Microbial and nutrient pollution of coastal bathing waters in Mauritius

Abstract

The coastal pollution problem in Mauritius is exacerbated by the hydrogeology of the volcanic substratum. Bacterial contamination of bathing waters and nutrients, water temperature, salinity, and dissolved oxygen (DO) were monitored at three different spatial and temporal scales along the coastline of Mauritius during 1997–1998. Standard techniques for water sample collection and analysis set by the American Public Health Association [APHA. Standard methods for the examination of water and wastewater. 19th ed. Washington, DC: APHA, 1995.] were used at: (a) 16 sites around the island over a period of 7 months; (b) 12 stations along a recreational beach over an 18-month period; and (c) at an underground freshwater seepage point over 1 day. Total coliform (TC), faecal coliform (FC), and faecal streptococci (FS) contamination reported during all surveys varied randomly (e.g., with maximum densities in the ranges of 346–2020 TC, 130–2000 FC, and 180–1040 FS at one site) and at times exceeded the established EEC and Environment Protection Agency (EPA) standards for bathing water (e.g., in >90% of samples) to qualify for beach closure. Computed FC:FS ratios were used to pinpoint human faecal matter as the main source of contamination. Nitrate, phosphate, and silicate concentrations in seepage water were high (3600–9485, 38–105, and 9950–24,775 μg l −1, respectively) and a cause for concern when compared with levels (5–845, 5–72, and 35–6570 μg l −1, respectively) in cleaner lagoon water samples. Statistical analysis showed significant correlations (for TC and NO 3: r=.75, P<.02; for TC and PO 4: r=.779, P<.02; for TC and SiO 4: r=.731, P<.05; for FC and NO 3: r=.773, P<.02; for FC and SiO 4: r=.727, P<.05; for FS and SiO 4: r=.801 P<.01) between microbial densities and nutrients recorded, confirming the pathogen-contaminated water to be highly eutrophic. There is an urgency for Mauritius to properly address the issue of sewage treatment and wastewater discharge to safeguard its coastal environment, public health, and tourism expansion.