Comparison of spatial Cu stream water concentrations with intra- and inter- annual monitoring data

The Geochemical Baseline Survey of the Environment (G-BASE) is the long established high resolution geochemical baseline mapping project of the British Geological Survey. The geochemical mapping is based on the systematic sampling and analysis of soils, stream sediments, and stream waters, and this study concerns the latter. The central aim of this study is to establish whether the spatial variation, caused by geology, topography etc, predominates over temporal variations; and establish whether such temporal variations in trace element concentrations limit the representativeness of spatial distribution maps. Water concentrations are known to vary on a diurnal basis, and in response to external factors such as rainfall. This report addresses an assumption that stream water chemistry significantly varies over prolonged sampling periods. This report describes the temporal stream water Cu data from samples collected during the summer field seasons in central and eastern England between 1997 and 2007. These temporal samples were collected in parallel with the primary samples used for mapping. The temporal data are obtained from sampling “monitor sites”: a carefully selected site sampled each day from each temporary fieldbase used by the field teams. Comparison of these data showed that the variations of Cu concentrations sampled over time at monitor sites, were less than spatial variations determined by factors such as geology, topography and landuse. The concentration of Cu in the monitor site samples varied by as much as 13 mg/L at one site, so the relevance of outliers, and their effect on the interpretation and mapping of spatial data were examined. In comparison to the spatial variations, temporal variations were limited.