. t h i s suggests that at least 90 percent of t i d a l exchange occurs d i r e c t l y with the Outer Barbour through the Gap, The magnitude of the t i d a l volume changes and the effect 25 TABLE I Percent Changes in Volume of Inner Ladysmith Harbour on Various Tidal Ranges Tidal Range £ Change in Vol, Tidal Range % Change in Vol. 1 5 * 1 2 f t . 1 3 . 7 36 1 2 - 3 f t . 5936 1 5 * 9 2 7 . 4 1 2 - 0 6 9 1 5 - 6 4 1 . 1 9-6 1 9 . 3 15-3 5 3 . 3 9-3 3 5 . 6 1 5 - 0 6 2 , 0 9-0 4 7 . 6 1 2 - 9 1 6 . 0 6-3 2 0 , 4 1 2 - 6 3 2 . 0 6-0 3 5 . 4 26 60 IOO ISO 20.0 VOLUME ( MILLIONS OF CUBIC METERS) 27 of the constriction at the Gap in producing a jet stream which should enhance horizontal mixing suggests that tidal exchange may be an important factor in the renewal of water in the Inner Bay* It seems unlikely that a l l the water entering on flood tides would be the same as that which l e f t on the preceding ebb or that i t i s a l l new water. This suggests that 70 per-cent of the mean high tide volume per day Is an approximate upper limit to the rate of water renewal* 2* Renewal Rates from Changes in Salinity If known changes in salinity i n the Inner Harbour occur as a result of horizontal exchange and i f the salinity of the water causing these changes i s known, the volumes of water exchanged can be calculated i f volume continuity i s assumed. The amount of salt i n a body of water of constant volume after a change in salinity resulting from volume exchange can be expressed as: V S 2 • VS 1 - A V S X * A V S 2 , where V • volume of the body of water; AV • volume of water replaced; « mean salinity of the body of water at t j before the change; S_ s mean salinity of the body of water at t 2 , after the 2 change; and s the salinity of the water causing the change in salinity* The volume replaced i s : 2$ Expressed as JP , percent of the volume of the body of water replaced per day, this becomest The data required are the average salinity of the body of water before and after the change in salinity, .the salinity of the dilutant (replacement water) and the time interval* Salinity data froa th© summer of 1954 indicate that three periods of dilution from seaward, occured in the Inner Bay. Between the periods of dilution, salinities in the Inner Harbour increased ( f i g . 4 ) . The pertinent data are from Stations I, II and II I . In order to calculate exchange rate© for the Inner Harbour from this data the following assumptions must be made: a. It i s assumed that salinities from Station I repre-sent the average for the Inner Harbour. Data from the grid of stations in the Inner Bay i n 1955 suggest that this tends to be the case. b. It i s assumed that salinity changes in th® Inner Harbour result froa exchange with water having the salinities observed at Station II in the Outer Harbour. It has been stated that these salinity changes result from exchange with water to seaward of the Inner Bay. Ihe movement each day of 70 percent of the mean high tide volume of the Inner Bay into the Outer Harbour through the jet stream affords ample opportunity for horizontal mixing to I 2 9 occur. C a l c u l a t i o n s indicate thet the mean volume of water moving out of the Inner Harbour on an ebb t i d e would cover the area i n the Outer Harbour, the center of which i s approx-imately the position of Station I I . While few observations o f the d i s t r i b u t i o n of s a l i n i t y were made w i t h i n this area, those a v a i l a b l e suggest that s a l i n i t y gradients w i t h i n the area are s m a l l . S t a t i o n I I s a l i n i t i e s w i l l therefore be accepted as an approximation to the mean values f o r Sr,. c. Freshwater discharge i s assumed to cause negligible changes i n s a l i n i t y . Discharge rates i n t o the Inner Bay range between 0.3 and 3 cubic meters per second and average about one cubic meter per second f o r the period being considered. d. I t i s assumed that exchange between the Inner Har-bour and B u r l e i t h Arm i s n e g l i g i b l e . Since i t i s suggested t h a t at l e a s t 90 percent of the t i d a l volume changes i n the Inner Harbour occur d i r e c t l y with the outer harbour, error from this assumption may be small. I f the use of S t a t i o n I I s a l i n i t i e s as values f o r S D i s accepted two problems concerned with averaging must be considered. F i r s t , the question of whether the s a l i n i t y , Srj, should be a time average must be d e a l t w i t h . Secondly, s i n c e the depth at S t a t i o n I I i s about three times that at Station I , a depth to which s a l i n i t i e s at Station I I should be averaged must be chosen. As used here the expression f o r obtaining renewal rates represents- an integration of s a l i n i t y changes over s e v e r a l days, b e t t e r results would be obtained i f 30 calculations could be made for each tide or each day, since Station II salinities w i l l change continuously be-tween cruises. The data are insufficient for this. In order to take into account the fact that Station I salinities at t 2 w i l l be the result of exchange with waters of the f u l l range of Station II salinities between t 5 and t , S should consist of the average of Station II salinities at t± and t 2 * Whether or not this average i s valid depends on the way salinities varied between cruises. Such time averages appear to work for some periods during which salinities i n * creased but not for periods of dilution* Dilution occurs suddenly, suggesting that discrete clouds or fronts of fresh water move into the Ladysmith area mixing with and replacing water of high salinity. This la supported by the fact that S D »s for periods of dilution based on time averages are higher than Station I salinities at tg. The time average gave good results for a l l but one period of salinity increase* The average depth of the Inner Harbour i s about 24 feet* I f no vertical mixing occurs with water from below this depth and only horisontal mixing need be considered , averages of Station II salinities to a depth of 24 feet snould be satis-factory for S D, It could be argued that th© strong vertical gradients of salinity and temperature with resulting stab-i l i t y would tend to dampen vertical mixing and reduce error from this source. This appears tenable for periods of salin-i t y decrease but not for increases in salinity. 31 SQ'S for the f i r s t two periods of dilution, based on 24 foot % 2 averages give renewal rates of 19.3 and 16.Q percent per day* The magnitudes appear reasonable and agree-ment i s ©lose. SD for the third period of dilution (July 24-August 2 ) , averaged in the same way, cannot be used since this S D i s greater than the salinity supposedly resulting from i t s influence. The configuration of isohalines in the longitudinal section for August 2 suggests that an inflow of dilute water above a depth of 15 feet occurred. S c averaged to this depth gave a renewal rate of 19.5 percent per day which agrees well with the above two rates. The fact that vertical mixing has been assumed negligible does not mean that i t has been inoperative* The 24-and 15-foot averages used here may be more saline than the corresp-onding averages for the true dilutant, but the added concentration due to time increase in salinity could correct for possible effects of vertical mixing. There seems to be no clear cut approach to averaging salinities to obtain SQ for periods during which Inner Harbour salinities increased. During the middle of August Inner Harbour salinities increased in spite of an apparent decrease in salinity toward the mouth of the harbour above the