Major, minor, trace element and suspended sediment variations in the River Tweed: results from the LOIS core monitoring programme

A wide range of major, minor and trace element data is presented for three sites in the Tweed basin. These are located at the downstream freshwater limit, the upland-lowland transition point and a major tributary, the Teviot. In comparison to the agricultural, industrial and urban impacted rivers of the UK, water quality in the study region is good with low levels of dissolved nitrogen, phosphorus, many trace elements, micro-organic compounds, and carbon dioxide. Sodium, chloride and sulphate, mainly derived from atmospheric sources, are positively correlated. These components show increasing concentrations downstream due to the influence of evapotranspiration and sewage effluent. Base cation concentrations, alkalinity and some trace elements such as barium, strontium, lithium and uranium are enriched under baseflow conditions, exhibiting an inverse relationship with flow. These variations are associated with chemical weathering reactions of the bedrock. The particulate trace metals show high correlations in line with an aluminium and iron oxide/hydroxide soil source. In the case of copper and chromium, two linear relationships are observed because of an additional industrial source. Particulate nitrogen, phosphorus and carbon are highly correlated due to soil derived organic matter. However, the dissolved forms of nitrogen, phosphorus, organic carbon and silicon show complex patterns between concentration and flow due to the interplay of hydrological and biological processes. There is a large biological reactivity within the rivers. This is reflected by variable but often low partial pressures of carbon dioxide throughout the year and dissolved silicon concentration minima during the summer months when algal activity is maximal.