Estimating pothole wetland connectivity to Pipestem Creek, North Dakota: an isotopic approach.
Citation:
Brooks, J. Renee, D. Mushet, M. Vanderhoof, S. Leibowitz, J. Christensen, B. Neff, D. Rosenberry, W. Rugh, AND L. Alexander. Estimating pothole wetland connectivity to Pipestem Creek, North Dakota: an isotopic approach. American Water Resources Association’s 2017 Spring Specialty Conference, Snowbird, Utah, April 30 - May 03, 2017.
Impact/Purpose:
Prairie Potholes are a special class of wetlands under the new clean water rule, and their designation as waters of the United States is dependent on their connectivity to downstream navigable waters. This research using an isotopic approach to explore hydrologic connectivity within the Pipestem watershed. This abstract contributes to SSWR 3.01G.
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 wetland-stream hydrologic connectivity within the Pipestem Creek watershed, North Dakota, a watershed dominated by prairie-pothole wetlands. During a wetter-than-normal decade, Pipestem Creek exhibited an evaporated-water signal that had approximately half the isotopic-enrichment signal found in most evaporatively enriched pothole wetlands. If evaporation was mainly occurring within the stream, we expected the evaporation signal to increase from upstream towards 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 evaporative enrichment. 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 35 to 2380 ha of open water contributing to streamflow over time, and varied primarily with the amount of discharge. The median value (417 ha) was well above the surface area of the Pipestem Creek network (245 ha), and only two periods were below. This indicated that prairie-pothole wetlands were important sources of stream flow in Pipestem Creek throughout the summer, as well as during snowmelt. This also demonstrated that at the lowest flows, the stream itself became disconnected from headwater stream reaches. We believe that this dynamic connectivity between pothole wetlands and Pipestem Creek occurred primarily when evaporatively-enriched water stored in pothole wetlands spilled into the stream during precipitation events.