Pk. Weiskel et al., COLIFORM CONTAMINATION OF A COASTAL EMBAYMENT - SOURCES AND TRANSPORTPATHWAYS, Environmental science & technology, 30(6), 1996, pp. 1872-1881
Fecal bacterial contamination of nearshore waters has direct economic
impacts to coastal communities through the loss of shellfisheries and
restrictions of recreational uses. We conducted seasonal measurements
of fecal coliform (FC) sources and transport pathways contributing to
FC contamination of Buttermilk Bay, a shallow embayment adjacent to Bu
zzards Bay, MA. Typical of most coastal embayments, there were no dire
ct sewage discharges (i.e., outfalls), and fecal bacteria from human,
domestic animal, and wildlife pools entered open waters primarily thro
ugh direct deposition or after transport through surface waters or gro
undwaters. Direct fecal coliform inputs to bay waters occurred primari
ly in winter (December-March) from waterfowl, similar to 33 x 10(12) F
C yr(-1) or similar to 67% of the total annual loading. Effects of wat
erfowl inputs on bay FC densities were mitigated by their seasonality,
wide distribution across the bay surface, and the apparent limited di
spersal from fecal pellets. On-site disposal of sewage by septic syste
ms was the single largest FC source in the watershed-embayment system,
460 x 10(12) FC yr(-1), but due to attenuation during subsurface tran
sport only a minute fraction, < 0.006 x 10(12) FC yr(-1), reached bay
waters (< 0.01% of annual input to bay). Instead, surface water flows,
via storm drains and natural streams under both wet- and dry-weather
conditions, contributed the major terrestrial input, 12 x 10(12) FC yr
(-1) (24% of annual input), all from animal sources. Since most of the
surface water FC inputs were associated with periodic, short-duration
rain events with discharge concentrated in nearshore zones, wet-weath
er flows were found to have a disproportionately high impact on nearsh
ore FC levels. Elution of FC from shoreline deposits of decaying veget
ation (wrack) comprised an additional coliform source.