Using Fallout Radionuclides to Quantify Timescales of Soil Deflation due to Ecological Change in Owens Valley, California
Abstract
The deflation of soils in arid and semi-arid regions is a global environmental problem, as it can mobilize particulate matter into the atmosphere and remove essential nutrients from sensitive ecosystems. In recent years, losses of native grass cover have been quantified in areas of accelerated groundwater pumping in Owens Valley, California. While there is some field evidence of soil deflation in areas of groundwater decline, erosion rates and timescales resulting from this land use change remain unknown. Here we characterize the timescales of deflation in Owens Valley using measurements of short-lived fallout radionuclides in soils collected in 2008-2009 and a 22 year dataset of vegetative cover and groundwater levels in the region. In February, 2008, soil inventories of 7Be (T1/2 = 53 d) ranged from 100 to 180 Bq m-2 and were not statistically distinguishable across six sites with different groundwater pumping histories and percent native grass coverage, suggesting that (i) long-range sediment transport and redistribution over the winter months may be minimal, and (ii) our sites receive similar meteoric inputs. However, soil inventories of 137Cs and 210Pb varied widely across these sites, from undetectable in some areas to over 1200 Bq m-2 in others. Generally, sites that experienced groundwater decline 15-20 years ago exhibit lower inventories of both 137Cs and 210Pb, indicating a period of significant soil deflation. The inventory ratio of 210Pb/137Cs is particularly sensitive to the timescale of erosion, and we use these data to distinguish between sites that eroded in the past but have since stabilized as vegetation recovered, from sites that continue to actively erode.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMEP21A0584K
- Keywords:
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- 0476 BIOGEOSCIENCES / Plant ecology;
- 1130 GEOCHRONOLOGY / Geomorphological geochronology;
- 1809 HYDROLOGY / Desertification;
- 1815 HYDROLOGY / Erosion