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Physical and chemical aspects of water repellent soils affected by slashburning at Vancouver, British… Henderson, Greg 1981

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PHYSICAL AND CHEMICAL ASPECTS OF WATER REPELLENT SOILS AFFECTED BY SLASHBURNING AT VANCOUVER, BRITISH COLUMBIA by Greg Henderson M. Sc., The Univers i ty of B r i t i s h Columbia, 1981 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Faculty of Forestry, Forest Hydrology) We accept th i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA Ju ly , 1981 (c) Greg Henderson In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by h i s or her representatives. It i s understood that copying or p u b l i c a t i o n of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Forestry  The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date 18 September 1981 ACKNOWLEDGEMENT I would f i r s t l i k e t o thank my supervisor, Dr. D. Golding, f o r suggesting t h i s t h e s i s t o p i c and f o r h i s valuable c r i t i c i s m s of my various d r a f t s . I a l s o g r e a t l y appreciate the comments and encouragement of my other cramrdttee members, Drs. T. Ba l l a r d , 0. Slaymaker, and J . Thirgood, at th e s i s write-up and al s o throughout my graduate programme. Special thanks are extended to Drs. M. Barnes and L. Lowe, both of whcm took extra time to explain and advise on many aspects of s o i l chemistry. Dr. Barnes was e s p e c i a l l y h e l p f u l i n the development of the extr a c t i o n procedure, as was Mr. B i l l Yeung. Dr. Lowe reviewed the chemical r e s u l t s i n Chapter 5, and aided i n the i n t e r p r e t a t i o n of the i n f r a r e d spectrum. Dr. K. Fl e t c h e r g r a t e f u l l y permitted the use o f h i s microbalance. I would l i k e to thank Raymond Wong, Ken Rai, Kuochi Rai and B i l l Yeung f o r t h e i r f i e l d and laboratory assistance at various stages o f the pr o j e c t . Mike Decker helped i n the execution of several column chromatography runs. Ms. Suzanne Macvey expressed her professionism i n the drawing of the figures and Mrs. V a l e r i e Nay typed the f i n a l d r a f t . i i ABSTRACT The persistence and severity of water repellency i n s o i l s as affected by slashburning was examined i n the municipal watersheds of Vancouver by the water drop penetration time (WDPT) and contact angle method, respectively. Also, hydrophobic materials were extracted from s o i l , separated by column adsorption chromatography, and analysed f o r functional groups by infrared absorption. Slashburning increased s o i l water repellency, as indicated by the WDPT method. Precise responses of s o i l repellency to slashburning were not consistent, as many s i t e s p e c i f i c factors are involved, but increased repellency was evident i n s o i l up to s i x years following burning. The severity of increased s o i l repellency caused by slashburning could not be assessed because contact angle determinations using the c a p i l l a r y r i s e equation and Darcy's Law were not r e l i a b l e . The WDPT method was more consistent, r e l i a b l e and simpler than the contact angle method, hence the WDPT method was considered best to indicate the presence of s o i l water repellency. A combination of polar and non-polar organic solvents, methanol and benzene respectively, extracted hydrophobic compounds from s o i l . The extractant separated into three fr a c t i o n s , using benzene and increasing proportions of acetone as eluting agents. V i r t u a l l y a l l of the extract (90%) was recovered i n Fraction I , indicating that the extraction was predominantly non-polar. Fraction I I and I I I accounted for 4 and 6 per cent, respectively, of the applied extractables. Material i n a l l Fractions i i i induced repellency i n wettable sand when 1 mg or more was applied to 5 gm of sand. Repellency was increased by heating the extracted materials i n sand to 250°C for 10 minutes and was eliminated after heating to 300°C i n inverse proportion to the mass applied. At 350°C, hydrophobic materials v o l a t i l i z e d and the sand regained w e t t a b i l i t y . Analysis of an extraction by infrared absorption revealed that hydrophobic substances have hydrophilic and hydrophobic components. Adsorption of hydrophobic materials to s o i l p a r t i c l e s i s therefore l i k e l y i n i t i a l l y by the hydrophilic end leaving the hydrophobic end of the organic molecule to form the outer surface thus preventing water from i n f i l t r a t i n g . During slashburns, adsorption of hydrophobic materials i s probably enhanced by optimization of close range van der Waals and London forces. iv TABLE OF CONTENTS Page TITLE i AUTHORIZATION ABSTRACT i i TABLE OF CONTENTS i v LIST OF TABLES v i LIST OF FIGURES v i i ACMCWI^LX;EMENT Chapter 1. INTRODUCTION 1 Chapter 2. CONCEPTS OF WATER REPELLENCY AND LITERATURE REVIEW 5 2.1 De f i n i t i o n of S o i l Water Repellency 5 2.2 Factors Influencing S o i l Water Repellency 5 2.2.1 S o i l c haracteristics 5 2.2.2 Vegetation 6 2.2.3 Fungi 7 2.2.4 F i r e 7 2.3 The Nature of Water Repellency 8 2.4 Measuring Water Repellency 9 2.4.1 Contact angle 12 2.4.2 Water drop penetration time 13 2.4.3 Other methods of assessing water repellency 13 2.5 Chemistry of Water Repellency 14 2.5.1 Composition 14 2.5.2 Origin of hydrophobic materials 16 2.5.3 Influence of f i r e 16 2.5.4 Extraction of hydrophobic substances 18 Chapter 3. DESCRIPTION OF STUDY AREA 19 3.1 Climate 19 3.2 Geology 24 V Page 3.3 Soils 24 3.4 Vegetation 25 3.5 Selection of Sampling Blocks 25 Chapter 4. METHODS 27 4.1 Field 27 4.2 Laboratory 27 4.2.1 Physical 28 Contact angle 28 Water drop penetration time 31 4.2.2 Chemical 31 Soil samples 32 Extraction procedure 32 Fractionation of extracted 34 materials 34 4.3 Infrared Analysis 35 Chapter 5. RESULTS AND DISCUSSION 35 5.1 Soil Water Repellency 35 5.1.1 Water drop penetration time ' 38 5.1.2 Contact angle 43 5.2 Chemistry 43 5.2.1 % C 43 5.2.2 Extractions 45 5.2.3 Fract ionation 47 5.2.4 Infrared absorption analysis 54 Chapter 6. SUMMARY AND CONCLUSIONS 59 BIBLIOGRAPHY 65 APPENDICES 71v i LIST OF FIGURES Number T i t l e Page 1. Comparison of i n f i l t r a t i o n rates for a wettable and 9 repellent s o i l (after DeBano 1969a). 2. A water droplet on a hydrophobic surface at mechanical equilibrium, expressed as Y S V = Y S L + Y L C O S 0 . 3. The geographic setting of the study area. 20 4. The location of the sample sites within Seymour and 21 Coquitlam Watersheds. 5. Maximum, minimum and mean monthly temperature at Seymour 22 Dam, 1972-1976 (data courtesy of K. Rai). 6. Mean monthly precipitation at Seymour Fal l s , Seymour River 23 Basin, 1941-1970 (from Cheng 1975). 7. Apparatus for measuring capillary rise of water in s o i l 30 tubes. 8. Plot of EU (mg/g) vs. % C for repellent and wettable s o i l 48 samples. 9. Representative elution curve for the chromatographic 49 separation of the substances extracted from s o i l . 10. Infrared spectrum of Fraction I. 55 v i i LIST OF TABLES Number Title Page I Water repellency of soils, by depth. 35 II Water repellency of soils, a l l depths. 35 III Frequency of burned (B) and control (C) samples in 38 individual cutblocks repellent or wettable, by slash-burn age. (Burn intensity shown in brackets, when appropriate). IV Per cent carbon (% C) and repellency for soil not 44 burned, and soil 1 year after a slashburn, by depth. V. Characteristics of extractions from a repellent and 46 a wettable soil profile. VI Water repellency of Fractions I, II, and III at 51 different temperatures. VII Minimum amount (mg) of extractables required to 53 produce repellency (WDPT > 5 seconds) and severe repellency (WDPT > 60 seconds) in sand. VIII IR-spectrum data of Fraction I. 56 1 1. INTRODUCTION The occurrence of d i f f i c u l t - t o - w e t or water repellent, s o i l s i s a global phenomenon. Water repellency has been reported for example, i n A u s t r a l i a (Bond 1969), Finland (Orr 1979 pers. comm), New Zealand (John 1978), Japan (Nakaya et a l . 1977) throughout the United States (e.g. DeBano 1969b), and Canada (Jamieson 1969). Most reports, however, deal with the hot sandy areas of the world due mainly to the undesirable environmental consequences of water repellent s o i l s i n such areas. For example, i n F l o r i d a , Jamison (1942, 1945) observed a decline i n productivity of c i t r u s f r u i t trees resulting from water repellent s o i l conditions under the trees, especially i n s o i l s within the area of the leaf d r i p . A s i m i l a r problem ex i s t s today i n s o i l s under c i t r u s trees i n Egypt (Hartmann et a l . 1976). In A u s t r a l i a , Prescott and Piper (1932, i n Bond 1969) noted that patches of s o i l under Eucalyptus trees remained dry even under the impact of winter rai n s . Since then, Bond (1968, 1969) has found large areas i n A u s t r a l i a where s o i l water repellence occurs. Researchers i n the western United States f i r s t began concentrating on non-wettable s o i l s about 1962 (DeBano 1969b) due to erosion of s o i l from burned watersheds. As a consequence, the focus of many subsequent studies has been the effect of f i r e on s o i l water repellency. To forest managers, water repellency i s important because of the potential impact on the forest resource. Increased erosion, due to water repellent s o i l increased by slashburning, can remove s o i l needed for regrowth and substantially reduces the regeneration potential of the land. 2 Also, the displaced soil may be deposited in lakes or streams deleteriously affecting water quality and upsetting the aquatic ecosystem. This has already become such a frequent occurrence in parts of the southern United States that, in some cases, soil has been aerially sprayed with chemicals to make i t more wettable. Little research into water repellency of soils and s t i l l less towards an understanding of the effects that fire has on forming or increasing water repellency has been undertaken in British Columbia. In British Columbia, slashburning is a very common forestry practice, yet the potential consequences of intensified soil water repellency are often overlooked. To further the knowledge of soil water repellency, this paper investigates water repellency in slashburned soils of the municipal watersheds of Vancouver, British Columbia. Research into water repellency of soils is difficult for a variety of reasons. First, repellency is highly time dependent. It may persist for only a short time period after a fire, or i t may last many years. Soil may exhibit seasonal or permanent repellency, and this may be dependent on vegetative cover. Second, repellency is influenced by several factors, such as microorganisms, soil texture, vegetation and fire. However, the contribution of each of these factors towards observed repellency is unknown and probably varies from site to" site. Third, there is a very incomplete knowledge of the chemistry of water repellency. There is great difficulty in extracting the chemicals responsible for repellency from soil to study them. Also, an extraction technique applicable to one soil type may not apply to a different soil. Finally, there