The hydrochemistry of a Chalk aquifer during recovery from drought

Chalk groundwater levels typically decline markedly in response to drought, and rebound strongly when the drought breaks. Chalk streams, largely groundwater-fed, are of ecological importance but little research has been conducted on possible water-quality effects accompanying fluctuations in groundwater level. This study monitored springs, boreholes and surface water in the Pang and Lambourn catchments in southern England during a major recovery in 2006-2008. Hydrochemistry, stable isotopes and age indicators were used to characterize the waters. Perennial springs showed little change in water quality over the monitoring period, and even seasonal springs soon became consistent in their hydrochemistry. A similar lack of change was observed in borehole waters and in the River Lambourn. Stable isotopes demonstrated the high degree of damping relative to rainfall inputs, and residence time indicators showed that Chalk groundwater is basically a mixture with an 'old' (pre-1950s) component of >= 50%. This being the case, any water quality changes owing to water level fluctuations would inevitably become diluted. Therefore, although future climate predictions for southern Britain include greater extremes in rainfall and temperature, and consequently water level changes of greater amplitude, the buffering effect of the Chalk aquifer should protect the quality of Chalk springs and streams.