Wetland Connectivity Influences Water Quality of Downstream Waters
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Hydrologic connections between wetlands and downstream waters moderate surface water quality across watersheds. However, large-scale studies elucidating this phenomenon are lacking – approaches to classify hydrologic connectivity of wetlands for large spatial extents do not exist. Here we developed a hydrologic connectivity classification system for 6.7 million wetlands to 2.6 million downstream stream segments across the conterminous US (CONUS). This first of its kind study found that wetlands occupy 5.4% of the CONUS but “filter” 24.6% of the area. Yet there is a spatial mismatch between where nitrogen inputs and wetlands that can filter nitrogen occur. Wetlands in the watershed with low connectivity generally reduced stream nitrogen concentrations, and those with high connectivity increased stream carbon concentrations. High connectivity riparian wetlands, however, increased nitrogen and reduced carbon stream concentrations. Quantifying where and how wetland connectivity occurs at watershed scales is important for safeguarding surface water quality – both across the CONUS and globally.