Long‐term nitrate trends in the river trent and four major tributaries

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Abstract
Nitrate levels which have been rising in many British rivers for at least thirty years have become of particular interest since Britain adopted the EC Drinking Water Directive. The literature examining nitrate trends in the rivers of the U.K. and Eire is reviewed. Long‐term nitrate concentration trends are derived for eight sites in the River Trent drainage system. These include sites on two rural tributaries, two urbanized tributaries, and the main river. Currently, mean annual concentrations for these sites range from about 4.0 mg1−1N in the rural catchments, to 12.4 mg 1−1 N in the urbanized tributaries, and to between 8.7 mg 1−1N and 11.0 mg 1−1 N along the mainstream. Moreover rates of increase of nitrate concentration of approximately 0.06 mg 1−1 N yr −1 in the rural catchments, contrast with values up to 0.20 mg 1−1 N yr −1 in the two urbanized tributaries and River Trent. Long term nitrate loads have been calculated for the River Trent at Nottingham using a discharge weighted mean interval method. This method probably provides the best available estimate of nitrate loads calculable from irregular data of variable sampling frequency for lowland rivers. Annual nitrate loads varied between 10700t yr −1 and 29 800t yr −1 over the period of record. A rate of increase in nitrate load of 455 t yr −1 was obtained. The increases in nitrate concentrations and loads within the Trent basin are matched by similar rates of increase in other European catchments.