Sources of recently deposited sediments in playa wetlands

Abstract

There are more than 20,000 playa wetlands in the Southern High Plains of Texas and New Mexico. Playas with cropland watersheds have lost most of their basin volume due to sedimentation, and they have lost more volume than playas with rangeland watersheds. To determine the source (wind vs. water transport) of sedimentation in playas and develop management recommendations to lessen sediment impacts, we examined the particle size distribution (PSD) of soils in 8 playas with rangeland and cropland watersheds. The distribution curves of sand in playa sediments plotted against relative distance coincided with playa elevational profiles, and the PSD of deeper sediments contained more sand, especially at the playa margins. In contrast, more clay had been deposited in the central portion of the playa basin, and clay content decreased with sediment depth. Sand content at playa edges was greater in crop than in range playas. Sediments eroded from the surrounding watershed resulted in deposition of coarser soil particles at the playa margin, whereas finer particles dominated playa centers. Because most sediments in playa wetlands orginate from the immediate watershed and are deposited through water erosion, management activities should concentrate on practices that reduce watershed erosion.