is no one method, 3 accepted by a l l , that accurately and quantitively characterizes water repellency. This makes comparisons of water repellency between regions d i f f i c u l t and potentially spurious. The principal objectives of this paper are: to determine the degree and persistence of increased s o i l water repellency caused by slashburning and to investigate some chemical characteristics of the compounds which contribute to water repellency* Specifically, water repellency w i l l be assessed by two popular methods, droplet penetration time and the liquid-solid contact angle, and their usefulness and r e l i a b i l i t y w i l l be c r i t i c a l l y evaluated. Water repellent compounds w i l l be extracted from s o i l and separated by adsorption column chromatography for subsequent study of the effective waterproofing components of the extractant. Infrared absorption analysis of a separation w i l l hopefully provide clues of the origin and identity of s o i l waterproofing agents, as well as their behaviour during slashburns. The watersheds of Vancouver are maintained by personnel of the Greater Vancouver Water Dist r i c t (GVWD). The mandate of the GVWD is to provide water for residents of Vancouver and surrounding communities. Small areas of the watersheds are logged to offset the cost of operations, and the GVWD has produced comprehensive maps on forest cover, topography and hydrologic characteristics of the watersheds. There are also concise records of the time and location of slashburns conducted over the past 20 years. Researchers, particularly those from the University of British Columbia, have taken advantage of the proximity and accessibility of the pristine forested land in the watersheds to conduct various experiments, and a substantial amount of data has been gathered on climate and s o i l 4 characteristics, as well as the impact of forestry ac t i v i t i e s on the environment. It was considered that the coarse textured soils in the watersheds, coupled with slashburning activities and the desire of the GVWD to minimize erosion for maintaining water quality, were excellent combinant factors for ini t i a t i n g a study of s o i l water repellency at this location. The thesis is divided into five additional chapters, the f i r s t of which introduces basic concepts of water repellency, with emphasis on those pertinent to this study, through a review of the literature. The study area is described next, including location, s o i l types, geology, climate and details of the selection of the study blocks. Chapter 4 i s a description of the methods used. The chapter i s subdivided into two parts dealing with f i e l d and laboratory methods respectively. The following chapter i s a substantive section of the thesis in which results of f i e l d and laboratory work are provided and discussed. Subsections on physical and chemical aspects of water repellency are presented to correspond to their respective sections in Methods. The last chapter contains a summary and conclusions of the information presented, and also provides some suggestions for future research on water repellency. In this paper, the term 'hydrophobic' refers to the actual chemicals which cause s o i l water repellency and not to the nature of the s o i l i t s e l f . The terms 'repellent', 'repellence', 'water repellent' or water repellency' are a l l synonymous with s o i l water repellency. 5 2. CONCEPTS OF WATER REPELLENCY AND LITERATURE REVIEW 2.1 De f i n i t i o n of S o i l Water Repellency A s o i l that i s water repellent i s resistant to i n f i l t r a t i o n by water due to hydrophobic organic compounds which have coated s o i l p a r t i c l e surfaces. Hydrophobic compounds are derived from the decomposition of vegetative matter, and the al t e r i n g of organic matter by a c t i v i t i e s of microorganisms, high temperatures, or di r e c t production of hydrophobic substances by s o i l fungi. The term 'repellent' i s perhaps a misnomer because s o i l never actually repels water, but the natural attraction between s o i l and water can be severely reduced. Prolonged exposure to water w i l l almost always break the repellency b a r r i e r . However, upon drying, the s o i l can regain i t s repellent c h a r a c t e r i s t i c . Repellency i s r e s t r i c t e d to the uppermost s o i l layers where chemical and microbiological a c t i v i t i e s are greatest. Rarely does s o i l exhibit repellent characteristics 30 cm below the mineral layer, and usually repellency i s most pronounced within the top 10 cm. 2.2 Factors Influencing S o i l Water Repellency 2.2.1 S o i l c h a r a c t e r i s t i c s Water repellency i s most commonly associated with coarse textured s o i l s . This i s attributed to the smaller s p e c i f i c surface area of coarse textures s o i l s compared to f i n e r textured s o i l s . Thus, with a given amount 6 of hydrophobic materials, a greater volume of sand can be coated than s i l t and clay. Organic matter is needed to impart water repellent conditions in soils. However, correlations between soil organic matter content and observed repellency have been inconsistent. For example, Bond (1969) found that some soils with 5% organic carbon (C) wet easier than soils with 0.1%C. DeBano et al. (1976) determined that neither the amount of organic C nor organic matter was closely related to water repellency. Bond (1969) found that water repellency was most pronounced in Australian soils when clay content was less than 7%, although extreme repellency was also observed in soils with up to 20% clay. 2.2.2 Vegetation There is a wide variety of vegetation types which can cause water repellency, and specific relationships have been reported. Holzhey (1969) recognized, in California, a year-round repellency in soils covered with forest floor l i t t e r , and seasonal repellency in soils dominated by herbaceous species with bare patches of exposed mineral soil which become dry in low rainfall periods. Bond (1964) noted water repellency was greatest in Australia under an old pasture of Phalasis tuberosa+ and beneath scrubs such as Leptospermum myrsinoides.+ Leaf drip from citrus trees causes severe repellency in Egypt and Florida. In California, l i t t e r from chamise, scrub oak, redshank, deerbursh and manzanita are prominent producers of repellent soils (DeBano 1969b, Holzhey 1969). Conifer + This symbol used to indicate that author identification of the species was not supplied in the reference cited. 7 species contribute to water repellency in more northern climes, due probably to a suberized layer of wax on needles. Jamieson (1969), in examining soils near Vancouver, British Columbia, determined that extracts (with water and 0.1 N NH4OH) from li t t e r of three conifer species, Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], Western red cedar (Thuja plicata Donn), and Western hemlock [Tsuga heterophylla (Raf.) Sarg.] a l l contained hydrophobic materials. Also, there is some evidence that certain plant species exude hydrophobic substances as an evolutionary strategy for survival (Mooney and Dunn 1970 in Foggin and DeBano 1971). 2.2.3 Fungi Filamentous fungal hyphae and substances produced by fungi contribute to water repellency. Bond (1964) and Bond and Harris (1964) noted a relationship between fungi and fungal mycelia of basidiomycetes and zones of water repellency in soil. Savage (1969) established that specific fungi isolated from water repellent soils could produce limited water repellency, even in the absence of plant materials. In another study, Savage et al. (1969a) determined that a bacterium, Stachybotrys atra,+ could make a silica sand water repellent. 2.2.4 Fire Fire is undoubtedly the most important factor in causing soil water repellency. High soil temperatures from fire can translocate and broaden a water repellent layer to depth (DeBano 1966). Also, fire can induce a non-wettable layer in a soil that was initially wettable, provided sufficient organic material is present. 8 Varying degrees of water repellency can develop in the so i l , depending on the severity and duration of the fire. For example, DeBano (1981) found that light burns in chaparral over dry soils produced highly water repellent soils, while least water repellency was produced in light intensity burns over wet soils. A potential result of an induced or intensified water repellent layer in the soil is increased runoff and erosion. Accelerated erosion has occurred to such an extent in areas of the south-west United States that wetting agents have been applied to soil to induce wettability (e.g. Rice and Osborn 1970). However, results to date have been inconclusive. In some instances, wetting agents have been found uneconomical to apply (Dr. Rice pers. comm). Persistence of a water repellent layer caused by fire varies greatly, and depends on such factors as intensity and duration of the fire, and resultant soil temperatures. Dyrness (1976) found non-wettability in soils 5 years after a wildfire in Oregon. Most commonly, fire produces increased repellency in soils for short durations, usually under two years (e.g. Reeder 1978). 2.3 The Nature of Water Repellency Infiltration of water in non-wettable soils is greatly impeded (Figure 1). DeBano (1971) determined that the rate of infiltration in a non-wettable soil can be up to 25 times slower than that for the same soil made wettable. There is an ini t i a l resistance to infiltration in the 9 FIG. 1. Comparison of i n f i l t r a t i o n rates for a wettable and repel lent so i l (after DeBano 1969a). 10 non-wettable soil, but the infiltration rate gradually increases over time to more closely approximate that of a wettable soil. At low moisture contents, then, the effect of water repellency is greatest. Unsaturated flow in water repellent soils may be predominantly by vapour diffusion, as opposed to viscous flow in a wettable soil (DeBano et a l . 1969a). Evaporation can also be reduced in water repellent soils (DeBano 1969a). This is believed due to a decreased capillary action in drawing water up to the surface. Thus, surface wettable layers above a repellent layer may dry out and impose moisture stresses on plants. If roots penetrate the repellent layer, however, considerable moisture may be obtained, as water repellent soils retain more moisture during desorption than do contiguous wettable layers (DeBano 1969a). 2.4 Measuring Water Repellency Common to a l l determinations of water repellency is an understanding of the liquid-solid contact angle. This is best illustrated in Figure 2. A droplet of water applied to the surface of a smooth flat surface forms an angle e . Physically, at mechanical equilibrium, Young's equation states (from Zisman 1964), Y s v = Y s L + Y L vcos8 (1) where, Y s v = surface tension at the interface of the solid and vapour Y s L = surface tension at the interface of the solid and liquid vapour 12 Y L v = surface tension at the i n t e r f a c e of the l i q u i d and vapour 0 = l i q u i d - s o l i d contact angle. T h e o r e t i c a l l y , when 0 = 90°, the s o l i d i s non-wettable and the droplet does not spread out. At 0 = 0 ° , the s o l i d i s sa i d to be completely wetted and the droplet f l a t t e n s . A water r e p e l l e n t s o i l has a large contact angle (>_ 90°) and a wettable s o i l a very small contact angle (close to 0°). Equation (1) i s not appropriate to porous media, such as s o i l (DeBano 1969a), therefore, the usual approach to obtain contact angle data i s with models des c r i b i n g water flew i n s o i l that include a contact angle v a r i a b l e . 