Across the western Great Plains of North America, groundwater pumping for irrigated agriculture has depleted regional aquifers that sustain stream flow for native fishes. Surface flows over the High Plains Aquifer declined during the past half-century as a consequence of unsustainable groundwater extraction. The Great Plains Landscape Conservation Cooperative (GP LCC) recently funded a study to better understand the impacts of groundwater removal within the Kansas River Basin (KRB). The project produced a decision-support tool that will allow the LCC partners to prioritize allocation of conservation resources. The final report, Mapping and Predicting Groundwater-mediated Hydrologic Connectivity for Great Plains Prairie Rivers and Streams, is available online and project leader, Dr. Josh Perkin, will host a webinar to present results on March 9, 2016 at 2:00 p.m. MST.

Since the 1950s, the total area irrigated with groundwater from the High Plains aquifer increased dramatically, resulting in a depletion of more than 270 million acre-feet of stored water volume. Groundwater provides a major contribution to flows in Great Plains streams and helps maintain connections among habitats important for the persistence of aquatic life. Given the demand for agricultural products, groundwater depletions are likely to continue in the future. Reduced flows have led to habitat fragmentation or even dewatering of streams, with serious implications for conservation of prairie fishes.

Led by Dr. Josh Perkin of Tennessee Technical University, with GP LCC funding administered by WMI, the study analyzed the relationship between groundwater depletion and stream flows in the upper KRB in Colorado, Kansas, and Nebraska. Specific goals of the research included mapping stream segments with connection to the High Plains Aquifer in the upper KRB; developing projections for changes in hydrologic connectivity; measuring and predicting changes in hydrologic connectivity at spatial scales that influence fishes; identifying locations where fragmentation of hydrologic connectivity occurred in the past, will occur in the future, and where conservation resources should be focused; and synthesizing the past and future expectations for stream fish diversity in the region. This study extends conservation assessment criteria for streams on the Great Plains beyond surface conditions to include historical and projected changes in hydrologic connectivity with the High Plains Aquifer. It also demonstrates how these changes might influence stream fish assemblages.

The research found the greatest magnitude of change in streams connected to the High Plains Aquifer in the western portion of the KRB. In the eastern part of the basin, flows were maintained to a greater extent but habitats were fragmented by surface structures such as dams. The study found mixed responses among fish species to changes in water availability, consistent with other recent studies. A key recommendation is that allocation of limited conservation resources should be directed to portions of the basin in which past and projected hydrologic connectivity to the High Plains Aquifer has been or will be maintained. Maps produced as a part of this study provide decision-support tools that will aid in determining such allocations.