This paper presents information on the spatial and seasonal patterns of river water
chemistry at approximately 800 sites in North West England based on data from the
Environment Agency regional monitoring programme. Within a GIS framework, the linkages
between average water chemistry (pH, sulphate, base cations, nutrients and metals)
catchment characteristics (topography, land cover, soil hydrology, base flow index
and geology), rainfall, deposition chemistry and geo-spatial information on discharge
consents (point sources) are examined. Water quality maps reveal that there is a clear
distinction between the uplands and lowlands. Upland waters are acidic and have low
concentrations of base cations, explained by background geological sources and land
cover. Localised high concentrations of metals occur in areas of the Cumbrian Fells
which are subjected to mining effluent inputs. Nutrient concentrations are low in
the uplands with the exception sites receiving effluent inputs from rural point sources.
In the lowlands, both past and present human activities have a major impact on river
water chemistry, especially in the urban and industrial heartlands of Greater Manchester,
south Lancashire and Merseyside. Over 40% of the sites have average orthophosphate
concentrations >0.1mg-Pl(-1). Results suggest that the dominant control on orthophosphate
concentrations is point source contributions from sewage effluent inputs. Diffuse
agricultural sources are also important, although this influence is masked by the
impact of point sources. Average nitrate concentrations are linked to the coverage
of arable land, although sewage effluent inputs have a significant effect on nitrate
concentrations. Metal concentrations in the lowlands are linked to diffuse and point
sources. The study demonstrates that point sources, as well as diffuse sources, need
to be considered when targeting measures for the effective reduction in river nutrient
concentrations. This issue is clearly important with regards to the European Union
Water Framework Directive, eutrophication and river water quality.
Copyright 2009 Elsevier B.V. All rights reserved.