Temporal and spatial variability in stream waters of Wales, the Welsh borders and part of the West Midlands, UK — 2. Alumino-silicate mineral stability, carbonate and gypsum solubility

Stream water chemical composition, which in many systems represents the integration of weathering throughout the catchment, has been used to predict the stability and degree of saturation with respect to a range of minerals, based on the assumption of a pure closed system, and in the case of alumino-silicates, the hydrolysis reaction of a primary mineral phase. The distributions of predicted mineral stability and saturation have been mapped for Wales, the Welsh borders and part of the West Midlands. The incorporation of monitoring data from a site-specific study (Plynlimon, mid-Wales) has been used to interpret the significance of factors such as seasonality and hydrological regime on mineral stability and solubility. The derived maps can be used to identify: (i) regions in which streams are most susceptible to freshwater acidification and (ii) local variations in bedrock geochemistry, such as calcite mineralisation, which cannot be identified by conventional field mapping.