108 



BIOLOGICAL REPORT 31 



studies producing similar results. Because deposi- 

 tion to the bay surface is direct, it represents a ma- 

 jor nitrogen input of 433 t/year; however, deposi- 

 tion also occurs on the watershed surface. In im- 

 permeable areas (rooftop, paved surfaces, etc.) 

 rainfall collects an additional nitrogen load that, if 

 directed into bay waters or shunted to subsurface 

 leaching pits, transports much of its nitrogen load 

 (37 t/year) intact to the bay (Table 6.2). 



Fortunately, most of the watershed surface is 

 permeable and vegetated so that deposition on most 

 of the surface is not washed off but enters the soil 

 system where plant uptake and microbial nitrogen 

 transformations can occur. In these areas, most of 

 the nitrogen deposited from the atmosphere is re- 

 moved in transport, being denitrified or held in 



Table 6.2. Annual inputs of nitrogen to Buzzards 

 Bay waters 



"Surface area = 55000 ha, 75 mg N/L (Valiela and Teal 1979), total 

 Nitrogen (TN), 105 cm rain/year TN was used since other inputs (i e , 

 outfalls) include dissolved organic Nitrogen + particulate organic Ni- 

 trogen pools 



"SAIC 1991 and Buzzards Bay Project 1990 



'Land area = 1 , 1 03 km 2 (SAIC 1 991 ). 1 9 M in groundwater (Weiskel and 



Howes 1991). 54 cm recharge/year (Fnmpter et al 1990) 

 Terkla et al. 1990, SAIC 1991, Weiskel and Howes 1991 

 •20 1% seasonal (U S Census, Terkla et al 1990), 155 mol N person/year 



(Weiskel and Howes 1991) and estimate of 4P, 4 mo/H (Herr 1984) 

 '2.695 ha bogs in watershed (Terkla et al 1990) and 13 kg/ha/year (total 



bog export. Howes and Teal 1992) 

 'Terkla et al 1990 



organic forms in soil. The result is that the perme- 

 able areas with almost twice the deposition of im- 

 permeable areas represent less than 4% ( 1 6 t/year) 

 of the total nitrogen delivery to bay waters. Com- 

 paring all of the nonpoint sources, atmospheric 

 deposition accounts for almost half (46%) of the 

 total loading. While some portion of this atmospheric 

 deposition is certainly from within the watershed, 

 the limited population and industry and the relatively 

 small area involved indicate that most is probably 

 due to the movement of nitrogen-contaminated re- 

 gional air masses. 



Boat discharges that place nutrient inputs directly 

 into bay waters have not been quantitatively evalu- 

 ated, but they represent a very small potential 

 source. There are 4,300 slips and moorings asso- 

 ciated with Buzzards Bay, but the vast majority are 

 summer usage and typically occupied only a few 

 days per week. In addition, pump-outs for boat 

 wastes are available around the bay (the nutrients 

 then becoming a part of the treatment facility in- 

 puts), and direct discharges are prohibited 

 nearshore. The result is a potential input from this 

 source less than 0. 1 % of the total loading to bay 

 waters and an input distributed throughout the bay. 

 Compliance with proper discharge procedures re- 

 duces this source to near zero. The problem with 

 boat discharges appears to be more associated with 

 bacterial and pathogenic contamination of the wa- 

 ters than with cultural eutrophication. 



Comparisons of the various sources of " k new" 

 nitrogen to Buzzards Bay waters clearly indicate 

 that disposal of human wastes accounts for most of 

 the inputs (70%), with treatment facilities account- 

 ing for 55% and septic disposal 1 5% (Table 6.2). 

 Of the remaining inputs, precipitation accounts for 

 22%, agriculture for 5%, and lawn fertilizers 3%. 

 While each embayment requires its own nitrogen 

 management scheme focusing on the site-specific 

 sources and tolerances (Costa et al. 1 994), it ap- 

 pears that the major management issues must focus 

 on waste disposal. 



The potential impacts of nitrogen inputs from 

 treatment facilities and residential inputs, septic sys- 

 tems, and lawn fertilizers differ in several ways. First 