2.4.1 Contact angle One equation commonly used to c a l c u l a t e the contact angle i s the c a p i l l a r y r i s e . The assumption i s that s o i l pores are long c y l i n d r i c a l c a p i l l a r i e s through which water flows. The c a p i l l a r y r i s e equation i s expressed as, 2 a cos 0 Pgr where, h = equilibrium height of rise a = surface tension of the liq u i d g = gravitational constant r = s o i l pore radius 0 = solid-liquid contact angle P = density of the liquid (2) 13 In the c a p i l l a r y r i s e equation, most of the variables can be obtained from standard chemical tables, except f o r r, and ©. 2.4.2 Water drop penetration time This method, abbreviated hereafter as WDPT, involves p l a c i n g a water droplet on s o i l and observing the time f o r i n f i l t r a t i o n . I f the droplet remains i n t a c t f o r longer than 5 seconds,* the s o i l i s considered water r e p e l l e n t . The advantage of t h i s method i s that i t i s simple and easy to administer; the disadvantage i s that i t does not c a l c u l a t e a contact angle, but merely indicates whether a s o i l i s wettable or non-wettable. 2.4.3 Other methods o f assessing water repellency A number of a d d i t i o n a l methods e x i s t f o r c h a r a c t e r i z i n g water repellency, and some of these are l i s t e d below. Most of these methods are expensive, complex, time consuming, o r not suited t o the s o i l s o f the Vancouver Watersheds, and therefore I chose not to use them. Fink (1970) reported a threshold water-entry pressure method f o r determining contact angle f o r extremely water-repllent s o i l s whose contact angle exceeds 90°. Watson and Letey (1970) developed wetting indices based on surface tension-contact angle r e l a t i o n s h i p with water drop penetration * t h i s f i g u r e i s a r b i t r a r y , and r e f l e c t s the value most frequently reported i n the l i t e r a t u r e . 14 times. Bahrani et al. (1970) proposed two wetting coefficients for water repellent sand, one based on Young's "work of adhesion", another on Moilliet's "work of droplet adhesion". Miyamoto and Letey (1971) evaluated water repellency by determining the solid-air surface tension of the medium, using Fowkes' dispersion theory and the capillary rise equation. In an effort to reduce the 'contact time' of solutions with soil, Bahrani et al. (1973) used horizontal positive head-driven infiltration trials with n-heptane and water into soil columns. Finally, DeBano (1969a) used unsaturated flow measurements to calculate liquid-solid contact angles, employing the concept of intrinsic soil-water diffusivity in horizontal infiltration trials. 2.5 Chemistry of Water Repellency Compared to physical attributes of water repellency in soils, such as water flow characteristics, relatively l i t t l e is known about the actual chemistry of the materials which make a soil non-wettable. This is due, no doubt, in part, to the natural variability of different soil systems, as well as to the complex composition and behaviour of chemical constituents in individual soil systems. 2.5.1 Composition The effective components of hydrophobic molecules are believed to be aliphatic hydrocarbons (Savage et al . 1972). These are non-polar linear or branched binary compounds of carbon and hydrogen. Hydrocarbons undergo oxidation to carbon dioxide and water at high temperatures, i f sufficient 15 oxygen is present. Grease and o i l are typical examples of hydrocarbons, hence their appearance upon extraction from soils as, "black and tarry" (Savage et al. 1972). Lipids, including fats and waxes, are also water insoluble and hydrophobic. These materials are common constituents of plants. Amphiphatic organic molecules are probably responsible for most of the waterproofing in a soil. They are essentially similar to the above group of molecules, in that they have a predominant hydrocarbon component, but they differ in that they also have small hydrophilic components. Therefore, these amphophilic molecules contain both hydrophilic (polar) and hydrophobic (non-polar) groups. Such surfactants, as they are called, cause a reduction in surface tension (gas-liquid interfaces) and interfacial tension (liquid-liquid and solid-liquid interfaces), and can either render a soil non-wettable (e.g. Fink and Myers 1969), or a non-wettable soil wettable (Valoras 1969). Adsorption is amphiphatic in nature, that is, the hydrophilic end of the molecules adsorbs onto soil particles leaving a 'new' surface consisting of the hydrophobic portion of the molecule (Bozer et al. 1969). Adsorption of hydrophobic molecules is probably by van der Waals-London interactions, effective when hydrophobes come very close to or in direct contact with soil particle surfaces. A major group of soil waterproofing chemicals are the amphophilic substituted phenols. Bozer et al. (1969), states that phenolic compounds are common in natural resins and vegetative matter and therefore are probably a prominent group of compounds which naturally waterproof soils. 16 2.5.2 Origin of hydrophobic materials Virtually a l l of the hydrophobic materials extracted from soil are found in the humus layer. Aliphatic hydrocarbons, for example, are abundant in humic substances (Chen and Schnitzer 1978). Humic acids (HA) have been found to contribute greatly to water repellency, especially when of microbial origin (Adhikari and Chakrabarti 1976). This is not always the case, however, as Savage et al^. (1969b) concluded that humic acid substances and polysaccharides do not contribute substantially to water repellency. Fulvic acid (FA) was implicated as the agent responsible for repellency on non-wettable golf greens (Miller and Wilkinson 1977). Finally, Chen and Schnitzer (1978) found that both FA and HA could either create water repellency or improve wettability, depending on pH. 2.5.3 Influence of fire As stated previously, fire can translocate and intensify a water repellent layer to depth. The persistence of a water repellent layer induced or aggravated by fire can be long lasting or of short duration. In any case, the behaviour of hydrophobic materials are clearly altered at high temperatures. DeBano (1966) proposed the hypothesis that hydrophobic substances in soil are volatilized during a fire and translocated to depth by steep temperature gradients where they condense and cool on soil particles. Savage et al. (1972) showed that a natural fractionation of substances capable of causing water repellency produced in the heated li t t e r layer occurs^as the substances move through the underlying soil. Three main 17 fractions were obtained using methods described in Savage et al . (1972) with a methanol-benzene extract. Savage et al. (1972) and Savage (1974) proposed that the more polar substances of Fractions II and III are 'fixed' in place, when soil temperatures exceed 250°C. The less polar substances of Fraction I diffuse further downward before recondensing. This process results in an increase of the width of the water repellent layer. It is probable that at elevated temperatures, the soil system essentially becomes saturated with hydrophobic organic substances released from the accelerated decomposition of plant materials and partially decomposed organic matter. The anhydrous situation created by the passing of heat enhances adsorption of hydrophobic compounds. The strength of retention of the adsorbed hydrophobic substances on soil surfaces during a fire could be high, depending on the length of the hydrocarbon chain, as points of contact are additive. This could explain the potential for increased water repellency in burned soils. It is not clear why hydrophobic bonding should predominate over hydrophilic bonding, as i t is suspected many hydrophilic molecules are also vapourized during a fire. It is possible that since hydroxylation is lessened during a fire, hydrophilic bonding is correspondingly decreased (Tschapek and Wasowski 1976). TAlso, i t is not certain why the more polar hydrophobic substances become 'fixed' at temperatures of 250°C. It would seem that due to the polarity of the amphipathic compounds they would already be firmly bound to soil surfaces. It is suggested that at 250°C, van der Waals-London forces are at a maximum, and further diffusion is reduced. Hydrogen bonding may also occur. At temperatures greatly 18 exceeding 280°C for a prolonged period of tijne, hydrophobic substances are completely destroyed (Wells et al. 1979). 2.5.4 Extraction of hydrophobic substances Water repellency has often been characterized by the ability of organic solvents to extract hydrophobic substances. Roberts and Carbon (1972) found that hydrophobic materials on sand could not be removed by cold water, concentrated acid, diethyl ether, ethanol, benzene, chloroform or acetone and were only partially removed with hot diethyl ether, ethanol and benzene. Miller and Wilkinson (1977) extracted organic coatings on non-wettable sand grains with 5% NaOH. Studies by van't Woudt (1959) and Bond (1969) in New Zealand and Australia respectively showed that extraction for oils and waxes by ether, methyl, and ethyl alcohols had no effect on water repellence in soils. But Wander (1949) extracted repellent material from sands in Florida and methyl alcohol after ether extraction and soils became wettable by water. Thus, ether extracted the non-polar hydrocarbons and methyl alcohol extracted the remainder of the hydrocarbons, those most likely tied up in amphipathic organic molecules. Morrison and Bick (1967) state that more material is extracted by strongly polar than by weakly polar solvents and the greatest amount by mixtures of the two. These authors used a benzene-methanol extraction procedure, as did Savage et al. (1972), to determine the bituminous or waxy materials of mineral soils. 19 3 DESCRIPTION OF STUDY AREA Field work for the project was performed in the summer of 1980 in the Seymour and Coquitlam Watersheds, part of the Greater Vancouver Water District, located slightly N and NE of Vancouver (Figures 3 and 4). 3.1 Climate The climate of the area is characterized by mild and wet winters and warm and dry summers. Scant temperature data are available, although a monthly distribution, recorded for a four year period at Seymour Dam, is shown in Figure 5. The mean annual temperature is approximately 9°C, with highs reaching 24°C during July and August, and lows to -3°C in January and February. Mean temperature is likely lower in the higher reaches of the watersheds. The mean monthly distribution of precipitation at Seymour Falls, a lower valley station in the Seymour Watershed, is shown in Figure 6. The 30 year mean annual precipitation is 3,733 mm, of which approximately 3,504 mm (94%) falls as rain (Zeman 1973). There is a pronounced winter maximum of precipitation, and snow may f a l l October through April. Maximum annual water equivalent of snowfall has been recorded to 3,721 mm at Orchid Lake, situated at 1,190 m ASL (Ministry of Environment 1981) where maximum snow depth can be greater than 7.6 m in forest openings (K. Rai - pers. comm.). At 305 m ASL, towards the base of Seymour Watershed, maximum snow depth is commonly 1.5-2.1 m (K. Rai - pers. comm.) 20 FIG. 3. The geographic setting of the study area. FIG. 4. The locat ion of the sample s i tes within Seymour and Coquitlam Watersheds. 