RESEARCH - PHASE III
To examine patterns of Hg deposition, transport, fate and bioavailability across the Adirondacks, we will conduct a regional phase of this study. In the early 1990s, we analyzed patterns of water column Hg species and Hg concentrations in yellow perch from 26 lake/watersheds in the Adirondacks. As part of this study, we plan to resurvey these lakes to evaluate if changes in lake concentrations of Hg species or fish Hg have occurred in response to changes in atmospheric Hg deposition of acidic deposition. To help interpret changes in fish Hg patterns we will also measure zooplankton Hg and MeHg as part of this survey.
Based on the results of the resurvey we will select six of the surveyed watersheds for additional study and model application. We will select these lake-watersheds based their lake classification of hydrologic flowpaths, and changes in water column and fish Hg and acid-base chemistry. Nominally we will select perched seepage lakes, drainage lakes with shallow deposits of glacial till in the watershed and drainage lakes with thick deposits of glacial till in the watershed. Given the importance of wetlands in the transport of Hg and the supply of MeHg to downstream lakes ecosystems, we will also select watersheds with small and large wetland areas, particularly focusing on riparian wetlands.
Overstory forest vegetation (i.e., deciduous vs. conifer), the presence of riparian wetlands and the flowpaths water follows enroute to entering surface waters play a major role in determining MeHg concentrations in fish and surface waters. Given the importance of these factors, it is essential to accurately map the watersheds of the selected sites. Data layers currently exist of forest vegetation composition and wetlands for the Adirondacks based on remotely sensed images. Hydrologic flowpaths will be established by field observations, analysis of topographic maps and areal photographs, and the application of digital elevation models.
Following watershed mapping, we plan to collect extensive information
on Hg deposition, soil Hg pools, Hg species in wetland porewaters and
Hg species in lakewater and aquatic biota at these six sites. The MCM:HD
model will be applied to each of the six watersheds in order to compare
patterns of Hg deposition and cycling across the Adirondacks, and to evaluate
our understanding of the transport, fate and bioavailability of Hg in
forest and aquatic ecosystems as depicted in the model.
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