PARENT SESSION
Tuesday, August 8, 1:30-5:00 pm
COS 43 - Aquatic ecology III: lake ecosystems
Mississippi, Mezzanine Level, Cook Convention Center
Presiders: O Sarnelle

Sulfate dynamics in Mirror Lake: a 30-year mass balance.

Bade, Darren^*,1, Likens, Gene¹, ¹ Institute of Ecosystem Studies, Millbrook, NY

ABSTRACT- Since 1970, surface concentrations and water-column mass of sulfate have declined by greater than 30% in Mirror Lake (NH, USA). Many other studies have shown recovery of lakes from acid deposition indicated by decreasing sulfate concentrations. Mechanisms that could lead to decreased sulfate concentration include decreased deposition onto the lake surface, decreased watershed loading, or increased sediment burial. Rarely are lakes examined in detail to determine which of these mechanisms most contributes to the recovery. In Mirror Lake, we used mass balance to estimate sulfate sediment burial for 30 years (1971-2000). The largest component of the sulfate budget, loading from the watershed, has not declined substantially over the study period. Over the 30 year period, sulfate burial has declined. Seasonally, sulfate burial ranges from net positive (loss from the lake) during the summer to net negative during the winter. Annually, there is generally net burial, in agreement with previous sediment record estimates. Sulfate concentrations are declining in ML because inputs are slightly less than combined outflow and burial. However the rate of decline in sedimentation is greater than the rate of decline in inputs less outputs. If this continues, sulfate may again begin to accumulate in Mirror Lake.

Key words: freshwater lake, sulfate dynamics, acid rain