Rain infiltration into loess soils from different geographic regions

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CATENA ELSEVIER

Catena 25 (1995) 21-32

Rain infiltration into loess soils from different geographic regions M.J.M. R~Smkens a S.H. Luk b, J.W.A. Poesen c, A.R. Mermut d a USDA-ARS National Sedimentation Laboratory, P.O. Box 1157, Oxford, MS 38655, USA b Department of Geography, University of Toronto, Erindale College, Mississauga, Ont. L5L IC6, Canada c National Fund for Scientific Research, Laboratory for Experimental Geomorphology, K.U. Leuven, Redingenstraat 16bis, 3000 Leuven, Belgium d Department of Soil Science, Univ. of Saskatchewan, Saskatoon, Sask. S7N OWO, Canada Received 2 May 1993; accepted after revision 5 January 1994

Abstract Loess soils are among the most erodible soils. Therefore, evaluating and enhancing infiltration is paramount in controlling soil loss. A laboratory study was conducted to evaluate the relative difference in infiltration among selected loess surface and subsurface soils from Belgium, Canada, China, and the United States, representing the major loess belts of the Northern Hemisphere. Soils were subjected to simulated rainstorms of constant intensity ( I = 41.1 m m - h - l ) , duration (2 hours), and energy rate (27.0 J • m - 2 per mm of rain). Infiltration, runoff, and soil water pressure were continuously monitored. Infiltration was described by a linear relationship for the pre-ponding period and by a power series for the post-ponding period. Differences in infiltration response were attributed to differences in soil properties such as differences in organic matter, particle size, swelling clay content, Fe-oxyhydroxides, and carbonates. Despite the high organic carbon content and coarser texture of the Canadian loess surface soil, the presence of highly expansive smectitic clay caused a rapid reduction in infiltration rates indicating the importance of soil mineralogical constituents in surface seal development.

1. Introduction Infiltration is a much studied subject, that is of interest to hydrologists, agronomists, soil erosion specialists, environmentalists, and others who are concerned with water requirements and water quality. Erosion specialists are primarily concerned with excess rain water, that accumulates on the soil surface, collects in depressions, and concentrates as runoff in rills, gullies, streams, and channels. In fact, most dynamic soil erosion models are driven by hydrologic considerations in which the generation of excess rain 0341-8162/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved

SSDI 0 3 4 1 - 8 1 6 2 ( 9 4 ) 0 0 0 3 9 - 5

22

M.J.M. Rfmkens et al. / Catena 25 (1995) 21-32

water is of major concern. Thus, the importance of accurately partitioning rain water into a surface and subsurface component is paramount. Rain infiltration is determined by a number of factors including rainfall characteristics, soil hydraulic properties, antecedent soil and soil water conditions, and topographic factors. In recent years, increased attention is given to the effect of surface sealing and crusts on infiltration (Baumhardt et al., 1990; Mualem et al, 1990; RSmkens et al., 1990a,b). Of particular interest has been the effect of rainfall characteristics (R/Amkens et al., 1986; Baumhardt et al., 1991), chemical and mineralogical soil properties (Shainberg, 1992), soil physical parameters (Mualem and Assouline, 1989; Bradford and Huang, 1992), and surface slope gradient and length (Poesen, 1986; Poesen and Bryan, 1989) on surface seal development. While most of the studies attempted to demonstrate the role of specific soil properties, soil surface, or storm characteristics on infiltration and surface seal development, much less attention has been given to the infiltration and surface sealing within special classes of soils. This study presents results of an infiltration experiment involving loess soils from different, major loess regions of the Northern Hemisphere (i.e., Northwest Europe, North America and Asia), which are highly erodible and for which sealing susceptibility and reduced infiltration would substantially affect soil erosion processes and soil loss. The objectives are (1) to determine rain infiltration into representative soils from different geographic loess regions using identical equipment, procedures, and methodology, and (2) to determine the sealing susceptibility of those soils and to relate qualitatively their differences to specific properties of those soils.

