Quantifying Septic Nitrogen Loadings to Receiving Waters: Waquoit Bay, Massachusetts

Waquoit Bay, a shallow bay on Cape Cod, Massachusetts, is exhibiting symptoms of eutrophication, largely attributed to septic nitrogen inputs. This study assessed septic nitrogen inputs by linking a three-dimensional ground-water model, a geographic information system (GIS), and a customized spatio-temporal nitrogen loading program. Owing to the slow speed of ground-water movement, the bulk of septic nitrogen entering the bay lags behind development by nearly a decade. Even if residential development is held at 1989 levels, nitrogen input from septic systems will increase by 36% over the current levels. At ful l residential build-out (i.e., development), septic nitrogen loading will eventually increase to more than twice the current levels.