Effects of Biological Soil Crusts on Water Redistribution in the Negev Desert, Israel: a Case Study in Longitudinal Dunes

Abstract

The important role of biological crusts in arid ecosystems is widely recognized (see reviews in Isichei 1990; West 1990; Belnap 1994). However, their hydrological role is not clear. Studies from regions with soil freezing (and therefore pinnacled or rolling crusts; see Chap. 15) or fine-grained soils show that soil crusts can increase infiltration and soil moisture content (Booth 1941; Fletcher and Martin 1948; Loope and Gifford 1972; Brotherson et al. 1983; Eldridge and Tozer 1997; Perez 1997). Bare loamy soils are very sensitive to surface sealing by raindrop impact (McIntyre 1958; Morin and Benyamini 1977). Under such conditions, the cohesive and flexible biological elements absorb raindrop energy and prevent the rapid development of a rain crust conducive to runoff generation. Quite different conditions prevail in hot sandy deserts, which are characterized by extremely high infiltration rates. Here, smooth biological crusts generally reduce infiltration and generate runoff (Bond 1964; Roberts and Carson 1971; Dekker and Jungerius 1990; Yair 1990; Bisdom et al. 1993; Danin 1996; Kidron and Yair 1997). This phenomenon is explained by clogging of soil pores by microbially-produced polysaccharides (Avnimelech and Nevo 1964), the inherent water-repellent properties of some crusts, and surface-sealing processes caused by the combined swelling of microorganisms and soil fine particles when wetted (Campbell 1979; Wang et al. 1981; Verrecchia et al. 1995).