twenty-four-foot level. Due to lack of data i t ean only be assumed that the increase was a result of upward intrusion of more saline water from beneath the 24 foot level. To take the effect of upward intrusion or vertical mix-ing into account the depths to which salinities were averaged 32 were increased, thereby increasing the value of 3^. Wo one depth gave satisfactory results. Averages to a depth of 30 feet in two calculations and to 40 feet in two others were necessary to produce salinity changes in the observed dir-ection* Although this method of averaging is arbitrary, long-itudinal sections of temperature indicate that at times water from these and greater deptns may move up the sloping bottom and through the constriction into the Inner Harbour* The rate of renewal for July 16*20, a period of increase in salinity, was obtained in two ways. The first used an Sn consisting of t 2 salinities averaged to a depth of 24 used feet and the second of the mean of Sts&on II salinities at as S]> the two dates averaged to a depth of 40 feet* The respective rates are 27 percent and 21 percent of the mean volume per day, and are In good agreement with the other values (Table 2), TABLE 2 Renewal Eates from Salinity Changes Summer 1954 Date " % Tx ~ z ' f June 22-27 25.10 o/oo 26M6* o/oo 2$.21 o/oo 19*3 o/o July 12-16 23.35 25.57 24.15 16.0 July 16-20 25.16 24.15 25.0? 27.0 25.21 21.7 July 24-Aug2 23.74 25.06 24.22 19*5 Aug 2-Aug 5 2 5 . U 24.22 25.07 32.0 Aug 5-Aug 12 25.72 25.07 25.62 12.0 Aug 12-20 26.74 25.62 26.63 13.0 33 T«« mean of th© seven rates calculated by this method Is 20.1 percent of the mean volume per day with a standard deviation of 6.5 percent. A l l values are within the 70 percent upper limit obtained from a consideration of changes of volume with tide. According to the mean value, about one third of the water moving to the Outer Harbour on an ebb tide i s exchanged. The results for periods of dilution agree well and were obtained with a minimum of manipulation. The agreement among rates from periods of increase in salinity may be apparent rather than real because of the arbitrary way in which averages were adjusted in order to produce salinity changes i n the observed direction. It may be inferred from the necessity to manipulate averages that! a. the data on the distribution of salinity in both space and time was inadequate. b. the assumptions discussed above are not valid. c. the variability in small Inshore bodies of water i s such that even cruises separated by intervals of a few days may miss significant changes in properties and distributions. d« velocity gradients or net circulations exist and should have been taken into account in choosing salinities for S D. 3* Circulation Telocity observations and distributions of salinity, temperature and density suggest that net circulations do 34 exi s t . Longitudinal distributions of s a l i n i t y , temperature and sigma-t, the density anomaly ( f i g s . 15, 17, 18, 19), suggest that during most of the year a two layer system of ci r c u l a t i o n with outflow i n the upper layers and inflow i n the deeper layers exists. During periods of di l u t i o n from seaward i n summer t h i s c i r c u l a t i o n reverses and inflow occurs In the upper layers ( f i g . 16), The mean dis t r i b u t i o n of velocity with depth at a Station occupied f o r twenty-four hours In the Gap indicated a net flow outward of about 10 centimeters per second above a depth of about nine feet and a net flow inward of about the same speed below th i s l e v e l . Taking into account the mean cross-sectional areas above and below the depth of no net motion transports of 54 cubic meters per second outward and $9 cubic meters per second inward were calculated. According to these transports a net flow Inward of 35 cubic meters per second occurred during the course of these observations. Predicted t i d a l heights at the start and termination of this station were approximately equal. I© appreciable change i n the volume of the harbour was observed. Fresh water drainage rates f o r this period suggest that transport out should have exceeded the flow i n by about 3 cubic meters per second i f continuity of volume was to be maintained. It may be concluded that th© ve l o c i t i e s from this station did not represent the mean fo r the cross-section, that a l a t e r a l circulation existed or that a net outflow OUT 30 CM/SEC 0 IH 30 CM/SEC 20 MEAN DISTRIBUTION OF VELOCITY WITH DEPTH '• GAP , MAY 29-30, 1954 STN- CDS , AUG- 10- II, 1955 FIGURE 20 36 through the two small passes into Burleith Arm occurred ( f i g . 1). At the August 10-11 anchor station the mean velocity p r o f i l e f o r the 24 hours ( f i g . 20) suggests that a three-layer c i r c u l a t i o n with outflow near the surfaee and bottom and inflow i n the mid-depths existed. Marked ebb currents near bottom occurring near the end of the two flood tides gave r i s e to the net outward v e l o c i t i e s near the bottom. Again, since a net inflow was observed i t can be suggested that th© v e l o c i t i e s did not represent the mean for the cross-section, that a l a t e r a l circulation existed or that a net outflow Into Burleith Arm occurred The significance of the ebb currents near the bottom while flood currents were observed i n the rest of the water column i s not known. Observations of the movements of free drags suspended at different depths from surface floats indicate that on the flood tide v e l o c i t i e s at mid depths (10-15 f t . ) are greater than those near the surface i n spite of the prevailing up-harbour wind. Ho such observations are available during ebb tides. While the water transports calculated from v e l o c i t i e s observed at the stations occupied for 24 hours do not indicate continuity of volume they can be used to support the exist-ence of the two-layered system of circ u l a t i o n inferred from the longitudinal distributions of s a l i n i t y , temperature and density. 37 The pressure forces maintaining the outward flow in the surface layers of water appear to result from fresh-water drainage In winter, drainage and heating in spring and f a l l and from differential heating in the summer. Observations on the movements of dettritu® and foam-lines on calm evenings at and just before high tide periods indicated that surface current® may ebb on th® west side of the Inner Harbour while the surface water on the east side is stationary or moving inward. The few observations on the lateral distribution of velocity indicate that th® flood tide currents are stronger on the east side of the harbour. The on® set of observations of velocities at several depths at a station on th® west side of the harbour just after the turn of the tide to the ebb indicates that ebb currents along the west shore may be ©bout the same speed as flood currents along the east shore. These scattered observations suggest that an anticlockwise lat-eral circulation exists. Some distributions of surface temperature© are compatible with such a circulation. On the other hand some studies of the surface flow patterns using wooden floats suggest that the flood tide may be stronger along the western shore in the inner half Of the Inner Bay. Some surface distributions of surface properties, the existence of semi-permanent tide-lines extending diagonally across the harbour and the movements of surface floats suggest that water of low density originating near the head - 3a -of the harbour tends to move seaward against aad ever denser water awing inward on th® flood tide* Other observations on disiribntions of How patterns and properties at th® surf m® suggest that slight upwelHng of relatively eold and saline water may occur at times .in the Inner naif of the Inner Harbour* thus lateral water aovemeat® in the Inner Harbour appear te be confused and variable. Ske* appear to be related to tidal fasters and others to distributions of density* However* the ntpiser and quality of current observations allow a© definite oonolusions to be drawn eoneera&ng lateral eireulatioa® ia the Jjaaor Harbour. 