Solute Evidence for Hydrological Connectivity of Geographically Isolated Wetlands

Hydrological connectivity describes the water‐mediated transfer of mass, energy, and organisms between landscape elements and is the foundation for understanding how individual elements such as wetlands and streams integrate to support ecosystem services and nature‐based solutions in the landscape. Hydrological connectivity of geographically isolated wetlands (GIWs)—that is, wetlands without persistent surface water connections—is particularly poorly understood. To better understand GIW hydrological connectivity, we use a novel chloride mass‐balance approach to quantify the local runoff generation (defined as precipitation minus evapotranspiration, assuming negligible long‐term water storage) for 260 GIW subcatchments across North America. To evaluate hydrological connectivity, we compare the estimated local runoff from GIW subcatchments with the catchment‐average runoff. These comparisons provide three novel insights regarding the magnitude and variability of GIW hydrological connectivity. First, across 10 study regions, GIW subcatchments generate runoff at 120% of the mean catchment rate, implying they are well‐connected elements of the larger hydrologic landscape. Second, there is substantial heterogeneity in runoff generation among GIW subcatchments, which may enable support for a wide array of ecosystem functions and services. Finally, observed heterogeneity in runoff generation was largely uncorrelated to simple linear geographic predictors, indicating that GIW landscape position cannot reliably predict hydrological connectivity. In stark contrast to a priori legal assumptions that GIWs exhibit low or no hydrological connectivity, our results suggest that GIW subcatchments are active landscape features in runoff generation