Estimating Wetland Connectivity to Streams in the Prairie Pothole Region: An Isotopic and Remote Sensing Approach

Abstract

Understanding hydrologic connectivity between wetlands and perennial streams is critical to understanding the reliance of stream flow on inputs from wetlands. We used the isotopic evaporation signal in water and remote sensing to examine wetland‐stream hydrologic connectivity within the Pipestem Creek watershed, North Dakota, a watershed dominated by prairie‐pothole wetlands. Pipestem Creek exhibited an evaporated‐water signal that had approximately half the isotopic‐enrichment signal found in most evaporatively enriched prairie‐pothole wetlands. Groundwater adjacent to Pipestem Creek had isotopic values that indicated recharge from winter precipitation and had no significant evaporative enrichment, indicating that enriched surface water did not contribute significantly to groundwater discharging into Pipestem Creek. The estimated surface water area necessary to generate the evaporation signal within Pipestem Creek was highly dynamic, varied primarily with the amount of discharge, and was typically greater than the immediate Pipestem Creek surface water area, indicating that surficial flow from wetlands contributed to stream flow throughout the summer. We propose a dynamic range of spilling thresholds for prairie‐pothole wetlands across the watershed allowing for wetland inputs even during low‐flow periods. Combining Landsat estimates with the isotopic approach allowed determination of potential (Landsat) and actual (isotope) contributing areas in wetland‐dominated systems. This combined approach can give insights into the changes in location and magnitude of surface water and groundwater pathways over time. This approach can be used in other areas where evaporation from wetlands results in a sufficient evaporative isotopic signal.

Modeling Connectivity of Non‐floodplain Wetlands: Insights, Approaches, and Recommendations

“…Here, it is also important to highlight that Neff and Rosenberry's () modeling results comport with results from Brooks et al. (), an empirical study that used water isotopes (e.g., δ 2 H and δ 18 O) as a hydrologic tracer to examine connectivity between Prairie Pothole wetlands and an adjacent water body. Both studies were based on the same watershed (e.g., The Pipestem Watershed in North Dakota — USGS Gage 06469400), and together, provide strong evidence that groundwater mounding can limit subsurface connectivity between NFWs and downstream water bodies in the Prairie Pothole Region.…”

“…), and water isotope analysis to examine potential contribution of wetlands to streamflow (Brooks et al. ). These empirical studies then informed modeling studies that examined variability and drivers of hydrologic fluxes at the watershed scale and, importantly, how different scenarios of wetland loss (and restoration) may impact the watershed and downstream hydrology (e.g., Evenson et al.…”

Hydrological, Physical, and Chemical Functions and Connectivity of Non‐Floodplain Wetlands to Downstream Waters: A Review

“…; Brooks et al. ). NFW fill‐and‐spill behavior occurs in other physiographic regions (e.g., California vernal pools, Rains et al.…”

“…; Brooks et al. ; Evenson et al., in press). Hydrologic models have demonstrated that when contributing area flow terminates at a NFW, near‐surface and groundwater recharge functions maintain baseflow in downgradient streams (e.g., Evenson et al.…”

Featured Collection Introduction: Connectivity of Streams and Wetlands to Downstream Waters

“…); empirical observations of spatial and temporal surface wetland‐stream hydrodynamics at field (Brooks et al. ) and landscape scales (Vanderhoof et al. ); models that integrate observational data into mechanistic simulations of hydrologic function (Evenson et al.…”