The use of microbiotic crusts as biomarkers for ponding, subsurface flow and soil moisture content and duration

Abstract

Previous work at the Hallamish dunefield in the western Negev Desert defined and mapped 5 mature types of microbiotic crusts (MCs). Crust definition and sampling were based on 4×4m pixels. Yet within these pixels, microhabitats with different crust types could be noted. This was also the case within crust type A that extends over the south-facing slope and the sandy interdune. There, close examination mainly at <0.5×0.5m pixels revealed a high variability in crust types, as was also the case at fine-grained playa surfaces, scattered within the sandy interdune. These microhabitats belonged to two groups: habitats that received water from an additional source (runoff or subsurface flow), i.e., water-enriched habitats (WE) and habitats having a better water regime due to shading (SH), such as by shrubs.Daylight wetness duration and crust biomass were monitored during 1991–1994 in 12 habitats. WE habitats, which exhibited the highest biomass also exhibited longer wetness duration in comparison to SH habitats. Both groups exhibited higher biomass and wetness duration than the control. When the relation between daylight wetness duration and the chlorophyll content of the crust was compared, a positive linear relation with a good correlation (r2=0.74) was found. The findings indicate that crust biomass may be used as a biomarker for surface wetness duration and may thus point to habitats subjected to particular hydrological processes such as water ponding and subsurface flow. They may also point to soil patches having high moisture content and therefore long wetness duration. Higher moisture content that lasted for a longer duration was indeed recorded during preliminary measurements that were carried out at 0–40cm soil patches subjected to subsurface flow (as indicated by their MC) during the end of the winter season of 1994/95 and 1996/97. The findings may attest to differential rates of pedogenesis, thus highlighting the use of MCs as possible biomarkers for small soil habitats with variable pedogenesis.