• Shanley, James B.
  U.S.Geological Survey
  jshanley@usgs.gov
  

Like acid rain, mercury pollution enters the Northern Forest landscape via the atmosphere in rain, snow, and dry deposition. Mercury is a neurotoxin that affects wildlife and humans who eat a lot of fish, where mercury bioaccumulates and poses a risk to consumers. Most of the incoming mercury is retained in forest soils, but we conducted this study to better understand the magnitude, timing, and processes that lead to mercury leaving the forest headwaters in streamflow, toward its ultimate uptake by fish downstream. It takes many stream samples to observe mercury behavior, and each sample is expensive to analyze, so we sought a cheaper alternative. Our previous work demonstrated that stream mercury was transported in association with certain components of dissolved organic carbon (DOC), the breakdown product of decaying plant and animal matter. Our approach was to use an in-stream fluorometer, an optical sensor that measures fluorescing dissolved organic matter (FDOM), which represents the Ņreactive DOCÓthought to carry the mercury. We measured FDOM continuously at 15-minute intervals and conducted periodic sampling to test whether the FDOM was a valid proxy for mercury. We conducted the study at three established long-term research watersheds in the Northern Forest that spanned a range of DOC and mercury: Hubbard Brook, NH (low DOC); Sleepers River, VT (intermediate DOC); and Arbutus, NY (high DOC). Despite the inevitable glitches inherent in a novel application, we acquired mostly high- quality data for the one year of measurements, even during the harsh northern winter.