Ecosystem controls over deep water percolation beneath desert playa wetlands
Playas are ephemeral desert wetlands situated at the bottom of closed catchments. Desert playas in the Southwestern US have not been intensively studied despite their potential importance for the functioning of desert ecosystems. We want to know which geomorphic and ecological variables control of the water deep percolation rates beneath playas. We hypothesize Variability in deep water percolation rates among playas in similar climatic settings are best explained by both geomorphic variables: (1) catchment area, (2) catchment slope (3) catchment soil texture and ecological variables: (4) catchment vegetation cover and (5) catchment bare-ground patch size. We chose twenty playas from across the Jornada Basin (Las Cruces, NM) ranging from 0.005-0.60 km2 in area and with varying catchment characteristics. We used the available 5m digital elevation map (DEM) to calculate the catchment size and catchment slope for these thirty playas. We measured biomass, percent cover, and patch size using the point-intercept method with three 10m transects in each catchment. We used the bouyoucos-hydrometer soil particle analysis to determine catchment soil texture. From each study playa we will sample of one 5m deep, 10cm diameter soil core with soil samples collected every meter. To estimate deep percolation rates, we will use the chloride mass balance (CMB) approach.
Using the available 5m DEM data we calculated the catchment sizes of the twenty playas, these ranged from 0.10-26.99 km2. We used the same data to calculate the slope of each catchment, these range from 0.015-0.21% rise. Differences in deep percolation rates were found beneath the twenty different playas. The results of a regression analysis show a positive relationship between catchment size, catchment slope, and deep percolation rate. These data support part of our hypothesis that catchment geomorphic variables control deep percolation rates in desert playas. No ecological variables were found to control playa carbon or nitrogen. This result suggests that future changes of ecosystem variables (vegetation type, patch size) may not impact playa deep percolation rates.