Monitoring Acid Waters in the UK: 1988–1998 Trends

Since 1988, a network of lakes and streams has been monitored in areas of the UK sensitive to surface water acidification. Analysis of 10 years data has focused on the identification and quantification of time-trends in chemical parameters, to establish whether declines in emission of acidifying pollutants have resulted in recovery of acidified surface waters. A national decline in S deposition in the UK since 1988 has not generally been accompanied by a significant improvement in freshwater chemistry. At the three sites where xSO₄ concentrations have declined, NO₃ has increased and there has been no increase in pH or alkalinity. Upward trends in pH and alkalinity observed at several other sites are not associated with downward trends in acidic anions. Temporal variation in xSO₄, NO₃, acidity, DOC and other important meaures of surface water quality can all be linked to decadal-scale variation in climate, and this has important implications for the detection of recovery-related trends.