Eric Edgley, Department of Botany and Range Science
Abstract
The purpose of this study is to evaluate the impact of microbiotic (also called cryptogamic) crusts on soil surfaces on water infiltration and evaporative rates on a soil developed from fine textural lake sediments in Utah County, Utah. Twenty study plots (10 with cryptogamic cover and 10 without) are adjacent to the Camp Floyd Cemetery near Cedar Fort, Utah. They were established to evaluate the effect of cryptogamic cover on rates of water infiltration. Two aliquots of 150 ml of water were applied sequentially to each plot through standing water infiltration rings. The infiltration time of each aliquot was recorded. Immediately following disappearance of the second aliquot, soil samples were taken to determine percent soil moisture at field capacity. A standard T-test was used to compare water infiltration time on crusted versus uncrusted plots. Results of three trials show that water infiltration rates were significantly faster on crusted plots than uncrusted plots for all but one aliquot, Thus, water infiltration is more rapid on areas with cryptogamic crusts. The influence of microbiotic crusts on rates of evaporation were inconclusive in this study.
Introduction
Cryptogamic crusts are soil surface growths of cyanobacteria, fungi, lichens and/ or mosses. These crusts are common features of desert soil surfaces around the world. Cryptogamic crusts on desert soils are becoming more widely accepted as integral parts of desert ecosystems. Such crusts are a significant feature of desert ecosystems in Utah and throughout the Great Basin.
It is becoming widely accepted that cryptogamic crusts are a major factor in control of erosion of desert soils (Campbell eta!. 1989). Biotic crusts that include cyanobacteria also improve plant nutrition by fixing nitrogen in biologically available form (Cameron and Fuller 1960). Studies testing the effect of biotic crusts on infiltration of water into soils have sometimes given contradictory results. The rate of water infiltration into soil is important, because the faster water enters the soil, the less of it there is to be lost to runoff. If runoff is reduced, sedimentation in surface flows is also likely to be reduced, and more water will be available for support of living organisms on the site. Some observers have proposed that microbiotic crusts seal the soil surface, either through water inhibition and resulting hypha! swelling or through production of hydrophobic compounds thereby diminishing the amount of water that can infiltrate the soil (Williams 1994). In contrast, Eldridge (1993) found microbiotic crusts associated with significantly greater water infiltration on grazed sites in Australia. No significant differences in infiltration rates were observed between plots with crusts dominated by blue-green algae and those from which such crusts had been removed with spray from high pressure hoses in Kansas, Oklahoma, and Texas (Booth 1941), The lack of a clear understanding of the influence of crusts on infiltration is confounded by failure in earlier reports to describe in detail the composition (algae, lichen, or moss) of the microphyte community forming the crust (Williams 1994).
In theory, the effect of cryptogamic crusts on water infiltration into soil could operate through improved aggregate stability and improved soil structure. More stable aggregates and a better soil structure shorten water Infiltration rates.
The purpose of this study is to evaluate the effect of cryptogamic crusts on water infiltration and water evaporation rates from a silt loam soil.
Study Site
This study was conducted adjacent to the Camp Floyd Cemetery near Cedar Fort, Utah, during the months of May and June 1995. The elevation of the site was approximately 1524 m. Annual precipitation in the area averages 29 em (11.4 in.) per year. The mean annual temperature for the area Is 9.2′ C (48.6′ F) (data from Utah Lake Station as represented by Brough eta!. 1987). The most dominant natural vegetation types In the area Include the shrubs: greasewood (Sarcobatus vermiculatus), rubber rabbitbrush (Chrysothamnus nauseosus), and big sagebrush (Artemesia tridentatal,and various grasses such as Agrouyron and Poa species.
Materials and Methods
Twenty Infiltration plots (10 with microbiotic crust and 10 scalped) were established. Each scalped plot was within 2.0 m of a control plot. A 15.2 em diameter round infiltration ring was inserted 5.7 em Into moist soil at each experimental plot. The metal quadrate was driven into the ground leaving 2.5 em of the infiltration ring above the soil surface.
The nature of living cover on each experimental plot was described from ocular estimates of the percentage of the plot surface covered by algae, lichens or moss tissue. On each of three visits, soil samples were taken from the plots using a 1.5 em diameter cork borer. Holes where soil samples were taken were filled in with comparable soil from outside the study plot. Two aliquots of !50 ml of water were applied separately to each plot and the Infiltration time for each was recorded. Soil temperature was also recorded at each plot with the thermometer being placed so as to record temperature within the top 1.0 em of the soil surface.
In order to test whether infiltration rate was affected by the presence or absence of cryptogamic cover, the mean and standard deviation of the infiltration time for !50 ml of water into the crusted and uncrusted plots was calculated. The mean and the standard deviation of the soil temperatures, and the percent soil moisture values were also calculated. These values were tested for statistical significance using a standard T-test. Different Ttest models were used depending on whether variances were not statistically different for control and treatment samples. Models employed forTtests are those suggested by Steele and Torrie (1960).
Results and Discussion
The results of the T-tests show that all of the 1st aliquots were statistically significant at a -levels of .1 or better. All of the 2nd aliquots were significant at a-levels of .05 or better (Table !). These results are In agreement with those of an earlier study by Gary Holmstead and K.T. Harper (1985) at a different site in Utah County, Utah. Results demonstrate that cryptogamic crusts significantly increase water infiltration rates on the soils considered in this study. Results were especially clear under conditions when the equivalent of 12 mm of rainfall were received at the study plots. Since the likelihood of quantities of precipitation in excess of 12 mm In a single storm is high in the areas considered in this study, cryptobiotic crusts are probably significantly reducing surface runoff over any given annual cycle.
The differences in water infiltration time can probably be best explained by the difference in soil surface topography between crusted and uncrusted plots. Cryptogamic crusts create a distinct micro-topography on affected soil surfaces. Resultant micro-depressions allow for more water to be retained and to infiltrate into the soil.
The monitoring of soil surface temperature and rates of evaporation from soil surfaces showed no significant correlation with the amount of cryptogamic cover on the soil in this set of trials (Table 2). Table 1. Means and standard deviations (minutes) of water infiltration times of study plots near Cedar Fort, Utah
References
- Booth, W.E. “Algae as Pioneers in Plant Succession and Their Importance in Erosion Control.” Ecology. 1941. 22:38-46.
- Brough, C.R., D.L. Jones, and D.J. Stevens. Utah’s Comprehensive Weather Almanac. Publishers Press, Salt Lake City, Utah, 1987. p. 455.
- Eldridge, D.]. “Cryptogam Cover and Soil Surface Condition: Effects on Hydrology on a Semiarid Woodland Soil.” Arid Soil Research and Rehabilitation. 1993. 7:203-217.
- Cameron, R.E., and W.H. Fuller. “Nitrogen Fixation by Some Algae in Arizona Soils.” Soil Sci. Soc. Amer., Proceed. 1960. 24:353-356.
- Campbell, S.E., ]. Seeler, and S. Golubic, “Desert Crust Formation and Soil Stabilization.” Arid Soil Res. and Rehab. I. 1989. 3:217-228.
- Steele, R.G.D. and ].H. Torrie. Principles and Procedures of Statistics. MaGraw Hill Book Co., Inc., New York, 1960.
- Williams, J.D. Microbiotic Crusts: A Review in Press. 1994. 27-31.
- Cryptogamic crusts at Camp Floyd Cemetary near Cedar Fort, UT.