ECOLOGY OF BUZZARDS BAY: An Estuarine Profile 1 05 



pristine and in many ways similar to that experi- 

 enced by early settlers in the region, there has been 

 a major modification affecting the whole of the bay 

 This system-wide change involves nutrients, prima- 

 rily nitrogen. In 1 602 when Gosnold was sailing the 

 waters of Buzzards Bay the nitrogen inputs to the 

 bay systems, especially in the shallow marginal ar- 

 eas, were substantially lower than they are today 

 Population increases (Fig. 1 .5) of more than 1 00- 

 fold from early colonial occupation to greater than 

 250,000 persons today are the primary causes for 

 the increased loading, although regional develop- 

 ment leading to increased atmospheric deposition 

 of nitrogen has also been significant. 



Nitrogen is a natural and essential part of all eco- 

 systems, aquatic and terrestrial. For Buzzards Bay, 

 as for most temperate coastal systems, nitrogen is 

 limiting to phytoplankton, algal, and rooted plant 

 productivity and therefore secondary production, 

 especially shellfish. It would, therefore, seem that 

 increasing nitrogen inputs would be a benefit to the 

 system, increasing fisheries harvests. However, there 

 is much current discussion about the problems as- 

 sociated with nitrogen loading to coastal systems 

 and there are multimillion to billion dollar projects 

 to reduce nitrogen loading to the coastal zone. The 

 apparent paradox stems from the fact that at low 

 levels of nitrogen in coastal waters, increased load- 

 ing stimulates secondary production (e.g., fish and 

 shellfish); at higher levels increased yields may still 

 be achieved, but changes in community structure 

 may begin to occur (e.g., phytoplankton species, 

 benthic animal species, and impacts to eelgrass habi- 

 tats). At higher loadings, however, the increased 

 oxygen demand in the water column and sediments 

 stemming from increased plant production exceeds 

 the rate of oxygen input from photosynthesis and 

 by atmospheric mixing, and lowered oxygen con- 

 centrations can occur (hypoxia, anoxia). It is the 

 stress associated with low oxygen concentrations 

 that has the most deleterious effects on plant and 

 animal communities, and that at higher frequencies 

 and durations results in the loss of stable popula- 

 tions and their replacement with opportunistic spe- 

 cies. This sequence of nitrogen inputs leading to 

 low oxygen concentrations in aquatic systems is 



called eutrophication. and when the nitrogen inputs 

 are the result of human activity (as opposed to natu- 

 ral processes), the process is termed "cultural 

 eutrophication." Cultural eutrophication is the great- 

 est potential long-term threat to the Buzzards Bay 

 ecosystem. While toxic impacts (e.g., oil spills) can 

 have serious consequences, they tend to be rela- 

 tively localized. The difficulty with managing nitro- 

 gen loading is its widespread distribution from a wide 

 array of sources. 



Current nitrogen inputs to Buzzards Bay include 

 natural inputs from undisturbed areas, microbial ni- 

 trogen fixation, exchanges with offshore waters, and 

 inputs due to development: directly through sewer 

 outfalls, precipitation, and runoff, and indirectly 

 through groundwater transport from septic systems, 

 lawn and agricultural fertilizers, and animal farming. 

 Although the population of the Buzzards Bay wa- 

 tershed has been increasing steadily since colonial 

 days, only recently have significant signs of incipi- 

 ent cultural eutrophication become apparent in many 

 of the embayments. One reason for this is that both 

 the distribution and the total mass loading of nitro- 

 gen that determine the impact are related not to the 

 rate of population increase but to the number of 

 persons present. The population of the watershed 

 has doubled this century (Fig. 1.5), but equally im- 

 portant has been the change in population distribu- 

 tion to a more widely dispersed occupation of the 

 watershed surface. 



The importance of the changing land uses and 

 associated nutrient loading to the watershed, hence 

 to bay waters, can best be evaluated by comparing 

 the amounts and modes of input from the major 

 sources. In addition, since there is no evidence that 

 the "natural" sources of nitrogen have changed sig- 

 nificantly over the past 350 years and since the as- 

 similative capacity (the ability of the system to re- 

 ceive more nutrients without deleterious effects) has 

 only recently been approached for most of the 

 embayments. evaluation of "sources" will focus on 

 the "new" sources related to human activities (i.e.. 

 the ones capable of being managed). 



Point sources of nutrient pollution tend to be dis- 

 crete and easily quantifiable, and nonpoint sources. 



