ASSESSING THE EFFECTIVENESS OF FLOODPLAIN RECONNECTION IN THE POST-GLACIAL NORTHEASTERN US

Floodplain reconnection has been used to allow urban channelized streams to sequester sediment, nutrients, and industrial pollutants, effectively improving downstream water quality. To restore these functions, efforts have focused on lowering aggraded floodplains to give the stream the ability to access its floodplain. Most studies focused on determining effectiveness are from the Piedmont region in mid-to southeastern USA. Critically, studies evaluating the efficacy of floodplain reconnection in the post glacial Northeastern US, where landscape erosion rates are an order of magnitude lower than in the Piedmont, are lacking. This study focuses on a project in the town of Amherst, MA, where polluted water in the Fearing Brook, a highly channelized urban stream, flows into the Fort River, a tributary to the Connecticut River. This study began before floodplain reconstruction, which was completed in August 2021, and is ongoing. To date, we have collected soil and water samples along Fearing Brook, both above and below its confluence with Fort River and along a number of smaller brooks with the watershed. Preliminary results confirm previous data that Fearing Brook is responsible for runoff containing higher concentrations of E. Coli and various dissolved nutrients. Average alkalinity values, often a good proxy for microbial activity, are 1.4 meq/L for the Fearing Brook, whereas alkalinity within the Fort River averages around 0.30 meq/L. Water quality nutrient testing indicates that NH₄, PO₄, and NO₃ values generally remain low in stream surface waters, however, these values rise with discharge and conductivity patterns during periods of heavy rainfall. Further analysis of soil, sediment and water will be done to determine grain size, C:N ratios, C and N isotopic composition, heavy metal values, and cation exchange capacity of the floodplain. This coupling of sediment and aqueous geochemistry will enhance our understanding of floodplain reconnection efficacy in the Northeastern US.