Monitoring acid waters in the U.K.: an overview of the U.K. Acid Waters Monitoring Network and summary of the first interpretative exercise

1. The U.K. Acid Waters Monitoring Network (AWMN) was established in 1988. It comprises eleven lake and eleven stream sites located throughout the U.K. in areas sensitive to acidification. The principal objective of the AWMN is to provide a long-term, high-quality chemical, biological and palaeolimnological record which, in conjunction with the U.K. precipitation monitoring networks, will facilitate the assessment of trends within U.K. surface waters.
2. The first interpretation of results generated by the AWMN (April 1988–March 1993) has recently been completed and is summarized. During this period there have been no sustained changes in atmospheric deposition in the U.K. Trends are recognized in certain chemical and/or biological parameters at individual AWMN sites, but despite some (regional) patterns no regional trends toward increasing or decreasing acidification are apparent. The data comprise an excellent baseline with which future changes may be compared.
3. The methodology of the AWMN is reviewed and some amendments are suggested in the light of the first 5 years experience. These include: additional determinations for nitrogen species and total phosphorus; changes to the frequency of macrophyte and palaeolimnological sampling; new emphasis on data generated by sediment traps at lake sites; and the addition of extra sites to address better the full extent of acid-sensitive surface waters revealed by the national critical loads mapping programme, and to pay particular attention to the acidifying role of nitrogen.
4. The contribution of AWMN data to other national and international environmental monitoring programmes is highlighted. In addition, AWMN sites provide data to develop and validate critical loads models and dynamic models of acidification, and could also be used to monitor the impact of other air pollutants such as trace metals and persistent organic compounds on the freshwater environment.