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Anthropogenic nitrogen (N) inputs to the landscape have serious consequences for inland and coastal waters. Reservoirs are effective at mitigating downstream N fluxes but measurements have generally focused on large reservoirs and have not considered seasonal variability or all N forms. In this study, we conducted an N mass balance in eight small reservoirs (surface area <0.55 km2) in coastal New England over annual time periods, including both inorganic and organic forms of N. We found that small reservoirs have high capacity for dissolved inorganic N (DIN) retention during low and moderate discharge, but are roughly in balance for DIN at higher discharge. Because proportional DIN retention occurred when N inputs were at their lowest, their effect on downstream N fluxes is small over annual time frames. Further, dissolved organic N (DON) was also evident during low flow late in the warm season. Accounting for DON production, the net effect of reservoirs on total dissolved N (TDN) fluxes was limited. These transformations between inorganic and organic N should be considered when evaluating the effect of small reservoirs on TDN fluxes over seasonal and annual timescales. With dam removal becoming a common solution to aging, unsafe dams, their ability to retain or produce N must be scrutinized at longer time scales while accounting for the complete N pool to better comprehend the effect their reservoirs have on downstream waters. Plain Language Summary: Excess nitrogen in the environment can negatively impact both freshwater and coastal ecosystems. However, water bodies such as reservoirs have been shown to reduce the amount of nitrogen flowing downstream. This has led to the idea that if reservoirs are removed, there will be more nitrogen exported downstream. Many studies on reservoir influence on nitrogen flowing downstream have not explicitly included small reservoirs, transformations between forms of nitrogen, or seasonal variability of nitrogen processing. We found that while small reservoirs do decrease inorganic nitrogen during the warm season, organic nitrogen is also produced, leading to a lesser impact on total nitrogen. Dissolved inorganic nitrogen retention is highest during low flows. When flows are higher and nitrogen transport is greater, small reservoirs are not as biologically active, leading to very little nitrogen being transformed. We conclude that small reservoirs are not a nitrogen sink when accounting for transformations between nitrogen forms and accounting for nitrogen processing across all seasons. Removal of small reservoirs will likely not lead to increased annual nitrogen exports to coastal areas. Key Points: Small reservoirs were not a significant nitrogen sink over annual timescales when considering both inorganic and organic forms of NSeasonal variability in nitrogen processing led to small reservoirs acting as temporary sinks or sources for different forms of nitrogenIn contrast to previous predictions, small dam removals do not always lead to greater nitrogen exports to coastal ecosystems [ABSTRACT FROM AUTHOR]

Households' willingness to pay (WTP) for water quality improvements--representing their economic value--depends on where improvements occur. Households often hold higher values for improvements close to their homes or iconic areas. Are there other areas where improvements might hold high value to individual households, do effects on WTP vary by type of improvement, and can these areas be identified even if they are not anticipated by researchers? To answer these questions, we integrated a water quality model and map-based, interactive choice experiment to estimate households' WTP for water quality improvements throughout a river network covering six New England states. The choice experiment was implemented using a push-to-web survey over a sample of New England households. Voting scenarios used to elicit WTP included interactive geographic information system (GIS) maps that illustrated three water quality measures at various zoom levels across the study domain. We captured data on how respondents maneuvered through these maps prior to answering the value-eliciting questions. Results show that WTP was influenced by regionwide quality improvements and improvements surrounding each respondent's home, as anticipated, but also by improvements in individualized locations identifiable via each respondent's map interactions. These spatialWTP variations only appear for low-quality rivers and are focused around particular areas of New England. The study shows that dynamic map interactions can convey salient information for WTP estimation and that predicting spatial WTP heterogeneity based primarily on home or iconic locations, as typically done, may overlook areas where water quality has high value. [ABSTRACT FROM AUTHOR]

Fecal contamination is a significant source of water quality impairment globally. Aquatic ecosystems can provide an important ecosystem service of fecal contamination removal. Understanding the processes that regulate the removal of fecal contamination among river networks across flow conditions is critical. We applied a river network model, the Framework for Aquatic Modeling in the Earth System (FrAMES-Ecoli), to quantify removal of fecal indicator bacteria by river networks across flow conditions during summers in a series of New England watersheds of different characteristics. FrAMES-Ecoli simulates sources, transport, and riverine removal of Escherichia coli (E. coli). Aquatic E. coli removal was simulated in both the water column and the hyporheic zone, and is a function of hydraulic conditions, flow exchange rates with the hyporheic zone, and die-off in each compartment. We found that, at the river network scale during summers, removal by river networks can be high (19–99%) with variability controlled by hydrologic conditions, watershed size, and distribution of sources in the watershed. Hydrology controls much of the variability, with 68–99% of network scale inputs removed under base flow conditions and 19–85% removed during storm events. Removal by the water column alone could not explain the observed pattern in E. coli, suggesting that processes such as hyporheic removal must be considered. These results suggest that river network removal of fecal indicator bacteria should be taken into consideration in managing fecal contamination at critical downstream receiving waters. [ABSTRACT FROM AUTHOR]