22 24 22 20 18 16 O 14 o 12 10 8 6 4 2 0 -2 -4 <D v. 3 "5 o. E a> -r maximum °C mean °C minimum °C M A M J J A S O N D month FIG. 5. Maximum, minimum and mean monthly temperature at Seymour Dam, 1972-1976 (data courtesy of K. Ra i ) . 23 6001 500 4 400 ] (0 .tr 300 a 200 i 100 M A M J J A S O N D month FIG. 6. Mean monthly prec ip i ta t ion at Seymour Fa l l s , Seymour River Basin, 1941-1970 (from Cheng 1975). 24 3.2 Geology The watersheds form part of the Pacific Ranges, of the western system of the Canadian Cordillera whose mountains are essentially granitic (Holland 1964). The bedrock lithology consists mainly of five major silicate minerals; plagioclase, hornblend, biotite, quartz and potassium feldspar (Zeman 1973). A veneer of glacial t i l l from Pleistocene glaciations of various depths forms the surficial geology (Holland 1964). Impervious basal or lodgement t i l l is commonly encountered at 0.5 to 1.2 m below the surface and this is overlain by looser ablation and weathered t i l l (Zeman 1973). Thickness of t i l l is largely controlled by slope steepness. For example, colluvial action has removed t i l l from the steep upper valley slopes and deposited i t on the gentle slopes of the lower valley walls. 3.3 Soils A survey of the soil types in the watersheds has been undertaken by Lavkulich (1973). Soils were classified into Series on the basis of their development over glacial t i l l , shallow t i l l over bedrock, bedrock, glacial outwash, recent alluvium, fans, colluvium and associations with talus and rock outcrop. Soils are predominantly podzols, although regosols and organic folisols also occur, albeit less frequently. Soil texture is usually sand, sandy loam, loamy sand, or gravelly sand. A typical soil profile is shown in Appendix I. 25 3.4 Vegetation Coquitlam and Seymour Watershed are covered predominantly by mature and over-mature coniferous forest. According to Krajina (1965) below elevations of approximately 1,280 m, in the wet Coastal Western Hemlock Biogeoclimatic Zone, the most productive trees are Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], western hemlock [Tsuga heterophylla (Raf.) Sarg.], western red cedar (Thuja plicata Donn.), and amabilis f i r [Abies amabilis (Dougl.) Forbes]. Above elevations of approximately 914 m, the climax plant community of this subalpine Mountain Hemlock Biogeoclimatic Zone is represented by mountain hemlock .[Tsuga mertensiana (Bong.) Carr] and amabilis f i r (Krajina 1965). A variety of shrubs, herbs, mosses and lichens were collected at the sample sites, and these are listed in Appendix II. 3.5 Selection of Sampling Blocks Fourteen cut blocks were selected for sampling - eight from the Seymour Watershed and six from Coquitlam. All blocks were clear cut and logged by cable. Blocks were chosen on the basis of accessibility and slashburn age. Date of burns ranged from 1 to 19 years before present, although the majority were under 7 years, because i t was assumed the effects of fire on soil water repellency would be most apparent on recently burned soils. Elevation of blocks ranged from 180 m to 671 m ASL, cut block size ranged from 4.0 to 51.6 ha (mean size = 18.5 ha) and aspect included a l l directions of the compass, except N and NE. Slope angle, as measured by Abney level, ranged from flat to 36° (mean slope = 23°). 26 Three of the fourteen blocks were logged but not burned. These blocks were sampled to ascertain the effect on s o i l repellency of logging alone. Control plots were established contiguous to cut blocks. These were areas of mature and over mature timber of Douglas-fir, western hemlock and western red cedar. Vegetation cover i n cut blocks varied from v i r t u a l l y bare i n 1 and 2 year burns to extremely thick, almost impenetrable masses of s a l a l , huckleberry, thimbleberry, d e v i l ' s club and other thorny shrubs i n older burns (see /Appendix I I ) . Most cut blocks were replanted with Douglas-fir seedlings soon after slashburning. 27 4. METHODS 4.1 Field At each cut block, a 150 m paced transect was established and three profiles were excavated. A similar transect was established 50 m apart in a contiguous area of uncut timber (i.e. control site). Soil was sampled at the humus layer and at depths of 0-4 cm, 8-10 cm and 15+ cm from the mineral surface. Soil was stored in plastic Whirl Pak bags for the same-day trip to the laboratory. Sample mass ranged between 50 and 100 g. In total, 336 samples were collected. The transect in the cut blocks was selected such that soil collection was facilitated. Areas of very thick slash accumulation, steep precipices and exposed bedrock were avoided. An attempt was made to assess the intensity of the slashburn on the basis of organic mat consumption. Hence, at each pit, the depth of the organic layer was measured as well as other features of interest. These included soil mottles, soil horizon sequence, evidence of elevated water table and previous burns. A 500 m transect was established in a logged-only cut block in Coquitlam Watershed (see Fig. 4). The block is bordered by a control site and a slashburn block. Ten profiles were excavated and tested for water repellency. Soil was stored for further chemical extraction analysis. 4.2 Laboratory 28 4.2.1 Physical Soil samples were removed from the Whirl Paks, spread on newspaper and air dried for a minimum of 48 hours. Soil was sieved to less than 2 mm and large pieces of organic matter were removed by hand or by re-sieving. Contact angle The method of Emerson and Bond (1963) was used to calculate the advancing contact angle. The technique involves calculating capillary height of rise of water into soil tubes. Water is forced up tubes under a positive head, and height of rise is observed at a sharply defined wetting front, beyond which soil is air dry. Soil moisture content is assumed con-stant (i.e. close to saturation) behind the wetting front. Infiltration is described by Darcy's Law, expressed as: (h+_L_ _ 1 } ( 3 ) dt E X where, x = height of water in tube (cm) h = equilibrium height of rise of water in tube (cm) L = hydraulic head (cm) k - saturated hydraulic conductivity of soil (cm/s) e = fractional water-filled pore space behind the wetting front assumed constant (cmVcm^) t = time (minutes) dx At equilibrium rise, ^  = 0, and x = h + L. Height of rise dx 1 is observed for 15 minutes, and ^  vs. - is plotted to yield a straight curve. The linear equation is: 29 | J = a (-) + b (4) dt x where, a,b are regression coefficients. Equation (4) is solved for x when dx/dt = 0f and the value of x is inserted in x = h + L. Subtracting the hydraulic head, L, yields, h, equilibrium rise. Equilibrium rise is determined for the untreated, then ignited (500°C for 5 hours) soil sample. The capillary rise equation (p. 12) can be used to calculate the liquid-solid contact angle ( ), and the resultant equation is, COS 6 = r — : r- —3— (5) h ignited * ' Figure 7 depicts the apparatus for observing the height of capillary rise into soil columns. A clear, rigid, plexiglas container of dimensions 44 cm x 14 cm x 35 cm was constructed and filled with distilled water. Plastic tubes stoppered at one end with glass wool, 40 cm in length and 6.35 mm in internal diameter, were filled with soil. Packing was achieved by dropping the tubes an arbitrary number of times until the height of soil did not change (after Richardson and Hole 1978). Tubes were placed 20 cm beneath the water line in the tank. Uptake of water into the tubes relative to the volume of water in the tank was negligible, hence a constant hydraulic head of 20 cm can be assumed. Columns were held vertical by directing them through holes in shelves, one 1 30 FIG. 7. Apparatus for measuring capillary rise of water in soil tubes. 31 shelf at the waterline, another at 20 cm depth. Each shelf had holes enough to accommodate seven tubes. Rulers attached to the face of the tank permitted easy and accurate (+ 0.25 cm) measurements of capillary rise of water into the soil columns. When soil sample size was sufficient, two or three replicates on each sample were performed. Height of rise was recorded for every minute, except the fir s t , up to 5 minutes, then every two minutes until 15 minutes total time had elapsed. Water drop penetration time Soil was spread smoothly in a 10 cm diameter petri dish and 5 drops of distilled water were applied, one in each quadrant and in the centre. The dropper delivered approximately 0.05 ml droplets. Each drop was timed for infiltration into the soil with a stop watch. Two minutes was considered the upper time limit - after this period of time, the droplet is more likely to evaporate than penetrate. Data were analysed using the Z-statistic. 4.2.2 Chemical A primary objective of this section is to assess the ability of an extraction procedure to separate hydrophobic materials from soil, and subsequently, to isolate and characterize major components in the extractions by adsorption chromatography (after Savage et al. 1972). A secondary objective is to tentatively identify functional groups of hydrophobic materials by infrared absorption analysis. 32 Soil samples A transect, 500 m in length, was established in a logged, unburned cutblock in Coquitlam Watershed (see section 4."). Ten profiles 50 m apart were excavated, soil samples were brought to air dry moisture, and water repellency tested by the WDPT method. Repellency varied from non-wettable to wettable. Two profiles were chosen from the ten, one being non-wettable and the other wettable, for comparison purposes, and each were subjected to the extraction procedure outlined below. Percent C was determined by the Walkely-Black Method (Allison 1965) and a mean value of two or three replicates was recorded. Soil samples ranged in mass from 10 to 100 grams, although 30 grams was the norm. Extraction procedure Proportions of benzene (B) and methanol (MeOH) were used to extract hydrophobic materials from soil. This method, modified from Savage (1974), reportedly extracts hydrophobic substances from a wide polarity range of organic molecules. Two hundred ml of B/MeOH 7:4 (v/v) was added to soil and the sample was subjected to ultra sonic dispersion for five minutes. The supernatant extract, which was yellowish in colour, was poured off and gravity filtered into a one-litre beaker. This was repeated twice to produce a total of 600 ml of extract. Five spoonulas of anhydrous MgS04 were added to the supernatant solution to absorb excess water and the solution was filtered into a one li t r e round bottom flask. A Brinkman 33 Buchi Rotovapor-El was used to concentrate the solution to approximately 30 ml by evaporating B and MeOH. Analysis of the re-condensed fumes by a PYE Series 105 Gas Chromatograph at a temperature of 65°C, with 5% SE-30 silica gel, 80-100 mesh, indicated that no impurities were