CHANGING BIOGEOCHEMICAL RELATIONSHIPS IN MAINE HIGH ELEVATION LAKES AND WATERSHEDS AS PART OF RECOVERY FROM ACID RAIN

The Maine High Elevation Lake Monitoring (HELM) project was designed to sample the population of Maine lakes expected to be the most vulnerable to the affects of acidic deposition. All 90 Maine lakes greater than 600 m elevation, larger than 0.4 ha, and greater than 1 m deep have been sampled periodically for the past 20 years. The high elevation lakes are more acidic on average than the general population of Maine lakes because they receive more precipitation, the precipitation is more acidic, the watersheds supply more natural organic acids, and the watersheds are less able to neutralize acidic inputs because of steep slopes, shallow soils, and resistant bedrock. Many of the high elevation lakes of Maine historically had low ANC and some were even acidic in pre-industrial times. Thus, ‘recovery' for most of the high elevation lakes of Maine will be modest under any scenario of reduced acidic deposition, consistent with recent assessments of the extent and target for ‘recovery' of surface waters in the region. Given the remote nature of these lakes and therefore the relative lack of land use disturbance, this population of lakes is among the best suited in the northeast for tracking recovery from acidic deposition.