Microclimate control upon sand microbiotic crusts, western Negev Desert, Israel

Approximately 20% of the worldʹs arid zones are covered by eolian sand. Parts of the sand are occupied by microbiotic crusts or have the potential of sustaining microbiotic crusts, which may have a great impact upon geomorphological processes and the ecology of the ecosystem. Any attempt to understand the distribution of microbiotic crusts inevitably necessitates knowledge concerning the microclimate within these ecosystems and in particular moisture, temperature, and eolian input. In the Hallamish dune field in the western Negev Desert, Israel, cyanobacterial crusts with a chlorophyll a content of 15–20 mg m−2 characterizes the south-facing footslopes, whereas a moss-dominated crust with a chlorophyll a content of 50–60 mg m−2 covers the north-facing footslopes. Since the entire dune field was re-stabilized concurrently, following the 1982 peace treaty with Egypt, it was hypothesized that physical conditions, rather than time duration, may account for the differences observed. Microclimatological data, which included temperature, rainfall, runoff, dew and fog, surface moistness and eolian input were monitored. The differences in crust type could not have been attributed to rainfall, dewfall, temperatures, or eolian input. Although lower amounts of incident rain, lower temperatures and lower eolian input characterized the moss-dominated north-facing footslope, moss-dominated crusts were also found in restricted areas of high temperatures and eolian input at the interface between the mobile and the encrusted dune section of the south-facing aspect. High variability in daytime moisture duration following rain was however monitored with surface moisture duration being approximately 2.5 times longer at the moss-dominated habitat. These differences are seen responsible for crust-type distribution within the ecosystem, which may affect, in turn, variable geomorphological processes.