106 



BIOLOGICAL REPORT 31 



which are more widespread and more difficult to 

 identify and measure, generally reach Buzzards Bay 

 waters through groundwater transport. Point 

 sources have historically been regulated and quan- 

 tified, whereas nonpoint sources are a recent area 

 of research and have a larger error associated with 

 their estimates. 



Point Sources. The only major point source 

 of nitrogen in the Buzzards Bay watershed origi- 

 nates from sewage. Other potential point sources 

 like major river discharges and large-scale agricul- 

 ture do not contribute to bay waters (cf. Chapters 

 1 and 5, respectively). Residential and municipal 

 wastes are piped to wastewater treatment facilities 

 in the more heavily populated areas of the water- 

 shed. New Bedford, Wareham, Dartmouth, 

 Fairhaven, Falmouth, and Marion maintain these 

 facilities, and all except Falmouth discharge directly 

 to bay waters (Table 6. 1 ). The Falmouth facility 

 discharges to groundwater by rapid infiltration and 

 spray irrigation. Although the Falmouth facility at- 

 tempts to lower nutrient loading (about 1 % of the 

 region's total) to coastal waters by adding a plant 

 uptake and soil nitrogen removal step not used at 

 the other facilities, the facility still "imports" nitro- 

 gen into Buzzards Bay because the contributing ar- 

 eas are outside of the bay watershed (Howes et al. 

 1 992). In contrast the Marion facility (less than 1% 

 of total nutrient loading) discharges to surface wa- 

 ter at the head of a salt marsh, which performs lim- 

 ited tertiary treatment before discharge to Aucoot 

 Cove, and represents true removal (Howes 1 993). 



Table 6.1. Nitrogen inputs to Buzzards Bay from 

 sewage treatment plants. Adapted from SAIC 

 (1991). 



Treatment plant 



t N/year 



Almost all of the treatment facilities' input to the 

 bay is in the New Bedford/Fairhaven area, with the 

 New Bedford outfall and combined sewer over- 

 flows accounting for 80% of the total inputs from 

 this source. The New Bedford outfalls ( 1 1 3.6 mil- 

 lion L/day) serve 98% of the city's population plus 

 600 residences in Dartmouth and 60 in Acushnet. 

 Thirty-eight sewer overflows contribute to the 962 

 t/year entering New Bedford Inner and Outer Har- 

 bors, discharging nutrients, coliforms, and toxics to 

 bay waters. Combined sewer overflows are the fo- 

 cus of an ongoing remediation program (Camp, 

 Dresser, and McKee, Inc. 1990); these discharges 

 are responsible for restricted shellfishing in this area 

 throughout this century. Sewage treatment plants 

 and combined sewer overflows are the major source 

 of nitrogen loading to bay waters, 1.210 t/year. 

 These facilities service about half of the population 

 of the bay's watershed and most of its heavy com- 

 mercial and industrial area. 



Nonpoint Sources. These diffuse sources of 

 nitrogen to bay waters stem from residential waste 

 disposal and fertilizer use, agricultural fertilizers, dairy 

 and cattle farming, surface water runoff, and direct 

 precipitation. In total, they represent slightly less than 

 half of the "new" nitrogen loadings to the bay (Fig. 

 6.4). 



Dairy cattle - 1 .5% 



Uncontaminated Cranberry - 1 .5% 



qroundwater - I I I (-Agricultural fertilizer - 1 .7% 

 n 7 o/ ^--13- — ^mL»___j— Lawn fertilizer- 3 1% 



—Septic: Seasonal ■ 

 2.7% 



•Disposal by rapid infiltration and spray irrigation; transport through 

 groundwater to West Falmouth Harbor. Buzzards Bay 



Fig. 6.4. Relative sources of nitrogen inputs to 

 Buzzards Bay water Note that wastewater 

 (sewer and septic) accounts for two-thirds of 

 the total annual input 



