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Modelling nutrient fluxes from sub-arctic basin: Comparison of pristine vs. dammed rivers
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
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2008 (English)In: Journal of Marine Systems, ISSN 0924-7963, Vol. 73, no 3-4, 236-249 p.Article in journal (Refereed) Published
Abstract [en]

The deterministic Riverstrahler model of river functioning is applied for the first time to sub-arctic catchments. Seasonal nutrient (N, P, Si) deliveries to the coastal zone are simulated, and nutrient annual fluxes are established for the nearly pristine river Kalix (hereafter called Kalixälven) and the heavily dammed river Lule, (hereafter called Luleälven) both located in Northern Sweden and draining into the Bothnian Bay, Baltic Sea.

For Kalixälven simulations are performed with a runoff calculated from precipitation, evapo-transpiration and temperature data for the period 1990–1999, using a hydrological model calibrated on observed monthly discharges at the river outlet. The same hydrological parameters are used to calculate specific runoff for the Luleälven basin in absence of dam regulation. Reservoir filling and emptying are simulated using a simplified representation of their management rules. Diffuse sources of nutrient are evaluated according to land cover of the catchment. The simulated seasonal trends are within the range of the observed data, in particular for discharge, dissolved silica, total phosphorus, inorganic nitrogen and total organic carbon. Specific runoff is 50% higher in the Luleälven than in the Kalixälven watershed due to higher altitudes and precipitations. Average silica, nitrate and phosphorus concentrations are much lower in Luleälven than in Kalixälven. Comparison of model results for the Luleälven with and without dams shows a reduction of respectively 25% and 30% in silica and phosphorus fluxes delivered at the outlet, while nitrogen delivery is increased by 10% in the dammed vs. undammed river system. The model allows assessing the respective role of reservoir trapping of nutrient in the reservoir through algal uptake and sedimentation, and of changes in the vegetation induced by flooding the valley formerly covered by forests and wetlands.

Place, publisher, year, edition, pages
Elsevier B.V , 2008. Vol. 73, no 3-4, 236-249 p.
Keyword [en]
Nutrients; River modelling; Damming; Arctic pristine rivers; Kalixälven; Luleälven
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:su:diva-24973DOI: 10.1016/j.jmarsys.2007.10.012ISI: 000260563300003OAI: diva2:198606
Part of urn:nbn:se:su:diva-7560Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2010-12-22Bibliographically approved
In thesis
1. Linking landscape variables, hydrology and weathering regime in Taiga and Tundra ecoregions of Northern Sweden
Open this publication in new window or tab >>Linking landscape variables, hydrology and weathering regime in Taiga and Tundra ecoregions of Northern Sweden
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

High-latitude watersheds have been regarded as a carbon sink with soil carbon accumulating at low temperature. This sink is now believed to turn into a source, acting as positive feedback to climate warming. However, thawing permafrost soils would allow more water to percolate down to deeper soil layers where some of the carbon could be “consumed” in weathering and exported as bicarbonate to the sea. Using a hydrological mixing model showed that this could counterbalance the predicted positive feedback resulting from thawing soils.

Vegetation-covered riparian zones in headwater areas appear to have a significant role for the dissolved constituent fluxes. Higher concentrations of weathering products are found in taiga and tundra rivers with larger areas of forest and peat cover in the watershed. These landscape elements can thus be regarded as “hot spots” of river loading with dissolved constituents.

Comparing a regulated and an unregulated river tested the hypothesis that damming leads to a depletion of major elements also in oligotrophic river systems as a consequence of changes in landscape elements. A loss of upper soils and vegetation through inundation prevents the contact of surface waters with vegetated soil, and consequently reduces weathering fluxes. The hypothesis that the lower fluxes of dissolved silica (DSi) in the regulated river could also be explained by biological uptake was then tested using a model, and budget calculations indicate a significant reduction as a result of regulation. About 10% of this reduction can be attributed to the flooding of the fluvial corridor and the rest to diatom blooms in the reservoirs. A more detailed study of landscape elements for the headwaters of the river Luleälven showed that only 3% of the surface area has been inundated by reservoirs but ca. 37% of the deciduous forest. Such a significant loss of hot spots may indeed explain the observed lower DSi fluxes in the regulated watersheds of northern Sweden.

Place, publisher, year, edition, pages
Stockholm: Institutionen för tillämpad miljövetenskap (ITM), 2008. 31 p.
Taiga and tundra, high-latitude, carbon fluxes, weathering, hydrological alterations
National Category
Earth and Related Environmental Sciences
Research subject
Applied Environmental Science
urn:nbn:se:su:diva-7560 (URN)978-91-7155-652-3 (ISBN)
Public defence
2008-06-04, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 10:00
Available from: 2008-05-08 Created: 2008-05-08Bibliographically approved

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Smedberg, ErikHumborg, Christoph
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