黑料吃瓜网

Recent studies have shown that mercury (Hg) levels in many fish from remote lakes exceed the recommended guidelines for human consumption. Most of these studies conclude that the source of contamination lies in the atmosphere. Kejimkujik National Park (KNP), Nova Scotia, is considered to be a pristine ecosystem in which fish and loon Hg levels are anomalously high. Studies in the park have shown that atmospheric Hg concentrations may not be high enough to account for the Hg levels in the biota, indicating that the park may be an unusual system in terms of Hg distribution and migration.

A variety of new Hg data sets produced in the park over the last 5-10 years were integrated into a GIS database, using watersheds as the common parameter, to establish new relationships and correlations. In addition, the levels of Hg found in natural geological environments (i.e. bedrock and shear zones), and the potential for this Hg to be released to the environment were investigated.

The results indicate that

1. wetlands are an excellent source of Hg to downstream lakes,
2. relatively high levels of Hg are associated with watersheds underlain by biotite-rich granite,
3. the breakdown of biotite releases Hg to the environment, and
4. Hg vapor is also being released from structural features in the park (i.e. the TSZ and GHT).

Taken together, these results suggest that there are geological sources of Hg in the park that are affecting the Hg geochemical budget in the Kejimkujik system. However, since Hg has to be methylated for it to enter the food chain, for Hg to build up in a watershed and in the biota, there needs to be

1. a trapping mechanism that will keep Hg in the watershed (e.g. wetlands) and
2. conditions that favor the formation of methylmercury (e.g. high organics). In KNP, watersheds that are underlain by biotite-rich granite and have moderate to high percentages of wetlands tend to have higher Hg levels in their lakes and biota.

This study has applications for the evaluation of geological contributions to Hg contamination studies in the aquatic systems of moderate climates. Any watershed that is underlain by biotite-rich granite and has a high percentage of wetlands might be an area of anomalous Hg levels.

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Pages: 277
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