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Evaluation of the Stockholm archipelago, northwestern Baltic Sea proper, as a trap for freshwater-runoff organic carbon
Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
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2005 (English)In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 56, no 1-2, 167-178 p.Article in journal (Refereed) Published
Abstract [en]

Time-series data on the freshwater inflow of total organic carbon (TOC) to the Stockholm Archipelago, Baltic Sea, covering four full years, showed a distinct seasonal pattern with six times higher monthly flow in winter–spring than in the summer with an annual freshwater TOC input of 28 Gg year−1. Estimation of burial flux and source apportionment of sedimentary OC in the Inner Archipelago (IA) was based on extensive sediment sampling of seismically surveyed accumulation bottom areas. The resulting IA-averaged OC content was 56±16 mg g dw−1 sediment, yielding an IA-wide bottom sediment deposition for the 1992–1995 period of 3.1 Gg year−1.

The sediments in the eastern Lake Mälaren (LM), IA, and Outer Archipelago (OA) were geochemically distinguishable based on their stable carbon isotope signatures (δ13C). The δ13C values were −28.2±0.6, −25.4±1.0, and −23.6±0.3, respectively, for LM (n=15), IA (n=17), and OA (n=31). These spatial trends were consistent with the C:N ratios, which were 9.96±1.2, 9.29±0.73, and 9.13±0.22 for the same subsystems. Using a simple isotopic mass balance model, it was deduced that about one-third (39%) of the OC burial in the IA sediments was of Lake Mälaren runoff origin.

Hence, a low archipelago-trapping efficiency of only 4% for the runoff TOC was found to be accumulating in the sediments underlying the approximately 30 km transect through the IA eastward of Stockholm. This scenario suggests that the organic matter and associated substances added by the Lake Mälaren outflow, passing through urban Stockholm, are largely either remineralised and released to the IA water column, or transported with the currents to more pristine offshore Baltic ecosystems.

Place, publisher, year, edition, pages
2005. Vol. 56, no 1-2, 167-178 p.
Keyword [en]
Urban estuary, Carbon burial, Stable carbon isotopes
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-22894DOI: 10.1016/j.jmarsys.2004.11.001OAI: oai:DiVA.org:su-22894DiVA: diva2:189695
Available from: 2004-04-27 Created: 2004-04-27 Last updated: 2017-12-13Bibliographically approved
In thesis
1. An evaluation of the distributions of polychlorinated biphenyls and organic matter in coastal sediments
Open this publication in new window or tab >>An evaluation of the distributions of polychlorinated biphenyls and organic matter in coastal sediments
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objective of this thesis is to improve the understanding of what processes and mechanism affects the distribution of polychlorinated biphenyls (PCBs) and organic carbon in coastal sediments. Because of the strong association of hydrophobic organic contaminants (HOCs) such as PCBs with organic matter in the aquatic environment, these two entities are naturally linked. The coastal environment is the most complex and dynamic part of the ocean when it comes to both cycling of organic matter and HOCs. This environment is characterised by the largest fluxes and most diverse sources of both entities. A wide array of methods was used to study these processes throughout this thesis. In the field sites in the Stockholm archipelago of the Baltic proper, bottom sediments and settling particulate matter were retrieved using sediment coring devices and sediment traps from morphometrically and seismically well-characterized locations. In the laboratory, the samples have been analysed for PCBs, stable carbon isotope ratios, carbon-nitrogen atom ratios as well as standard sediment properties. From the fieldwork in the Stockholm Archipelago and the following laboratory work it was concluded that the inner Stockholm archipelago has a low (≈ 4%) trapping efficiency for freshwater-derived organic carbon. The corollary is a large potential for long-range waterborne transport of OC and OC-associated nutrients and hydrophobic organic pollutants from urban Stockholm to more pristine offshore Baltic Sea ecosystems.

Theoretical work has been carried out using Geographical Information Systems (GIS) and statistical methods on a database of 4214 individual sediment samples, each with reported individual PCB congener concentrations. From this work it was concluded that the continental shelf sediments are key global inventories and ultimate sinks of PCBs. Depending on congener, 10-80% of the cumulative historical emissions to the environment are accounted for in continental shelf sediments. Further it was concluded that the many infamous and highly contaminated surface sediments of urban harbours and estuaries of contaminated rivers cannot be of importance as a secondary source to sustain the concentrations observed in remote sediments. Of the global shelf PCB inventory < 1% are in sediments near population centres while ≥ 90% is in remote areas (> 10 km from any dwellings). The remote sub-basin of the North Atlantic Ocean contains approximately half of the global shelf sediment inventory for most of the PCBs studied.

Place, publisher, year, edition, pages
Stockholm: Institutionen för geologi och geokemi, 2004. 13 p.
Series
Meddelanden från Stockholms universitets institution för geologi och geokemi, ISSN 1101-1599 ; 319
Keyword
Polychlorinated biphenyls (PCBs), organic carbon, sediment, stable carbon isotopes
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-125 (URN)91-7265-884-3 (ISBN)
Public defence
2004-05-18, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-04-27 Created: 2004-04-27Bibliographically approved

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Mörth, Carl-MagnusMeili, MarkusGustafsson, Örjan
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