Forestry Influence by Stump Harvest and Site Preparation on Methylmercury, Total Mercury and Other Stream Water Chemistry Parameters Across a Boreal Landscape

• Published in: Ecosystems (New York) 2012-12, Vol.15 (8), p.1308-1320
• Main Authors: Eklöf, Karin, Kraus, Andrea, Weyhenmeyer, Gesa A., Meili, Markus, Bishop, Kevin
• Format: Article
• Language: English
• Subjects: Biomedical and Life Sciences; Boreal forests; Catchments; Creeks & streams; Earth Science with specialization in Environmental Analysis; Ecology; Environmental impact; Environmental Management; Environmental Sciences; Forest management; Forest Science; Forest soils; Forestry; Forests; Forests and forestry; Geoecology/Natural Processes; Geovetenskap med inriktning mot miljöanalys; Hydrology/Water Resources; Life Sciences; Mercury; Methylation; Methylmercury; Miljövetenskap; Organic carbon; Organic matter; Plant Sciences; Runoff; Skogsvetenskap; Soil pollution; Soil water; spatial variation; Streams; stump; Surface water; Timber industry; Water chemistry; Water pollution; Watersheds; Zoology
• ISSN: 1432-9840; 1435-0629; 1435-0629
• DOI: 10.1007/s10021-012-9586-3

Forestry has been reported to cause elevated mercury (Hg) concentrations in runoff water. However, the degree to which forestry operations influence Hg in runoff varies among sites. A synoptic study, covering 54 catchments distributed all over Sweden, subjected to either stump harvest (SH), site preparation (SP) or no treatment (Ref), was undertaken to reveal the degree of forestry impact and causes of eventual variation. All streams were sampled twice, in autumn 2009 and summer 2010. There were no significant differences in total mercury (THg) and methylmercury (MeHg) concentrations between the three treatments in either 2009 or 2010. However, when pooling the treated catchments (that is, SH and SP) and taking catchment properties such as latitude into account, the treatment had a significant influence on the THg and MeHg concentrations. Although the treatment effect on THg and MeHg did not differ between SH and SP, the study did reveal significant forestry effects on potassium (K) and total nitrogen (TN) that were greater in the SH catchments and lower in the SP catchments. Partial least square (PLS) regressions indicated that organic matter was the most important variable influencing both the THg and MeHg concentrations. There were no significant differences between the treatment groups when comparing the ratios of THg/total organic carbon (TOC) and MeHg/TOC, suggesting that the high concentrations of THg and MeHg observed at some of the treated catchments are associated with increased concentrations of TOC rather than new methylation or increased mobilization caused by factors other than TOC.