Modelling the effect of drought on estuarine water quality

Long-term data assembled for monitoring the water quality of the Thames estuary between 1977–1992 were used to examine the changing influences of physico-chemical variables on estuarine water quality during drought conditions. Seasonal and monthly means were computed and tested for significant differences. Time series data were used to estimate regression models explaining observed variations in water quality parameter measurements during the predrought (1977–1988) and drought (1989–1992) periods. Stability tests were used to establish significant differences in predrought and drought models and to make inferences about the significance of drought induced low flows on water quality. Significant mean seasonal and monthly differences were found for flow, chlorinity, temperature, dissolved oxygen, pH and suspended solids. Total oxidisable nitrogen showed no significant change. Regression analyses were consistent with these results and highlighted the significance of drought related changes in flow and temperature for the determination of estuarine water quality. This suggests that management policies designed to mitigate the effects of drought be extended to consider their effects on estuarine water quality given the ecological importance of these areas.