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  • 1.
    Algesten, Grete
    et al.
    Dept. och Ecology and Environmental Studies Umeå University.
    Brydsten, Lars
    Dept. of Ecology and Environmental Studies Umeå University.
    Jonsson, Per
    Inst. of Applied Environmental Res. Stockholm University.
    Kortelainen, Pirkko
    Finnish Environmental Inst..
    Löfgren, Stefan
    Dept. of Environmental Assessment SLU.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Räike, Antti
    Finnish environmental Inst..
    Sobek, Sebastian
    Dept. of Ecology and Evolution Uppsala University.
    Tranvik, Lars
    Dept. of Ecology and Evolution Uppsala University.
    Wikner, Johan
    Umeå Marine Science Center Umeå University.
    Jansson, Mats
    Dept. of Ecology and Environmental Studies Umeå University.
    Organic carbon budget for the Gulf of Bothnia2006In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 63, no 3-4, p. 155-161Article in journal (Refereed)
    Abstract [en]

    We calculated input of organic carbon to the unproductive, brackish water basin of the Gulf of Bothnia from rivers, point sources and the atmosphere. We also calculated the net exchange of organic carbon between the Gulf of Bothnia and the adjacent marine system, the Baltic Proper. We compared the input with sinks for organic carbon, permanent incorporation in sediments and mineralization and subsequent evasion of CO2 to the atmosphere. The major fluxes were riverine input (1500 Gg C year- 1), exchange with the Baltic Proper (depending on which of several possible DOC concentration differences between the basins that was used in the calculation, the flux varied between an outflow of 466 and an input of 950 Gg C year- 1), sediment burial (1100 Gg C year- 1) and evasion to the atmosphere (3610 Gg C year- 1). The largest single net flux was the emission of CO2 to the atmosphere, mainly caused by bacterial mineralization of organic carbon. Input and output did not match in our budget which we ascribe uncertainties in the calculation of the exchange of organic carbon between the Gulf of Bothnia and the Baltic Proper, and the fact that CO2 emission, which in our calculation represented 1 year (2002) may have been overestimated in comparison with long-term means. We conclude that net heterotrophy of the Gulf of Bothnia was due to input of organic carbon from both the catchment and from the Baltic Proper and that the future degree of net heterotrophy will be sensible to both catchment export of organic carbon and to the ongoing eutrophication of the Baltic Proper. © 2006 Elsevier B.V. All rights reserved.

  • 2.
    Conley, Daniel J
    et al.
    Lund University, Sweden.
    Humborg, Christoph
    Stockholm University.
    Smedberg, Erik
    Stockholm University, Sweden.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Papush, Liana
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Danielsson, Åsa
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Clarke, Annemarie
    National Environmental Research Institute, Denmark.
    Pastuszak, Marianna
    Sea Fisheries Research Institute, Poland.
    Aigars, Juris
    Latvian State University.
    Ciuffa, Daniele
    University Roma Tor Vergata.
    Mörth, Carl-Magnus
    Stockholm University, Sweden.
    Past, present and future state of the biogeochemical Si cycle in the Baltic Sea2008In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 73, no 3-4, p. 338-346Article in journal (Refereed)
    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.

  • 3.
    Danielsson, Åsa
    et al.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Papush, Liana
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Alterations in nutrient limitations - Scenarios of a changing Baltic Sea2008In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 73, no 3-4, p. 263-283Article in journal (Refereed)
    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.

  • 4.
    Humborg, Christoph
    et al.
    Stockholm University.
    Rahm, Lars
    Linköping University, Department of Thematic Studies, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Conley, Daniel J
    Lund University.
    Tamminen, Timo
    Finnish Environmental Institute.
    von Bodungen, Bodo
    Baltic Sea Research Institute.
    Silicon and the Baltic Sea Long-term Si decrease in the Baltic Sea - A conceivable ecological risk?2008In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 73, no 3-4, p. 221-222Article in journal (Other academic)
    Abstract [en]

    Since the pioneering work of Schelske and Stoermer (1971) and Schelske et al., 1983 C.L. Schelske, E.F. Stoermer, D.J. Conley, J.A. Robbins and R.M. Glover, Early eutrophication in the Lower Great-Lakes — new evidence from biogenic silica in sediments, Science 222 (1983), pp. 320–322. View Record in Scopus | Cited By in Scopus (56)Schelske et al. (1983) it has been known that eutrophication of aquatic systems leads to depletion in dissolved silicate (DSi). Early studies on the Nile River have shown that the construction of dams leads to DSi decrease downstream due to the formation of additional deposition sites of biogenic silica (BSi) that was thought to consist mainly of diatoms. In the Baltic Sea there was a perception in the scientific community that DSi concentrations were high and therefore, that DSi concentrations were not limiting for diatom growth. Long-term trend analyses on DSi concentrations in the Baltic have shown decreasing trends in the 1970s and 1980s, whereas similar analysis for the 1990s concluded that DSi concentrations were no longer decreasing, but rather levelling off. Consequently, observations of reduced abundance of diatoms in the early 1990s were attributed to mild winters rather than low DSi concentrations, i.e., a low turbulence regime in the water column favouring non-siliceous algae. However, decadal nutrient trends in the Baltic Sea are significantly influenced by the large and varying internal Si pools in the sediments and deep water masses similar to that described for P dynamics in the Baltic Sea. No one seriously addressed the longer trends in DSi concentrations over the last century, whereas many studies estimated these changes for N and P.

