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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.
    Alling, Vanja
    et al.
    Stockholm University.
    Humborg, Christoph
    Stockholm University.
    Morth, Carl-Magnus
    Stockholm University.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Pollehne , Falk
    Rostock, Germany.
    Tracing terrestrial organic matter by delta S-34 and delta C-13 signatures in a subarctic estuary2008In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, no 6, p. 2594-2602Article in journal (Refereed)
    Abstract [en]

    A key issue to understanding the transformations of terrestrial organic carbon in the ocean is to disentangle the latter from marine-produced organic matter. We applied a multiple stable isotope approach using delta S-34 and delta C-13 isotope signatures from estuarine dissolved organic matter (DOM), enabling us to constrain the contribution of terrestrial-derived DOM in an estuarine gradient of the northern Baltic Sea. The stable isotope signatures for dissolved organic sulfur (delta S-34(DOS)) have twice the range between terrestrial and marine end members compared to the stable isotope signatures for dissolved organic carbon (delta C-13(DOC)); hence, the share of terrestrial DOM in the total estuarine DOM can be calculated more precisely. DOM samples from the water column were collected using ultrafiltration on board the German RV Maria S Merian during a winter cruise, in the Bothnian Bay, Bothnian Sea, and Baltic proper. We calculated the terrestrial fraction of the estuarine DOC (DOCter) from both delta C-13(DOC) and delta S-34(DOS) signatures and applying fixed C: S ratios for riverine and marine end members to convert S isotope signatures into DOC concentrations. The delta S-34(DOS) signature of the riverine end member was +7.02 parts per thousand, and the mean signatures from Bothnian Bay, Bothnian Sea, and Baltic proper were +10.27, +12.51, and +13.67 parts per thousand, respectively, showing an increasing marine signal southwards (d34SDOS marine end member = 18.1 parts per thousand). These signatures indicate that 87%, 75%, and 67%, respectively, of the water column DOC is of terrestrial origin (DOCter) in these basins. Comparing the fractions of DOCter in each basin-that are still based on few winter values only-with the annual river input of DOC, it appears that the turnover time for DOCter in the Gulf of Bothnia is much shorter than the hydraulic turnover time, suggesting that high-latitude estuaries might be efficient sinks for DOCter.

  • 3.
    Andersson, Lars
    et al.
    Dept. of Oceanography Göteborg University.
    Rahm, Lars
    Dept. of Oceanography Göteborg University.
    On the dynamics of a neutrally-buoyant float in a non-linear stratified fluid1984In: Geophysica, ISSN 0367-4231, E-ISSN 2324-0741, Vol. 19, no 2, p. 157-167Article in journal (Refereed)
    Abstract [en]

    The transient properties of a neutrally-buoyant float in a non-linearly stratified fluid is studied both theoretically and experimentally. Numerical experiments from a theoretical model based on a quadratic drag law are in agreement with data from field experiments.

  • 4.
    Andersson, Lars
    et al.
    Ocean. Lab. SMHI.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Thermally driven circulation within an experimental enclosure1990In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 30, p. 111-129Article in journal (Refereed)
    Abstract [en]

      

  • 5.
    Bonaglia, S.
    et al.
    Stockholm University, Sweden.
    Bartoli, M.
    University of Parma, Italy.
    Gunnarsson, J. S.
    Stockholm University, Sweden.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Raymond, C.
    Stockholm University, Sweden.
    Svensson, O.
    Stockholm University, Sweden.
    Shakeri Yekta, Sepehr
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Brüchert, V.
    Stockholm University, Sweden.
    Effect of reoxygenation and Marenzelleria spp. bioturbation on Baltic Sea sediment metabolism2013In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 482, p. 43-55Article in journal (Refereed)
    Abstract [en]

    Nutrient reduction and the improvement of bottom water oxygen concentrations are thought to be key factors in the recovery of eutrophic aquatic ecosystems. The effects of reoxygenation and bioturbation of natural hypoxic sediments in the Baltic Sea were studied using a mesocosm experiment. Anoxic sediment box cores were collected from 100 m depth in Kanholmsfjärden (Stockholm Archipelago) and maintained in flow-through mesocosms with 3 treatments: (1) hypoxic: supplied with hypoxic water; (2) normoxic: supplied with oxic water; and (3) Marenzelleria: supplied with oxic water and the polychaete Marenzelleria spp. (2000 ind. m–2). After a 7 wk long conditioning period, net fluxes of dissolved O2, CH4, Fe2+, Mn2+, NH4+, NO2-, NO3-, PO43- and H4SiO4, and rates of nitrate ammonification (DNRA), denitrification and anammox were determined. Phosphate was taken up by the sediment in all treatments, and the uptake was highest in the normoxic treatment with Marenzelleria. Normoxic conditions stimulated the denitrification rate by a factor of 5. Denitrification efficiency was highest under normoxia (50%), intermediate in bioturbated sediments (16%), and very low in hypoxic sediments (4%). The shift from hypoxic to normoxic conditions resulted in a significantly higher retention of NH4+, H4SiO4 and Mn2+ in the sediment, but the bioturbation by Marenzelleria reversed this effect. Results from our study suggest that bioturbation by Marenzelleria stimulates the exchange of solutes between sediment and bottom water through irrigation and enhances bacterial sulfate reduction in the burrow walls. The latter may have a toxic effect on nitrifying bacteria, which, in turn, suppresses denitrification rates.

