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Landscape control on the hydrogeochemistry of As, Co and Pb in a boreal stream network
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
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Number of Authors: 5
2017 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 211, 194-213 p.Article in journal (Refereed) Published
Abstract [en]

In a boreal stream network, stream water concentrations of As, Co and Pb (filtered, <0.4 lm) of 10 nested streams were studied during two consecutive years in order to evaluate the influence of land cover on the temporal and spatial variability of metal concentrations and speciation. Mean concentrations of Co and Pb showed significant but contrasting relationship to landscape type, while As concentrations were not related to landscape type. Highest concentrations of Pb were found in the wetland dominated streams (>30% wetland), which was suggested to be controlled by atmospheric deposition in combination with high DOC release from the wetlands. For Co, the highest concentrations were found in the forest dominated sites (>98% forest), which were attributed to the weathering of minerogenic sources. Contrasting response to runoff events could also be related to landscape type; during the spring flood, decreasing concentrations of As, Co and Pb were observed in the wetland dominated catchments due to dilution, while increasing concentrations during spring flood were observed in the mixed catchments (2-30% wetland) and to some degree in the forested catchments, probably due to flushing of the organic-rich riparian sources. Further, metal speciation was calculated using the geochemical equilibrium model Visual MIN-TEQ. This suggests that dissolved inorganic species of As and Co dominated in headwater streams with low pH while DOC had a major influencing role for Pb. In the larger mixed streams where pH was higher and precipitation of e.g. colloidal Fe and Mn (hydr) oxides was favoured, the major influencing factor was instead adsorption to colloidal Fe for As and Pb, while association to organic matter and colloids of e.g. Mn influenced the concentrations of Co. We thus conclude that landscape type and the magnitude of the runoff events are of great importance for the spatial and temporal variations of As, Co and Pb in this boreal stream network. Projected climate change, with increasing runoff, may therefore influence riverine concentrations and fluxes differently, depending on the prevailing landscape type.

Place, publisher, year, edition, pages
2017. Vol. 211, 194-213 p.
Keyword [en]
Metal geochemistry, Geochemical modelling, Visual MINTEQ, Speciation, DOC, Iron
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
URN: urn:nbn:se:su:diva-145841DOI: 10.1016/j.gca.2016.08.030ISI: 000405786800012OAI: oai:DiVA.org:su-145841DiVA: diva2:1135838
Available from: 2017-08-24 Created: 2017-08-24 Last updated: 2017-08-24Bibliographically approved
In thesis
1. Landscape hydrogeochemistry of Fe, Mn, S and trace elements (As, Co, Pb) in a boreal stream network
Open this publication in new window or tab >>Landscape hydrogeochemistry of Fe, Mn, S and trace elements (As, Co, Pb) in a boreal stream network
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The transport of elements by streams from headwater regions to the sea is influenced by landscape characteristics. This thesis focuses on the influence of landscape characteristics (e.g. proportion of wetland/forest coverage) on temporal and spatial variations of Fe, Mn, S and trace elements (As, Co, Pb) in streams located in northern Sweden, a boreal region characterized by coniferous forests and peat wetlands.

Water samples from a network of 15 streams revealed a different hydrogeochemistry in forested catchments compared to wetland catchments. The temporal variation was dominated by spring flood, when concentrations of Fe, Mn and trace elements increased in forested headwaters. However, in streams of wetland catchments concentrations decreased, but Pb concentrations were higher in comparison to other streams. Both Fe and Pb showed positive correlations with wetland area, while Co correlated with forest coverage. The anthropogenic contribution of As and Pb appear to be larger than the supply from natural sources.

During spring flood SO42- decreased in most streams, although concentrations increased in streams of wetland catchments. Concentrations of SO42- were higher in streams of forested catchments than in wetland dominated streams, the former being net exporters of S and the latter net accumulators. Isotope values of stream water SO42-34SSO4) were close to that of precipitation during spring flood, indicating that the major source of S is from deposition. The results show that, although emissions of anthropogenic S have been reduced, there is still a strong influence of past and current S deposition on runoff in this region.

In conclusion, wetlands are key areas for the hydrogeochemistry in this boreal landscape. The findings emphasize the importance of understanding stream water chemistry and element cycling from a landscape perspective. This may be important for predicting how boreal regions respond to environmental disturbances such as climate change.

Place, publisher, year, edition, pages
Stockholm: Institutionen för geologi och geokemi, 2008. 30 p.
Series
Meddelanden från Stockholms universitets institution för geologi och geokemi, ISSN 1101-1599 ; 332
Keyword
landscape hydrogeochemistry, boreal streams, spring flood, Fe, Mn, S, As, Co, Pb, sulphur isotopes, sulphate, organic S, DOC, spatial variability, temporal variability, wetlands
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-8130 (URN)978-91-7155-694-3 (ISBN)
Public defence
2008-09-12, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 13:00
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Supervisors
Available from: 2008-08-27 Created: 2008-08-27 Last updated: 2017-08-24Bibliographically approved

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