The Ecological Consequences of Groundwater Depletion in Great Plains Riverscapes

Across the western Great Plains of North America, groundwater pumping for irrigated agriculture has depleted regional aquifers that sustain surface flow for native fishes. This loss of surface flow and subsequent fragmentation of fish habitat has contributed to population declines for 70% of endemic fishes. We used a network of observation wells distributed across portions of Colorado, Kansas, and Nebraska to measure changes in depth to water table (DTWT) over the High Plains Aquifer during 1950-2010. Based on DTWT values, we estimated the spatial distribution of stream segments that maintained connectivity to the aquifer and therefore surface flow to support fishes. We then used the relationship between time and DTWT to project future losses in aquifer-connected stream segments. Model results suggest >500 stream-km in the Republican River watershed disappeared during 1950-2010 as aquifer levels fell, and an additional 250 km will be lost by 2060 if withdrawal practices are not modified or reduced. We synthesize the ecological consequences of past and expected future changes in surface flow using existing fish assemblage data collected from across the region.