4* Two, layered..^iroulati^i. ..and.^ ssh^ tMe .Sates a. eontinuity of Salt and folwa® The relationship between transports of water and salt for a body ©f water receiving freshwater drainage and in which continuity of salt and volume are aalntained by a two layer circulation s»y be ©pressed as: (1) Si f l * $u Ta, where Si - salinity of th® Inflowing l u p r j Tl • the rate of transport of water inward* Su » salinity ef th© outflowing layer* and fn * the rat© of transport ©f water out-ward. Since continuity of volwae has been asswued, (2) t » •» t l * S» *fh®r® D * th© rate of freshwater discharge. (3) ••' (1) ** U ) » » ' -39 -Thus, i f th® rate of freshwater discharge aad the mean salin-ities of the inflowing and outflowing layers ar® known, water trans-ports and hence renewal rates can be calculated. As already indicated, although ao drainage data are available for ladysmith larbour, a stream ia a neighbouring watershed similar in sia® to that ®f the Inner larbour is metered. Th© products ©f the ratio of th® drainage area of the Inner larbour to that of Haslam Greek and discharge rates from Haslam Creek are assumed to represent th® rate® of freshwater dis-charge into Inner ladysmith larbour* Bistributioa® of salinity, temp-erature, and density indicate that the retired two layered system of circulation obtains for most of the year. Th© depth of a© net motion, necessary to obtain Si aad S», was t&kets to be th© inflection point of the signa-t profile. On th® basis of salinity data taken in the Inner Barbour in the spring and suawer of 1955, Statist! 1 salinities were accepted as approximations to the waa salinities of the upper aad 3©wer layers. The mean salinity ab©v© th® depth ef a© net motion was used as Su and that below as S i . fhe salinity data indieate that •while the mm annual salinity of th© Inner larbour remains relatively constant salinities within aay year fluctuate eentiauously* lowever, at periods of salinity maxima sad minima the change of salinity with time is «®r© md continuity of salt may be considered satisfied. fhe velum® of the Inner Barbour was assumed t© be constant. Th© data used and th© results ar© presented in Table 3* The results may be summrieed as follows* (1) 1951* the mm ©f the 15 rates calculated is 29*5 percent ©f the mean volume renewed per day* (2) 1952t nine values were computed the aean of which was 35 percent of the mean volume per day. (3) 1954: the mean of th® six renewal rate® calculated is 2? percent per day. (4) 19551 three rates were calculated* their mean is 35 percent per day. (5) The mean of all renewal rates calculated by this method is 32 percent of the mean volume ©f the Inner larbour per day. The 195i rates are more closely clustered around their aean than are those for the other years. It may be significant that 1951 was the only period during which surface salinities were observed. S®v®ral sources of error may exist t (1) Since observations were not continuous th® observed maxima and minima may be apparent rather than real. (2) The freshwater discharge rates used say not represent th© true rates for Inner 3*ady smith Harbour* (3) fhe salinities used for Si and Bm. aay not represent the true values. This would be the case if Station I salinities were not the mean values for the Inner larbour or if th® ©hole© of th® depth ef no motion was in error. (4) Occasionally freshwater drainage into the Outer Harbour may 41 tmm 3 Mater Transports aad Renewal Eate® fro® Oontlnaity of Salt and foltw Date Depth of no motion 0 8a SI f l F 1951 Feb. 9 5 f t . 13*9ffl?/s 20.50/00 27»70/o© 40/af'/® If 11 2.8 24.2 27.3 22 11 Mar 19 2 3*3 22.0 27.3 17 9 April 12 5 5.5 27.6 28.3 21? n o 23 6 3.0 26*3 28.1 44 23 Kay 2D 7 2.2 26.1 27.5 41 22 29 1.5 27.1 27.7 68 36 •Tune 7 14 0.* 25.5 26.3 26 13 7 0.6 254 27.1 10 5 so 10 0.4 25.7 26.2 21 U 26 10 0.2 26.1 36,8 7 4 ©et 8 5 2.0 27.2 29.0 42 22 IS 24 2.9 28.2 29.0 104 55 25 6 6.4 27.5 2ft *6 160 84 30 Her 29 5 6.9 23.1 28.1 32 17 1952 4m 31 6 12.9 24.1 29.2 64 34 Feb 7 6 10,1 27.8 29.1 216 114 14 6 4-8 22.f 27.9 18 f 26 6 44 27.7 28.7 131 69 liar 21 3 2.1 27 »6 29.1 3f . 20 Apr i l 2 11 2.8 28 .C 28.9 41 22 toy 1 10 11.8 27.5 29.0 216 114 17 7 5.4 m .2 28.8 212 133 30 Sept 12 10 0.25 27.3 28.3 7 4 1954 l«s 6 a 2.6 27.6 28.1 133 70 22 i i 2.0 27.9 28.4 114 60 M y 12 14 2.1 24.6 26.5 38 20 20 12 0.8 23.9 25 4 9 5 Aug 20 * 0.3 25.1 27.2 4 2 27 12 0.3 26.0 26.7 12 7 1955 May 30 $ 2.9 284 28.9 109 57 •fan® 25 12 1.2 26.8 27.3 67 35 29 8 0.7 26 .a 27*4 24 13 42 influence Inner Harbour salinities. If sources of freshwater in addition t® loeal drainage are present renewal rates based on local drainage only will be in error. (5) If the lateral circulation mentioned earlier became important, freshwater discharge from a stream emptying dosm-harbour from Station 1 night not influence salinities at that station. In such a ©ase renewal rates based on Station. I salinities would be la error. Al-though the lateral circulation is not known to be significant in spring and simmer i t could be important in fall and winter. (6) In some longitudinal distributions of salinity, teaperature and density the two layered circulation is not well defined. This aay result from small longitudinal gradients or from almost neutral stability. At such times renewal rates calculated on the assumption of a two layer circulation will be in error. The fact that exchange rates do not appear to vary seasonally with freshwater drainage aay b© due to several reasons. The fact that rates close to the wean are distributed around the year suggests that tidal action* which I® relatively constant, may control the rate of exchange. The lack of variation of the rate with freshwater drainage could indicate that the influence of differential heating takes over as the influence of drainage decreases. It is also possible that ex-change is related to the rate of freshwater discharge but that th© in-adequacies of the date ©bseure the relationship* b. Continuity ©f Seat aad folmme. .  A method of obtaining renewal rates analogous to th® method used h3 above exists if continuity of heat and volume can be the following expression equates the factors in the heat budget of a body of water if continuity of heat and volume are maintained: Q* * Qr + Qe * Qh • Qv » 0, where Qs * Incident solar radiation! Qr » solar radiation reflected fro® th® surface of the water; Qe » heat used for evaporation} Qh * heat gained or lost by conduction! and Qv *> the net transport of heat by water movements* A H these factors ar© measured in gram calorie® per square centimeter per minute* If continuity of heat is maintained and th© appropriate meteor-ological and oceanographic data are available, (-Qv) can be calculated, f hen if the circulation and th® distribution of temperature ar® known the water transports necessary to supply or remove (-Qv) can b© calculated* 1. (-Qv)A « C Y -J^-k ^ ' where (-Qv) « the amount of heat passing through a stpare centimeter of upper water surface per unit time} A * the area of the upper water surface; C » the specific heat of the water; p • the density of the water; <(-. » th© temperature of the upper layer; ftt • the rate of water transport out; ji • the temper-ature of the lower layer; and K. - the rate of transport of water inward* 2. If it is assumed that fa and f i are approximately equal, (-Qv)A -oCTK'j **i i) and P - iW>Ti H "^-W I » where t - percent of th© volume replaced per dayj ? » the mean volume of the body of water) aad 1440 * the number of ainutea in a day. The product, , was neglected in the ealeulationa since its value i s ©lose to unity. Data required are air temperatures, relative humidities, wind speed, cloud cover* incident solar radiation* sea surfaee temper-atures and the distribution of temperature in the body of water, fhe two layer circulation in ladysmith Harbour has been indisated previously. Meteorologies! data from Cassidy Airport, about four sdlcs north of Ladysmith Harbour were wed. Values of solar radiation were taken from tables prepared by Kliaball (1923). Water temperatures from Station I and from lateral section 0 (fig. 3) were assumed t© be the mean for the Inner Harbour. Data from the simmer of 1955 suggest that this tends to be the ease, for the methods of calculating the factors in the heat budget the reader is referred to Sverdrup et aJL (1942). The transports and renewal rates calculated by th© heat budget method ar® presented in fable 4« The mm of the 15 rates e<naputed using the heat budget is 32.2 percent of the mean volume of the Inner Harbour per day. This method is subject to most of the sources of error discussed in the calculation of renewal rates from considering continuity of salt. two additional sources ©f error say exist in the heat budget method. First, there may be a difference in the meteorological eonditions at Cassidy Airport and Inner Ladysa&th Harbour, feoondly, 45 1 111 1 1| g R ^ f i ^ s g w i S I I I a i l f l l S I I i 4 » a^s^^ssspias lis i l§| f t K l | ^ o o o o o o o o o o o o o o o S S ! i lilt v*5 46 the source and sink of heat present in the large area of intertidal flats was not taken into account• Agreement between the rates calculated for the few dates on which both heat and salt budget methods could be used is poor and the rang® of values is large. This aay result from the many assumptions made and th© faot that they may not have been justified in each ©alcula-tion. However, since the mm of th© heat budget rate® (32 %) agrees with the mean ©f those ©omputed from the salt budget (32 %) it is felt that the mean ean be used with more confidence than the individual rates. fhe mean of all rates calculated ia 32.2 percent of the mm volume of the Inner Harbour per day with a standard deviation of 13.2 percent. How much of this deviation can be attributed to real variations in the exchange rate and how ranch to the inadequacies of the data is not known. Values between about 15 and 50 percent per day do not appear unreasonable as rates of exchange. However, the values near the limits of the range* those below 10 aad above 100 percent, seam likely to be the result of faulty assumptions. Variations in the gradients of density do occur and could result in fluctuations in the renewal rate If longitudinal density gradients and exchange rates are related. As a result of wind, tide or ©ther factors such as density distributions and Corielis force, water from the Inner Earbour could ebb out along one side of the Outer Harbour and be replaced by water flooding in along the other side. Variations such a tendency would 47 result is a fluctuating renewal rate whether exchange was dominated hy tw® layer circulation or hy horizontal mixing* Velocity observation® and distributions of salinity, temper-ature and density indicate that a tw® layer circulation does operate in Ladysmith Harbour, fhe effect of th® constriction at th® ©ap in produelag a jet stream from tidal currents suggests that horizontal mixing may contribute significantly to renewal of the water in th® Inner Barbour* The relative magnitude of these two processes is not known aad probably varies:, gewever* in subsequent sections i t i® assumed that water exchange results entirely from the two layer circulations* 48 F. Distribution of khytoplankton 1. Abundance Four phytoplankton blooms may occur in Ladysmith Harbour during the growing season. The spring bloom in Ladysmith Harbour may start early In May and last from three to six weeks. During this time, although patchiness i s evident and concentrations vary with time, the gradients of concentration along the length of the Harbour ere generally small. A second bloom or series of blooms may occur in midsummer. Concentrations during the midsummer blooms generally increase toward the mouth of the Harbour and may be low in t he Inner Harbour. Observations in late August and early September of 1954 indicate that a third bloom, confined to the Inner Harbour, occurred. Concentrations of plankton from the only cruise made during the f a l l bloom increased toward the mouth of the Harbour* The maintenance of the concentrations of phytoplankton in the shallow Inner Harbour during the spring blooms suggests that water exchange may be important in supplying either organisms or nutrients or both. Since concentrations of plankton and nutrients ere usually higher in the lower layers, the two-layer circulation during this period would tend to advect both plankton and nutrients into the Inner Harbour. The fact that the establishment of a gradient with con-centrations of phytoplankton decreasing to seaward coincided with the reversal of circulation during the f i r s t dilution in 49 the Burner of 1954 aay further Indicate the Importance of the spring circulation i n maintaining phytoplankton populations i n the Inner Harbour* The surfsee inflow associated with dilution would tend to replace water l a the Inner Harbour with water from the plankton-poor and nutrient-depleted upper layers to seaward* Another factor could operate i f the sporadic reversal of the circulation during dilution proved to be unimportant* When depletion of nutrients to seaward of the Inner Harbour reached a certain depth, the inflow in the lower layer might f a i l to advect sufficient nutrients into the Inner Harbour to maintain production at the level prevailing during the spring bloom. Two mechanisms may be responsible for the occurrence of blooms of phytoplankton i n midsummer at a time when plankton concentrations have frequently been observed to be low in other geographical areas. Temperature and salinity sections for July 7$ 1954 suggest that relatively dilute water was moving into Ladysmith Harbour over the more saline deep layers* ( f i g . 21). The vertical gradient of salinity was strong* Tongues of temperature suggest that strong velocity gradients existed between the two layers f f i g . 22). Between t he two layers and associated with a tongue of low temperature was a narrow band of very high concentrations of diatoms (fig. 2$)* This may indicate that entrainment of nutrients into the upper layer gives rise to production, or that mixtures of the two layers are fe r t i l e * so F I G U R E 2 3 51 This phenomenon of high standing crops in the interface between low salinity Georgia Strait water and the deeper layers i s not always evident. However, such entrainment or mixing could result in conditions suitable for production which could persist after the structures revealing the processes had deteriorated. Also plankton so produced might persist after the processes had ceased* Some data (fig*24) suggest that the area in Trincomali Channel between Forlier Pass and the north end of Thetis Island i s a highly productive one. This area i s adjacent to a region of intense t i d a l mixing which could supply the nutrients necessary to maintain a large standing crop of phytoplankton* The distribution of salinity on *JuLy 2, 1954 ( f i g . 