2. Methods and materials 2.1. Materials

The infiltration measurements were conducted under simulated rainfall conditions on prepared cylindrical columns of air dry loess soils which originated from different geographic regions. The loess soils used in this study include materials from the A2, Bt, and C horizons of a Bierbeek silt loam (Glossic Hapludalf) from Bierbeek in central Belgium; the Ap, Bt, and Btx2 horizons of a Grenada soil (Typic Fragiudalf) from the MAFES Experiment Station in Holly Springs, Mississippi in the USA; the surface material from a severely eroded experimental site in the Wangjiagou Experimental Basin of the Shanxi Institute of Soil and Water Conservation near Lishi, Shanxi Province, China; and the A and B horizons of a Saskatchewan silt loam (Typic Haploboroll) located 50 ° 10'N and 107° 40'W in Saskatchewan, Canada. The excavated soils were air dried, ground to pass a 2 mm sieve, packed in plastic bags, and shipped in appropriate containers to Oxford, Mississippi with a USDA-APHIS permit (where necessary), without further manipulation or fumigation. 2.2. M e t h o d s

Soil columns were prepared to a maximum attainable density by packing soil in 3 incremental stages into a 0.30 m by 0.30 m cylindrical plexiglass container with a screen

23

M.J.M. R6mkens et al. / Catena 25 (1995) 21-32

Rainfall Simulator

....7 7 > .......

.rs / 3Ocrn

> Aspirator

I Infiltration Balancet

Fig. 1. Schematic representation of the experimental set-up for measuring infiltration and surface seal development.

covered, perforated bottom. Following each incremental addition the soil was packed by dropping the container with soil 10 times onto a 50 mm thick foam rubber mat from a height of about 200 mm. Excess soil was removed with a fiat, 1.5 mm thin, S-shaped aluminum scoop with rounded edge to match the curvature of the container. A table flat surface was obtained by scraping the soil surface with a flat, 6 mm thick plexiglass plate which had a straight, baffled edge in the center and recessed, flat edged handles on the sides that could slide, over the container rim. The center edge had a length equal to the diameter of the container and extended 50 mm into the container. Successive rotations with this scraper followed by excess soil removal yielded a table flat soil surface. A final, compacting touch with the aluminum scoop and a brush yielded a compacted soil column with a table flat soil surface 5 cm below the rim. The soil columns were placed with a 9% slope (arbitrarily selected but consistent with many runoff studies) on an electronic balance which allowed continuous weight recordings. Portholes at 10, 20 and 100 mm depth below the soil surface allowed tensiometers to be inserted at selected moments during a storm event. Portholes in the container wall at the lowest elevation of the soil surface, permitted drainage of excessive rain water through a manifold which was connected to an aspirator. Excess water was collected in a flask situated on an electronic balance, which allowed continuous runoff measurements. A schematic representation of the experimental set-up is given in Fig. 1. A 2 hour simulated rainstorm with a nominal intensity of 41 mm • h - 1 and an energy rate of 27 J • m-2 per mm of rain was applied to two replications of each soil material. The rainfall intensity was calibrated before each storm with an empty plexiglass container similar in size to those used for the soils. Tensiometers, consisting of 25 mm by 6 mm cylindrical, stainless steel, porous cups with an air entry value of about 11 kPa, were horizontally inserted into the soil columns at the designated locations following passage of the wetting front. The cups, with a 3.2 mm internal diameter, were connected

24

MJ.M. R6mkens et al. / Catena 25 (1995) 21-32

0

o

~

cg

II O

II

r..=

II

¢q

v~

I I I

I

I

I

cq

I

I

I

25

M.J.M. ROmkens et al. / Catena 25 (1995) 21-32

with nylon tubing to Validyne pressure transducers. A Validyne data acquisition system, interfaced with a digital computer, allowed continuous monitoring of soil water pressure changes. Likewise, the electronic balances were interfaced with a computer, allowing automatic recordings (programmed for every 30 seconds) of cumulative infiltration and runoff. 2.3. Data p r o c e s s i n g

The pre-ponding and post-ponding cumulative infiltration data were regressed to a linear and curvilinear relationship, respectively. These are i l=a 1+bit

(1)

O
i2=ip+a2(t-tp)+b2(t-tp)3/2+c2(t-tp)2+d2(t-tp)5/2

t>tp

(2)

where i is the cumulative infiltration in cm 3 • cm -2, ip is the cumulative infiltration at incipient ponding, t is the time since the start of the rainstorm, t o is the time of incipient ponding, and a i, bi, ci, and d i (i = 1, 2) are regression constants. In regressing these relationships to the data, continuity in the functional value and the first derivative at incipient ponding were the imposed boundary conditions. Thus: iI = i2 di a dt

=

ip

t = tp

(3)

t = tp

(4)

di 2 -

dt

Incipient ponding is closely estimated from runoff measurements. The linear relationship (Eq. 1) represents the inherent requirement that all rain before ponding infiltrates. The hydraulic conductance, fl, of the post ponding surface seal can now readily be determined at any time ~- during a storm from the relationship fl = ( d i 2 / d t ) t = r / h

s

(5)

where h s is the measured subsurface matrix potential. In this study h s was taken at the 1 cm soil depth. The conductance measurements or their reciprocal value, the hydraulic impedance, thus evaluated are indicative of the sealing susceptibility of the soils.

