Decadal trajectories of land-sea couplings: Nitrogen loads and interception in New England watersheds, discharges to estuaries, and water quality effects

Couplings between coastal watersheds and estuaries were assessed in a series of sites across SE New England. Nitrogen loads to watersheds increased during 1985–1996, but decreased afterwards due to lowered atmospheric deposition. Within-watershed nitrogen interception was high and linked to forest cover. Loads to estuaries also responded to lowered atmospheric inputs. Concentrations of nitrogen compounds were higher in estuaries subject to larger nitrogen loads from land. Estuarine nutrients showed large scatter and decreased from less-saline to saltier reaches. Chlorophyll concentrations were less reliable indicators of coupling to watershed loads. Water quality variables were lagging indicators of changing nitrogen loads, with shifts in concentrations becoming detectable several years after the 1996 shift in total nitrogen loads. Lag delays will be of significance for assessment of the effectiveness of estuarine water quality management.