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

Excess nitrogen (N) in the environment contributes to eutrophication that can result in "dead zones" and fish kills. Most of the anthropogenic N is retained or removed by terrestrial and aquatic systems within watersheds, preventing this N from reaching the coast. Much research has focused on N removal in channelized stream reaches but recent studies have suggested that fluvial wetlands 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 deployment of new in situ nitrate analyzer technology to conduct experiments in long residence time, wetland dominated stream reaches (e.g. beaver ponds, flood plains, natural wetlands). These sensor based 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 a beaver pond reach show that N removal (as a percentage of inputs) was greater than in similar length channelized streams in the same region, but that most of this was due to longer residence time rather than increased biological uptake rates. This suggests that increased abundance of fluvial wetlands due to beaver activity will enhance network-scale retention. Use of the in situ sensor allows us to capture fine-scale variability, allowing for a better understanding of different flow paths taken by water parcels traversing a wetland and providing a better estimate of N removal compared to the discrete grab sampling method.