25) suggests that the water causing the summer dilutions in Ladysmith Harbour enters the Stuart-Trincomali Channel system through Forlier Pass* If this i s the case, then movement of plankton-bearing water from Trincomali Channel into the Ladysmith Harbour area i s also possible. Sporadic intrusions of water from Trincomali Channel into Stuart Channel eould result in email Clouds or masses of water rich in phytoplankton which could occasionally pass by or enter Ladysmith Harbour* Probably both advection of plankton originating in Trin-comali Channel and entrainment are at least partly responsible for the midsummer bloom® in Ladysmith Harbour* The third bloom, confined to the Inner Harbour, follows the decomposition of large amounts of eelgrass and sessile algae which appear floating in the late summer. Since the LADYSMITH HARBOUR REGION PORLIER PASS RES ION FIGURE 24 MEAN RELATIVE MAGNITUDES OF STANDING CROPS OF PHYTOPLANKTON IN THE LADYSMITH HARBOUR AND PORLIER PASS REGIONS FOR THE DATES : JUNE 4, 1984 JULY 2 SEPT 9 MAY 17, I98B JULY II 53 relative concentration of these forms is higher in the Inner Harbour than to seaward plankton blooms resulting from the release of nutrients through decay of sessile plants would be more intense in the Inner Harbour0 Data taken from the Inner Harbour during May, June and July of 1955 indicate that distributions of phytoplankton there may reveal either even gradients or at times patehlness* Patchiness in the distribution of phytoplankton may result from small areas of productivity or from localised grasinge Both factors probably operate in the Inner Harbour. Inter-mittent flow of fertile water in through the Gap on strong flood tides could result in small masses of water which could produce localised blooms. Lateral water movements in the Inner Harbour have been described previously as compli-cated and variable. If masses of water were retained in intermittent or temporary eddies in regions of the Inner Harbour where concentrations of sessile and bottom grasers were high, an otherwise even distribution of phytoplankton could become patchy through grazing. Flow patterns suggest that this may sometimes occur. The occurrence of copepods and larval decapods in swarms could also result in patch-iness due to uneven grazing. a* Distribution of Genera of Phytoplankton The generie composition of phytoplankton in Ladysmith Harbour varies in both time and space. Results from 1954 and 1955 suggest that the sequence of genera in time is as follows: Thalassiosira. Chaetoceros, gkeletonema, 54 Chaetoceros, and. in late summer a complex of dominant genera. No one type of distribution of genera along th© Harbour appears common. It can only be said that the generic compos-ition of the phytoplankton in the Inner Harbour tends to differ from that to seaward. Ketchum (1954) shows that exchange rates may be important in determining the types and distributions of plankton in estuaries, After considering known division rates of phyto-plankton he concludes that endemic phytoplankton populations should be able to maintain themselves in estuaries having exchange ratios of 0.5 or less. The exehenge ratio is de-fined as the proportion of water moving seaward from the estuary on the ebb tide and not returning on the following flood tide. Inner Ladysmith Harbour, with a daily renewal rate of about thirty percent of the mean volume per day (exchange ratio less than 0.15), should thus be able to main-tain endemic phytoplankton populations. That i s , the rates of division of plytoplankters are such that they could maintain or increase their numbers in the Inner Harbour in spite of depletion to seaward by the circulation. However, i f the rate of reproduction of the plankton f e l l below a critical level due to grazing or nutrient depletion the endemic population would be unable to maintain i t s e l f . In this case the compos-ition of the plankton in t he Inner Harbour would resemble that to seaward providing that the composition to seaward remained constant. If the composition to seaward varied the time lag between the changes in the composition of the 55 phytoplankton in the two parts of the Harbour would give rise to apparent endemism. The increase In the proportion of the total population of phytoplankton formed by Ghaetoceros between May 3» 1955 and May 18-19 appears to have been a form of population succession. On May 3 tThallaaioslra was the dominant genus at a l l depths in Ladysmith Harbour. The composition varied l i t t l e long-itudinally ( f i g . 26). By May 10, Ghaetoceros had become dominant in the upper layers on the east side of the Inner Harbour. The proportion of the population formed by this genus decreased markedly to seaward (fi g . 27). The obser-vations taken at the six stations sampled over a 24 hour period on May 18-19 Indicated that Ghaetoceros had extended i t s distribution farther to seaward in the upper layer of the Harbour by this date (fig. 28). At each of these stations except Hlt the proportion formed by Ghaetoceros varied inversely with tidal height ( f i g . 29), suggesting that the genus was dispersing from the Inner Harbour. In the Inner Harbour the greatest concentrations of phytoplankton during the 24 hour period were associated with increases in the proportion of Ghaetoceros. This would be expected i f Ghaetooeros was en-demic to the Inner Harbour. During the same period, the high-est concentrations In the Outer Harbour were associated with high proportions of Thalassiosira. A cruise into Stuart and Trincomali Channels on May 17 Indicated that Thalassioslra was dominant throughout these bodies of water. Thus, between -T6 20 40 % CHA^ TQCEWQS LADYSMITH HARBOUR MAY 19, 1958 FIGURE 28 57 May 3 and May 18-19 Chaetoceros had increased from a relatively minor form to a dominant one in spite of depletion to seaward by circulation in the upper layers and the advectlon of other forms into the Harbour in the lower layer. Through population succeaaion Chaetoceros had become endemic to the Inner Harbour. The change appeared to have been associated with an increase i n temperature and a slight drop in salinity. The change in the composition of the plankton between June 12 and June 22, 1954 may have been brought about by the circulation. On June 12 Chaetoceros was the dominant genus in the Harbour* Skeletoneroa formed less than 50 percent of the phytoplankton but the proportion i t formed increased with depth and to seaward ( f i g . 