    The EU funded research project SIBER (Silicate and Baltic Sea Ecosystem Response; EVK3-CT-2002-00069) began in 2002 with the objectives of understanding the major changes in Si dynamics in the Baltic Sea during the last century. The SIBER project addressed various aspects of the biogeochemical Si cycle in the Baltic Sea including constraining Si budgets for the Baltic Sea and its catchment, experiments describing the growth characteristics of Baltic diatoms related to the long-term trends in monitoring data of Baltic Sea diatoms.

    Si budgets are addressed by several papers in this special issue. Humborg et al. and Sferratore et al. describe riverine Si fluxes. Pastuszak et al. address estuarine Si fluxes. Redfield ratios including DSi and their development in the Baltic Sea are described by Danielsson et al.

    Possible ecosystem effects of changes in Redfield nutrient ratios are analysed in the paper by Olli et al. who examine phytoplankton responses in the Gulf of Riga and by Wasmund et al. who investigate long-term trends in phytoplankton species in the Kiel Bight. Spilling and Markager describe growth characteristics of Baltic Sea diatoms. Finally, in their paper Conley et al. present a long-term Si budget for the entire Baltic Sea for the first time.

    The Baltic Sea biogeochemical Si cycle has been fundamentally changed within the last century not only as a consequence of river regulation and lake eutrophication, but also through increases in the sediment accumulation of BSi (Conley et al.). Sediment accumulation of BSi has increased by a factor on 1.9 due to increased diatom growth from marine eutrophication. Results from the SIBER project indicate that DSi concentration were ca. 36 µM a century ago in the Baltic proper compared to ca. 13 µM observed today (Conley et al.). In fact, DSi concentrations have changed much more dramatically compared to N and P regarding the total changes in the available nutrient stocks. Similar changes have occurred in other large water bodies with respect to size and volume, i.e. the North American Great Lakes with long residence times where DSi decreased from 80–100 µM to ca. 25 µM. Surprisingly, such a major change in nutrient inventories has not been reported earlier in this well investigated coastal system. We are only starting to understand the possible ecological consequences, such as the occurrence of different diatom species that are less silicified and its implication for the sedimentation fluxes and carbon flux to benthic communities. The SIBER project has shown that a dramatic change in DSi concentrations is possible within a very short time period, although the situation appears stable today, perhaps since the drivers for this change, i.e. eutrophication and river regulation, have not changed within the last 30 years. However, even a slight increase in N and P loads and/or further damming of rivers may drive the Baltic Sea into Si-limitation.

  • 5.
    Kumar Das, Supriyo
    et al.
    Presidency University, India.
    Routh, Joyanto
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Roychoudhury, Alakendra N.
    Stellenbosch University, South Africa.
    Veldhuis, Marcel J. W.
    Marine Ecoanalyt, Netherlands.
    Ismail, Hassan E.
    Department Environm Affairs Oceans and Coasts, South Africa.
    Connecting pigment composition and dissolved trace elements to phytoplankton population in the southern Benguela Upwelling zone (St. Helena Bay)2017In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 176, p. 13-23Article in journal (Refereed)
    Abstract [en]

    Rich in upwelled nutrients, the Southern Benguela is one of the most productive ecosystems in the world ocean. However, despite its ecological significance the role of trace elements influencing phytoplankton population in the Southern Benguela Upwelling System (SBUS) has not been thoroughly investigated. Here, we report pigment composition, macronutrients (nitrate, phosphate and silicate) and concentrations of dissolved Cd, Co, Fe and Zn during late austral summer and winter seasons in 2004 to understand the relationship between the selected trace elements and phytoplankton biomass in St. Helena Bay (SHB), which falls within the southern boundary of the SBUS. Chlorophyll a concentrations indicate higher phytoplankton biomass associated with high primary production during late summer in SHB where high diatom population is inferred from the presence of fucoxanthin. Diminished phytoplankton biomass and a shift from diatoms to dinoflagellates as the dominant phytoplankton taxa are indicated by diagnostic pigments during late winter. Dissolved trace elements (Cd, Co and Zn) and macronutrients play a significant role in phytoplankton biomass, and their distribution is affected by biological uptake and export of trace elements. Continuous uptake of Zn by diatoms may cause an onset of Zn depletion leading to a period of extended diatom proliferation during late summer. Furthermore, the transition from diatom to dinoflagellate dominated phytoplankton population is most likely facilitated by depletion of trace elements (Cd and Co) in the water column.

