Influence of Variable Precipitation on Coastal Water Quality in Southern California

Author： Dwight Ryan H Caplan Joshua S Brinks Mitchell V Catlin Sandra N Buescher Guido Semenza Jan C

ISSN： 1061-4303

Source： Water Environment Research, Vol.83, Iss.12, 2011-12, pp. : 2121-2130

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Abstract

To examine the consequences of changing precipitation levels on southern California's recreational coastal water quality, and compare the responses of watersheds with differing levels of urban development. The geo-temporal relationship for six years (2000‐2005) of precipitation levels, discharge rates for the ten primary waterways, and coastal water bacteria concentrations at seventy-eight southern California beaches were examined. Precipitation levels, river-creek discharge rates, and coastal water bacteria concentrations were significantly correlated (p < 0.01)="" for="" all="" ten="" watersheds="" investigated.="" water="" bacteria="" concentrations="" significantly="" increased="" with="" higher="" levels="" of="" precipitation="" across="" 95%="" of="" the="" seventy-eight="" beaches="" investigated.="" a="" heavily="" developed="" watershed="" had="" significantly="" higher="" median="" bacteria="" concentrations="" (186 cfu)="" in="" the="" adjoining="" coastal="" waters="" compared="" to="" an="" undeveloped="" watershed="" (10 cfu)="" of="" similar=""> Precipitation and ensuing runoff strongly control the rate of polluted water delivered to most beaches in southern California. Variable precipitation generates a greater response in coastal water bacteria concentrations in developed watersheds compared to undeveloped areas. Projected declines in regional precipitation as a consequence of climate change may result in less contaminated water delivered to coastal waters, thus decreasing risk of water associated illnesses during winter months.