MAJOR, MINOR, TRACE-ELEMENT AND SUSPENDED SEDIMENT VARIATIONS IN THE RIVER DERWENT

A wide range of major, minor and trace element data are presented toge ther with background information on hydrology and suspended sediments for the agriculturally impacted River Derwent to the north of the Humb er Estuary, eastern England. Water quality is generally reasonable wit h low levels of many minor and trace elements and suspended sediments. Nitrate and particulate aluminium, iron, manganese and lead concentra tions increase with increasing flow while soluble reactive phosphate ( SRP) concentrations decrease with increasing flow: there is a very poo r relationship with flow for all the other determinants. Some of the m ajor elements have elevated concentrations compared to other non-indus trial 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, C l and SO4 concentrations are also relatively high due to higher atmosp heric inputs and evapotranspiration, but, usually, they are weakly cor related with each other owing to the effects of pollutant sources. Wea thering reactions provide the main source of divalent base cations and alkalinity, but the lack of clear concentration-flow relationships in dicates high weathering in both the soil and groundwater areas. The hi gh weathering rates ensures that catchment acidification from atmosphe ric sources of acidic oxides is not significant at a basin wide scale. Environment Agency water quality information indicates relatively uni form average concentrations of base cations, nutrients and chloride al ong the length of the Derwent apart from in the upland source areas wh ere tributary influences become more important and there is less poten tial for dilution due to the lower flows. However, minor increases in concentration may occur due to increased evapotranspiration in the low er sections of the Derwent. The data also indicate that while the nitr ate concentrations have remained relatively constant over time, SRP in creased during the mid-1980s and has subsequently declined probably du e to changes in sewage treatment practices. (C) 1998 Elsevier Science B.V.