3. R e s u l t s 3.1. Soils

Selected physical properties and the dominant mineralogy of the soils are summarized in Table 1. The detailed particle size distribution for both the fully dispersed soil and the dry, undispersed soil used in this study are shown in Fig. 2. The particle size data indicate that within a given soil little difference existed between the textures from different horizons. Secondly, the textural distribution of the Bierbeek, Grenada, and

M.J.M. R6mkens et al. / Catena 25 (1995) 21-32

26

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M,J,M. R f m k e n s et al. / Catena 25 (1995) 2 1 - 3 2

t00

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SOIL PARTICLE DIAMETER,

J I 10-t

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mm

Fig. 2. Particle size distribution of loess soils. A, B, C denote soil horizon; d and u denote dispersed (primary) and undispersed condition, respectively.

Lishi soils were very similar, but the Saskatchewan soil showed a coarser soil texture. The soil water desorption relationships of these materials, obtained from unloaded 75 mm by 75 mm samples packed in a manner similar to the soil columns described, are given in Fig. 3. 3.2. Infiltration

Fig. 4 presents a summary of the observed infiltration data and the regressed relationships for all soils. Only every eighth data point has been plotted though regressions were based on all data points. Rain infiltration into these loess soils is very well described by Eqs. (1) and (2). In most cases, only a 3-term solution is required to describe infiltration for the post-ponding period. Table 2 summarizes the coefficients ai, hi, c i and d i (i = 1, 2) of Eqs. (1) and (2), incipient ponding time, and the coefficient of determination for each run on each soil and soil horizon. For most soils good replication is obtained between runs on the same soil. The slope of the pre-ponding linear infiltration relationship generally agreed with the

M.J.M. Rfmkens et a L / Catena 25 (1995) 21-32

28 100

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B I E R B E E K SOIL

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40

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MATRIC POTENTIAL, kPa Fig. 3. S oil w a t e r d e s o r p t i o n r e l a t i o n s h i p s o f l o e s s soils. A , B, C d e n o t e soil h o r i z o n ; n u m b e r in p a r e n t h e s e s indicates bulk density of sample.

calibrated rainfall intensity. Differences must be attributed to splashed water losses, which would lead to an underestimate of the numerical values of the coefficient b 1. Small differences in the placement of the calibration container and soil container under the rainfall simulator could yield either an over- or underestimate of the b 1 value. However, the error was generally within 2.5% of the average rainfall calibration value.

3.3. Incipient ponding The variation in incipient ponding time among these soils is very substantial. The Bierbeek A2 horizon soil material has the largest incipient ponding time ( > 2 h), followed by the Grenada Btx2 horizon material ( = 0.85 h), and Bierbeek C horizon ( = 0.78 h). The Saskatchewan B horizon material had the smallest incipient ponding time ( = 0.18 h) followed by the Grenada Ap horizon soil ( ~ 0.28 h) and the Bierbeek Bt horizon soil ( = 0.31 h). For all other soils, the ponding time varied between those of the Saskatchewan A horizon (0.44 h) and Grenada Ap horizon soil (0.58 h).

29

M.J.M. ROmkens et al. / Catena 25 (1995) 21-32 sOl i - - ~, ' , I

I

~ 11

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sOt- . . . . . .

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i=

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GRENADA - Ap Hor.

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ols

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SASKATCHEWAN - A Hor.

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,

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TIME INTO RAINSTORM, h Fig. 4. Cumulativeinfiltration during the 2 hour rain storm. Data of replicated runs are denoted by circles and dots, respectively.Regression relationships are indicated by the broken and solid lines, tp is incipient ponding time.