  • 6.
    Carman, R.
    et al.
    SU.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Interstitial and bottom water composition of some Baltic proper deep stations1999In: Journal of Sea Research, ISSN 1385-1101, E-ISSN 1873-1414, Vol. 37, p. 25-47Article in journal (Refereed)
  • 7.
    Carstensen, J
    et al.
    DMU.
    Conley, D.
    DMU.
    Danielsson, Åsa
    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.
    Toompuu, A.
    University of Tartu.
    Muller-Karulis, B.
    University of Latvia.
    Spatial heterogeneity and temporal reconstruction of data for phytoplankton modelling.2000Report (Other academic)
  • 8.
    Carstensen, J.
    et al.
    DMU.
    Conley, D.
    DMU.
    Lophaven, S.
    DMU.
    Danielsson, Åsa
    Linköping University, Department of Thematic Studies, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Rahm, Lars
    Linköping University, Department of Thematic Studies, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Toompuu, A.
    University of Tartu.
    Muller_Karulis, B.
    University of Latvia.
    Statistical analysis and modelling of phytoplankton dynamics: exploitation of data in the Nordic and Baltic monitoring programs2002Book (Other academic)
  • 9.
    Conley, D.
    et al.
    DMU.
    Humborg, C.
    SU.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Savchuk, O.
    SU.
    Wulff, F.
    SU.
    The myth of the Baltic stagnation period.2003In: Environmental Science and Technology, ISSN 1086-931X, E-ISSN 1520-6912, Vol. 36, p. 5315-5320Article in journal (Refereed)
  • 10.
    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.

  • 11.
    Conley, D.J.
    et al.
    Department of Marine Ecology, Natl. Environ. Research Institute, P.O. Box 358, DK-4000 Roskilde, Denmark.
    Humborg, C.
    Department of Systems Ecology, Stockholm University, SE-106 91 Stockholm, Sweden.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Savchuk, O.P.
    Department of Systems Ecology, Stockholm University, SE-106 91 Stockholm, Sweden.
    Wulff, F.
    Department of Systems Ecology, Stockholm University, SE-106 91 Stockholm, Sweden.
    Hypoxia in the baltic sea and basin-scale changes in phosphorus biogeochemistry2002In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 36, no 24, p. 5315-5320Article in journal (Refereed)
    Abstract [en]

    Deep-water oxygen concentrations in the Baltic Sea are influenced by eutrophication, but also by saltwater inflows from the North Sea. In the last two decades, only two major inflows have been recorded and the lack of major inflows is believed to have resulted in a long-term stagnation of the deepest bottom water. Analyzing data from 1970 to 2000 at the basin scale, we show that the estimated volume of water with oxygen, <2 mL L-1, was actually at a minimum at the end of the longest so-called stagnation period on record. We also show that annual changes in dissolved inorganic phosphate water pools were positively correlated to the area of bottom covered by hypoxic water, but not to changes in total phosphorus load, thus addressing the legacy of eutrophication on a basinwide scale. The variations in phosphorus pools that have occurred during the past decades do not reflect any human action to reduce inputs. The long residence time and internally controlled variation of the large P pool in the Baltic Sea has important implications for management of both N and P inputs into this eutrophicated enclosed basin.

  • 12.
    Conley, D.J.
    et al.
    DMU.
    Stockenberg, A.
    SU.
    Johnstone, R.
    University of Queensland.
    Wulff, F.
    SU.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Sediment-water nutrient fluxes along a eutrophicated gradient in the Gulf of Finland, Baltic Sea1997In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 45, p. 591-598Article in journal (Refereed)
  • 13.
    Danielsson, Åsa
    et al.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Carman, R.
    SU.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Aigars, J.
    SU.
    Spatial estimation of nutrient distributions in the Gulf of Riga sediments using cokriging.1998In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 46, p. 713-722Article in journal (Refereed)
  • 14.
    Danielsson, Åsa
    et al.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Cato, I.
    SGU.
    Carman, R.
    SU.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Spatial clustering of metals in the sediments of Skagerrak/Kattegat.1999In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 14, p. 689-706Article in journal (Refereed)
  • 15.
    Danielsson, Åsa
    et al.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Jönsson, Anette
    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.
    Resuspension patterns in the Baltic proper2007In: Journal of Sea Research, ISSN 1385-1101, E-ISSN 1873-1414, Vol. 57, no 4, p. 257-269Article in journal (Refereed)
    Abstract [en]

    Waves induce resuspension of surface sediments and contribute to the long-term mobilisation of particulate matter from erosion to accumulation bottoms. This has a major impact on the nutrient cycle in shallow seas by enhancing degradation, microbial production and recycling. The Baltic Sea represents such an area. The aim of this work is to analyse the spatial and temporal resuspension patterns in the Baltic Sea. To estimate the bottom friction velocity, modelled wave data are used in combination with data on grain size. This new data set is compared to a resuspension threshold of friction velocity to estimate the events of resuspension.

