Isotopic and microbial indicators of sewage pollution from Stone Town, Zanzibar, Tanzania

Moynihan, Molly A.; Baker, David M.; Mmochi, Aviti J.

Isotopic and microbial indicators of sewage pollution from Stone Town, Zanzibar, Tanzania

2012

Moynihan, Molly A. | Baker, David M. | Mmochi, Aviti J.

In Stone Town, Zanzibar, sewage treatment is minimal, with a biological oxygen demand reduction to 60% and no removal of bacteria or nutrients. Here, Stone Town’s sewage pollution was studied by measuring Enterococci and NH₄ ⁺ concentrations in seawater and δ¹⁵N of benthic organisms; samples were collected along the Stone Town shoreline and from offshore coral reefs. Public perceptions of sewage pollution were investigated via interviews. Enterococci from the Stone Town shoreline exceeded USEPA guidelines for recreational use. Benthic organisms from two of the four reefs were relatively enriched (δ¹⁵N>10‰), indicative of sewage derived N. δ¹⁵N values of organisms from Stone Town exceeded 16‰. A strong correlation was found between Enterococci and δ¹⁵N across sites, while step-wise regression indicated rainfall and tidal stage as important predictors for bacterial concentrations. These data provide an important impact assessment from which the efficacy of future policy and management change can be assessed.

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