Reversal of acidification in tributaries of the River Duddon (English LakeDistrict) between 1970 and 1998

Long-term changes in stream water chemistry in the upper Duddon catchment ( southwest Lake District, UK) were investigated. Ten streams were sampled an d analysed weekly during 1998, and the results compared with data for the e arly 1970s and 1986. The waters exhibited a range of pH, average values for 1998 being 5.04-7.04. For all the streams, the average pH in 1998 was grea ter than that during 1971-73. Statistical analysis was carried out, using t he 1970s data to estimate the magnitude of inter-annual variation, and taki ng discharge into account on the basis of antecedent rainfall. The results showed that for two of the streams the pH increase was significant at the 2 .5% level, while for a further three it was significant at the 10% level. C omparison of the 1998 concentrations of nitrate and non-marine sulphate wit h data obtained for five streams in 1973-74 showed that average nitrate con centration had increased from 11 to 20 mu eq dm(-3) while that of non-marin e sulphate had decreased from 94 to 50 mu eq dm(-3). For four of the stream s, comparisons were also made between the 1998 data and those for 1986. In three cases, pH in 1998 was generally higher, and Al generally lower, than the values for 1986, but in the fourth case little difference was evident. The present results support observations for five nearby standing waters, s trengthening the evidence for a general reversal of acidification in the so uthwest part of Lake District, due to a decline in the deposition of pollut ant sulphur. (C) 2000 Elsevier Science Ltd. All rights reserved.