3.4. Surface seal development

Fig. 5 summarizes the computed hydraulic conductance relationship (Eq. 5) for all soils and soil horizon material. Only the relationships for post-ponding seal development have been presented. Several observations can be made: (1) The hydraulic conductance of the upper 1 cm of the soil, which includes the sealing zone, ranges from 0.25-0.015 h -1 for all soils studied. (2) The conductance value decreased with increasing rain during the post-ponding phase of the storm for nearly all soils. However, the rate of change in the conductance value decreased with increased rain. Only the Saskatchewan B horizon soil appears to have reached a final conductance value under the conditions of this experiment. (3) At the end of the 2 hour storm, the Saskatchewan B horizon material had the lowest conductance value (0.015 h - ] ) in the upper 1 cm of the soil followed by soils of the Lishi and Saskatchewan A horizon (0.025 h - l ) , Grenada Btx2

30

M.J.M. Rfmkens et al. / Catena 25 (1995) 21-32

0.25

[

I

I

F

I

r

0.25~

I

I

I

,~IERBEEK SOIL 0.20 r.. o.15

I

I

I

0.20 ~B Hor. ~ .

0.15 i

u~ z

I

GRENADA SOIL

0.10

0.10

0.05

0.05

Bt Hot.

Btx2 Hor. ~..~.

O

a ~ I Z o.o 0.5 O ~ 0.25 I

I

I

I _ I

1.0 t

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1.5 I

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SASKATCHEWAN SOIL 0.20

l"Ir" 0.15 =

0.15

o,o!

A Hor.

0.10 AHor.

B

~

r

~

0.05 I

0.0

I

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LISHI SOIL

•"i o.20

0.05f

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TIME I N T O R A I N S T O R M , h Fig. 5. Hydraulicconductancerelationshipsfor loess soils.

horizon (0.04 h 1), Bierbeek Bt horizon (0.07 h - l ) , and Grenada Bt horizon (0.075 h-l).

4. Discussion

Rain infiltration and surface sealing are closely related processes. High susceptibility to surface sealing invariably leads to reduced infiltration, if unprotected soil surfaces are exposed to raindrop impact that destroy the soil surface structure. The rapidity of surface structure degeneration depends on the presence of soil structure stabilizing characteristics such as the amounts of organic matter, Fe- and Al-oxyhydroxides, carbonates, etc. Reduced infiltration also occurs if rain (or irrigation) water is applied to soil containing swelling clay minerals with significant amounts of exchangeable sodium. In the latter case, a chemically favorable disposition for dispersion exists, that requires some

M.J.M. Rbmkens et aL / Catena 25 (1995) 21-32

31

mechanical energy such as that of impacting raindrops for dispersion to occur (cf. R6mkens et al., 1990a). Among the soils of this study, significant differences in sealing occurred due to differences in the type and amount of sealing conducive and resistive soil properties 1 The Saskatchewan B horizon material contained about 24% clay (Table 1) of which a sizeable fraction (60%) consisted of highly dispersive, fine, smectific clay ( < 0.2 /zm). In this soil, infiltration rates rapidly decreased to nearly negligible rates after about 0.25 h of the experiment. At that time, sufficient dispersion and sealing had taken place to effectively reduce water intake to negligible amounts. On the other hand, many loess soils especially loess soils from severely eroded sites such as those in which exposed B horizons contain Fe-oxyhydroxides (B horizons of the Grenada and Bierbeek soils) or parent materials (C horizons) rich in calcite (Bierbeek C horizon, Lishi soil), have a more stable soil structure, that requires more mechanical energy for surface structure breakdown. Such is the case for the Bierbeek C horizon, which contains about 14% CaCO 2. These soils showed a high degree of stability as indicated by its ability to maintain high infiltration rates. This was true to a lesser degree for the Lishi soil. The Lishi soil was collected at a severely eroded site, where the surface material did not appreciably differ from the parent material. The mean annual rainfall at this unprotected site is about 500 mm of which 2 / 3 falls primarily during the summer months from July to September. This soil showed little leaching effects due to a combination of factors besides the presence of calcite, such as fairly low rainfall amounts, high runoff and soil erosion rates on the prevailing steep slopes and desiccation cracks. Similarly, soils with significant amounts of organic matter such as the Saskatchewan A horizon (3.5%) and Bierbeek A2 horizon (1.9%) are more stable than their B horizon counterparts, which have less organic matter and also tend to have more clay. The Grenada Ap horizon (2.0%) appears to be an exception in this regard. The high and sustained infiltration rate on the Bierbeek A2 horizon soil with relative low organic matter content in comparison to the Saskatchewan A horizon soil must be attributed to both the destabilizing presence of substantial amounts of smectitic clay in the latter soil and the inherent stability of the former soil obtained from a virgin forest site. Presumably, the nature and distribution of the organic compounds in the Bierbeek A2 horizon soil must have a strong stabilizing effect against the destructive impact of raindrops. The Bt horizon of the Grenada soil had an appreciably higher 2 - 4 /zm particle size fraction (fine silt) than the other soils studied. However, considering the presence of Fe-oxyhydroxides this size fraction may likely consist of aggregates of primarily clay size particles. The greatest difference in infiltration after 2 hours of rain occurred between the Bierbeek A2 horizon soil and the Saskatchewan B horizon soil under otherwise similar rain storm regimes. It is not clear whether different storm regimes would alter the conclusions of this study. Therefore, future experimentation must include storm regimes with different intensities, energy rates, and different antecedent soil conditions.

