Monitoring Water Content Dynamics of Biological Soil Crusts.

Biological soil crusts (BSC) dominate soil surfaces in nearly all arid environments and they play a critical role in soil hydraulic and nutrient processes. To better understand, model and predict the impact of soil moisture on BSC function, particularly carbon cycling, we assessed the ability of thermal measurement techniques, specifically dual-probe heat pulse (DPHP), to measure changes in near surface soil water contents. We compared the responses of 8 DPHP sensors, 4 each installed in two research plots (a control plot and a heated plot), to a frequency domain reflectometer (FDR) probe that was installed horizontally in each plot at 2-cm depth.  The study was conducted near Moab, Utah and extended ~160 days, covering the April – September time period. Results showed no difference in peak water content response between plots, but significant differences between DPHP and FDR technologies. The DPHP probe was sensitive enough to measure precipitation events of ~2 mm and larger, thus capturing the majority of events in this semi-arid site. Accurate near surface water content measurements have enabled coarse estimation of C flux at this site. Use of DPHP technology will provide the needed future measurements to help model the role BSC play in arid ecosystem C dynamics.