    The variation in bottom friction velocity, resuspension frequency and duration are related to wind climate, fetch, water depth and sediment type. Substantial resuspension can be found down to 40–60 m, with durations from one day to as much as two weeks. The highest winds in the area are highly anisotropic with a dominance of S-SW-W winds and the highest resuspension frequencies are found along the shallow eastern coasts. A seasonal pattern is observed with relatively high friction velocities and high resuspension frequencies during winter. There is also a variation depending on grain size, where sediments with fine and medium sand have a considerably higher percentage of resuspension events than bottoms with other dominant grain sizes. Five sub-areas are identified, characterised by different sediment types, resuspension and wind characteristics. If, in the future, wind speed increases as predicted, resuspension of sediments will also increase with effects on the nutrient cycle.

  • 16.
    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.

  • 17.
    Danielsson, Åsa
    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.
    Conley, D. Neri
    Carstensen, J.
    dentification of characteristic regions and representative stations: A study of water quality variables in the Kattegat2004In: Environmental Monitoring & Assessment, ISSN 0167-6369, E-ISSN 1573-2959, Vol. 90, no 1-3, p. 203-224Article in journal (Refereed)
    Abstract [en]

    Gradients in nutrient distributions and the effects of eutrophication are common features in most coastal marine areas. These structures occur in aquatic systems due to spatial differences in hydrography, nutrient loading and key biogeochemical processes. Two statistical methods, cluster analysis and probability mapping, have been used in the present study to determine characteristics and patterns in water quality variables. Combined, these two methods provide a useful toot to statistically determine spatial homogeneity and representativity of areas and stations. A case study is presented here in which water quality variables (salinity, dissolved inorganic nitrogen, dissolved inorganic phosphorus and chlorophyll) in surface waters of the Kattegat are analysed for the time period 1993-1997. It was found that morphology, the proximity to sources of nutrient loading from land, nutrient uptake and the infrequent water exchange between the Baltic Sea in the south and the Skagerrak in the north all contribute to create distinct regions of water quality. Regions with concentrations significantly different from the overall mean are identified. In addition to identification of regions with similar characteristics, representative stations (as well as not representative stations) for the respective regions were made. This type of information can be used to design new or revise old monitoring programs.

  • 18.
    Danielsson, Åsa
    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.
    Wihlborg, Peter
    TEMA LiU.
    Large-scale mercury variations in Lake Vänern (Sweden) 1974-1998.2001In: Environmental Monitoring & Assessment, ISSN 0167-6369, E-ISSN 1573-2959, Vol. 75, p. 223-234Article in journal (Refereed)
    Abstract [en]

    Lake Vanern, the largest lake in Sweden, has been seriously contaminated with mercury during the 20th century. In the 1970's and 80's the direct load, mainly from a chlor-alkali industry in the area, of mercury was drastically reduced as a response to new legislation, from three to five tons down to between five and ten kg yr(-1). Large amounts of the disposed pollutant have accumulated in the sediments. The question posed in this work is now, is the effect of the drastic load reduction after more than two decades visible in the sediments? The question is relevant as large areas still are blacklisted for fishing, but also as a follow-up of a major remedy action. The lake also serves as a freshwater reservoir for even Sweden's second largest city. This work synthesises and compares data of mercury in the sediments from three major field programs, in 1974, 1984 and 1998. The interest is focused on both spatial heterogeneity and temporal trends. In 1974, the surface concentrations are significantly higher than in subsequent surveys. Significant differences are also found between 1984 and 1998. Significant spatial differences within the lake are found for respective year. The most contaminated area is located in the north, close to the major point source (a former chlor-alkali industry). This is also the area with the largest improvement, as a direct response to the reduction in load. Further from the outlet, the recovery is more affected by burial and transport processes out into the deeper basins.

  • 19.
    Danielsson, Åsa
    et al.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Wihlborg, Peter
    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.
    Large-scale mercury variations in Lake Vänern (Sweden) 1974-19982000In: Environmental Monitoring & Assessment, ISSN 0167-6369, E-ISSN 1573-2959, Vol. 75, p. 223-234Article in journal (Refereed)
  • 20.
    Davies, Peter A.
    et al.
    Department of Civil Engineering, The University, Dundee, United Kingdom.
    Rahm, Lars
    Oceanographic Institute, University of Gothenburg, Gothenburg, Sweden.
    The interaction between topography and a nonlinearly stratified rotating fluid1982In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 25, no 11, p. 1931-1934Article in journal (Refereed)
    Abstract [en]

    Laboratory experiments have been conducted in which a spherical solid obstacle has been towed steadily through a thermally stratified rotating fluid in order to determine the effects of the density‐profile shape upon the attenuation with height of the disturbance produced by the obstacle. The existence of a cutoff level in the fluid beyond which the disturbance is not detected is illustrated, and the dependence of this level upon local variations in density profile is studied. Measurements of velocity above and behind the obstacle are reported.

