Major, minor, trace element and suspended sediment variations in the River Derwent

Abstract

A wide range of major, minor and trace element data are presented together with background information on hydrology and suspended sediments for the agriculturally impacted River Derwent to the north of the Humber Estuary, eastern England. Water quality is generally reasonable with low levels of many minor and trace elements and suspended sediments. Nitrate and particulate aluminium, iron, manganese and lead concentrations increase with increasing flow while soluble reactive phosphate (SRP) concentrations decrease with increasing flow: there is a very poor relationship with flow for all the other determinants. Some of the major elements have elevated concentrations compared to other non-industrial north-eastern UK rivers. For example, nitrate concentrations are elevated due to agricultural runoff at high flows and carbon dioxide partial pressures are higher than less intensively farmed areas. Na, Cl and SO 4 concentrations are also relatively high due to higher atmospheric inputs and evapotranspiration, but, usually, they are weakly correlated with each other owing to the effects of pollutant sources. Weathering reactions provide the main source of divalent base cations and alkalinity, but the lack of clear concentration–flow relationships indicates high weathering in both the soil and groundwater areas. The high weathering rates ensures that catchment acidification from atmospheric sources of acidic oxides is not significant at a basin wide scale. Environment Agency water quality information indicates relatively uniform average concentrations of base cations, nutrients and chloride along the length of the Derwent apart from in the upland source areas where tributary influences become more important and there is less potential for dilution due to the lower flows. However, minor increases in concentration may occur due to increased evapotranspiration in the lower sections of the Derwent. The data also indicate that while the nitrate concentrations have remained relatively constant over time, SRP increased during the mid-1980s and has subsequently declined probably due to changes in sewage treatment practices.