30). By June 22 Skeletonema had Increased until i t had formed the major constituent of the phytoplankton (fig. 31). The proportion of the population i t formed was greatest in the Inner Harbour. This change in distribution could be interpreted to mean that the inflow of water In the deeper layers had earried Skeletonema into the Harbour where i t largely replaced the formerly dominant Chaetoceros. The fact that Chaetoceros formed a higher fract-ion of the population in the Outer Harbour than in the Inner Harbour on June 22 could have resulted from i t s advectlon out of the Inner Harbour or from changes beginning in the population after Skeletonema had attained dominance. If Skeletonema had attained dominance in the Inner Harbour through advectlon followed by population change® in the Outer 5-8 r x b 3r HI FIGURE 30 59 Harbour resulting from either succession or sequence the greater proportion of this genus in the Inner Harbour is a case of apparent endemisisu However, the time interval be-tween these two cruises, 10 days, is too great to allow definite conclusions to be drawn. The division rate of diatoms, which may be as high as one and a half per day, is such that the change In numbers and proportion of Skeletonema could have resulted from population succession. The distributions of the genus Chaetoceros cannot be re-lated to any particular conditions of salinity and temperature. This genus contains many species adapted to a wide variety of conditions. Only one species of the genus Skeletonema, i>. costatum, has been observed in British Columbia coastal waters. The o f this occurrenceAspeeies did not appear to be related to particular values of salinity or temperature. On June 12, 1954 i t was associated with the deeper and more saline layers. On August 2, 1954 the highest numbers and proportions of this genus were associated with low salinities. In general Skeletonema was most prominent during July, 1954, the period during which dilutions were occurring. Few generalisations concerning the distribution of genera can be drawn. The increase in the proportions of Skeletonema following the period when Chaetoceros was dominant was associated with dilution. Following this, Chaetoceros again became the most prominent genus, although Skeletonema. 60 Thalassiosira, and Kitaschla at times formed significant proportions of th® populations. The generic composition of the phytoplankton tends to vary vertically and longitudinally as do salinity and temperature. The lateral gradients of composition are usually small. Except for the f i r s t Instance discussed above no clear relationships between distributions of genera and physical-chemical factors or circulation are evident. A statistical study of the relationship® between species of phytoplankton occurring in Ladysmith Harbour and the salinity and temperature observations might prove fruit* ful but Is beyond the scope of this study* G* Advectlon, Graaing and Growth of Phytoplankton in the Inner Harbour 1* Advectlon of Phytoplankton It has been indicated that a two-layer circulation operates in Ladysmith Harbour. The net transport of phyto-plankton in a body of water with such a circulation can be expressed as: PT s PiTi - PuTu, where Pi • the mean concentration of phytoplankton In the Inward flowing layer; Pu a the mean con-centration of phytoplankton in the seaward moving layer; TI s the rate of transport of water In; and Tu » the rate of trans* port of water to seaward* If PT is positive a net gain of phytoplankton results from advectlon. If PT i s negative the reverse is true* The 6 1 expression applies to phytoplankton only. For aooplankton, which perform diurnal vertical migrations, the amount of time spent in each layer would have to be considered* In calculating net transports of phytoplankton for Inner Ladysmith Harbour, i t is assumed that plankton concentrations at Station I represent the mean for the Inner Harbour and that the mean transport of water inward, 78 cubic meters per second, prevailed throughout the period studied (June 6 , 1954 to August 27, 1954). During periods of outflow in the upper layer, Pi and Fu were taken to be the mean concentrations below end above the depth of no net motion respectively. Whan the circulation reversed during dilution Pi and Pu were taken from the upper and lower layers respectively. Variations in the mean standing crop in the water column at Station I and in the net rate of transport of phytoplankton are presented in Figures 32 and 33, The products of the mean of the rates for each pair of consecutive cruises and the time interval between each pair of cruises were summed to obtain th« total amounts of phytoplankton advected Into the Inner Harbour (fig. 34), (Table 5). 2. Gracing The principal grazers on phytoplankton in the Inner Harbour were assumed to be th® aooplankton and the populations of oysters (Crassostrea gigas) and clams (principally Protothaoa). Changes in the mean concentration of zooplankton in the water column at Station I are shown in Figure 32. 62 The rate of grazing by zooplankton ean be expressed as the volume of water cleared of phytoplankton per u n i t time. I t i s assumed here that the zooplankton f i l t e r phytoplankton from the water continuously and i n d i s c r i m i n a t e l y . Although there i s some evidence that some zooplankters feed i n t e r m i t t e n t " l y and are able to s e l e c t the species of phytoplankton con-sumed there are also data suggesting the contrary (Marshall and 0rr 9 1955, JoVgenson, 1955)* In a recent summary of f i l t e r feeding i n i n v e r t e b r a t e s , Gal anus flnmarchie^f, Stage I I I i s quoted to have a f i l t r a t i o n capacity of 1.2 m i l i l i t e r s per hour at a temperature of 17°G» Pseudocalanus minutus, Temora l o n ^ i c o r n i s , and .fiwftropaflea, hamatus are quoted to f i l t e r 0.18, 0.35 and 0.54 m i l i l i t e r s per hour r e s p e c t i v e l y at a temperature of 10°C (J^rgenson, 1955). Since these fou r species of copepods are of about the same s i z e as the organisms counted as zooplankton i n t h i s study the mean of t h e i r f i l t r a t i o n r a t e s , about 14 m i l i l i t e r s per day per organism, i s used here. Zooplankton concentrations at St a t i o n I are assumed to represent the concentrations for the Inner Harbour. There are about 2 m i l l i o n oysters and 5 m i l l i o n clams i n the Inner Harbour (D.l.Quayle, personal communication). The mean r a t e of f i l t r a t i o n of water by the A t l a n t i c oyster {Qstrea v i r g i n i e a ) having a mean wet weight of sof t parts of about 20 grams i s about 10 l i t e r s per hour per organism at temperatures between 9°C and 32°C (J^rgenson, 1955)• 63 The mean wet weight of soft part® of Crasaoatrea gigas from the inner Harbour is about 50 grams (Quayle, unpublished data), more than twice the weight of the 0, vir&lnica used to obtain filtration rates. Accordingly, the rate of filtration for oysters in the Inner Harbour is calculated at about 20 liters per hour per oyster. The clams filter about one liter per hour per clam (Quayle, personal communication). However, the clams and oysters are situated principally In the intertidal zone and therefore spend only part of th® time submerged and filtering. The distribution of bivalves with respect to variations in tidal height is assumed to be such that these organisms filter water only one half of the time. Taking this into account the rate of filtration by clams and oysters is calculated to be 5.4 x 10^ liters per day. It is further assumed that this rate remains constant over the period considered and that the water filtered by the bivalves has a concentration of phytoplankton equal to the mean for th® water column at Station I. The rat® of removal of phytoplankton (fig. 33) by grazing is calculated as the product of th® filtration rate of the graaers and the concentration of phytoplankton. The total amounts of phytoplankton removed from the Inner Harbour by grazing are shown in Figure 34. The values were obtained by taking the product of the mean of th® grazing rates between pairs of consecutive cruises and the time interval and summing the values obtained. ADVECTION AND GRAZING OF PHYTOPLANKTON 1954 65 3. Growth Figure 31 indicates that the total crop of phytoplankton in Inner Ladysmith Harbour for the period being considered i s greater than the amount recruited by advectlon. The difference must be due to production of phytoplankton by growth in the Inner Harbour. The total production of cells by growth necessary to make up this difference Is plotted in Figure 3 4 * In Table 5 the standing crop, changes in the standing crop, the number of cells recruited by advectlon, and the number of cells