  • 21. Geernaert, G.
    et al.
    Humborg, C.
    SU.
    Jordao, L.
    University of Lisboa.
    Langenberg, H.
    GKSS.
    Meire, P.
    Otter, H.S.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Salomons, W.
    GKSS.
    Vidal, M.
    Wallbaum, V.
    Workshop on System Dynamics of the Continuum River Catchment to the Coastal Region.1998In: A trans-disciplinary Euroconference on Coastal Management Research,1997, Haag: RIKZ , 1998Conference paper (Refereed)
  • 22.
    Gidhagen, Lars
    et al.
    Hof SMHI.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Water exchange and dispersion modelling in coastal regions: A method study1990In: Vatten : tidskrift för vattenvård, ISSN 0042-2886, Vol. 46Article in journal (Other academic)
  • 23.
    Gidhagen, Lars
    et al.
    Hof SMHI.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Nyberg, Leif
    Hof SMHI.
    Lagranian modelling of dispersion, sedimentation and resuspension processes in marine environments1989In: Deutsche Hydrographische Zeitschrift, ISSN 0012-0308, Vol. 42, no 3-6, p. 249-270Article in journal (Refereed)
  • 24.
    Humborg, C.
    et al.
    SU.
    Conley, D.
    DMU.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Wulff, F.
    SU.
    Cociasu, A.
    Ittekot, V.
    University of Bremen.
    Silicon retention in river basins: Far-reaching effects on biogeochemistry and aquatic food webs in coastal marine environments2000In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 29, no 1, p. 45-50Article in journal (Refereed)
    Abstract [en]

    Regulation of rivers by damming as well as eutrophication in river basins has substantially reduced dissolved silicon (DSi) loads to the Black Sea and the Baltic Sea. Whereas removal of N and P in lakes and reservoirs can be compensated for by anthropogenic inputs in the drainage basins, no such compensation occurs for DSi. The resulting changes in the nutrient composition (DSi:N:P ratio) of river discharges seem to be responsible for dramatic shifts in phytoplankton species composition in the Black Sea. In the Baltic Sea, DSi concentrations and the DSi:N ratio have been decreasing since the end of the 1960s, and there are indications that the proportion of diatoms in the spring bloom has decreased while flagellates have increased. The effects on coastal biogeochemical cycles and food web structure observed in the Black Sea and the Baltic Sea may be far reaching, because it appears that the reductions in DSi delivery by rivers are probably occurring worldwide with the ever increasing construction of dams for flow regulation.

  • 25.
    Humborg, C.
    et al.
    SU.
    Rahm, Lars
    Linköping University, Department of Thematic Studies, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Smedberg, E.
    SU.
    Mörth, M.
    SU.
    Danielsson, Åsa
    Linköping University, Department of Thematic Studies, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Dissolved silicate dynamics in boreal and subarctic rivers - vegetation control over temperature?2005In: The Silicon Cycle: Human Perturbations and Impacts on aquatic systems / [ed] Venugopalan Ittekkot E, Daniela Unger, Christoph Humborg, Nguyen Tac An, New York: Island Press , 2005, 1, p. 53-69Chapter in book (Other academic)
    Abstract [en]

    Silicon is among the most abundant elements on earth. It plays a key but largely unappreciated role in many biogeochemical processes, including those that regulate climate and undergird marine food webs. The Silicon Cycle is the first book in more than 20 years to present a comprehensive overview of the silicon cycle and issues associated with it. The book summarizes the major outcomes of the project Land-Ocean Interactions: Silica Cycle, initiated by the Scientific Community on Problems of the Environment (SCOPE) of the International Council of Scientific Unions (ICSU). It tracks the pathway of silicon from land to sea and discusses its biotic and abiotic  modifications in transit as well as its cycling in the coastal seas. Natural geological processes in combination with atmospheric and hydrological processes are discussed, as well as human perturbations of the natural controls of the silicon cycle.

  • 26.
    Humborg, Christoph
    et al.
    Department of Systems Ecology, Stockholm University.
    Smedberg, Erik
    Department of Systems Ecology, Stockholm University.
    Blomqvist, Sven
    Department of Systems Ecology, Stockholm University.
    Mörth, Carl-Magnus
    Department of Geology and Geochemistry, Stockholm University.
    Brink, Jenni
    Department of Geology and Geochemistry, Stockholm University.
    Rahm, Lars
    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.
    Sahlberg, Jörgen
    Swedish Meteorological and Hydrological Institute,.
    Nutrient variations in boreal and subarctic Swedish rivers: Landscape control of land–sea fluxes2004In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 49, no 5, p. 1871-1883Article in journal (Refereed)
    Abstract [en]