present, thus i t is unlikely that hydrophobic substances were also drawn off during rotary evaporation. One additional spoonula of anhydrous MgS04 was added and the solution was filtered into a 100 ml round bottom flask. Rotary evaporation was performed again to concentrate further the solution until a precipitate formed or the solution became cloudy. The solution was transferred by syringe into 5 ml, 10 ml or 25 ml flasks. The volume was made up to the appropriate mark with anhydrous benzene. In order to estimate the total amount of "extractables"* in the flasks, two subsamples each 50 ul, were transferred from each flask by syringe and injected into capillary tubes which were sealed immediately. A 5 ul "microcap" portion of each subsample was evaporated on a weighing pan of a Cahn 26 Automatic Electrobalance. The balance was calibrated to record weights as low as 10~6g. The average of three weights of each extraction was recorded and the concentration (mg/1) of extractable (i.e. hydrophobic) substances calculated by: mass of residue concentration = 5~~ul Multiplying the above equation by the volume in the respective flask yielded the total weight of extracted materials. * this term refers to the materials which were extracted from the soil. 34 Fractionation of extracted materials Extractions were fractionated by s i l i c a gel adsorption chromato-graph. Glass columns, with dimensions 250 mm by 5 mm i . d . , were f i l l e d with a s l u r r y of s i l i c a gel (0.040-0.063 mm mesh size) and anhydrous benzene. The column was equipped with a 50 ml reservoir with f r i t t e d glass at the base and flow was controlled with a t e f l o n stopcock. S i l i c a was activated by heating at 40°C for f i v e hours. Uniform packing i n the column was aided by pushing through excess benzene with an applied pressure of gaseous nitrogen at 5 p . s . i . Five ml of the extracted solution was introduced to the column and separated using the following proportions of benzene and acetone; 15 ml B, 15 ml 95:5 B/acetone, 15 ml 90:10 B/acetone, 15 ml 80:20 B/acetone, 15 ml 50:50 B/acetone, and 15 ml of acetone. The elutants were pushed through the column at a constant rate, 5 ml at a time, with gaseous nitrogen at a pressure of 5 p . s . i . Effluent was collected i n 5 ml preweighed test tubes. 4.3 Infrared Analysis In an e f f o r t to obtain information concerning functional groups of hydrophobic materials, a Beckman IR-20A Infrared Spectrometer was u t i l i z e d . Samples were analysed at a 10 minute fast scan using KBr p e l l e t s . 35 5. RESULTS AND DISCUSSION 5.1 Soil Water Repellency 5.1.1 Water drop penetration time Soil samples with a WDPT of less than 5 seconds were classified as wettable, and those with a penetration time of 5 seconds or greater were considered water repellent. Humus was only initially tested for water repellency; in a l l cases samples were extremely repellent (i.e. WDPT >^  60 seconds). The range of penetration times on a sample was occasionally large. This was believed due to microsite differences in repellency of soil in the petri dish and also possibly to surface roughness effects. Overall, results were reproducible and the method was easy to administer. Results of mineral soil repellency for slashburned and control sites are shown, by depth, in Table I, and for a l l depths, in Table II. There was a significantly (P = 0.05) greater proportion of soils that were water repellent in the burned cut blocks than in control sites. Thirty-five per cent of a l l burned soils were repellent, compared to 21% of control soil samples. At the 0-4 cm depth, burned soil samples were significantly (P = 0.10) more frequently repellent than control samples. However, at 8-10 cm and 15+ cm depths, differences were not significant. Frequency of repellency in soil samples decreased with depth, in both burned and control sites. Fifty-two per cent of burned soils were repell-ent at 0-4 cm, 32% at 8-10 cm and 21% at 15 cm. The respective values for control soils were 31% at 0-4 cm, 17% at 8-10 cm and 14% at 15+ cm. 36 TABLE I. Water repellency of soils, by depth. Depth Character Frequency of Occurrence (cm) Burn Control 0-4 Wettable 14 23 Repellent 15 11 8-10 Wettable 19 29 Repellent 9 6 15+ Wettable 22 29 Repellent 6 5 TOTALS 85 103 188 TABLE II. Water repellency of soils, a l l depths Frequency of Occurrence Character Burn Control Totals Wettable 55 (64.7%) 81 (78.6%) 136 (72.3%) Repellent 30 (35.3%) 22 (21.4%) 52 (27.6%) TOTALS 85 103 188 37 Hence, proximity to the humus layer appears conducive to the formation of water repellency. However, severe repellency ( i . e . WDPT 2. 60 seconds) was observed at a l l depths, i n both c o n t r o l and burned s o i l s . I t was hoped that burn i n t e n s i t y could be estimated by assessing organic mat reduction i n burned s o i l . However, measurements revealed no di f f e r e n c e s i n organic mat depths between con t r o l and burned s i t e s . Hence, burn i n t e n s i t y was estimated by v i s u a l inspection as follows: a l i g h t burn was a f i r e that r e s u l t e d i n l i t t l e reduction i n ground cover (e.g. mosses, l i c h e n s ) , an intense burn res u l t e d i n great reduction i n ground cover, often exposing patches of mineral s o i l and creating erosion g u l l i e s , and a moderate burn shewed c h a r a c t e r i s t i c s of both a l i g h t and severe burn. Also, burn i n t e n s i t i e s were estimated only f o r 1 and 2 year burns; i n a l l olde r burns, dense regrowth masked the i n i t i a l e f f e c t of the f i r e . Increased s o i l water repellency induced by slashburning i s shown i n Table I I I . In general, f i r e increased the proportions of r e p e l l e n t s o i l samples, up to approximately 6 years, but thereafter the e f f e c t was n e g l i g i b l e . Sample s i z e was i n s u f f i c i e n t t o detect s i g n i f i c a n t differences of increased repellency. The e f f e c t o f f i r e v a r i e d i n each cut block, but i n a l l except one 1 and 2 year burns, increased repellency i s apparent, regardless of burn i n t e n s i t y . In the 12 and 19 year burns, the e f f e c t of f i r e was not noticeable, i n fact, i n the l a t t e r burn, more con t r o l samples were r e p e l l e n t than the burn. The break point appears to be approximately 6 years, as data f o r the 6 year burns i n d i c a t e repellency was greater or 38 TABLE III. Frequency of burned (B) and control (C) samples in individual cutblocks, repellent or wettable, by slashburn age. (Burn intensity shown in brackets, when appropriate). Burn age: 19 yrs. B C Wettable 7 0 Repellent 2 4 Burn age: 12 yrs. B C Wettable 4 5 Repellent 2 4 Burn age: 6 yrs. B C Wettable 8 7 Repellent 1 2 Burn age: 6 yrs. B C Wettable 5 8 Repellent 4 1 Burn age: 6 yrs. B C Wettable 9 8 Repellent 0 1 Burn age: 2 yrs. (severe) B C Wettable 0 4 Repellent 9 5 Burn age: 1 yr. (moderate) B C Wettable * fi Repellent 4 0 Burn age: 1 yr. (moderate-B C severe) Wettable 6 4 Repellent 3 3 Burn age: 1 yr. (light) B C Wettable 3 9 Repellent 6 0 Burn age: 1 yr. (moderate) B C Wettable 8 6 Repellent 1 0 39 slightly less in burned soils than control soils. In logged only sites there was no increase in repellency in soils, as compared to samples in the control sites (data not shown). Hence, increases in water repellency in burned soils can be ascribed to slashburning. It appears that increased repellency, in general, has not caused severe erosion or hampered regeneration efforts in the watersheds. In one instance, however, a steep (slope angle = 29°) shallow-soil slope, burned two years previously, was severely repellent and exhibited active surface erosion. Mthough more research into the effect of repellency on erosion is required, i t is likely that the effects are most prominent on steep slopes. The phenomenon of a repellent layer situated at depth and overlain by a wettable layer, as reported by others (e.g., DeBano 1966), was not observed. This may be due to the difficulty of sampling precisely at small depth intervals in forest soils, or to the absence of steep temperature gradients in mineral layers during slashburns as a result of the insulating properties of thick organic mats. 5.1.2 Contact angle The method of Emerson and Bond (1963) was reproduced with sand from Spanish Banks Beach, Vancouver. Results of several samples were similar and the contact angle of the wettable sand was calculated to be 52°57'. This value served as a baseline with which soil samples were compared. In subsequent experiments with soil, the hydraulic head was adjusted to 20 cm and capillary rise was observed for two or three 40 replicates of each sample. In the linear regression analysis of dx/dt vs. 1/x, only curves with an R2 of greater than 0.65 (arbitrarily chosen) were accepted. Results of calculated contact angles were not reliable. For many samples, i t was difficult to determine the exact position of the wetting front after approximately five minutes had elapsed. The wetting front would become increasingly vague, and soil pores would often f a i l to f i l l with water. As a result, even though high R2 values were produced, replicates of a sample had large differences in contact angle. Further, when contact angles were compared with WDPT values, there was l i t t l e correspondence. That is, soil samples with a low WDPT (e.g. 0-20 seconds) could have either a high (e.g., >L 80°) or low (40°-80°) contact angle. Very repellent soil samples (i.e., WDPT_> 60 seconds) usually had high contact angles but in some cases, the contact angle was lower (i.e., 60°-80°). It was also evident that ignited soil packed much denser in soil tubes. This occasionally resulted in capillary depression, where h in equation (2) was negative. Packing was therefore adjusted in tubes to different bulk densities (e.g., 0.2 g/cm^  and 0.4 g/cm3) b ut capillary rise results remained inconsistent. Thus, i t was concluded that soil pore geometry, and particularly, soil pore radii, were drastically altered by igniting soils and therefore equation (5) was not applicable. Capillary rise with ethanol was then tested for reproducibility. Different bulk densities were attempted. Tight packing (i.e., 0.4 g/cm3) sometimes prohibited upward•flow of ethanol, but in general results were 41 more consistent than those for water and ignited soil. S t i l l , however, determination of the wetting front after a short period of time was difficult and hence equilibrium heights of rise varied considerably for a sample. Several conclusions were reached from the attempts at determining the contact angle of soil. It was felt results were inconsistent and therefore unreliable due to: 1. deficiencies in the execution of the experiment, and 2. deficiencies in the theory of the experiment. It is clear that packing in tubes is very important. Filling tubes with soil and then tapping or dropping them creates a variable bulk density through the length of the tube. At the base, soil will be more compact, with smaller soil pore radii, than soil towards the top of the tube. Wetting of soil by water or ethanol is influenced greatest by the largest pore (Hillel 1971) where the suction is much less than the suction to f i l l a small pore. As a consequence, a low bulk