| 1. |
- Andrén, Elinor, et al.
(författare)
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Defining Reference Conditions for Coastal Areas in the Baltic Sea
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The overall aim of DEFINE is to provide a methodology to define reference conditions for nutrient concentrations in the coastal zone of the Baltic Sea. This will aid the national authorities that surround the Baltic basin in implementing the EU's Water Framework Directive (WFD) by providing decision-makers with a methodology to assess reference conditions and the degree of past and present departure from this state, such that appropriate policy and management measures can be taken at national and European levels. DEFINE adopts a palaeoecological approach grounded on diatom-based transfer functions, which can then be applied to define background total nitrogen (TN) concentrations in estuaries and coastal areas over the entire Baltic Sea. All transfer functions and necessary supporting documentation will be publicly available as a coherent management tool and accessible via the MOLTEN/DEFINE web page (http://craticula.ncl.ac.uk/Molten/jsp/).
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| 2. |
- Conley, Daniel, et al.
(författare)
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Past, present and future state of the biogeochemical Si cycle in the Baltic Sea
- 2008
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 73:3-4, s. 338-346
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Tidskriftsartikel (refereegranskat)abstract
- The Baltic Sea is one of many aquatic ecosystems that show long-term declines in dissolved silicate (DSi) concentrations due to anthropogenic alteration of the biogeochemical Si cycle. Reductions in DSi in aquatic ecosystems have been coupled to hydrological regulation reducing inputs, but also with eutrophication, although the relative significance of both processes remains unknown for the observed reductions in DSi concentrations. Here we combine present and historical data on water column DSi concentrations, together with estimates of present river DSi loads to the Baltic, the load prior to damming together with estimates of the long-term accumulation of BSi in sediments. In addition, a model has been used to evaluate the past, present and future state of the biogeochemical Si cycle in the Baltic Sea. The present day DSi load to the Baltic Sea is 855 ktons y(-1). Hydrological regulation and eutrophication of inland waters can account for a reduction of 420 ktons y(-1) less riverine DSi entering the Baltic Sea today. Using published data on basin-wide accumulation rates we estimate that 1074 ktons y(-1) of biogenic silica (BSi) is accumulating in the sediments, which is 36% higher than earlier estimates from the literature (791 ktons y(-1)). The difference is largely due to the high reported sedimentation rates in the Bothnian Sea and the Bothnian Bay. Using river DSi loads and estimated BSi accumulation, our model was not able to estimate water column DSi concentrations as burial estimates exceeded DSi inputs. The model was then used to estimate the BSi burial from measured DSi concentrations and DSj load. The model estimate for the total burial of BSi in all three basins was 620 ktons y(-1), 74% less than estimated from sedimentation rates and sediment BSi concentrations. The model predicted 20% less BSi accumulation in the Baltic Proper and 10% less in the Bothnian Bay than estimated, but with significantly less BSi accumulation in the Bothnian Sea by a factor of 3. The model suggests there is an overestimation of basin-wide sedimentation rates in the Bothnian Bay and the Bothnian Sea. In the Baltic Proper, modelling shows that historical DSi concentrations were 2.6 times higher at the turn of the last century (ca. 1900) than at present. Although the DSi decrease has leveled out and at present there are only restricted areas of the Baltic Sea with limiting DSi concentrations, further declines in DSi concentrations will lead to widespread DSi limitation of diatoms with severe implications for the food web.
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| 3. |
- Olli, Kalle, et al.
(författare)
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Diatom stratigraphy and long-term dissolved silica concentrations in the Baltic Sea
- 2008
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Ingår i: JOURNAL OF MARINE SYSTEMS. - : Elsevier BV. - 0924-7963. ; 73:3-4, s. 284-299
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Tidskriftsartikel (refereegranskat)abstract
- In many parts of the world coastal waters with anthropogenic eutrophication have experienced a gradual depletion of dissolved silica (DSi) stocks. This could put pressure on spring bloom diatom populations, e.g. by limiting the intensity of blooms or by,causing shifts in species composition. In addition, eutrophication driven enhanced diatom growth is responsible for the redistribution of DSi from the water phase to the sediments, and changes in the growth conditions may be reflected in the sediment diatom stratigraphy. To test for changes in diatom communities we have analyzed four sediment cores from the Baltic Sea covering approximately the last 100 years. The sediment cores originate from the western Gulf of Finland, the Kattegat, the Baltic Proper and the Gulf of Riga. Three out of the four cores reveal only minor changes in composition of diatom assemblages, while the Gulf of Riga core contains major changes, occurring after the second World War. This area is set apart from the other Baltic Sea basins by a high frequency of low after spring bloom DSi concentrations (<2 mu mol L-1) during a relatively well defined time period from 1991-1998. In 1991 to 1993 a rapid decline of DSi spring concentrations and winter stocks (down to 5 mu mol L-1) in the Gulf was preceded by exceptionally intense diatom spring blooms dominated by the heavily silicified species Thalassiosira baltica (1991-1992; up to 5.5 mg ww L-1). T baltica has been the principal spring bloom diatom in the Gulf of Riga since records began in 1975. DSi consumption and biomass yield experiments with cultured T baltica suggest that intense blooms can potentially exhaust the DSi stock of the water column and exceed the annual Si dissolution in the Gulf of Riga. The phytoplankton time series reveals another exceptional T baltica bloom period in 1981-1983 (up to 8 mg L-1), which, however, took place before the regular DSi measurements. These periods may be reflected in the conspicuous accumulation of T baltica frustules in the sediment core corresponding to ca. 1975-1995.
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