    We examined the hypothesis that the extent of vegetation cover governs the fluxes of nutrients from boreal and subarctic river catchments to the sea. Fluxes of total organic carbon (TOC) and dissolved inorganic nitrogen, phosphorus, and dissolved silicate (DIN, DIP, and DSi, respectively) are described from 19 river catchments and subcatchments (ranging in size from 34 to 40,000 km2) in northern Sweden with a detailed analysis of the rivers Lulea¨lven and Kalixa¨lven. Fluxes of TOC, DIP, and DSi increase by an order of magnitude with increasing proportion of forest and wetland area, whereas DIN did not follow this pattern but remained constantly low. Principal component analysis on landscape variables showed the importance of almost all land cover and soil type variables associated with vegetation, periglacial environment, soil and bedrock with slow weathering rates, boundary of upper tree line, and percentage of lake area. A cluster analysis of the principal components showed that the river systems could be separated into mountainous headwaters and forest and wetland catchments. This clustering was also valid in relation to river chemistry (TOC, DIP, and DSi) and was confirmed with a redundancy analysis, including river chemistry and principal components as environmental variables. The first axis explains 89% of the variance in river chemistry and almost 100% of the variance in the relation between river chemistry and landscape variables. These results suggest that vegetation change during interglacial periods is likely to have had a major effect on inputs of TOC, DIP, and DSi into the past ocean.

  • 27.
    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.

  • 28.
    Ittekot, V.
    et al.
    University of Bremen.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Swaney, D.
    Cornell University.
    Humborg, C.
    SU.
    Perturbed Silicon Cycle discussed.2000In: Eos, ISSN 0012-7825, Vol. 81, no 18, p. 198-200Article in journal (Refereed)
  • 29.
    Ittekot, Venu
    et al.
    University of Bremen.
    Humborg, Christoph
    SU.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    An, Tac
    Viet Nam.
    Carbon Silicon Interactions.2003In: Interactions of the Major Biogeochemical Cycles: Global Change and Human Impacts / [ed] Jerry M. Melillo, Christopher B. Field, Bedrich Moldan, New York: Island Press , 2003, 1, p. 311-336Chapter in book (Other academic)
    Abstract [en]

    The circulation and interactions of major elements such as carbon, nitrogen, phosphorus, sulphur, oxygen, and hydrogen are critical for the maintenance of the earth's ecosystems. Human activities including agriculture, industry, and urbanization alter element interactions and contribute to major environmental problems ranging from climate change and depletion of the ozone layer to acidification of soils to the destruction of coral reefs.

    Interactions of the Major Biogeochemical Cyclesis a new scientific assessment of element interactions in the biosphere. It provides an up-to-date review of biogeochemistry and its effects on earth's systems, with leading experts in biogeochemical cycling in atmospheric, land, freshwater, and marine environments offering chapters that summarize and synthesize information in each discipline.

    The book opens with chapters on cross-cutting issues that have significance in understanding global change effects and their potential management. These chapters address:

    * trends in element interactions in response to global change

    • the effects of natural disturbances
    • new approaches and methods for advancing our understanding of element interactions
    • the potential for managing element interactions to address major environmental issues
  • 30.
    Jönsson, Anette
    et al.
    TEMA LiU.
    Broman, B.
    SMHI.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Wave dynamics of the Baltic2002In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 30, p. 107-126Article in journal (Refereed)
  • 31.
    Jönsson, Anette
    et al.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Broman, Barry
    SMHI, S-601 76, Norrköping, Sweden.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Variations in the Baltic Sea wave fields2003In: Ocean Engineering, ISSN 0029-8018, Vol. 30, no 1, p. 107-126Article in journal (Refereed)
    Abstract [en]

    The surface waves in the Baltic Sea are hindcast with the spectral wave model HYPAS during a 12-month period. The model results show a strong temporal and spatial variation in the wave field due to the physical dimensions of the different basins and the predominant wind field. The highest waves in the area are found in the outer part of Skagerrak, as well as in the central and southern parts of the Baltic Proper. To get significant waves above 6 m high, strong winds (15–20 m/s) must have been blowing for 6 to 24 h from a favourable direction over a deep area.

  • 32.
    Jönsson, Anette
    et al.
    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.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Bottom type distribution based on wave friction velocity in the Baltic Sea2005In: Continental Shelf Research, ISSN 0278-4343, Vol. 25, no 3, p. 419-435Article in journal (Refereed)
    Abstract [en]

    Surface waves play an important role for the sediment distribution in the shallow Baltic Sea. This paper presents the large-scale spatio-temporal distribution of wave-induced bottom friction velocity, u*, based on modelled wave data for the years 1999 and 2000. The highest values of u* are found along the eastern coasts of the Baltic Proper and Bothnian Sea—areas characterised by long fetches for the dominant winds. Temporally, the dynamics follow that of the wind climate with higher velocities during winter and lower during summer.

    A smooth bottom is assumed for the calculations. To test this assumption, u* is compared to other estimates of u* assuming rough bottoms. The spatio-temporal patterns are similar, although the present approach gives a slight underestimation of u* at areas with coarse grain sizes.

