Session Title :

Clear cutting, swidden and sustainable forestry: watershed-scale impacts on mercury dynamics

Description :

Mercury in fish remains both a major environmental problem and a scientific puzzle. Research from the boreal-nemoral zone, as well as the tropics, indicates a strong connection between forestry operations and the input of mercury/methylmercury to aquatic ecosystems. As more studies have been completed, however, large differences are appearing in the magnitude of the Hg response to forest operations (harvest, site preparation, drainage, drain-blocking) with respect to leakage and bioaccumulation of methylmercury. This presentation will synthesize results from a dozen recently completed and on-going studies in Finland, Sweden, Norway, Canada and the Amazon. Both intensive catchment-scale studies and larger, synoptic surveys are included. In some cases mercury concentrations in waters and the biota were largely unchanged, while in other cases, manifold increases persisting for up to a decade have been observed. Understanding why there are differences in catchment sensitivity can improve management strategies to mitigate the contribution of forest operations to the mercury problem in freshwater fish. Alternative hypotheses will be considered, including the possibility that it is the increases in water tables associated with forest harvest that inundate previously oxic soils explains some of the more extreme harvest effects on methylmercury.

Objective :

It is hoped that understanding why there are differences in catchment sensitivity can improve management strategies to mitigate the contribution of forest operations to the mercury problem in freshwater fish. This session will present the latest developments in the understanding of the relationship between forestry and the mercury problem from some of the world’s leading mercury researchers

The goals of the session will be to :

1) Quantify the importance of forestry for the mercury problem
2) Clarify the varying sensitivity of different catchments to harvest impacts,as well interactions with climate change
3) Evaluating Countermeasures

Importance to conferees :

Forestry is an important livelihood in many regions where populations are exposed to harmful levels of mercury through freshwater fish. From the initial recognition that forestry was a major factor in exacerbating the mercury problem some 15 years ago, major research efforts have focused on understand the connection of mercury to forestry in order to help break that connection – if possible. . A special session that takes stock of this rapidly developing field has both practical significance for management as well as an occasion to advance the understanding of the biogeochemical processes that influence mercury cycling in ecosystems.