Fate of nitrogen during oxic submarine groundwater discharge into Stony Brook Harbor, Long Island, NY

Submarine groundwater discharge (SGD) nutrient fluxes from un-sewered suburban landscapes pose a significant eutrophication risk to coastal waters. In unconsolidated coastal aquifers, nutrients recharged to groundwater undergo diffuse discharge to the coastline during SGD. Defining pathways of nutrient attenuation is required for land management professionals to take effective nutrient remediation action. During diffuse SGD, geochemical transformations in at the freshwater-saltwater boundary, known as the subterranean estuary (STE), can dramatically reduce nutrient loads over short (less than 50m) spatial scales (Kroeger and Charette, 2008). Nitrogen loading calculations for Long Island Sound assume conservative transport of nitrogen during submarine groundwater discharge through the subterranean estuary (Team et al., 2007). In this study, electrical conductivity surveys, piezometer porewater sampling and ultrasonic seepage meter measurements were used to investigate nitrogen attenuation in a subterranean estuary in Stony Brook Harbor, an embayment with a direct connection to Long Island Sound.