    To compare the results, the co-variation between the u* distribution and bottom type distribution from a digitised sediment map is analysed. It shows upon a good agreement. This is also found when comparing critical levels for resuspension found in the literature with the same from modelled u*. In addition, other processes important for bottom stress, such as mesoscale eddies and coastal jets, are discussed.

  • 33.
    Lundberg, Peter
    et al.
    Dept. of Oceanograpphy Göteborg University.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Frequency locking in a periodically forced thermal two-phase oscillator1984In: Dynamics of atmospheres and oceans (Print), ISSN 0377-0265, E-ISSN 1872-6879, Vol. 8, p. 59-72Article in journal (Refereed)
  • 34. Lundberg, Peter
    et al.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Lundberg, Peter
    Dept. of Oceanography Göteborg University.
    A nonlinear convective system with oscillatory behaviour for cewrtain parameter regimes1984In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 139, p. 237-260Article in journal (Refereed)
  • 35.
    Morth, Carl-Magnus
    et al.
    Stockholms universitet.
    Humborg, Christoph
    Stockholms universitet.
    Eriksson, Hanna
    Stockholms universitet.
    Danielsson, Åsa
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Medina, Miguel Rodriguez
    Stockholms universitet.
    Lofgren, Stefan
    SLU.
    Swaney, Dennis P.
    Cornell University.
    Rahm, Lars
    Linköping University, Faculty of Arts and Sciences. Linköping University, The Tema Institute, Department of Water and Environmental Studies.
    Modeling riverine nutrient transport to the Baltic Sea: A large-scale approach2007In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 36, no 02-Mar, p. 124-133Article in journal (Refereed)
    Abstract [en]

    We developed for the first time a catchment model simulating simultaneously the nutrient land-sea fluxes from all 105 major watersheds within the Baltic Sea drainage area. A consistent modeling approach to all these major watersheds, i.e., a consistent handling of water fluxes (hydrological simulations) and loading functions (emission data), will facilitate a comparison of riverine nutrient transport between Baltic Sea subbasins that differ substantially. Hot spots of riverine emissions, such as from the rivers Vistula, Oder, and Daugava or from the Danish coast, can be easily demonstrated and the comparison between these hot spots, and the relatively unperturbed rivers in the northern catchments show decisionmakers where remedial actions are most effective to improve the environmental state of the Baltic Sea, and, secondly, what percentage reduction of riverine nutrient loads is possible. The relative difference between measured and simulated fluxes during the validation period was generally small. The cumulative deviation (i.e., relative bias) [Sigma(Simulated - Measured)/Sigma Measured X 100 (%)] from monitored water and nutrient fluxes amounted to+8.2% for runoff, to-2.4% for dissolved inorganic nitrogen, to +5.1% for total nitrogen, to +13% for dissolved inorganic phosphorus and to +19% for total phosphorus. Moreover, the model suggests that point sources for total phosphorus compiled by existing pollution load compilations are underestimated because of inconsistencies in calculating effluent loads from municipalities.

  • 36.
    Pacini, N
    et al.
    Ministry of Environment Italy.
    Harper, DM
    Department of Zoology Egerton University, Kenya.
    Ittekkot, V
    Center for Tropical Marine Ecology Bremen, Germany.
    Humborg, C
    ITM Stockholm University.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Nutrient Processes and Consequences.2008In: Ecohydrology; Processes, Models and Case Studies / [ed] David Harper, Maciej Zalewski and Nic Pacini., Oxford: Oxford University Press , 2008, p. -391Chapter in book (Other academic)
    Abstract [en]

        This book contains 15 chapters dealing with the integration of ecology with hydrology at the river basin scale. The patterns and processes in the catchment including nutrients, lotic vegetation and aquatic faunal processes are covered. In addition, the benefits and risks of ecological modelling to water management and nutrient budget modelling for lakes and watershed restoration are discussed. The roles of ecohydrology in managing the savannah ecosystem, agricultural landscape, and watershed development are explored.

  • 37.
    Papush, Liana
    et al.
    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.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Dissolved silica budget for the Baltic Sea2009In: Journal of Sea Research, ISSN 1385-1101, E-ISSN 1873-1414, Vol. 62, no 1, p. 31-41Article in journal (Refereed)
    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.

  • 38.
    Papush, Liana
    et al.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Henningsson, Markus
    Linköping University, Department of Management and Engineering, Industrial Marketing and Industrial Economics. Linköping University, The Institute of Technology.
    Rahm, Lars
    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.
    Optimised water budget of the Gulf of Bothnia (Baltic Sea)2008Manuscript (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.

