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A whole-lake basin analysis of the spatial distribution of total- and methylmercury in relation to the sediment matrix using WD-XRF and FT-IRS
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (CIRC)
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The aim of this study was to try and identify some of the factors controlling the spatial distributions of total- and methyl-Hg across a single whole-lake basin. In order to achieve this we analyzed the geochemical composition of 83 surface sediment samples from the lake Stor-Strömsjön using WD-XRF and FT-IRS. Our results show that in the north-western basin (i.e., the main recipient of the dominant inlet) total-Hg distribution is controlled by fine-grained mineral matter, while the eastern basin (which lacks major inlets) the main controlling factor is organic matter. There is only a weak correlations between methyl-Hg concentrations and either total-Hg (r2=0.12) or organic matter (r2=0.15) concentrations. Instead the distribution of methyl-Hg is largely controlled by water depth and sulfur (59 %). The spatial patterns for total-Hg concentrations vs. inventories (mass per unit area) are rather different. Even if total-Hg concentrations are about the same in locations controlled by organic matter and fine-grained mineral matter, the total-Hg inventories are much higher in the latter. For methyl-Hg the spatial distribution is patchy both for concentrations and inventories, and the highest methyl-Hg inventory was found in a shallow location with coarse-grained minerogenic sediment. The large variations in the controlling factors, even within a single whole-lake basin, suggest that lake type and surrounding catchment have an effect on the behavior of Hg. This needs to be recognized both when studying Hg loading on ecosystems, and when using lake sediments to reconstruct atmospheric Hg deposition.

Keyword [en]
Mercury, Methylmercury, Lake sediment, Spatial distribution, Sediment composition, WD-XRF, FT-IRS
National Category
Environmental Sciences
Research subject
biology, Environmental Science
Identifiers
URN: urn:nbn:se:umu:diva-38423OAI: oai:DiVA.org:umu-38423DiVA: diva2:377693
Available from: 2010-12-14 Created: 2010-12-14 Last updated: 2010-12-21Bibliographically approved
In thesis
1. Studies of an elusive element: processes that influence the net retention of mercury in lake sediments and peatlands
Open this publication in new window or tab >>Studies of an elusive element: processes that influence the net retention of mercury in lake sediments and peatlands
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Because of its toxic nature mercury is a threat to both wildlife and human health, and thus, it is an element of concern in the environment. Currently much of the mercury emitted to the atmosphere is derived from anthropogenic sources – both direct emissions and re-emission of already deposited anthropogenic mercury. Following deposition mercury is affected by a long array of processes, and this thesis has focused on trying to increase our knowledge on the net retention of mercury in lake sediments and peatlands. This information is vital in order to understand how mercury behaves in the environment and where mercury is at risk of becoming a problem. Knowledge about the retention of mercury is also important when using lake sediments and peat records as environmental archives over past mercury deposition.

By using varved, annually laminated, sediments I have determined that lake sediments are reliable archives for inorganic mercury, but not for methylmercury. A study of the spatial distribution of mercury in a whole-lake basin shows that inorganic- and methylmercury are controlled by different sediment properties. Inorganic mercury is controlled by combination of fine-grained mineral matter and organic matter concentrations, whereas methylmercury is controlled by water depth and sulfur concentration. This study also shows that especially methylmercury have a very heterogeneous spatial distribution across the lake basin, something that might be of large importance when using lake sediments to calculate whole-lake burdens of mercury. In a study regarding the effects of vegetation on the net retention of mercury in a peatland I showed that there are considerable differences in both plant- and peat-mercury concentrations depending on vegetation type. This might have implications for the use of peat records as archives over atmospheric mercury deposition. Finally I have used a combination of a peat and a lake sediment record to study how past and recent climatic changes affects the stability of a peatland currently underlain by permafrost. Here we are able to show that destabilization of peatlands, as a result of permafrost melt, can cause a significant release of organically bound mercury from the mire to the surrounding aquatic environment. Considering the currently warming climate there is a risk of sub-arctic peatlands turning into mercury sources, which might be important to recognize when assessing current mercury pollution pathways.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2010. 20 p.
Keyword
Mercury, retention, lake sediments, peatlands, environmental archives, sedimentation, diagenesis, vegetation, permafrost
Research subject
biology, Environmental Science
Identifiers
urn:nbn:se:umu:diva-38424 (URN)978-91-7459-113-2 (ISBN)
Public defence
2011-01-14, KBC-huset, KB3A9 (lilla hörsalen), Umeå universitet, Umeå, 10:00 (English)
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Supervisors
Available from: 2010-12-21 Created: 2010-12-14 Last updated: 2010-12-21Bibliographically approved

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