  • 6.
    Laznik, M
    et al.
    Jordforsk, Ctr Soil & Environm Res, N-1432 As Nlh, Norway Latvian Hydrometeorol Agcy, LV-1019 Riga, Latvia Linkoping Univ, Dept Math, SE-58183 Linkoping, Sweden Swedish Meteorol & Hydrol Inst, SE-60176 Norrkoping, Sweden.
    Stalnacke, P
    Jordforsk, Ctr Soil & Environm Res, N-1432 As Nlh, Norway Latvian Hydrometeorol Agcy, LV-1019 Riga, Latvia Linkoping Univ, Dept Math, SE-58183 Linkoping, Sweden Swedish Meteorol & Hydrol Inst, SE-60176 Norrkoping, Sweden.
    Grimvall, Anders
    Linköping University, Faculty of Arts and Sciences. Linköping University, Department of Mathematics, Statistics .
    Wittgren, Hans Bertil
    Linköping University, Faculty of Arts and Sciences. Linköping University, Department of Thematic Studies.
    Riverine input of nutrients to the Gulf of Riga - temporal and spatial variation1999In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 23, no 1-3, p. 11-25Article in journal (Refereed)
    Abstract [en]

    Riverine transport is the, most important pathway for input of nutrients to the Gulf of Riga. The present study focused on updating existing estimates of the riverine nutrient contributions and on improving the favailable information on temporal and spatial variation in such input. The results show that the gulf received an average of 113,300 tons of nitrogen, 2050 tons of phosphorus and 64,900 tons of dissolved silica (DSi) annually during the time period 1977-1995. There was large interannual variation in loads, e.g., a factor two difference was found between the two most extreme years (1984 and 1990), this was attributed mainly to natural variation in water discharge. The seasonal distribution of nutrient loads exhibited a distinct pattern for practically all studied constituents, especially nitrate. Loads were high during the spring-flow and relatively low during the low-flow summer period. Examination of the spatial variation of nutrient loads showed that the Daugava River alone accounted for approximately 60% of the total riverine load. The highest area-specific loads of nitrate and phosphate were observed in the agriculturally dominated Lielupe River, and the highest loads of organic-nitrogen (org-N) and total phophorus (tot-P) were found in the Parnu River. However, the values for all the studied rivers and constituents were rather low (phosphorus) or moderate (nitrogen and silica) compared to those reported for many other drainage areas of the Baltic Sea. This was true despite the inefficient sewage treatment and intensive agriculture in the studied basins in the 1970s and 1980s. (C) 1999 Elsevier Science B.V. All rights reserved.

  • 7.
    Pers, Charlotta
    et al.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Changes in apparent oxygen removal in the Baltic proper deep water2000In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 25, no 3-4, p. 421-429Article in journal (Refereed)
    Abstract [en]

    By developing a steady state diagnostic model for a stratified deep-water mass, one is able to quantify both the mass flows and apparent oxygen removal in the Baltic proper deep water. The model is based on continuity of the assumed conservative observable volume, salinity and temperature. Second degree polynomials are fitted to observed vertical profiles of temperature as well as oxygen concentration to give a functional correspondence with the used spatial variable salinity. These relations are used in the model that calculate the water flows, oxygen flows and oxygen removal during four periods between 1959 and 1997. The model forms a boundary value problem, which is solved with a finite difference scheme. The model seems to give reasonable estimates of the flows. The oxygen removal is mainly balanced by inflow of oxygen with incoming water. The oxygen consumption is 4-8 ╡1 O2 1-1 day -1, which corresponds to a degradation of organic matter in the range 30-60 g C m-2 year-1. (C) 2000 Elsevier Science B.V.

  • 8.
    Sferratore, Agata
    et al.
    University of Paris.
    Billen, Gilles
    University of Paris.
    Garnier, Josette
    University of Paris.
    Smedberg, Erik
    Stockholm University.
    Humborg, Christoph
    Stockholm University.
    Rahm , Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Modelling nutrient fluxes from sub-arctic basins: Comparison of pristine vs. dammed rivers2008In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 73, no 3-4, p. 236-249Article in journal (Refereed)
    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 Kalixalven) and the heavily dammed river Lule, (hereafter called Lulealven) both located in Northern Sweden and draining into the Bothnian Bay, Baltic Sea.

    For Kalixalven 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 Lulealven 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 Lulealven than in the Kalixalven watershed due to higher altitudes and precipitations. Average silica, nitrate and phosphorus concentrations are much lower in Lulealven than in Kalixalven. Comparison of model results for the Lulealven 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.

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