Groundwater controls on episodic soil erosion and dust emissions in a desert ecosystem

Feedbacks between vegetation, soils, and sediment transport processes maintain arid landscapes in geomorphically active degraded states or in more biologically productive and geomorphically stable states. Landscape evolution models and resource management strategies require a detailed understanding of thresholds that limit sediment transport in deserts, but it can be difficult to quantify geomorphic responses to abrupt environmental change. Here we use measurements of fallout radionuclides and salt content in soils, horizontal sediment fluxes, vegetation cover, and saturated zone depth in Owens Valley, California (USA), to quantify the geomorphic response of a desert landscape to changes in groundwater availability. Owens Valley has a well-documented history of surface-water diversions and pumping during the A.D. 1987–1992 drought, and we studied 11 sites having a gradient of ~0.5 m to 8 m of groundwater decline during this time. We show that short-length-scale (<50 m) sediment redistribution is active in areas with a range of environmental histories, but centimeter-scale net soil loss occurred when photosynthetic vegetation cover declined to <20% where local groundwater remained shallow enough to produce evaporite salts. Erosion and dust emissions are most severe in central Owens Valley when groundwater falls below the 2 m effective rooting depth of native meadow vegetation but remains shallow enough (<6 m) so that capillary action maintains loose erodible sediment at the surface.

from Geology Current Issue http://geology.gsapubs.org/cgi/content/abstract/44/9/771?rss=1