Metla Project 3412

Effects of harvesting drained peatland forests on the leaching of mercury and other heavy metals to surface waters

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Duration: 2005-2006   Keywords: Blackshield, final felling, forest harvesting, leaching, methyl mercury, peatland
Research project group: Distinct projects 1 - Structure and function of forest ecosystems

Objectives

While mercury (Hg) deposition in Finland has decreased over the last decade, Hg concentrations in fish have increased, posing a human health threat. The Hg in fish is assumed to come from natural (soil and bedrock) and deposition Hg sources and released as a result of disturbance associated with forest management practices such as harvesting. High MeHg concentrations in water leaching from harvested sites have been shown. Particularly high Hg concentrations in leaching waters from peatland catchments have been observed, indicating greater methylation of Hg occurs in peatlands. There are 4,5 million ha of drained peatland forests in Finland, and much of it will be harvested after 10 to 30 years. The objective of this study is to investigate whether the harvesting of drained peatland forests can lead to the release of Hg and MeHg from peat and result in increased leaching to surface waters. Sites with high geochemical sources of Hg (black shale) will be compared with adjacent sites where deposition is the main source of Hg.

Results

Suitable catchment areas have been identified to the project. We have carried out preliminary sampling and analysis of ditch water and peat cores, including total Hg and MeHg; and tested the analytical method for determining Hg in water. Preliminary results showed that there is a difference in ditch water concentrations between peatlands underlain by black shale and granitic bedrock. Especially Cd, Cu, Ni and SO4- concentrations were higher in ditch water underlained by black shale (Cd 0.4 µg L-1, Cu 3.66 µg L-1, Ni 9.57 µg L-1 and SO4 8.29 mg L-1), compared to ditch water underlained by granitic bedrock (Cd 0.08 µg L-1, Cu 1.68 µg L-1, Ni 4.32 µg L-1 and SO4 1.85 mg L-1). Instead there was not notable difference in total Hg or MeHg concentrations in ditch water between peatlands underlined by different bedrocks. Results from peat cores showed Hg concentration was slightly higher in peatland underlined by black shale.

Project will continue under BIO program (347702 Stem only vs. whole-tree harvesting - the effects of harvesting in forested peatlands on the leaching of nutrients and heavy metals)

Project leader: Ukonmaanaho, Liisa
The Finnish Forest Research Institute, Vantaa Unit, PL 18, FI-01301 VANTAA, FINLAND
Phone: +358 29 532 5115
E-mail: liisa.ukonmaanaho@metla.fi

Other researchers: Lindroos, Antti-Jussi, VA (2007), Nieminen, Tiina, VA (2005-07), Piispanen, Juha, MU (2005)


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Updated 12.06.2012
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