density exhibited sudden spurts of rise, the so-called Haines jumps phenomenon (Hillel 1971). It is suggested, therefore, that soil-tube packing be carefully controlled. DeBano (1971) segmented 40 cm tubes into one cm lengths and packed each segment to the same bulk density with a mechanical soil packer. Lengths of tube were then joined by tape. The method of Emerson and Bond (1963) assumes soil is a "Green and Ampt" soil, where moisture content behind the wetting front is constant and close to saturation. This was found to be not always true. By observation, after 15 minutes of capillary rise, there was a definite 42 variable soil moisture content behind the wetting front. At the column base, soil was saturated but moisture decreased up the column towards the wetting front. Indeed, in some samples the front was indistinguishable from the air dry soil beyond i t . Contact angles measured in soil ranged from approximately 40° to 95°. These values are difficult to trust because of factors listed above and also to theoretical considerations. First, a single value of contact angle is rarely found in a soil (Adam 1963). There is a strong hysteresis effect whereby the advancing contact angle during sorption is larger than the smaller receding contact angle, obtained in desorption. Second, the effective contact angle of soil is the sum of the actual contact angle and the angle of the divergence of the soil pore from parallel (Bond and Hammond 1970). If pore walls are straight and parallel and the actual contact angle does not exceed 90°, water will enter readily. If, however, the soil pore walls diverge from parallel creating an angle of divergence and actual contact angle in excess of 90°, water is impeded from penetrating until the hydrostatic pressure inside the drop exceeds the resistence to penetration in the pore. Philip (1971) points out that soils are not bundles of long cylindrical capillaries, hence observations on contact angles are at best only apparent angles. Further, apparent contact angles cannot be related directly to the actual contact angle at the soil-liquid interface, because internal soil-pore geometry is complex. Hence, scaling soils by apparent contact angles may be of limited value. 43 Due to the difficulty of obtaining reliable contact angle data in soil , a l l subsequent determinations of water repellency and comparisons of repellency to other soil properties were performed with the WDPT method. 5.2 Chemistry 5.2.1 %_C Per cent organic carbon was obtained in soil to determine if water repellency is related to i t . Results indicated there was no apparent trend (selected sample results are shown in Table IV). For example, in a one-year burn, a l l soils were repellent or severely repellent, yet % C ranged from 3.05 to 12.74, and repellency did not increase or decrease with % C. Similar results were found in unburned soil where % C for wettable samples were lower or higher than those for repellent samples. Also, % C did not increase or decrease with depth in a consistent manner, for either burned or unburned soils. It is concluded that the relationship between % C and WDPT is not a simple one. Both % C and WDPT for soil are affected by a multiplicity of microsite factors, and further, these factors may or may not be interrelated. Also, i t may not be organic carbon which is important in soil water repellency, but rather the type of molecule carbon which is contained within (Dr. Griffin, pers. comm.). 44 TABLE IV. Per cent carbon (% C) and repellency for soil not burned, and soil 1 year after a slashburn, by depth. Repellency^" Slashburned % C Depth cm Not Burned % C Repellency"1" severe severe severe 7.82 7.30 7.76 0-1 8-10 15+ 4.11 5.64 2.99 repellent wettable wettable severe severe severe 3.05 3.26 4.35 0-4 8-10 15+ 5.12 5.50 6.14 repellent wettable wettable repellent repellent repellent 11.50 13.04 12.74 0-4 8-10 15+ 5.23 4.25 4.02 wettable wettable wettable. + repellent indicates soil sample had, on average, an WDPT of > 5s; 'severe' a WDPT of > 60s; and 'wettable' a WDPT of < 5s. 45 5.2.2 Extractions The extraction procedure was tested to ascertain i f in fact hydrophobic materials were recovered from soil. Sieved, less than 2 mm quartz sand, washed twice with 7:4 B/MeOH, was used to test the extracted solution. Sand was chosen because of its relative particle size homogeneity, compared to other mineral soils. The sand had an initial WDPT of zero. Residue from an extraction of a water repellent soil was placed in solution with anhydrous benzene, and 2 to 6 mg of extractables were applied to three replicate samples of 5 g of sand. TAliquots of B and MeOH, separately and together, were also applied to sand to test for inducement of water repellency. The solvents were vacuum desiccated and the soil samples were air dried for 24 hours. In every case, WDPT increased from pretreatment WDPT, with penetration times ranging from 30 seconds to over two minutes. Sand exposed only to B and/or MeOH remained wettable. Further, soil from which the extractables were obtained had a significantly lower post-extraction WDPT. The results of this experiment indicated that; 1. the extraction procedure is capable of recovering hydrophobic substances, and 2. hydrophobic substances are transferrable. Data for extractions from soil are shown in Table V. On average, EU (amount of extractables per unit mass of soil) was higher in water repellent than wettable soils. Absolute values ranged widely, from a high of 86.38 mg/g for a non-wettable soil to a low of 0.20 mg/g in a wettable soil. No trend was discernible with depth, however, for either wettable or non-wettable soils, but this may be due to the small sample size. TABLE V. Characteristics of extractions from a repellent and a wettable soil profile Soil Depth EU* % C (cm) (mg/g) Repellent 0-4 2.40 6.42 4-8 86.38 12.40 8-10 1.83 7.37 15+ 0.46 5.10 Wettable 0-4 0.20 1.47 4-8 2.0 1.98 8-10 0.93 4.40 15+ 1.49 3.76 * mass of extractables (mg) per unit gram of soil. 47 5.2.3 Fractionation Separation of extractions by adsorption column chromatography were collected in pre-weighed test tubes. Residue remaining on the test tube walls was weighed and a graph of residue weight vs. volume of effluent was plotted. The results of several extractions of soil samples with contrasting initial water repellency showed similar elution curves, although absolute weights varied considerably (Figure 9). There was one major peak, after 10 ml of effluent, and two very much smaller broad peaks, at approximately 45 ml and 75 ml. Hence, the first peak, up to 30 ml, was considered Fraction I, Fraction II was between 30 and 60 ml and Fraction III occurred after 60 ml. Fraction I was least polar and Fraction III most polar. All fractions were pale yellow in colour, although 90% of the applied extractables were obtained by Fraction I, Fraction II collected approximately 4%, and Fraction III accounted for about 6%. Occasionally, greater than 100% of the applied extractables were collected, and this was believed due to fine silica particles which slipped through the fritted glass. The simplified version of elution sequence followed, in order to obtain amounts of the three Fractions, was: 30ml of 95:5 B/acetone (Fraction I), 30 ml of 80:20 B/acetone (Fraction II), and ''O ml of acetone (Fraction III). Fractions were collected in 150 ml beakers, and solvents were evaporated by vacuum desiccation. Low heat (up to 40°C) was frequently applied to accelerate the process. The three Fractions could be collected in approximately one hour. 4 8 FIG. 8 . Plot of EU (mg/g) vs. % C for repel lent and wettable so i l samples. EU (mg/g) 3 . 0 2 . 8 2 . 6 2 . 4 2 . 2 2 . 0 1 . 8 1 . 6 1 . 4 1 . 2 1 . 0 0 . 8 0 . 6 0 . 4 0 . 2 © A © A A © A » 8 1 0 1 2 %C Legend -© = water repellent soil sample A = wettable soil sample 49 0 10 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 vo lume of e f f luent (ml) FIG. 9. Represen ta t i ve e l u t i o n curve fo r the chromatographic separa t ion of the substances ex t rac ted from s o i l . 50 Results of tests to determine the degree of water repellency of each fraction are shown in Table VI. Known amounts of hydrophobic materials from each fraction were applied to wettable sand and the increased repellency was tested by the WDPT method. It was difficult to apply equal amounts of hydrophobic substances from each Fraction, thus i t is difficult to compare results between Fractions. It is recommended that in the future the volume of solvent be increased once the concentration is known, rather than evaporating the solvent to greater concentrations. Despite this difficulty, trends were evident and some generalizations can be stated. Each Fraction was capable of inducing soil water repellency. This was found to be true regardless of the soil's water repellency, or whether the soil had been slashburned or unburned. Repellency was induced by applying 0.9 mg of extractables per 5 g of sand. At levels less than 0.9 mg, repellency was not produced, either at air dry moisture or by heating. For higher levels, the following effect was observed; repellency was increased by heating sand for 10 minutes at 250°C, i t was reduced in most cases at 300°C, and eliminated in a l l cases at 350°C. At 325°C, repellency was completely destroyed if amounts were less than 16 mg. At greater than 16 mg, repellency was only partially broken. This suggests that the destruction of the hydrophobic barrier is inversely proportional to the amount of extractables applied. In another example (data not shown) at 1.0 mg, repellency was increased at 200°C but eliminated at 250°C. Table VII summarizes the minimum amount of extractables required to impart water repellency and severe water repellency in sand. TABLE VT. Water repellency of Fractions I, I I , and I I I , at d i f f e r e n t temperatures Mass of extractables applied t o sand (Mg) a i r dry WDPT (range, i n seconds) 250°C 300 °C 325°C 350°C F r a c t i o n I F r a c t i o n II F r a c t i o n I I I 8.0 12.4 20.1 4.2 8.3 16.6 1.4 2.8 5.6 1.4 2.8 5.6 10.9 10.8 - >120 >120 >120 7.8 - 37.8 >120 >120 <1 <1 - 6.0 1 - 11.4 <1 1.8 - 7.2 1.8 - 22.8 >120 >120 >120 >120 >120 >120 113.4 - >120 >120 >120 NO DATA NO DATA NO DATA 94.2 - 118.8 NO DATA <1 <1 - >120 >120 NO DATA NO DATA NO DATA <1 <1 <1 - >120 <1 <1 >120 >120 <1 <1 <5 - >120 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 52 There was l i t t l e difference between Fractions in terms of the potential to induce water repellency in sand. That is, equal amounts of any Fraction produced equal repellency. This may be due to the relatively narrow polarity range of the eluting agents (benzene and acetone). These solvents are biased towards extracting mainly non-polar molecules and are not capable of capturing polar molecules such as polysaccharides which may play a minor yet important role in a soil's water repellency. Further, lipid material may be linked in combination with proteins or carbohydrates whose complexes can be insoluble in organic solvents (Chae 1979). Hence, i t is suggested the entire extraction be considered as one relatively non-polar Fraction, as the fractionation procedure failed to resolve differences in hydrophobic-material behaviour. For this to be apparent, a much greater polarity range in solvents should be considered. It is difficult to relate the chromatographic results bo processes occurring naturally in soils or to soils in other regions, but recent results of Chae and Lowe (1981) are useful here. The authors fractionated soil lipids into four categories by column chromatography using the following elutants: 1. CHCI3, 2. CHCl3-acetone, 3. acetone and 4. methanol. Results from a geographically diverse selection of soils in British Columbia, including coastal soils, showed that glycolipids (Fraction 2) was consistently the dominant lipid class, at 64%, while polar lipids (Fraction IV) constituted only 4% of the total soil lipids. The benzene- acetone elutants and the three resulting Fractions of this paper correspond in polarity range to those of the first three Fractions in Chae 53 TABLE VII. Minimum amount (mg) of extractables required to produce repellency (WDPT > 5 s) and severe repellency (WDPT > 60s) in sand. Temperature °C Repellency Severe repellency room 0.9 12.0 250 2.5 3.0 300 3.0 - 9.0 17.0 350 16.0 20.0 54 and Lowe. Specifically, Fraction I in this paper is roughly equivalent to Fraction II (the glycolipids) of Chae and Lowe (Lowe - pers. coram), hence i t is concluded that this Fraction is most relevant in soils and probably the most important soil-lipid constituent. 