Non-Perennial Surface Waters Play Outsized Watershed-Scale Roles

Non-perennial streams and non-floodplain wetlands (NFWs), i.e., wetlands outside of floodplains, are vulnerable surface waters undergoing rapid destruction and degradation globally. Their limited protections and underrepresentation in surface water databases contribute to this loss. Yet these systems are foundational to attenuating potential floods, droughts, and poor water quality conditions in watersheds worldwide. In this presentation, we demonstrate how non-perennial streams and NFWs cumulatively impact streamflow and water quality, from headwater catchments to large river basins. We specifically highlight multiple modeling-based case studies in different regions of the United States, asking questions related to how (1) variations in headwater intermittency affect catchment-outlet flows, (2) the presence of NFWs affects flood return intervals in a meso-scale watershed, and (3) depressional wetlands in the landscape modify peak flows, baseflow, and nitrate concentrations and loads across a large river basin. Through these studies, we show that these vulnerable surface waters play an outsized watershed-scale role in mediating streamflow and water quality. Therefore, specifically focusing non-perennial streams and non-floodplain wetlands research at watershed scales will benefit their future protection, restoration, and presence in spatial databases used for management and decision making.