South Sweden, Baltic Sea region

BIOGEOCHEMICAL CASE STUDIES 5.1. South Sweden, Baltic Sea region 

Much of the Hgt pool was found in the upper part of the soil, which is rich in organic matter. This pattern is likely due to an elevated atmospheric deposition of Hgt over the extended period and immobilization of mercury by organic functional groups and accumulation of organic matter as part of the soil-forming process. The retention of mercury in the mor humus layer was almost complete due to the very strong association between Hgt and humic substances. 

The runoff export was about 0.03 g/ha of Hgt per year. This value lies within the range of 0.008 to 0.059 g Hg/ha/yr, derived from a number of catchment studies in Sweden. The output of methylmercury from catchment area was 0.0015 g/ha/yr of Hg. This is substantially lower than the input to the catchment. There appears to be an ongoing net accumulation of Hgm in the terrestrial ecosystems, similar to the pattern previously shown for the total mercury. 

Driscoll et al. (1994) have studied the mercury species relationships among water, sediments, and fish (yellow perch) in a series of Adirondack lakes in New York state, USA. In most lakes, approximately 10% of the total mercury loading was in the form of C2HsHg+. Mercury concentrations increased as pH fell, but the best correlation was found between [dissolved Al] and [dissolved Hg] suggesting that the same factors are responsible for mobilizing both these metals. Methylmercury concentrations correlated strongly with the dissolved organic carbon content in the water. Fish muscle tissue was analyzed for mercury and showed an increase with age. However, the study was unable to resolve the question of whether the principal source of mercury to these lakes was atmospheric deposition or dissolution from bedrock due to acid rains. 

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