  • 39.
    Pers, C
    et al.
    Swedish Meteorol & Hydrol Inst, SE-60176 Norrkoping, Sweden Linkoping Univ, Dept Water & Environm Studies, SE-58183 Linkoping, Sweden Climate Impacts Res Ctr, SE-98107 Abisko, Sweden Umea Univ, Dept Ecol & Environm Sci, SE-90187 Umea, Sweden.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Jonsson, A
    Bergstrom, AK
    Jansson, M
    Modelling dissolved organic carbon turnover in humic Lake Ortrasket, Sweden2001In: Environmental Modelling and Assessment, ISSN 1420-2026, E-ISSN 1573-2967, Vol. 6, no 3, p. 159-172Article in journal (Refereed)
    Abstract [en]

    The organic carbon balance of a lake with high input of allochthonous organic carbon is modelled integrating physical, chemical and biological processes. The physical model captures the behaviour of real thermal stratification in the lake for different flow situations during the period 1993-1997. The dissolved organic carbon model is based on simulated trajectories of water parcels. By tracking parcels, account is kept of environmental factors such as temperature and radiation as well as DOC quality for each parcel, The DOC concentration shows seasonal variations primarily dependent on inflow. The organic matter degradation (bacterial- and photodegradation) in the lake amounts to 1.5-2.5 mg C l(-1) yr(-1), where photooxidation is responsible for approximately 10%. The estimated DIC production in the lake is large compared to sediment mineralisation and primary production. The main conclusion is that the model with the selected parameterisations of the degradation processes reasonably well describes the DOC dynamics in a forest lake.

  • 40.
    Pers, Charlotta
    et al.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Hansson, Sture
    Dept. of Systems Ecology, Stockholm University, Sweden.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Long term changes in spawning volume for Baltic Sea cod (Gadus morhua)Manuscript (preprint) (Other academic)
    Abstract [en]

    In the brackish Baltic Sea, cod (Gadus morhua) can reproduce only in a few deep areas, of which the Eastern Gotland basin and the Bornholm basin are the most important ones. Successful spawning requires oxygen concentrations larger than 2 ml r-1 and salinity larger than 11. The water domain that meets these requirements is referred to as the cod spawning volume. Salinity and oxygen data were collected during the period 1905-1997 and 1923-1997 from the Eastern Gotland basin and the Bornholm basin respectively. They have been analysed for changes in spawning volume over time. For each sampling occasion the spawning volume was calculated based on depth specific vertical distribution of salinity and oxygen concentration, combined with bathymetric data. The Bornholm basin constitutes a stable but limited spawning area for cod, contrary to the Eastern Gotland basin where the spawning volume is more uncertain but can be much larger. The estimated spawning volume decreased over time in the Eastern Gotland basin. This change is probably caused by increased deepwater oxygen demand due to increased organic material load from primary production. The latter is an effect of the ongoing eutrophication.

  • 41.
    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.

  • 42.
    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.
    Model simulation of the effects of climate change and river regulation on a humic lakeManuscript (preprint) (Other academic)
    Abstract [en]

    Allochthonous dissolved organic matter (DOM) plays an important role in the food web of boreal lakes in the temperate zone by providing energy and nutrients (Tranvik, 1992). It also governs environmental conditions like light attenuation of the water mass (Schindler et al., 1996). Allochthonous DOM is together with primary production the primary carbon source of the food web in these lakes. In some lakes rich in humic substances (HS), DOM is more important than the primary production for the microbial production (e.g. Jansson et al., 1999).

    However, our knowledge about fate and kinetics of the terrestrial DOM and thus TOC (total organic carbon) is poor. In spite of this, it has important implications for the terrestrial and marine ecosystems as well as the global carbon cycle. The role of rivers and lakes in this degradation process has been studied in the past and one result is that only those systems with long hydraulic residence time may significantly alter the TOC composition and concentration (Curtis, 1998; Pers et al., 2000). In fact, peat and sediments in lakes and coastal waters represent the only significant long-term carbon sinks in the ecosystem of northern Scandinavia (Erikssson, 1991 ). The riverine organic matter that escapes these systems will be most likely degraded in the marine environment. In fact, of the annual sedimentation of roughly 20 g C m·' yr·' in the Bothnian Bay, up to 90% may be remineralised, the carbon is probably released as COz, and only about 2 g C m·' yr'1 is assumed to be sequestered (Eimgren, 1984). These figures support a rapid decomposition of terrestrial humic substances in the marine environment. Also, Carlsson and Graneli (1993) have shown that organic bound nitrogen in humic substances may enhance marine phytoplanktongrowth. Thus the humic substances support the marine production in this Bay.

  • 43.
    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.
    Danielsson, Åsa
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Statistical modelling of the phosphate variations in the Baltic proper1997In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 2, no 3, p. 303-315Article in journal (Refereed)
    Abstract [en]

    A statistical model of the variation of phosphate concentration in the upper layers of the Baltic proper was formed, with the aim of studying the magnitude of this variation and to be able to adjust corrupted time series. The large variation observed is only partially explained by seasonal variations and geographical structures. Despite inclusion of longterm trends and annual variations, the residuals showed a substantial correlation within and between the time series.

