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Past, present and future state of the biogeochemical Si cycle in the Baltic Sea
Lund University, Sweden.
Stockholm University.
Stockholm University, Sweden.
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
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2008 (English)In: Journal of Marine Systems, ISSN 0924-7963, Vol. 73, no 3-4, 338-346 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2008. Vol. 73, no 3-4, 338-346 p.
Keyword [en]
Silica, Baltic Sea, model
National Category
Natural Sciences
URN: urn:nbn:se:liu:diva-16110DOI: 10.1016/j.jmarsys.2007.10.016OAI: diva2:133190
Available from: 2009-01-08 Created: 2009-01-07 Last updated: 2011-08-17Bibliographically approved
In thesis
1. Silicon cycling in the Baltic Sea: Trends and budget of dissolved silica
Open this publication in new window or tab >>Silicon cycling in the Baltic Sea: Trends and budget of dissolved silica
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Kisels kretslopp i Östersjön : Trender och budget av löst kisel
Abstract [en]

The dissolved silicon (DSi) has a crucial role for growth of a large group of primary producers – diatoms and, hence, impact on functioning of the aquatic food web. This thesis contributes to an increased understanding of the modifications of the DSi cycling in the Baltic Sea. The results provide new information about spatial and temporal changes in DSi concentrations and nutrient ratios for the period 1970-2001 as well as during the 20th century.

For the period 1970-2001, the declining DSi trends were found at the majority of monitoring stations all over the Baltic Sea. This decrease is assumed to be mainly due to the ongoing eutrophication. It is supported by the increasing trends of inorganic nitrogen and phosphorus. The trends have implications for the nutrient ratios, DSi:DIN and DSi:DIP, which are important indicators of the state of an ecosystem. The long-term retrospective DSi budget has shown that the DSi concentrations before major hydrological alterations and eutrophication were about twice the present ones. This decrease is related to both eutrophication and anthropogenic perturbations in the catchment.

The occurrence of DSi concentrations close to the potentially limiting levels has been also analysed. While DSi concentrations are still high in the northern regions of the Baltic, other areas may be at risk of developing Si limitation if the decrease in DSi concentrations persists. The results depict the Baltic Sea journey from being water body with DSi levels sufficient to support diatom production to one that may experience Si limitation and its adverse ecological consequences.

Abstract [sv]

Löst kisel (DSi) har en viktig roll för tillväxten av en stor grupp av primärproducenter – kiselalger, och därmed även påverkar hela den akvatiska näringskedjan. Denna avhandling bidrar till en ökad förståelse av förändringarna i DSi kretsloppet i Östersjön. Resultaten tillhandahåller ny information om rumsliga och tidsmässiga förändringar i DSi koncentrationer såväl för perioden 1970-2001 som för hela 1900-talet.

För perioden 1970-2001 återfanns minskade DSi koncentrationer på mätstationer över hela Östersjön. Minskningen antas främst bero på den pågående övergödningen. Detta antagande stöds av stigande halter av oorganiskt kväve och fosfor. Sammantaget har dessa trender en inverkan på ekosystemets tillstånd och näringsämnenas kvoter, DSi: DIN och DSi: DIP. Ur ett längre tidsperspektiv kan man se att innan övergödningen och de stora hydrologiska ombildningar i Östersjöområdet var DSi koncentrationerna ungefär dubbelt så höga som idag.

Dagens förekomst av DSi koncentrationer som ligger nära de potentiellt begränsande nivåerna har också analyserats. DSi koncentrationerna är fortfarande höga i norra delar av Östersjön, men är i andra områden i riskzonen för att utveckla Si begränsning om minskningen av DSi koncentrationer fortsätter. Resultaten skildrar Östersjöns resa från att vara ett havsområde med DSi halter som är tillräckliga för att understödja kiselalgernas produktion till ett sådant som kan uppleva Si begränsning och dess negativa ekologiska konsekvenser.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2011. 61 + papers 1-5 p.
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 535
Dissolved silica, trends, nutrient, nutrient ratios, diatoms, Redfield, limitation, eutrophication, riverine load, budget, fluxes, accumulation, retention, optimisation, Baltic Sea, Löst kisel, trender, näringsämne, näringsämnens kvoter, kiselalger, Redfield, tillväxtbegränsning, övergödning, flodtillförsel, budget, flöden, ackumulering, retention, optimering, Östersjön
National Category
Natural Sciences
urn:nbn:se:liu:diva-70071 (URN)978-91-7393-112-0 (ISBN)
Public defence
2011-11-24, TEMCAS, Hus T, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2011-08-17 Created: 2011-08-17 Last updated: 2014-10-08Bibliographically approved

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