ECOLOGY OF BUZZARDS BAY: An Estuarine Profile 1 09 



for more than 60 years in the distribution of the in- 

 puts, almost all of the treatment facility input to the 

 bay has been from a single region. New Bedford/ 

 Fairhaven. The nutrient-related ecological impacts 

 of these inputs have thus remained relatively local- 

 ized (Howes and Taylor 1 989; Costa et al. 1 992). 

 The result is that only a small portion of the bay has 

 been degraded, although it is receiving almost half 

 of the total loading to the entire bay. In contrast, 

 over the same 60 years there has been a rapid rise 

 in the nonurban population (Fig. 1 .5), which uses 

 septic waste disposal and is distributed primarily 

 along the tributaries to the bay's shallow 

 embayments. Although these systems in total re- 

 ceive lower loadings, they are shallow and poorly 

 flushed and mixed, giving them a lower assimilative 

 capacity; as a result, some are already exhibiting 

 eutrophic conditions. It also appears that there is a 

 much lower per capita nitrogen load from septic 

 systems versus treatment facility disposal; both sys- 

 tems cover about the same population base but dif- 

 fer in contribution by four-fold. Part of this differ- 

 ence is due to additional nitrogen sources (com- 

 mercial and industrial and combined sewer over- 

 flows) in the treatment facility fraction, but a major 

 factor is the removal of particulates, sorption, 

 and denitrification associated with septic disposal 

 (Weiskel and Howes 1991 ). The particulates form 

 most of the "septage" removed when tanks are 

 cleaned (Teal and Peterson 1 99 1 ), and the signifi- 

 cant nitrogen that they contain is transported to a 

 surface disposal site or is put through the treatment 

 facilities. 



The incipient cultural eutrophication of the 

 embayments compared to the bay proper stems 

 from their lower assimilative capacity and higher 

 relative nitrogen loadings. Although almost all treat- 

 ment facility discharges are to better flushed areas, 

 the embayments receive nearly all of the other wa- 

 tershed inputs, so that while they receive less than 

 25% of the "new" nitrogen load, they occupy less 

 than 14% of the area (75 knr) and even less of the 

 volume of the bay (calculated from Table 6.2). In 

 addition, much of the watershed nutrient load first 

 cycles through the embayment systems, which 



retain or remove some of the load, thus buffering 

 bay waters. Unfortunately, it is these same 

 embayments and nearshore waters that support the 

 most diverse ecological habitats and productive fish- 

 eries, as well as much of the recreational and aes- 

 thetic values of the bay. 



6.2. Natural Modification 



The land-sea interface of the coastal zone is al- 

 ways in transition, especially landscapes like those 

 surrounding Buzzards Bay, which are relatively re- 

 cent and are composed of unconsolidated glacial 

 till. In addition to the normal surficial weathering 

 that operates on geologic time scales, two processes 

 are altering the coastal zone on smaller time scales: 

 relative sea-level rise (the level of the sea relative to 

 the level of the land at any locale) and storms. Al- 

 though these processes have been acting on Buz- 

 zards Bay throughout its existence, the apparent re- 

 cent acceleration in the rate of relative sea-level rise 

 has increased the rate of erosion and coastal re- 

 gression to the point of easy observation in periods 

 much less than a lifetime. Coastal storms act in con- 

 cert with rising sea level; however, the two differ in 

 that rising sea level is continuous and gradual and 

 coastal storms are occasional but often dramatic. 



6.2.1. Relative Sea-level Rise 



There has been much recent concern over 

 changing sea levels and the potential effects on the 

 coastal zone; however, relative sea level has been 

 constantly changing through geologic time. The rela- 

 tive level of land and sea can be modified by changing 

 sea or ocean level (eustatic sea level) and by chang- 

 ing land level. There are many mechanisms that al- 

 ter land and sea levels: changes in the volume of 

 water in the oceans through changes in the volume 

 of the ocean basins by plate tectonics and sea floor 

 spreading, or even sedimentation or changes in land 

 levels through tectonics or isostatic adjustment. 

 While the whole variety of factors are at work in 

 the world's coastal zones today, in Buzzards Bay 

 two primary factors account for the rise in sea level 



