Land use effects on sedimentation and water storage volume in playas of the rainwater basin of Nebraska

Abstract

A region dominated by cropland, the Rainwater Basin (RWB) of Nebraska, contains playa wetlands of international importance but estimates of historic wetland numbers suggest that approximately 90% of wetlands have been lost through draining and filling. To reverse these losses and restore their ecosystem services, >2000ha of wetlands in the RWB have been enrolled into the US Department of Agriculture (USDA) Wetlands Reserve Program (WRP). Our goal was to compare water storage volume and sediment loads in RWB playas in surrounding cropland, reference condition, and restored (WRP) land uses. To do so, we measured characteristics of 48 playas that dictate water storage capabilities essential to their service provisioning (historic/current playa area, playa volume, and sediment depth to clay pan). Using historic wetland hydric soil footprints, we determined loss of historic area for wetlands in each land use type and using soil cores we estimated sediment depth and volume loss. Reference condition playas had 380% more functional wetland area and 8 times more volume than cropland playas, WRP playas were intermediate between reference and cropland playas. In addition, reference condition playas had lost the least amount of historic area (65%) followed by WRP (70%) and cropland (83%). Though cropland playas lost the greatest extent of historic wetland area, they had sediment depths (to Bt layer) similar to playas embedded in reference and WRP, indicating that all playas in the region have been impacted by watershed soil erosion. In order to increase the overall positive impact on wetland services provided by enrolling playas into the WRP, conservation practitioners should remove sediments down to the Bt layer in enrolled wetlands in the RWB and protect the immediate watershed to prevent further erosion.