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ARS Home » Pacific West Area » Pendleton, Oregon » Soil and Water Conservation Research » Research » Publications at this Location » Publication #96604

Title: MICROBIOTIC CRUST INFLUENCE ON UNSATURATED HYDRAULIC CONDUCTIVITY

Author
item Williams, John
item Dobrowolski, James
item West, Neil

Submitted to: Arid Soil Research And Rehabilitation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Microbiotic crusts are composed of soil bound by bacteria, algae, lichen, and mosses. They are found in rangeland soils around the world. These crusts might repel water (hydrophobic). Also, greater concentrations of clay, silt are found in the soil surface with these crusts. Because these conditions potentially influence arid land soil hydrology, they should also obe considered in the development of hydrologic and erosion models. However very few experiments have been conducted to investigate the influence of microbiotic crust on the rate water moves through the soil (hydraulic conductivity = (K). We designed and conducted such an experiment in southeastern Utah site. The site was characterized by its aridity (less than 6 inches of rainfall per year), its droughty soil (a sandy-loam), and restricted grazing for three years before the experiment. Using an infiltrometer, a device that releases measured amounts of water onto the soil surface, we determined K under three surface treatments, undisturbed, chemically killed -- representing dead microphytes within the crust --, and removed (scalped) microbiotic crusts. Microbiotic crusts at this site after three years of development did not influence on K. This finding supports results from research conducted around the world, in a range of soils from sandy to silt dominated, with a variety of microbiotic development. Because this research was site and time specific, and because the role of microbiotic crusts in the environment continues to be debated, additional research is warranted to determine how microbiotic crust stage of development influences soil hydrology.

Technical Abstract: Microbiotic crusts occur extensively in rangeland soils. Developed by filaments of cyanobacteria and algae, and thalli of lichen and moss entanglement of soil particles, they create a physical discontinuity in the surface profile with greater concentrations of clay, silt, and potentially hydrophobic organic matter. These conditions potentially contribute to variability in arid land soil hydrology and should be considered in the development of hydrologic and erosion models. However, limited manipulative research examining the functional relationships between soil and microbiotic crusts exists. We investigated the influence of cyanobacterial dominated microbiotic crust on measured hydraulic conductivity (K) in a sandy loam soil at a southeastern Utah site. Using a tension infiltrometer, we determined K under three surface treatments, undisturbed, chemically killed -- representing dead microphytes within the crust --, and removed (scalped) microbiotic crusts. We applied treatments to spatially interspersed intact surface soils within shrub interspaces. Microbiotic crusts at this site and in this stage of successional development had no discernable influence on K. This finding supports results from research conducted in a range of soils from sandy to silt dominated with a variety of microbiotic development. Because this research was site and time specific, and because the role of microbiotic crusts in the environment continues to be debated, additional research is warranted to determine how microbiotic crust stage of development influences soil hydrology.