removed by grazing and the recruitment of cells through growth are presented. The rates of production of cells per day are also tabulated. Four of the 12 rates of growth are negative. Thus, the rates of grazing for these dates must be too low or the rates of advectlon of phytoplankton are too high. The other rates of eell production are below or only slightly above the approximate upper limit to the rate of reproduction for dia-toms of one c e l l division per day. According to the calculations about 17x10**' cells were produced by growth in the Inner Harbour. Phosphate concen-trations observed in Stuart Channel in the winter of 1 9 5 4 (Waldichuk, unpublished data) suggest that the concentration of PQ^ -P i n Ladysmith Harbour before th® onset of the spring bloom i s about 2.5 micro-gram atoms per l i t e r . Using data recorded by Harvey ( 1 9 5 0 ) , J^rgenson ( 1 9 5 5 ) , and Scagel (personal communication), one micro-gram atom of phosphate-fABLE 5 Advection, Grazing and Growth of Phytoplankton i n Inner Ladysmith Harbour Standing' Change i n " r _ Date Crop in Standing Recruitment, Mortality, Recruitment, Sate of eells Crop Advection Grazing MSMM Growth June 6, 1954 34.4x10 § w $ -73.IxlQ1*cells 34 W * g . t o g g j f f June 12 1.6 128.0 -103.0 -23.O -2.3 ^^,22, 41.6 -31.2 ' ' 43.3 -23.0 -10.9 -2.2 June 27 """"" -6-9 -11.3 39.0 34.4 2.3 July 12 19.2 10.4 1.4 0.4 July 16 -g, 2 24.0 29.6 -2.6 -§.? July 20 .."£»f—. •1.1 6.1 26.8 19.6 4 . 9 «¥4f 24 '"' ' 1.6 -5.0 18 .9 22.3 2.5 A^. 2 „ 5.4 . • • „ A . t i S - . . . n . . . -2.9 5.1 7.7 2 . 6 Aug..^, 1*2 -1.5 1.4 -2.5 -0.4 Aug. 12 0.3 _ .,• irtft .11.1 2.2 0.1 5.6 7.7 0.9 Au^, 20 2.5 4.9 6 . 9 70.3 68.3 9.7 Aug. 27 7,4 67 phosphorus was calculated to be equivalent to about 5.52 x diatom eells. According to this equivalent the recruitment of cells by growth of phytoplankton in the Inner Harbour rep-resents the utilization of about 3.3 x 10 i 0 micro-gram atoms of phosphate-phosphorus. This represents a concentration of about two micro-gram atoms per l i t e r in the Inner Harbour, less than that i n i t i a l l y available. Through adveetlon and regeneration of organic phosphate the amount of phosphate available for photosynthesis in the Inner Harbour probably exceeds the amount indicated by the i n i t i a l concentration* However, phosphate utilization by sessile plants probably reduces the amount available for use by phytoplankton* The sequence of diatom maxima and minima in the sea during the growing season has been attributed to the grazing action of zooplankton whose maxima tend to alternate with those of the phytoplankton (Fleming, 1 9 3 9 ) . There appears to be some relation between the concentration of zooplankton and changes in phytoplankton concentration in the Inner Harbour* However, changes in the standing crop appear to be more close-ly related to variations in the rate of advection of cells into the Inner Harbour than to changes in the rate of removal of ceils by grazing (figs* 32, 33). Figure 34 and the vertical distribution of diatoms early in the spring bloom suggest that recruitment due to growth may exceed that resulting from advection at that time. Following this may be a period when advection contributes 68 more ©ells than reproduction. In late summer reproduction appears to Increase in importance as postulated previously. The mean standing crop in the Inner Harbour was about 15 13.1 x 10 cells. The mean recruitment by advectlon was about 2.8 x IO1** cells per day. Qraaing removes about 4.5 cells per day. Thus th® mean rat® of addition of cells by growth necessary to maintain the mean population was 1.7 x IO 1* cells per day. According to this, advectlon recruits about one and a half times as many tells as eell division In the Inner Harbour. In calculating grazing rates, only bivalves, copepods, eopepodids, coea of crab, polychaete larvae and nauplii of copepods and clrripedes were considered. Such benthonic organisms as barnacles, sponges, and some polyehaetes are also f i l t e r feeders and occur in the Inner Harbour. Present in the plankton samples but not counted were rotifers which were moderately abundant at times and were observed feeding on diatoms in fresh plankton samples. Probably present in the Harbour but not in the plankton samples ar® the larger and more active Copepod® and later larval stages of Peeapoda. The pump used in plankton sampl-ing may have failed to capture representative numbers of some of the forms counted, such as copepodlds and zoea. Thus It appears that number of grazers used in the calculations were minimal. If this i s the case the calculated removal of phytoplankton by grazing i s too small. Since the recruit-ment resulting from reproduction of phytoplankton was taken to be the difference between the total crop (standing crop plus 69 amount removed by grazing) and the recruitment by advection, the reproduction rate of phytoplankton should be higher than was calculated. The possibility of advection and regeneration of nutrients suggests that sufficient phosphate should be available for a significant increase in the calculated re-cruitment resulting from cell division, Several probable sources of error exist in the calcula-tion of th© relative magnitude of the contributions of growth and advection to the total crop of phytoplankton in Inner Ladysmith Harbour* a) It was assumed that water exchange in the Inner Bay was entirely the result of a two-layer circulation. It has been pointed out that horizontal mixing may also operate. Neglect of horizontal mixing in calculating the recruitment of phytoplankton due to water exchange w i l l result in too high a value for the recruitment of cells from this source* b) The renewal rate used may be in error. e) The renewal rat® was assumed constant which may not be the ease. d) The concentrations of phytoplankton and zooplankton at Station I were assumed to represent the mean for the Inner Harbour. Data from the summer of 1955 suggest that error from this source may be considerable and variable. e) Variation in the grazing rate due to the effeets of temperature changes on the activity of the grazers was neglected. f) The fact that the numbers of grazers used in calculat-ing grazing rates was minimal has been discussed above. 70 IV, CONCLUSIONS 1. The configuration of th® shoreline end distribution of depth i n Ladysmith Harbour have important effeets on the di s t r i b u t i o n of phytoplankton. Shore configuration divides the Harbour into a shallow inner bay and a deeper outer portion. The shallow depth® of the Inner Harbour l i m i t the production of phytoplankton d i r e c t l y by r e s t r i c t i n g the depth of the euphotic sone. In addition no deep reservoir of nutrients i s available there and competition between s e s s i l e and planktonic plants i s higher i n the Inner Harbour than to seaward due to the shallow depth. A second effect of the higher r e l a t i v e concentration of sessile plants occurs i n late summer when large amounts of Fosters and bottom dwell-ing algae die .and decompose, releasing nutrients which become available for use by phytoplankton. The configuration of the shoreline and distri b u t i o n of depth also tend to r e s t r i c t c i r c u l a t i o n and v e r t i c a l mixing i n the Inner Harbour with consequent effeets on the distributions of s a l i n i t y and temperature. 