The Impact of Small Pass-through Wetlands and Stormwater Retention Ponds on Dissolved Organic Matter

Retention ponds and mitigation wetlands have become more common throughout the urban and suburban landscape for stormwater management and nutrient removal. It is well known that wetlands can effectively remove nitrogen and phosphorus, but the effect of wetlands on dissolved organic matter (DOM) and its impact on water quality is often overlooked, in spite of the importance of DOM in aquatic ecosystems. We seasonally sampled the inflow and outflow of five natural wetlands, five created wetlands and ten stormwater retention ponds in the urban and suburban environment of Monroe County, New York, for dissolved organic carbon (DOC), dissolved organic nitrogen (DON), nitrate, ammonium, dissolved organic phosphorus (DOP), and phosphate to analyze how the quantity and quality of DOC, DON, and DOP change upon transit through wetland types. Vegetation community composition, wetland bathymetry and hydraulic retention time were also measured. DOC was similarly exported by all three types of wetlands, but there was significant seasonal variability with higher export in the spring and lower export in the winter. There was also a general trend of DON retention and DOP export, but only indirect evidence that the concentration of DON was related to season and DOP was related to the interaction between season and wetland type. There was a significant negative relationship between hydraulic residence time (HRT) and DOC to DON ratio, suggesting that the deeper retention ponds that lacked vascular plants are exporting more labile organic matter, while shallow wetlands with significant vegetation cover export more refractory organic matter. These results suggest that small wetlands are important in the quantity and quality of DOM export to receiving water bodies and that they play a significant role in the overall water quality of this region