QUANTIFICATION AND POTENTIAL ROLE OF OCEAN NUTRIENT LOADING TO BOSTONHARBOR, MASSACHUSETTS, USA

While tidal flushing helps export most of the nitrogen added to Boston Harbor (MA, USA) from land sources (>8000 mmol N m(-2) yr(-1); 90% in sewage effluent) to the offshore waters of Massachusetts Bay, the tid al inflow also brings material into the Harbor. For Boston Harbor and many other coastal embayments, tidal inputs must be quantified if we a re to develop complete nutrient budgets. This study quantifies tidal i nput of nutrients and suspended solids (i.e. 'ocean loading') and pred icts the future role of ocean loading after sewage effluent discharge is diverted away from the Harbor to a location about 15 km into the Ba y. Ocean loading is determined by simple box modeling using data sets available for the 1994 annual cycle. Critical data for modeling includ e a series of surveys on which high-resolution data for salinity and t urbidity were collected using in situ sensors housed in a towed instru ment package (i.e, a 'towfish'); surveys covered 2 transects in and ou t of the 2 Harbor inlets which regulate tidal exchange. Study results show that ocean loading dominates the input-output budgets of nutrient s and suspended solids, generally providing more than twice the loadin g from present land sources. Results further suggest that, although th e absolute values of ocean loading will decrease after effluent divers ion, the relative contribution of the ocean to the Harbor budget will increase. predictive modeling suggests that total nitrogen concentrati ons will decrease about 20 % and dissolved inorganic concentrations wi ll decrease about 50% from present levels; these predicted decreases a re smaller than one would calculate if the ocean loading term of budge ts were neglected. Ocean loading thus will have a role in the nature o f Harbor recovery from the planned sewage diversion.