Eutrophication is a major agent of change affecting freshwater, estuarine, and marine
systems. It is largely driven by transportation of nitrogen from natural and anthropogenic
sources. Research is needed to quantify this nitrogen delivery and to link the delivery to
specific land-derived sources. In this study we measured nitrogen concentrations and ?15N
values in seepage water entering three freshwater ponds and six estuaries on Cape Cod,
Massachusetts and assessed how they varied with different types of land use. Nitrate
concentrations and ?15N values in groundwater reflected land use in developed and pristine
watersheds. In particular, watersheds with larger populations delivered larger nitrate loads with
higher ?15N values to receiving waters. The enriched ?15N values confirmed nitrogen loading
model results identifying wastewater contributions from septic tanks as the major N source.
Furthermore, it was apparent that N coastal sources had a relatively larger impact on the N
loads and isotopic signatures than did inland N sources further upstream in the watersheds.
This finding suggests that management priorities could focus on coastal sources as a first
course of action. This would require management constraints on a much smaller population.