  • 44.
    Pers, Charlotta
    et al.
    Swedish Meteorological and Hydrological Institute.
    Rahm, Lars
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Jonsson, Anders
    Climate Impacts Research Centre, Abisko, Sweden \ Dept. of Ecology and Environmental Science, Umeå University, Sweden.
    Bergström, Ann-Kristin
    Dept. of Ecology and Environmental Science, Umeå University, Sweden.
    Jansson, Mats
    Dept. of Ecology and Environmental Science, Umeå University, Sweden.
    Modelling dissolved organic carbon turnover in humic Lake Örträsket, Sweden.2001In: Environmental Monitoring & Assessment, ISSN 0167-6369, E-ISSN 1573-2959, Vol. 6, no 3, p. 159-172Article in journal (Refereed)
    Abstract [en]

    The organic carbon balance of a lake with high input of allochthonous organic carbon is modelled integrating physical, chemical and biological processes. The physical model captures the behaviour of real thermal stratification in the lake for different flow situations during the period 1993–1997. The dissolved organic carbon model is based on simulated trajectories of water parcels. By tracking parcels, account is kept of environmental factors such as temperature and radiation as well as DOC quality for each parcel. The DOC concentration shows seasonal variations primarily dependent on inflow. The organic matter degradation (bacterial- and photodegradation) in the lake amounts to 1.5–2.5 mg C l–1 yr–1, where photooxidation is responsible for approximately 10%. The estimated DIC production in the lake is large compared to sediment mineralisation and primary production. The main conclusion is that the model with the selected parameterisations of the degradation processes reasonably well describes the DOC dynamics in a forest lake.

  • 45.
    Pettersson, Catharina
    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 molecular weight of humic substances in the Gulf of Bothnia1996In: Environment International, ISSN 0160-4120, E-ISSN 1873-6750, Vol. 22, no 5, p. 551-558Article in journal (Refereed)
    Abstract [en]

    Humic substances were isolated in the brackish Gulf of Bothnia utilizing two techniques: ion exchange on DEAE-cellulose and hydrophobic interaction on XAD-8 resin. The salinity of the water resulted in different yields for the two adsorbents. With XAD-8 resin, 30–80% of the organic carbon was isolated, whereas 5–20% was isolated on the DEAE-cellulose. The concentration of total organic carbon was rather constant but the concentration of humic substances decreased with increasing salinity. Gel filtration was used to measure the homogeneity of the humic fraction. Humic substances isolated in December were more homogeneous than those isolated in June, which indicates a degradation during the summer period which might be caused by photolysis or increased microbial degradation during the warm season.

  • 46.
    Pettersson, Catharina
    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.
    Allard, B.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Borén, H.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Photodegradation of aquatic humic substances: an important factor for the Baltic carbon cycle?1997In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 2, no 2, p. 209-215Article in journal (Refereed)
    Abstract [en]

    Although humic substances (HS) are often considered as chemically stable and non-biodegradable in a marine environment, it is well known that exposure to light will lead to a decomposition of these substances. Laboratory experiments of photodegradation by UV-irradiation of aquatic humic substances and natural water resulted in a rapid and quantitative degradation. Seasonal variations in the humic fraction of the total organic carbon (TOC) was indicated in field studies in humic-rich water in Sweden. The HS/TOC-ratio was considerably higher during the dark part of the year than during the light season. Both the laboratory results and the field studies indicate the potential importance of photodegradation of HS and formation of CO2 for the global carbon cycle, though other mechanisms like microbial degradation are possible. Furthermore, the formation of biodegradable low-molecular weight organic acids from terrestrial humic substances may be essential for partly heterotrophic systems like the Bothnian Bay.

  • 47.
    Rahm, Lars
    Swedish Meteorological and Hydrological Institute, Norrköping, Sweden.
    A note on some hydrographic properties of the Eastern Gotland Basin1988In: Beiträge fur Meereskunde, ISSN 0067-5148, Vol. 58, p. 47-58Article in journal (Refereed)
    Abstract [en]

    Mean values of salinity, temperature and oxygen concentrations are determined for the hydrographic station Gotland Deep (BY15) by field data obtained from the Fishery Board of Sweden for the period 1957-1982. These estimates are compared with the corresponding values of the entire basin, the Eastern Gotland Basin, which are attained by a volume-weighted procedure based on eight hydrographic stations in this area.

  • 48.
    Rahm, Lars
    Linköping University, Faculty of Arts and Sciences. Linköping University, The Tema Institute, Department of Water and Environmental Studies.
    A note on the heat-up of an initially isotherm fluid1985In: Mathematical Modelling, ISSN 0270-0255, E-ISSN 1878-7231, Vol. 6, p. 19-30Article in journal (Refereed)
  • 49.
    Rahm, Lars
    Linköping University, Faculty of Arts and Sciences. Linköping University, Department of Thematic Studies, Department of Water and Environmental Studies.
    Hur har närsalternas koncentration och fördelning ändrats i utsjön?1995In: Forskningsnytt, Vol. 3, p. 18-24Article in journal (Other (popular science, discussion, etc.))
  • 50.
    Rahm, Lars
    Department of Oceanography, University of Gothenburg, Göteborg, Sweden.
    Note on the occurrence of double-diffusive convection in the Baltic Proper1987In: Geophysica, ISSN 0367-4231, E-ISSN 2324-0741, Vol. 23, no 1, p. 47-57Article in journal (Other academic)
    Abstract [en]

    No abstract available.

12 1 - 50 of 100
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