5.2.4 Infrared absorption analysis There is clear evidence in the IR-spectrum of both hydrophobic and hydrophilic constituents (Figure 10 and Table XIII). The most prominent peak is the absorption at 2,900 cm-1 and 2,835 cm-1 which indicates a strong aliphatic presence. This is characteristic of hydrophobic non-polar molecules. The broad peak at 3,400 cm-1 and weaker peak at 1,720 cm-l indicate oxygen-containing functional groups which would contribute hydrophilic character to the Fraction, but this is far overshadowed in strength by the aliphatics. The grouping of peaks from 1,373 cm-1 to 1,575 cm-1 are more difficult to interpret. They may indicate an aliphatic character, possibly associated with the peak at 2,900 cm-1 or they may suggest the presence of carboxylate or aromatic components. The IR-spectrum is inconclusive for definite assignations. The broad, medium peaks from 1,220 to 900 cm-1 are difficult to assign, especially as the many shoulders are signatures of characteristics of individual molecules rather than of functional groups which appear at the opposite end of the spectrum. These peaks, as well as those in the less than 990 cm-l region, are considered as being L O L O FIG.' 10. Infrared spectrum of Fraction I . 56 TABLE VIII. IR-spectrum data of Fraction I. Band Position Group"1" (cm-1) 3400 (s)* 2900 (s), 2835 (s) 1720 (m) 1575 (m), 1440 (m) and 1375 (m) 1220 (m) to 990 (m) OH stretching, intermolecular polymeric H-bonding. aliphatic C-H stretching of CH3, CH2. carbonyl in a carboxyl C = 0 of COOH groups. carboxylase of deformation frequences of CH2 - CH3 groups. no definite assignation; perhaps C-0 of ethers and esters. * Symbols s = strong band intensity m = medium band intensity + interpretation of the spectrum was aided by Bellamy (1958), Meloan '1963) and Lowe (pers. comm.). 57 secondary in importance and their relevance towards water repellency in soils is probably marginal. Although IR-spectra of Fractions II and III were not obtained, i t is suspected they would be similar to that of Fraction I, with a slightly less prominent peak in the aliphatic region. The IR-spectrum revealed that organic molecules with hydrophobic (less polar) and hydrophilic (polar) components are involved in water repellency. This suggests that adsorption onto soil particle surfaces occurs as amphiphatic molecules, whereby the oxygen-containing groups initially coat the particle, leaving the non-polar aliphatic groups to form the outer surface. Adsorption mechanisms of hydrophobic materials to soil can only be speculated, but a combination of ligand exchange reactions, hydrogen bonding, and van der Waals - London interactions are probably involved. The most prominent mechanism, particularly at elevated temperatures, is van der Waals - London interactions, termed hydrophobic bonding by Griffin et al. (1980). Sorption follows the Freundlich adsorption equation, shown as: N = KCa (7) where N = amount absorbed C = concentration a,K = constants The Freundlich equation assumes there is no adsorption maximum, hence, input of hydrophobic materials to soil is theoretically cumulative. 58 Also, the degradation of l i p i d l i k e materials, which contain effective waterproofing agents in s o i l , is slow, particularly under anaerobic, acid s o i l conditions. Some waxes from higher plants may require geological time periods to decompose (Stevenson, in Chae 1979), as do aliphatic hydrocarbons in late sediments (Giger et a l . 1980). It was found, however, in Section 5.1.1 that water repellency decreased over time after slashburning and pre-burn repellency levels were re-established after approximately six years. Some polar l i p i d s may migrate with s o i l humic and fulvic acids and thus leach out of the s o i l , but i t is suspected that the breakdown of the repellency barrier over time is due to a gradual hydration of the s o i l particle surface resulting in a dispersion of hydrocarbons, thus rendering the hydrophobic materials ineffective. However, once conditions favour hydrophobic sorption, such as periods of drought or during f i r e s , a water repellent layer can re-establish. In this fashion, soils are beset with chronic water repellency, unless a burn of appropriate intensity vo l a t i l i z e s hydrophobic materials away from the s o i l into the atmosphere. 59 6. SUMMARY AND CONCLUSIONS The results of this project show that soil water repellency, as assessed by the WDPT method, was increased by slashburning. Burned soil was more frequently repellent than control (unburned) soil in a l l one and two year burns, but after approximately six years the effect of fire was negligible. Overall, a greater percentage of soil samples from burned blocks were repellent than in control sites. Also, frequency of repellent soil samples decreased with depth in both control and burned sites. Since proximity to the humus layer appears conducive towards the development of water repellent compounds, i t is suspected that chemicals released in decaying litter are chiefly responsible for observed soil repellency. The degree of increased soil repellency caused by slashburning was assessed by calculating the advancing liquid-solid contact angle. However, the method of Emerson and Bond (1963) was found to be unreliable and therefore inappropriate to the soils of Seymour and Coquitlam Watersheds. The failure of the method was considered to be due to a combination of practical and theoretical factors. Packing soil tubes to a constant bulk density was difficult. The result was a discontinuous wetting front and a variable moisture content up to the front. Soil pores are not long cylindrical capillaries, hence i t is misleading to use the capillary rise equation to describe vertical upward flow of water in soil. Baking soil at 500°C also changes soil pore radii as well as pore geometry. The liquid solid contact angle in soil is rarely attained in a single measurement. Notwithstanding hysteresis effects, the angle is the sum of the 60 contact angle and the angle of divergence of the s o i l pore. Further, the relationship between actual contact angle and s o i l pore geometry i s not simple. Water repellency i n s o i l was determined more simply and r e l i a b l y by the WDPT method. I t i s tangible; i t i s clear when a water droplet i s impeded from i n f i l t r a t i n g . There are drawbacks, however, i n that surface roughness may be responsible for the impedance, and the penetration time at which a sample i s considered repellent i s highly subjective. By contrast, the contact angle i s less tangible and much more elusive to obtain. From theoretical arguments alone, a true l i q u i d - s o l i d contact angle i s almost impossible to derive, except under idealized conditions. At the most, contact angle data are r e l a t i v e values; at the least they are of l i t t l e use when r e l a t i n g to f i e l d situations or comparing to other reported data. Water repellency i s a dynamic property of s o i l , changing with moisture content and time. Hence, i t i s perhaps misleading to provide a single WDPT (or contact angle) as an index of s o i l repellency. Rather, i t i s suggested that i t would be more revealing to document a series of penetration times for a s o i l over a range of moisture contents. In t h i s fashion, penetration time could be related to a corresponding f i e l d moisture. Should climatic conditions suggest that penetration times w i l l increase, say during dry summer months, preventive measures could be taken to avoid the formation of severe s o i l repellency. One preventive measure for example, would be to avoid slashburning during t h i s period, or mechanically mix repellent layers at the surface with more wettable layers below. 61 It is concluded that soil temperatures during slashburns in the Seymour and Coquitlam Watersheds are sufficient to cause increased soil repellency, although the persistence and severity of the fire-induced repellency is highly site specific, dependent on soil, vegetation, and fire characteristics. There was no evidence of a translocated water repellent layer situated below a wettable soil layer, but this may be due to sampling inadequacy. In general, increased repellency formed by fire does not appear to be a problem in terms of causing erosion thus affecting subsequent tree growth, except on steep slopes where even slight pert-urbations are exaggerated, although this aspect was not rigorously investigated. It is suggested, however, that soil repellency should be examined at a site prior to slashburning, especially on steep, shallow-soil slopes, in order to avoid potentially severe erosion. Also, i t is suggested that efforts should be taken to keep soil temperatures during slashburns as low as possible and burn duration as short as possible. For future research, i t is recommended that soil temperatures be monitored during slashburns and pre- and post-burn repellency be compared. For more accurate documentation of the persistence of water repellency over time, permanent plots should be established at a burned site, and sampling performed at a regular basis over several years. Also, work is required on the effect of water repellency on erosion and water quality, especially immediatedly after a fire. Such data would provide fire managers with another tool for estimating the effect of fire on forested land, and help decide when and if a burn should occur. 