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Estimating pothole wetland connectivity to Pipestem Creek, North Dakota: an isotopic approach
Citation:
Brooks, J. Renee, D. Mushet, L. Alexander, J. Christensen, S. Leibowitz, B. Neff, D. Rosenberry, W. Rugh, AND M. Vanderhoof. Estimating pothole wetland connectivity to Pipestem Creek, North Dakota: an isotopic approach. American Geophysical Union Annual Meeting, San Francisco, CA, December 12 - 16, 2016.
Impact/Purpose:
Under the new Clean Water Rule, the Prairie Potholes are designated under a special category where their inclusion into the Waters of the United States is case specific, and needs to be determined. For this determination, understanding hydrologic connectivity between wetlands and perennial streams is critical to understanding how reliant stream flow is on wetlands within their watershed. Using an isotopic approach were evaporation leaves a distinct signal in water, we determined the area of open water necessary to create the isotopic evaporation signal found in the perennial waterway. The evaporating surface area varied dramatically overtime, but was mostly much greater than the surface area of the stream network, indicating the importance of wetlands within the watershed. This dynamic connectivity between wetlands and the stream was primarily through surface-water flowpaths and driven by precipitation events that push evaporated water stored within individual potholes into the stream network. These results will help inform and validate the modeling efforts within the regions to determine the importance of Prairie Potholes to perennial waters within the region. This abstract contributes to SSWR 3.01.
Description:
Understanding hydrologic connectivity between wetlands and perennial streams is critical to understanding how reliant stream flow is on wetlands within their watershed. We used the isotopic evaporation signal in water to examine hydrologic connectivity within Pipestem Creek, North Dakota, with a watershed dominated by prairie potholes. During a decadal period of wet conditions, Pipestem Creek contained evaporated water that had approximately half the isotopic evaporative enrichment signal found in most evaporated permanent wetlands. If evaporation was mainly occurring within the stream, we expected the evaporation signal to increase from the headwaters with distance downstream. However, the signal either remained similar or decreased downstream over the two years of sampling. Groundwater measured at the water table adjacent to Pipestem Creek had isotopic values that indicated recharge from winter precipitation and had no significant evaporation. Using isotopic theory and discharge data, we estimated the surface area of open water necessary to generate the evaporation signal found within Pipestem Creek over time. The range of evaporating surface-area estimates was highly dynamic, spanning from 43 to 2653 ha and varying primarily with discharge. The average value (just over 600 ha) was well above the surface area of Pipestem Creek network (245 ha). This estimate of contributing area indicated that Prairie Pothole wetlands were important sources of stream flow in Pipestem Creek throughout the summer, as well as during snowmelt. At the lowest flows, the stream itself became disconnected with the headwaters, which effectively became isolated waters. This dynamic connectivity between wetlands and Pipestem Creek was primarily through surface-water flowpaths and driven by precipitation events that push evaporated water stored within individual potholes into the stream network.