2. Freshwater discharge has no direct effect on production of phytoplankton during the growing season. However, i t s influence oa s a l i n i t y distributions i n spring may result i n v e r t i c a l and longitudinal variations i n the composition of phytoplankton i n Ladysmith Harbour. Drainage i s important 71 in helping to maintain the pressure forces resulting in the two-layer circulation, 3« Salinity gradients in Ladysmith Harbour have no direct effect on the production of phytoplankton, but are important in conjunction with temperature gradients in determining the composition of the phytoplankton. Changes in salinities appear to be associated with changes in the composition of the phytoplankton. Salinity gradients and changes in them have important effects on the phytoplankton through their i n f l u -ence on th® distribution of density and thus circulation, 4, Temperature gradients in Ladysmith Harbour are such that their influence on metabolic rates result in a higher rate of turnover of biological products in the Inner Harbour, Growth, respiration, g r a z i n g and the rat© of regeneration of nutrients should a l l proceed at a higher rate i n th® Inner Harbour than to seaward. The importance of a higher rate of nutrient regeneration from organic combination i n th© Inner Harbour i s enhanced by the shallow depth. Temperature gradients i n Ladysmith Harbour are associated with longitudinal variations i n the generic composition o f th® phytoplankton. The effect of temperature gradients on density distributions i s important in determining the circulation, 5. A large proportion of the water i n Inner Ladysmith Harbour enters and leaves the inner bay each day due to tidal action. Temperature, salinity, th® concentration of phytoplankton and the composition of th© phytoplankton at any location in 72 Ladysmith Harbour tend to vary over each t i d a l cycle. The proportion of water i n the Inner Harbour involved i n t i d a l action and the existence of a jet stream through the Gap during periods of maximum t i d a l current suggest that horizont-a l mixing may be Important i n controlling the properties of the water i n the Inner Harbour* 6. The mean di s t r i b u t i o n of velocity with depth over twenty-four hour periods and longitudinal gradients of s a l i n i t y temperature and density indicate that a two-layer system of ci r c u l a t i o n operates i n Ladysmith Harbour. Throughout most of the year outflow occurs i n the upper layer and inflow i n the lower layer. When d i l u t i o n from seaward takes place i n midsummer this c i r c u l a t i o n i s reversed and inflow occurs i n the upper layers. 7. The mean rate of water renewal i n the Inner Harbour i s about 30 percent of the mean volume per day and probably varies between 10 and 50 percent per day. 8* Water exchange i n the Inner Harbour affects the d i s t r i b u t -ion of phytoplankton both d i r e c t l y and in d i r e c t l y . Through both maintaining and changing the properties of the water i n th© Inner Harbour water exchange exerts control on the abundance and composition of phytoplankton* In spring and early summer exchange tends to maintain the s a l i n i t y by removing fresh water and entrained salt water In the upper layer and advecting more saline water inward i n the lower layer* In midsummer a series of dilutions ar® brought about by water exchange. 73 Throughout th© growing season {except during d i l u t i o n ) the c i r c u l a t i o n tends to replace warm water i n the Inner Harbour w i t h colder water, thus c o n t r o l l i n g the r i s e i n temperature which would otherwise r e s u l t from the excess of r a d i a t i o n during the growing season. Thus, while the r a t e of water exchange i n the Inner Harbour I s low enough to permit the development of endemic phytoplankterf, water renewal through i t s co n t r o l of s a l i n i t y and temperature i s important i n determining the species which may f l o u r i s h * However, i f the r a t e of additloh of new e e l l s t o the endemic c i r c u l a t i o n f a l l s below a l e v e l d eter-mined by the c i r c u l a t i o n , the composition of phytoplankton i n the Inner Harbour w i l l depend on the forms advected i n -ward although temperature and s a l i n i t y could be such that endemic forms would develop I f they could reproduce. The normal c i r c u l a t i o n , with i n f l o w i n the lower l a y e r , tends t o maintain phytoplankton concentrations i n the Inner Harbour by advecting c e l l s and n u t r i e n t s inward on a net b a s i s . During d i l u t i o n c i r c u l a t i o n tends to lower Inner Harbour plankton concentrations on a net b a s i s . 9. C a l c u l a t i o n s i n d i c a t e that during the period June 6, 1954 to August 27, 1954 the recruitment of phytoplankton to the Inner Harbour by advection was one and one h a l f times the recruitment r e s u l t i n g from growth. While, f o r reasons mention-ed p r e v i o u s l y , the estimate of recruitment by growth i s thought to be low, i t i s c e r t a i n that advection of c e l l s con-t r i b u t e d a l a r g e proportion of the t o t a l crop of phytoplankton 74 in the Inner Harboar during t h i s p e r i o d . 10* Grazing i s responsible for most of the removal of phytoplankton from the Inner Harbour. However, fluctuations in the net rate of advection of eells into the Inner Harbour were closely associated with changes in the standing crop of phytoplankton* 75 1. Barlow, J.P. If52. Maintenance and dispersal ©f tae endemic aoeplasktom population of a t i d a l estuary, Qreat Pond, Falmouth, Massachusetts. Ph.D. Thesis, Department of Biology, Harvard Univ., Cambridge, lass, (not seen). 2. Fleming, S.I. 1939* The control of diatom populations by grassing. tot. pour l»a^>lorati« de l a J . du Conseil tot. j Mer. £4,. (2)s 1-20. 3. Gibbon®, 8 .G. aad Fraser, *f*H. 1937 Pump and suction hose sampling. J . du Sonsell Int. pour 1'Stqaleration d® l a Mer* U' (163) • 4. Harvey, B.tf. 1950* On the production of living matter i n th® sea off Plymouth. J.Maraiol.As®., U.K. &i 97-138. 5* tJorgensen, CB. 1955* A summary of f i l t e r feeding in invertebrates. Cambridge Philosophical Soc.Biol .Eev. %® t 6. Ketchum, B. 1954* Relation between circulation and plaaktonic populations i n estuaries. Seelogy. J| (2)» 191-200. 7* Ketchum, B., J. Ayers, and R. facarro. 1952. Processes contributing to the decrease of coliform bacteria i n a ti d a l estuary. Ecology. 247-258. (not 8. Kimball, H. 1928. The amount of solar radiation that reaches the surface of the earth en the land and on the sea, and the method® by which i t i s measured. Monthly Weather fteview. $6 t 393-399* 9« Marshall, S. and A. Orr. 1955* The Biology of a marine copepod StiaBtt SlflfrffifrU*. (Gunuerus). Edinburgh. 10.. Itttehard*. P.W. and W. Burt. 1951* An inexpensive and rapid technique for obtaining current profiles i n estuarine waters. J©ur*r.Ses. 1J>.(2) * 180-189. 11. Quayle, D.B. 1951*1955. unpublished data, 12. Scagel, E.f. 1955. Saanich Inlet gruises 1954, 1955. Institute ©f Oceanography, Oniv. of British 0©lumbia, Data Beport 5 • 76 LTTERATOHE CUED (concluded) 13• Seagel, ISbpubllshed data. 14. Sverdrup, H.b*., M. Johnson and E. Fleming. 1942* The Oceans. Pp®ntie@-8all. lew fork. 15. Tully, J.P. and M. Waldichuk. The ooeanographlc phase of the Hanaimo sewage problem. Joint Gcwittee on Oceanography. Pacific 0o®anographie ©roup, Nanaimo, B.C., Sept. 1, 1953• 16. WAtiwjfc* X. 1954« 17. Anonymous. 1955* 18. ©hpubilshed data. Surface water supply of Canada. Pacific Drainage, Climatic Tears 1950-51 and 1951-52. Department of Northern Affairs and lational Resources• Mater Resources Paper Mo. 114» Daily meteorological observations at Cassidy Airport. Ifay 1954 » August 1955• Canada Department of Transport, Air Services Slvislon. Unpublished. 

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