Responses of Maine surface waters to the Clean Air Act Amendments of 1990

Kahl, Steve

From Abstract: 'Sulfate concentrations in sensitive Maine lakes have declined by 12 to 22% since 1982, in part due to the 1995 implementation of Phase I controls of the Clean Air Act Amendments and in part to other long-term pollution reduction efforts. The expectation for these reductions in sulfate was a parallel reduction in lake acidity. However, the slight trend toward decreased lake acidity seen in the 1980s has slowed or reversed in the 1990s. Only in the seepage lakes is there evidence of a decrease in acidity, but the recent data for this lake group (collected only in 1998) are too limited to draw firm conclusions about possible trends or mechanisms. The reason for the widespread lack of recovery is the simultaneous decline in base cation concentrations (e.g. calcium, magnesium) which are important for reduction in acidity. This response is similar to that observed over the entire northeastern US. There is no scientific consensus on why base cations have declined so fast, but the explanation is related to several interacting factors: continued high atmospheric deposition of nitrogen, a lag time in response, or the inter-related influence of climate and acidic depositionon watershed response. Continued monitoring of sensitive aquatic systems is required to address these uncertanties.' /STUDY LOCATIONS:/ /ACADIA NATIONAL PARK/