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Abstract
Ecosystem function in rivers, lakes and coastal waters depends on the functioning of upstream aquatic ecosystems, necessitating an improved understanding of watershed-scale interactions including variable surface-water flows between wetlands and streams. As surface water in the Prairie Pothole Region expands in wet years, surface-water connections occur between many depressional wetlands and streams. Minimal research has explored the spatial patterns and drivers for the abundance of these connections, despite their potential to inform resource management and regulatory programs including the U.S. Clean Water Act. In this study, wetlands were identified that did not intersect the stream network, but were shown with Landsat images (1990–2011) to become merged with the stream network as surface water expanded. Wetlands were found to spill into or consolidate with other wetlands within both small (2–10 wetlands) and large (>100 wetlands) wetland clusters, eventually intersecting a stream channel, most often via a riparian wetland. These surface-water connections occurred over a wide range of wetland distances from streams (averaging 90–1400 m in different ecoregions). Differences in the spatial abundance of wetlands that show a variable surface-water connection to a stream were best explained by smaller wetland-to-wetland distances, greater wetland abundance, and maximum surface-water extent. This analysis demonstrated that wetland arrangement and surface water expansion are important mechanisms for depressional wetlands to connect to streams and provides a first step to understanding the frequency and abundance of these surface-water connections across the Prairie Pothole Region.
Highlights
Depressional wetlands provide critical hydrological services including storing precipitation and hydrologic inflows (Winter and Rosenberry 1998), which reduces peak stream flows and potential downstream flooding (Vining 2002; Yang et al 2010)
The percentage of wetlands classified as variabily connected (VC) wetlands exceeded the percentage of SI wetlands in every ecoregion except the Lowlands (Table 5), and was almost double the percentage of SI wetlands across the entire study area
The average distance an NCO wetland occurred in relation to a stream was smaller in the Lowlands, Des Moines Lobe and Prairie Coteau than the average distance that a VC wetland occurred from a stream in the Devils Lake ecoregion (Table 6; Fig. 4)
Summary
Depressional wetlands provide critical hydrological services including storing precipitation and hydrologic inflows (Winter and Rosenberry 1998), which reduces peak stream flows and potential downstream flooding (Vining 2002; Yang et al 2010). During flood events or wet periods, depressional wetlands that become connected to streams or subsumed by lakes exchange water and materials, but may experience the temporary loss of wetland function until water levels recede (Junk et al 1989; Galat et al 1998; Mortsch 1998). Understanding landscape drivers for the abundance of wetlands that cyclically or variably contribute water to streams is important for accurately predicting stream flow, during high flow events (Vining 2002; Yang et al 2010), as well as informing the process to determine the jurisdictional status of wetlands in compliance with the U.S Clean Water Act. Yet, relatively little research into variable surface-water connections, in particular landscape patterns and drivers of such connections, has been done (U.S EPA 2015)
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