DELIVERY OF MICROBIAL INDICATOR ORGANISMS TO COASTAL WATERS FROM CATCHMENT SOURCES

The introduction of ultraviolet disinfection of sewage effluent in Jer sey has served to focus attention on other sources of faecal pollution responsible for subsequent compliance failures in coastal water quali ty in St Aubin's Bay. Studies of microbial concentrations (total colif orms, faecal coliforms and faecal streptococci) in streams draining to the bay showed concentrations to be elevated by an order of magnitude or more following rainfall. Detailed monitoring of indicator organism s during hydrograph events showed rapid increases in concentration wit h flow associated with the rising limb of the hydrograph and transport of suspended solids. Microbial budget estimates suggested that betwee n 42 and 97% of microbial delivery was associated with high flows, whi ch account for just 20% of the total discharge. Budgets also revealed the relative importance of different catchment inputs, revealing the l ow bacterial input associated with UV treated effluent which provided 48% of the total volume discharged to the bay. Implications for water quality standards are discussed with reference to catchment management planning. Copyright (C) 1996 IAWQ. Published by Elsevier Science Ltd