Fecal coliform loadings and stocks in buttermilk bay,Massachusetts, USA,and management implications |
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Authors: | Ivan Valiela Merryl Alber Michael LaMontagne |
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Institution: | (1) Marine Biological Laboratory, Boston University Marine Program, 02543 Woods Hole, Massachusetts, USA |
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Abstract: | Abundance of fecal caliform bacteria is a weak index of the presence of human pathogens in wastewater entering coastal waters.
In spite of this, use of fecal caliform indices for management purposes is widespread. To gain insight into interpretation
of fecal coliform data, we evaluated size of stocks of fecal coliforms in water, sediments, and sea wrack, in Buttermilk Bay,
a coastal embayment in Massachusetts. Sediments contained most of the fecal coliforms. Fecal coliforms in sediments were as
much as one order of magnitude more abundant than in the water column or in sea wrack. The fecal coliforms in sediments of
Buttermilk Bay were so abundant that resuspension of fecal coliforms from just the top 2 cm of muddy sediments could add sufficient
cells to the water column to have the whole bay exceed the federal limit of fecal coliforms for shellfishing.
The major sources of fecal coliforms to the bay were water-fowls, surface runoff, groundwater, and streams. Waterfowl were
the largest source of fecal coliforms during cold months; surface runoff, streams, and groundwater were most important during
warm months. Redirection of surface runoff pipes is unlikely to be a very successful management action since contributions
via this source are insufficient to account for the measured increases in concentrations of fecal coliforms in water. Removal
of waterfowl is also unlikely to be useful, since fecal coliform concentrations leading to closures of shellfish beds and
swimming areas are most frequent during warm months when waterfowl are rarest. Rates of loss of fecal caliform cells from
the water column by death and tidal exchange were high. Mortality of cells was about an order of magnitude larger than losses
by tidal exchange.
The amounts of fecal coliforms brought into the bay by waterfowl, surface runoff, groundwater, and streams are an order of
magnitude smaller than the losses by mortality and tidal removal. This implies that there is an additional source of fecal
coliforms within the bay. We suggest that resuspension of the upper layers of sediments can easily account for the fecal coliforms
present in the water.
Fecal coliform content of water and shellfish were not correlated. In contrast, sediment and shellfish fecal coliform abundances
were significantly related. Monitoring of fecal coliforms in sediments may provide a better assessment of shellfish than sampling
of water.
The large fecal coliform stock in sediments should be the first priority for management. Efforts ought to be directed toward
the reduction of sediment fecal coliform stocks. Lowering nutrient additions to coastal water bodies may be one practical
approach. |
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Keywords: | Fecal coliforms Coastal waters Wastewater Waterfowl Groundwater |
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