Modelling of dripwater hydrology and hydrogeochemistry in a weakly karstified aquifer (Bath, UK): Implications for climate change studies

A better knowledge of dripwater hydrology in karst systems is needed to understand the palaeoclimate implications of temporal variations in Mg/Ca and Sr/Ca of calcareous cave deposits. Quantitative modelling of drip hydrology and hydrochemistry was undertaken at a disused limestone mine (Brownʹs Folly Mine) in SW England overlain by 15 m of poorly karstified Jurassic limestones, with sub-vertical fracturing enhanced by proximity to an escarpment. Discharge was monitored at 15 sites intermittently from the beginning of 1996, and every 10–20 days from later 1996 to early 1998. Samples for hydrochemical parameters (pH, alkalinity, cations, anions, fluorescence) were taken corresponding to a sub-set of these data and supplemented by bedrock and soil sampling, limited continuously logged discharge, and soil water observations. Three sites, covering the range of discharge (approximately 1 μL s−1 to 1 ml s-1 maximum discharge) and hydrochemical behaviours, were studied in more detail. A quantitative flow model was constructed, based on two parallel unit hydrographs: responsive and relatively unresponsive to discharge events, respectively. The linear response and conservative mixing assumptions of the model were tested with hydrogeochemical data.