The chemistry of the River Wye

Abstract

Samples collected during April 1975–December 1977 from 14 sites in the River Wye catchment were analysed for total dissolved solids, calcium, magnesium, sodium, potassium, bicarbonate, reactive silica, nitrate, orthophosphate, suspended solids and soluble organic carbon. The study period encompassed some of the most severe drought conditions recorded in the Wye catchment and comparisons of the spatial and temporal variation in concentrations and mass flows of determinands were made from contrasting flow periods, September 1975–August 1976 (dry) and September 1976–August 1977 (wet), when flows in the lower Wye were 38% and 118%, respectively, of the long-term average. Spatial variations in water quality were related principally to geology (e.g., calcium) and population and land use (e.g., orthophosphate, nitrate). Significant flow-concentration relationships were established and, at all sites in both wet and dry periods, concentrations of most anions and cations were reduced by increased flow: nitrate and suspended-solids concentrations increased with increased flow. Annual subcatchment yields per unit area were substantially greater during the wet than the dry period and this was most marked in the lower catchment where differences in runoff between the two periods were greatest. Orthophosphate loads in both periods and nitrate loads in the dry period were significantly related to population density.