Stream-water geochemical atlas of the Clyde Basin

Surveys of the inorganic chemical quality of stream water in rural and urban parts of the Clyde Basin, Scotland, have been collated in this investigation in order to characterise the chemical status and its spatial variability. The study has been carried out as part of the wider Clyde and Glasgow Urban Super Project (CUSP), a multidisciplinary collaboration between BGS and Glasgow City Council (GCC), in order to help inform decisions on regional planning and catchment management. Water samples were collected in three phases: from the inner estuary during 2002–2003, from tributaries of the River Clyde in Glasgow during 2003, and from rural parts of the catchment and upper reaches of the River Clyde during 2010. In total, 1892 sample sites were investigated and some 50 elements or compounds analysed by a range of analytical techniques. Maps of spatial distributions, summary statistics, box plots and summary information are presented here to provide an overview of the current status of stream water chemistry and likely controlling factors. The spatial variation in concentrations of a large number of solutes across the Clyde catchment is striking, with a great many, including most major ions, arsenic (As), boron (B), chromium (Cr), copper (Cu), fluoride (F), lithium (Li), molybdenum (Mo), phosphorus (P), antimony (Sb) and strontium (Sr) showing a clear pattern of highest concentrations in and around the urban centre of Glasgow. This is likely to reflect a combination of lower average rainfall total when compared to the catchment periphery, relatively high base flow index (BFI), geology dominated by argillaceous, sulphide- and organic-enriched Carboniferous sedimentary rocks of the Scottish Coal Measures Group and Strathclyde & Clackmannan formations, and urban and industrial land-use. The relative contributions of each of these are hard to quantify, but geology and land-use probably dominate for most analytes in this category. Stream water pH also reflects these spatial controls, with acidic waters predominating in the upland areas of heather moor and peat, and neutral to alkaline conditions in the low-lying central part of the Basin, where reactions with argillaceous sedimentary rocks and derivative soils predominate. The pH has an influence on a number of other solutes, including aluminium (Al), cadmium (Cd), iron (Fe), lead (Pb) and rare earth elements, all of which are comparatively mobile in acidic conditions. For Pb, mining and mineralisation are also locally important to the distributions of dissolved concentrations. High concentrations are a feature in streams around the former mining district of Leadhills in the southern part of the catchment. For other solutes, different factors appear influential. The distribution of nitrate (NO3) is patchy, with the highest concentrations occurring sporadically over a wider area of the catchment. The distribution reflects diffuse inputs of nitrate, especially from urban and agricultural sources, and demonstrates the impact of anthropogenic activities on stream water chemistry. Geology appears to be a strong control on the distributions of Ba and U in the stream waters, with highest concentrations of Ba observed over Inverclyde Group and Old Red Sandstone sedimentary rocks, and Old Red Sandstone also giving rise to the highest concentrations of U. As a result of this survey, the Clyde Basin is one of the best-characterised catchments in the UK in terms of spatial geochemistry and hydrochemistry. This volume contributes to the wider understanding of the catchment processes and chemical variability in combination with associated databases for stream sediment and soil, which are each reported separately