Littoral macroinvertebrates as indicators of lake acidification within the UK

1. The Water Framework Directive (WFD) requires the assessment of acidification in sensitive water bodies. Chemical and littoral macroinvertebrate samples were collected to assess acidification of clear and humic lakes in the UK. 2. Of three acid-sensitive metrics that were regressed against acid neutralizing capacity (ANC) and pH, highly significant responses were detected using the Lake Acidification Macroinvertebrate Metric (LAMM). This metric was used to assign high, good, moderate, poor and bad status classes, as required by the WFD. 3. In clear-water lakes, macroinvertebrate changes with increasing acidification did not indicate any discontinuities, so a chemical model was used to define boundaries. In humic lakes, biological data were able to indicate a distinct, good moderate boundary between classes. 4. Humic lakes had significantly lower pH than clear lakes in the same class, not only at the good moderate boundary where different methods were used to set boundaries, but also at the high good boundary, where the same chemical modelling was used for both lake types. These findings support the hypothesis that toxic effects are reduced on waters rich in dissolved organic carbon (DOC). 5. A typology is needed that splits humic and clear lakes to avoid naturally acidic lakes from being inappropriately labelled as acidified. 6. Validation using data from independent lakes demonstrated that the LAMM is transportable, with predicted environmental quality ratios (EQRs) derived from mean observed ANC, accurately reflecting the observed EQR and final status class. 7. Detecting and quantifying acidification is important for conservation, in the context of appropriate restoration, for example, by ensuring that naturally acid lakes are not treated as anthropogenically acidified. Copyright (C) 2009 John Wiley & Sons, Ltd and Crown Copyright 2009