| Precambrian Shield lakes are acid-sensitive and have a history of acidification from sulphate emissions. To determine whether these lakes have shown a positive response to reduced emission levels, water chemistry and benthic macroinvertebrate community data were analyzed for 17 lakes that were sampled from 1988 to the present. These lakes displayed long-term trends consistent with recovery from acidification, including increasing pH and alkalinity, and a shift in community dominance from Chironomidae to Ephemeroptera. There was strong coherence evident in the variation patterns of both chemical and biological variables in the study lakes, indicating the presence of an external influence on the system. This synchrony may have been a result of climatic signals, particularly El Nino cycles, which have been shown to cause re-acidification events in these lakes. Climate effects may have increased community variability in concordance with El Nino cycles, but this relationship requires further investigation. |