62 It is suggested that i f an indicator of soil repellency is desired, the WDPT method should be used as i t is simple and easy to administer. Another possible method, also quite simple, is to determine the critical surface tension required for water to enter the soil (Watson and Letey 1970). However, to obtain an indication of water movement through soil, i t is considered that infiltration trials remain the most appropriate method. Per cent carbon was not found to be simply related to observed repellency. Interestingly, the amount of extractables per unit mass of soil was positively correlated to % C in repellent samples but not for wettable samples. However, many more replicates are necessary before conclusive statements on the relationship between carbon atoms and water repellency can be deduced. Hydrophobic substances were extracted from soil with a combination of polar and non polar solvents, methanol and benzene respectively. All materials recovered contained waterproofing compounds, regardless of the repellency of the soil. Less than 1 mg of hydrophobic materials applied over 5g of wettable sand was sufficient to induce repellency. Further, that amount of hydrophobic substances could be extracted from less than 30g of soil. Repellency was increased by heating sand with hydrophobic materials to temperatures up to 250°C. Repellency gradually decreased after 250°C, in inverse proportion to the amount applied, and was eliminated at temperatures beyond 325-350°C. The enhancement of soil water repellency at elevated temperatures is believed due to the displacement of water molecules from soil particle surfaces, thus enabling greater adsorption of non polar molecules. 63 Fractionation of hydrophobic materials by adsorption column chromatography revealed only one major and two lesser peaks of adsorption, due probably to the narrow polarity range of the benzene and acetone eluting agents. Hydrophobic materials from the fractions behaved similarly when exposed to heat and applied to sand regardless of the soil sample's repellency. Differences in hydrophobic material behaviour could probably be observed with a wider polarity range of eluting agents thus separating hydrophobic materials into finer components, and this is suggested as a possible avenue of future research. Infrared absorption analysis of the extracted materials revealed that hydrophobic substances contain both hydrophilic and hydrophobic components. This suggests that adsorption of hydrophobic materials onto soil particles happens via the hydrophilic end. of the organic molecule which initially coats particle surfaces, thus leaving the hydrophobic end to form the outer surface. Longevity of the adsorbed molecule is potentially long lasted, and there is no theoretical limit to adsorption. Hence, once repellency forms, i t may be a permanent or chronic feature of the soil system. Knowledge of the chemistry of hydrophobic materials is scant, and is confounded by the natural complexity of the soil system. Much more research is required on identification and source of hydrophobic substances, adsorption mechanisms, and soil characteristics which favour the development and retention of hydrophobic materials. 64 To conclude, s o i l water repellency is clearly an important part of the s o i l ecosystem. 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Letey. 1971. Determination of solid-air tension of porous media. Soil Sci. Soc. of Amer. Proc. 35:856-859. Morrison, R.I. and W. Bick. 1967. The wax fraction of soils: Separation and determination of some com- ponents. J. Sci. Fd. Agric, 18:351-355. Nakaya, N., H. Yokoi and S. Motomura. 1977. The method for measuring of water repellency of soil. Soil Sci. Plant Nutr. 23(4):417-426. Philip, J.R. 1971. Limitations on scaling by contact angle. Soil Sci. Soc. Amer. Proc. 35:507-509. Reeder, C.J. 1978. Water repellent properties of forest soils in upper Michigan. M.S. Thesis, Mich. Tech. Univ., Midland, U.S.A. 16 p. Rice, R.M. and J.F. Osborn. 1970. Wetting agent fails to curb erosion from burned watershed. USDA For. Serv. Res. Note PSW-219. Richardson, J.L. and F.D. Hole. 1978. Influence of vegetation on water repellency in selected western Wisconsin soils. Soil Sci. Soc. of Am. J. 42(3):465-467. 69 Roberts, F.J. and B.A. Carbon. 1972. Water repellence in sandy soils of southwestern Australia, II. Some chemical characteristics of hydrophobic skins. Aust. J. Soil Res. 10:35-42. Savage, S.M. 1974. Mechanism of fire-induced water repellency in soil. Soil. Sci. Soc. Am. Proc. 38(4):652-657. Savage, S.M. 1969. Contribution of some soil fungi to water repellency in soil materials. In, "Water-Repellent Soils," pp. 241-258, L.F. DeBano and J. Letey, Symposium on Water Repellent Soils, U. of California, Riverside, U.S.A. Savage, S.M., J.P. Martin and J. Letey. 1969a. Contribution of some soil fungi to natural and heat-induced water repellency of sand. Soil. Sci. Soc. Amer. Proc. 33:405-409. Savage, S.M., J.P. Martin and J. Letey. 1969b. Contribution of humic acid and a polysaccharide to water re- pellency in sand and soil. Soil. Sci. Soc. Am. Proc. 33:149-151. Savage, S.M., J. Osborn, J. Letey and C. Beaton. 1972. Substances contributing to fire-induced water repellency in soils. Soil. Sci. Soc. Am. Proc. 36:674-678. Tschapek, M. and C. Wasowski. 1976 Adsorption of aliphatic alcohols by soil minerals as a method of evaluating their hydrophobic sites. J. of Soil Science 27(2):175-182. Valoras, U. 1969. Surfactant adsorption by soil materials In, "Water-Repellent Soils," pp. 143-148, L.F. DeBano and J. Letey, eds., Symposium on Water Repellent Soils, U. of California, Riverside, U.S.A. Van't Woudt, B.D. 1959. Particle coatings affecting the wettability of soils. J. Geophys. Res. 64:263-267. Wander, I.W. 1949. An interpretation of the cause of water-repellent sandy soils found in citrus groves of central Florida. Science 110 (2856):299-300. Watson, C.L. and J. Letey. 1970. Indices for characterizing soil-water repellency based upon contact angle surface-tension relationships. Soil Sci. Soc. Amer. Proc. 34:841-844. Wells, C.G., R.E. Campbell, L.F. DeBano, CE. Lewis, R.L. Fredriksen, E.C. Franklin, R.C. Froelich, P.H. Dunn. 19. Effects of fire on soil. USDA For. Serv. Gen. Tech. Rep. WO-7. 70 Zeman, L.J. 1973. Chemistry of tropospheric fallout and stream flow in a small mountainous watershed near Vancouver, British Columbia. Ph.D. Thesis 154 p., Faculty of Forestry, University of British Columbia, Zisman, W.A. 1964. Relation of the equilibrium contact angle to liquid and solid constitution. In, " Contact Angle, Wettability and Adhesion," pp. 1- 51, F.M. Fowkes, ed., Advances in Chemistry Series No. 43., American Chemical Society, Washington, U.S.A. APPENDIX I SOIL PROFILE DESCRIPTION 72 ORTHIC HUMO-FERRIC PODZOL Horizon Depth Description  (on) 25-24 very few roots; abrupt boundary; 1-2 cm thick. 24-20 abundant very fine, fine, medium and coarse roots; diffuse boundary; 4-6 cm thick; pH 5.30. H 20-0 very dusky red (2.5 YR 2.5/2m); plentiful very fine and coarse roots; abrupt smooth boundary; 11-20 cm thick; pH 5.28. Ae 0-5 light gray (10 YR 7/2m); sandy loam; single grained; slightly sticky, plastic; very few roots; < 5% gravel; clear, wavy boundary; 2.5-5 cm thick; pH 4.67. Bfl 5-42 yellowish red (5 YR 5/8m); sandy loam; single-grained; slighty stickly, non-plastic; few, coarse roots; 20% gravel; diffuse boundary; 37-40 cm thick; pH 5.48. Bf2 42+ reddish yellow (7.5 YR 6/8m); sandy loam; single grained; slightly stickly, non-plastic; 25% gravel; pH 5.75. 73 The profile was situated on gently rolling terrain at an altitude of approximately 245 m ASL. The profile description and location corresponds to characteristics of the Cardinal Soil Series (Lavkulich 1973). Soil developed from ablation t i l l deposits over basal t i l l . Drainage was moderately well. The profile was excavated to a depth of approximately 42 cm. Bulk density ranged from 1.07 g/cm3, 1.16 g/cm3 to 1.53 g/cm3 for the Ae, Bfl and Bf2 horizons respectively. Particle size analysis using the hydrometer method (Day 1965) classified the horizons into sandy loam or loamy sand (USDA and International system respectively), for the Ae horizon, and sand for the Bfl and Bf2 horizons (with both USDA and International system). pH was measured with a Bach-Simpson pH-meter 26 using a 1:1 g/ml mineral-soil-to-water ratio. Organic samples were diluted to 1:5 g/ml soil-to-water ratio. Reference: Day, Paul R. 1965. Particles fractionation and particle size analysis. In C.A. Black (ed.), Methods of Soil Analysis. I. Physical and mineralogical properties, incuding statistics of measurement and sampling. Am. Soc. Agron. Inc., Madison, Wise, U.S.A. Agronomy (9). APPENDIX II PLANT SPECIES IN CUT BLOCKS AND CONTROL SITES CUT BLOCKS Botanical Name Trees Tsuga heterophylla (Raf.) Sarg. Thuja plicata Donn. Populus trichocarpa Torr. & Grey Shrubs Rubus spectabilis Pursh. R. parviflorus Nutt. R. pedatus J.E. Smith Vaccinium parvifolium Smith V. ovalifolium Smith Acer cireinaturn Pursh A. macrophyllum Pursh Oplopanax horridum (Smith) Sambucus racemosa L. Rosa nutkana Presl Salix spp. L. Herbs Tolmiea menziesii (Pursh) T. & G. Streptopus amplexifolius (L.) DC. Smilacina racemosa (L.) Desf. Digitalis purpurea L. Tiarella trifoliata L. T. unifoliata (Hook.) Kurtz. Montia sibirica (L.) Howell Anaphalis margaritacea (L.) B. & H. Cornus canadensis L. Tellima grandiflorum (Pursh) Dougl. Mycelis muralis (L.) Fresen. Epilobium angustifoliun L. Aruncus S y l v e s t e r L. Hypochaeris radicata L. Solidago candensis L. Senecio slyvaticus L. Pyrola spp. L. Common Name western hemlock western red cedar black cottonwood salmonberry thimbleberry strawberry huckleberry oval leaf huckleberry vine maple big leaf maple devil's club elderberry rose willow species youth-on-age twisted stalk false salamon's seal foxglove foamflower coolwart Siberian montia pearly-everlasting bunch berry fringecup lettuce fireweed goatsbeard cat's ear goldenrod groundsel pyrola Ferns Blechnum spicant (L.) Roth. deer fern Polystichum muniturn (Kaulf.) Presl. sword dern Athyrium filix-femina (L.) Roth. lady fern Dryopteris austriaca (Jacq.) Woynar spiny wood fern Mosses Pleurozium schreberi (Brid.) Mitt. Plagiothecium undulatum (Hedw.) B.S.G. Polytricum commune Hedw. Rhyzomnium glabrescens (Kinberg) Kop. Dicranum spp. CONTROL SITES Botanical Name Trees Tsuga heterophylla (Raf.) Sarg. Pseudbtsuga menz ies i i (Mirb.)Franco Abies amabilis (Dougl.) Forbes Thuja plicata Bonn. Shrubs Rubus spectabilis Pursh R. parviflorus Nutt. Vaccinium parvifolium Smith V. membranaceum Dougl. Acer circinatum Pursh. Oplopanax horridum (Smith) Gaultheria shallon Pursh Sambucus racemosa L. Salix spp. L. Herbs Tiarella trifoliata L. T. unifoliata (Hook.) Kurtz. Anaphalis margaritacea (L.) B. & H. Cornus canadensis L. Tellima grandiflorum (Pursh) Dougl. Mycelis muralis (L.) Fresen. Cirsium arvense (L.) Scop. Gallium triflora Michx. Linnaea borealis L. Epilobium angustifolium L. Disporum hookerii var. oreganum (Wats.) Jones Veratrum spp. L. Ferns Blechnum spicant (L.) Roth. Polystichum munitum (Kaulf.) Presl. Athyrium filix-femina (L.) Roth. Dryopteris austriaca (Jacq.) Woynar Common Name western hemlock Douglas-fir amabilis f i r western red cedar salmonberry thimbleberry huckleberry blueberry vine maple devil's club salal elderberry willow species foamflower coolwort pearly-everlasting bunch berry fringecup lettuce thistle sweet scented bedstraw twinflower fireweed fairy bell false hellebore deer fern sword fern lady fern spiny wood fern Pleurozium schreberi (Brid.) Mitt. Plagiothecium undulatum (Hedw.) B.S.G. Rhtytidiadelphus lorens (Hedw.) Warnst. Claopodium crispyfolium (Hook.) Ren. & Card. Rhyzomnium glabrescens (Kinberg) Kop. Braceothecium spp. Polytricum spp. 


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