Evaluating the ecosystem service of nutrient removal in a coastal watershed: a case study of New Hampshire's Great Bay

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Berg, Chelsea Eden
New Hampshire's Great Bay, valued as one of 28 "estuaries of national significance," provides a host of economic, ecological, and social environmental services that are threatened by the deterioration of water quality and increased levels of nitrogen. The US Environmental Protection Agency has issued several National Pollutant Discharge Elimination System permits that mandate the reduction of point source pollution to the limits of technology. In order to meet the new strict permit limits, the aging built infrastructure must be updated, and the combined capital costs are about $354 million (Kessler, 2010). Alternatives, such as land conservation and natural infrastructure, provide ways of reducing nitrogen sources from nonpoint source pollution. Relying on expert stakeholder input, we developed two land use scenarios to model potential nitrogen reduction or input under increased conservation or increased development. Two modeling programs, the river network ecosystem model Framework for Aquatic Modeling of the Earth System (FrAMES) and the Natural Capital Project's Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) nutrient retention model, were utilized to execute the stakeholder-based scenarios. Holding point sources constant, FrAMES predicts that an average of 28.1 tons TN/yr and InVEST predicts that 3.1 tonsTN/yr or more will be added to the system per year under an increased development scenario compared to an increased conservation scenario. If Epping, a town in the Great Bay Watershed, upgraded its wastewater treatment facility to the limits of technology, it would remove an estimated additional 2.99 metric tons TN/yr (Kessler, 2010). A conservative estimate of the effect of realistic land conservation efforts across the watershed would provide analogous benefits to the town of Epping upgrading to the best available wastewater technology. The FrAMES estimate of 28.1 tons TN/yr is comparable to upgrading the Newmarket wastewater treatment facility, which will keep 26.5 tons TN/yr from entering the Great Bay Estuary.