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Silicon cycling in the Baltic Sea: Trends and budget of dissolved silica
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Kisels kretslopp i Östersjön : Trender och budget av löst kisel (Swedish)
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.
Series
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 535
Keyword [en]
Dissolved silica, trends, nutrient, nutrient ratios, diatoms, Redfield, limitation, eutrophication, riverine load, budget, fluxes, accumulation, retention, optimisation, Baltic Sea
Keyword [sv]
Löst kisel, trender, näringsämne, näringsämnens kvoter, kiselalger, Redfield, tillväxtbegränsning, övergödning, flodtillförsel, budget, flöden, ackumulering, retention, optimering, Östersjön
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-70071ISBN: 978-91-7393-112-0 (print)OAI: oai:DiVA.org:liu-70071DiVA: diva2:435240
Public defence
2011-11-24, TEMCAS, Hus T, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2011-08-17 Created: 2011-08-17 Last updated: 2014-10-08Bibliographically approved
List of papers
1. Silicon in the marine environment: Dissolved silica trends in the Baltic Sea
Open this publication in new window or tab >>Silicon in the marine environment: Dissolved silica trends in the Baltic Sea
2006 (English)In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 67, no 1-2, 53-66 p.Article in journal (Refereed) Published
Abstract [en]

Dissolved silica (DSi) is an important nutrient for primary production. During the last decades, negative trends in DSi concentrations have been observed in coastal areas globally, with implications for the marine ecosystem. This tendency is mainly attributed to two processes: decrease in river loadings (as a result of water regulation and building of dams) and eutrophication in the coastal zone, with subsequent silica depletion. One such area affected by both an intensive water regulation and eutrophication is the Baltic Sea. The present study focused on the pelagic DSi trends in different parts of the Baltic Sea for the last three decades. It was found that there are decreasing trends for most of areas and water depths ranging between -0.05 and -1.2 μmol Si l -1 yr-1. The trends are levelling out during the last decade. Since the riverine load of dissolved silica has not changed at a corresponding rate during the time period, the decrement is assumed to be mainly a result of the ongoing eutrophication within the marine water body. This assumption was strengthened by the increasing trends of inorganic nitrogen and phosphorus. © 2005 Elsevier Ltd. All rights reserved.

National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-30666 (URN)10.1016/j.ecss.2005.09.017 (DOI)16266 (Local ID)16266 (Archive number)16266 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2011-08-17Bibliographically approved
2. Alterations in nutrient limitations - Scenarios of a changing Baltic Sea
Open this publication in new window or tab >>Alterations in nutrient limitations - Scenarios of a changing Baltic Sea
2008 (English)In: Journal of Marine Systems, ISSN 0924-7963, Vol. 73, no 3-4, 263-283 p.Article in journal (Refereed) Published
Abstract [en]

Previous trend studies have shown increasing nitrogen and phosphorus as well as decreasing silica concentrations ill the water mass of the Baltic Sea. This has had an impact on the amount of primary production, but also on the quality and succession of plankton species. Present study examines the spatial and temporal patterns of potential nutrient limitations in the Baltic Sea for the time period 1970-2000. Generally, low concentrations of DSi can limit the diatom blooms and such conditions are found in the Gulf of Riga and Gulf of Finland during spring and summer. Nutrient ratios, DSi:DIN, DSi:DIP and DIN:DIP, are often used to determine which nutrient may limit the primary production. Annual long-term temporal trends of silica to inorganic nitrogen and phosphorus respectively show consistent decreasing patterns. The largest slopes are detected during spring and summer for DSi: DIN and during spring for DSi:DIP ratios. For the DIN:DIP ratio significant slopes are only found in a few locations despite increasing levels for both nutrients, displaying a large variation in trends. In the open Baltic Proper the present trends are positive during winter and negative during spring and autumn. Gulf of Finland and Gulf of Riga are areas where both DSi:DIP and DSi:DIN ratios are found close to the Redfield ratios for diatoms. Together with the evaluated trends these suggest that the Gulfs may become silica limited in a relatively near future. These findings give some implications on the development and impact of changing nutrient concentrations.