1Unpublisheddata.

32

M.J.M. Rfmkens et al. / Catena 25 (1995) 21-32

5. Summary A study was conducted to determine the infiltration response of loess soils from different geographic regions. The soils were subjected to rainstorms of identical characteristics vis ~t vis rainfall intensity, energy rate, and duration and received the same m e t h o d of preparation before rain application. Appreciable differences in infiltration were observed b e t w e e n soils and b e t w e e n horizons. These differences were attributed to differences in stabilizing and sealing susceptible soil properties, such as the presence of s w e l l i n g clays, particle size, organic matter, Fe-oxhydroxides, and carbonates.

Acknowledgements The financial support received from the N A T O Scientific Affairs Division headquartered in Brussels, B e l g i u m is gratefully acknowledged. Also, the assistance of Dr. J.A. Beckers in p r o v i d i n g profile information of the Bierbeek soil in B e l g i u m is gratefully acknowledged.

References Baumhardt, R.L., R6mkens, M.J.M., Whisler, F.D. and Parlange, J.-Y., 1990. Modeling infiltration into a sealing soil. Water Resour. Res., 26: 2497-2505. Baumhardt, R.L., R6mkens, M.J.M., Parlange, J.-Y. and Whisler, F.D., 1991. Predicting soil-surface seal conductance from incipient ponding and infiltration data. J. Hydrol., 128: 277-291. Bradford, J.M. and Huang, C.C., 1992. Mechanisms of crust formation. In: M.E. Sumner and B.A. Stewart (Editors), Soil Crusting - - Chemical and Physical Processes. Advances in Soil Science. Lewis Publishers, Boca Raton, FL, pp. 55-72. Mualem, Y. and Assouline, S., 1989. Modeling soil seal as a nonuniform layer. Water Resour. Res., 25: 2101-2108. Mualem, Y., Assouline, S. and Rohdenburg, H., 1990. Rainfall-induced soil seal. (C) A dynamic model with kinetic energy instead of cumulative rainfall as independent variable. Catena, 17: 289-303. Poesen, J.W.A., 1986. Surface sealing as influenced by slope angle and position of simulated stones in the top layer of loess sediments. Earth Surf. Process. Landforms, 11: 1-10. Poesen, J.W.A. and Bryan, R.B., 1989. Influence de la longueur de pente sur le ruiseUement: R61e de la formation de rigoles et de cro~tes de s6dimentation. Cah. ORSTOM S6r. P6dol., 25: 71-80. R6mkens, M.J.M., Baumhardt, R.L., Parlange, M.B., Whisler, F.D., Parlange, S.N. and Prasad, S.N., 1986. Rain-induced surface seals: Ann. Geophys., 4(4): 417-424. RiSmkens, M.J.M., Prasad, S.N. and Whisler, F.D., 1990a. Surface sealing and infiltration. In: M.G. Anderson and T.P. Burt (Editors), Process Studies in Hillslope Hydrology. Wiley, Chichester. Rtimkens, M.J.M., Prasad, S.N. and Parlange, J.-Y., 1990b. Surface seal development in relation to rainstorm intensity. Catena Suppl., 17: 1-11. Shainberg, I., 1992. Chemical and mineralogical components of crusting. In: M.E. Sumner and B.A. Stewart (Editors), Soil Crusting - - Chemical and Physical Processes. Advances in Soil Science. Lewis Publishers, Boca Raton, FL, pp. 33-53.