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Landscape hydrogeochemistry of Fe, Mn, S and trace elements (As, Co, Pb) in a boreal stream network
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
Responsible organisation
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 [en]
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: urn:nbn:se:su:diva-8130ISBN: 978-91-7155-694-3 (print)OAI: oai:DiVA.org:su-8130DiVA: diva2:199629
Public defence
2008-09-12, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 13:00
Opponent
Supervisors
Available from: 2008-08-27 Created: 2008-08-27 Last updated: 2017-12-01Bibliographically approved
List of papers
1. Hydrogeochemistry of Fe and Mn in small boreal streams: The role of seasonality, landscape type and scale
Open this publication in new window or tab >>Hydrogeochemistry of Fe and Mn in small boreal streams: The role of seasonality, landscape type and scale
2008 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, Vol. 72, no 12, 2789-2804 p.Article in journal (Refereed) Published
Abstract [en]

Stream water from a stream network of 15 small boreal catchments (0.03–67 km2) in northern Sweden was analyzed for unfiltered (total) and filtered (<0.4 μm) concentrations of iron (Fetot and Fe<0.4) and manganese (Mntot and Mn<0.4). The purpose was to investigate the temporal and spatial dynamics of Fe, Mn and dissolved organic carbon (DOC) as influenced by snow melt driven spring floods and landscape properties, in particular the proportion of wetland area. During spring flood, concentrations of Fetot, Fe<0.4, Mntot, Mn<0.4 and DOC increased in streams with forested catchments (<2% wetland area). In catchments with high coverage of wetlands (>30% wetland area) the opposite behavior was observed. The hydrogeochemistry of Fe was highly dependent on wetlands as shown by the strong positive correlation of the Fetot/Altot ratio with wetland coverage (r2 = 0.89, p < 0.001). Furthermore, PCA analysis showed that at base flow Fetot and Fe<0.4 were positively associated with wetlands and DOC, whereas they were not associated during peak flow at spring flood. The temporal variation of Fe was likely related to varying hydrological pathways. At peak discharge Fetot was associated with variables like silt coverage, which highlights the importance of particulates during high discharge events. For Mn there was no significant correlation with wetlands, instead, PCA analysis showed that during spring flood Mn was apparently more dependent on the supply of minerogenic particulates from silt deposits on the stream banks of some of the streams. The influence of minerogenic particulates on the concentration of, in particular, Mn was greatest in the larger, lower gradient streams, characterized by silt deposits in the near-stream zone. In the small forested streams underlain by till, DOC was of greater importance for the observed concentrations, as indicated by the positive correlation of both Fetot and Fe<0.4 with DOC (r2 = 0.77 and r2 = 0.76, p < 0.001) at the smallest headwater forest site. In conclusion, wetland area and DOC were important for Fe concentrations in this boreal stream network, whereas silt deposits strongly influenced Mn concentrations. This study highlights the importance of studying stream water chemistry from a landscape perspective in order to address future environmental issues concerning mobility of Fe, Mn and associated trace metals.

National Category
Geology
Identifiers
urn:nbn:se:su:diva-25378 (URN)10.1016/j.gca.2008.03.024 (DOI)000256674800005 ()
Note
Part of urn:nbn:se:su:diva-8130Available from: 2008-08-27 Created: 2008-08-27 Last updated: 2012-03-01Bibliographically approved
2. Landscape control on the hydrogeochemistry of As, Co and Pb in a boreal stream network
Open this publication in new window or tab >>Landscape control on the hydrogeochemistry of As, Co and Pb in a boreal stream network
Show others...
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.

Keyword
Metal geochemistry, Geochemical modelling, Visual MINTEQ, Speciation, DOC, Iron
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-145841 (URN)10.1016/j.gca.2016.08.030 (DOI)000405786800012 ()
Available from: 2017-08-24 Created: 2017-08-24 Last updated: 2017-08-24Bibliographically approved
3. Unravelling the origin of stream water DOM using δ34S-DOM
Open this publication in new window or tab >>Unravelling the origin of stream water DOM using δ34S-DOM
(English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851Article in journal (Refereed) Submitted
National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-25380 (URN)
Available from: 2008-08-27 Created: 2008-08-27 Last updated: 2017-12-13Bibliographically approved
4. Anthropogenic S-still important for sulphur dynamics in small boreal streams
Open this publication in new window or tab >>Anthropogenic S-still important for sulphur dynamics in small boreal streams
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In: Geochimica et Cosmochimica Acta, ISSN 0016-7037Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:su:diva-25381 (URN)
Note
Part of urn:nbn:se:su:diva-8130Available from: 2008-08-27 Created: 2008-08-27Bibliographically approved

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