Wetland Conservation in the Grand Lake St. Marys Watershed: Long Term Monitoring Data from Coldwater Creek Restored Wetland

Abstract Wetlands are becoming increasingly utilized to mitigate runoff as water quality issues from excess nitrogen, phosphorus, and sediment continue to exacerbate eutrophication. This study focuses on long term nutrient and hydrologic data from the Grand Lake St. Marys (Ohio) Watershed where harmful algal blooms have proliferated for decades as a result of a combination of natural habitat loss and nonpoint source agricultural runoff. The objective of this study was to monitor long-term nutrient reductions associated with the restored and managed Coldwater Creek Wetland in order to guide future restoration efforts in the watershed and inform restoration efforts elsewhere. From 2017 to 2023, water samples were collected year-round from the wetland inflow and outflow and analyzed for nutrients (SRP, TP, and NO 3 -N) and total suspended solids (TSS) in addition to flow measurements to develop a complete hydrologic budget for the wetland source (Coldwater Creek), inflow, and outflow. Over the monitoring period, Coldwater Creek Wetland was able to intercept approximately 10.5 million m 3 of water equating to ~ 10% of the total flow entering Grand Lake St. Marys from this subwatershed while showing average load reductions of at least 63% for SRP (1.85 g/m 2 /yr), TP (5.2 g/m 2 /yr), NO 3 -N (48 g/m 2 /yr), and TSS (657 g/m 2 /yr). The need for long-term monitoring of wetlands is essential as documentation of ecosystem function over longer periods of time (as opposed to one or two years of monitoring) is paramount in improving our understanding of these restored ecosystems may help improve water quality.