Keyword
DSi, DLN, DIP, Nutrient ratios, Redfield, Limitation, Trends, Baltic Sea
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16108 (URN)10.1016/j.jmarsys.2007.10.015 (DOI)
Available from: 2009-01-08 Created: 2009-01-07 Last updated: 2011-08-17Bibliographically approved
3. Past, present and future state of the biogeochemical Si cycle in the Baltic Sea
Open this publication in new window or tab >>Past, present and future state of the biogeochemical Si cycle in the Baltic Sea
Show others...
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.

Keyword
Silica, Baltic Sea, model
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16110 (URN)10.1016/j.jmarsys.2007.10.016 (DOI)
Available from: 2009-01-08 Created: 2009-01-07 Last updated: 2011-08-17Bibliographically approved
4. Dissolved silica budget for the Baltic Sea
Open this publication in new window or tab >>Dissolved silica budget for the Baltic Sea
2009 (English)In: Journal of Sea Research, ISSN 1385-1101, Vol. 62, no 1, 31-41 p.Article in journal (Refereed) Published
Abstract [en]

A budget model covering the Baltic Sea was developed for the time period 1980-2000 to estimate water and dissolved silica (DSi) fluxes as well as internal DSi sinks/sources. The Baltic Sea was resolved by eight basins, where the largest basin - the Baltic Proper - was divided laterally into north/west and southern/east parts as well as vertically to take into account the existence of the permanent halocline. The basins demonstrated rather different patterns with regard to silica cycling. The Gulfs of Finland and Riga together with the northernmost basins, Bothnian Bay and Bothnian Sea. are distinguished by substantial specific rates of silica removal accounting for 1.6-4.9 g Si m(-2) yr(-1). Bearing in mind the large total primary production, the basins comprising the Baltic Proper with the specific removal rates 0.2 and 1.2 g Si m(-2) yr(-1), do not appear as regions with a high silica accumulation. The Arkona and the Kattegat mainly behave as regions of rapid through-flows. These results point out the northernmost Gulf of Bothnia, the Gulfs of Riga and Finland as areas with a larger share of biogenic silica accumulation than in the Baltic Proper. It is attributed to hydrographic and hydrochemical features. An estimate of diatom export production was made for the Baltic Proper showing that the diatom contribution accounts for 19-44% of the net export production.

Keyword
Dissolved silica; Budget; Fluxes; Accumulation; Retention; Diatoms; Baltic Sea
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-20217 (URN)10.1016/j.seares.2009.03.001 (DOI)
Available from: 2009-09-02 Created: 2009-08-31 Last updated: 2011-08-17Bibliographically approved
5. Optimised water budget of the Gulf of Bothnia (Baltic Sea)
Open this publication in new window or tab >>Optimised water budget of the Gulf of Bothnia (Baltic Sea)
2008 (English)Manuscript (preprint) (Other academic)
Abstract [en]

A time-dependent water budget of the Gulf of Bothnia, based on inverse modelling with salinity as a conservative tracer, was developed to estimate monthly water flows for the period 1990-2000. When dealing with time-dependent inverse salinity models, such difficulties as non-physical water flows (too high flows or lack of non-negative flows) between adjacent basins are often encountered. Therefore, different model structures and solution methods were initially tested and evaluated on an array of generated data. The elaboration of the Gulf of Bothnia model was then based on the outcome of these tests. The results showed that the optimisation technique is capable of overcoming the above mentioned difficulties.

Keyword
Budget, water fluxes, optimisation, Gulf of Bothnia, Baltic Sea
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-70070 (URN)
Available from: 2011-08-17 Created: 2011-08-17 Last updated: 2011-08-17Bibliographically approved

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