Quantification of Fluvial Wetland Nitrogen Removal in Shallow Sloped, Coastal New England Watersheds

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Excess nitrogen (N) in the environment contributes to eutrophication that can result in “dead zones” and fish kills. In the northeastern US, typically about 80% of the total anthropogenic N inputs are retained or removed, while the remainder is exported from basin mouths. However, in the coastal New England river networks that drain the shallow sloped watersheds of the Plum Island Ecosystems (PIE) LTER (20% freshwater wetlands), watershed removal can be even greater (>90%). Channelized reaches have been studied extensively but recent studies in fluvial wetlands have suggested that they may play a larger role in the removal of anthropogenic N from aquatic ecosystems. We use the “Tracer Additions for Spiraling Curve Characterization” (TASCC) method coupled with new in situ nitrate sensor technology to conduct experiments in long residence time, wetland dominated aquatic ecosystems (e.g. beaver ponds, flood plains, natural wetlands). TASCC experiments were performed in three headwater fluvial wetlands in the spring and early summer and repeated in the fall and early winter during the 2014 field season. Preliminary results from one beaver pond show that N removal (as a percentage of inputs) was greater than published results for channelized streams in the same region but that most of this was due to longer residence time rather than increased whole system uptake rates. This suggests that increased abundance of fluvial wetlands, such as due to beaver activity, will enhance network-scale N retention.