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  • 1.
    Alling, Vanja
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Rahm, Lars
    Polehne, Falk
    Tracing terrestrial organic matter by delta34S and delta13C 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 34S and 13C 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 (34SDOS) have twice the range between terrestrial and marine end members compared to the stable isotope signatures for dissolved organic carbon (13CDOC); 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 13CDOC and 34SDOS signatures and applying fixed C: S ratios for riverine and marine end members to convert S isotope signatures into DOC concentrations. The 34SDOS signature of the riverine end member was +7.02‰, and the mean signatures from Bothnian Bay, Bothnian Sea, and Baltic proper were +10.27, +12.51, and +13.67‰, respectively, showing an increasing marine signal southwards (34SDOS marine end member 5 18.1‰). 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.

  • 2.
    Alling, Vanja
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Porcelli, D.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Anderson, L. G.
    Sanchez-Garcia, L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, P. S.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Degradation of terrestrial organic carbon, primary production and out-gassing of CO2 in the Laptev and East Siberian Seas as inferred from delta C-13 values of DIC2012In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 95, p. 143-159Article in journal (Refereed)
    Abstract [en]

    The cycling of carbon on the Arctic shelves, including outgassing of CO2 to the atmosphere, is not clearly understood. Degradation of terrestrial organic carbon (OCter) has recently been shown to be pronounced over the East Siberian Arctic Shelf (ESAS), i.e. the Laptev and East Siberian Seas, producing dissolved inorganic carbon (DIC). To further explore the processes affecting DIC, an extensive suite of shelf water samples were collected during the summer of 2008, and assessed for the stable carbon isotopic composition of DIC (delta C-13(DIC)). The delta C-13(DIC) values varied between -7.2 parts per thousand to +1.6 parts per thousand and strongly deviated from the compositions expected from only mixing between river water and seawater. Model calculations suggest that the major processes causing these deviations from conservative mixing were addition of (DIC) by degradation of OCter, removal of DIC during primary production, and outgassing of CO2. All waters below the halocline in the ESAS had delta C-13(DIC) values that appear to reflect mixing of river water and seawater combined with additions of on average 70 +/- 20 mu M of DIC, originating from degradation of OCter in the coastal water column. This is of the same magnitude as the recently reported deficits of DOCter and POCter for the same waters. The surface waters in the East Siberian Sea had higher delta C-13(DIC) values and lower DIC concentrations than expected from conservative mixing, consistent with additions of DIC from degradation of OCter and outgassing of CO2. The outgassing of CO2 was equal to loss of 123 +/- 50 mu M DIC. Depleted delta C-13(POC) values of -29 parts per thousand to -32 parts per thousand in the mid to outer shelf regions are consistent with POC from phytoplankton production. The low delta C-13(POC) values are likely due to low delta C-13(DIC) of precursor DIC, which is due to degradation of OCter, rather than reflecting terrestrial input compositions. Overall, the delta C-13(DIC) values confirm recent suggestions of substantial degradation of OCter over the ESAS, and further show that a large part of the CO2 produced from degradation has been outgassed to the atmosphere.

  • 3.
    Alling, Vanja
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Sanchez-Garcia, Laura
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Porcelli, Don
    Pugach, Sveta
    Vonk, Jorien E.
    van Dongen, Bart
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Stockholm Resilience Centre.
    Anderson, Leif G.
    Sokolov, Alexander
    Stockholm University, Stockholm Resilience Centre.
    Andersson, Per
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Stockholm Resilience Centre.
    Semiletov, Igor
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Non-conservative behavior of dissolved organic carbon across the Laptev and East Siberian Seas2010In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 24, p. GB4033-Article in journal (Refereed)
    Abstract [en]

    Climate change is expected to have a strong effect on the Eastern Siberian Arctic Shelf (ESAS) region, which includes 40% of the Arctic shelves and comprises the Laptev and East Siberian seas. The largest organic carbon pool, the dissolved organic carbon (DOC), may change significantly due to changes in both riverine inputs and transformation rates; however, the present DOC inventories and transformation patterns are poorly understood. Using samples from the International Siberian Shelf Study 2008, this study examines for the first time DOC removal in Arctic shelf waters with residence times that range from months to years. Removals of up to 10%–20% were found in the Lena River estuary, consistent with earlier studies in this area, where surface waters were shown to have a residence time of approximately 2 months. In contrast, the DOC concentrations showed a strong nonconservative pattern in areas with freshwater residence times of several years. The average losses of DOC were estimated to be 30%–50% during mixing along the shelf, corresponding to a first-order removal rate constant of 0.3 yr−1. These data provide the first observational evidence for losses of DOC in the Arctic shelf seas, and the calculated DOC deficit reflects DOC losses that are higher than recent model estimates for the region. Overall, a large proportion of riverine DOC is removed from the surface waters across the Arctic shelves. Such significant losses must be included in models of the carbon cycle for the Arctic Ocean, especially since the breakdown of terrestrial DOC to CO2 in Arctic shelf seas may constitute a positive feedback mechanism for Arctic climate warming. These data also provide a baseline for considering the effects of future changes in carbon fluxes, as the vast northern carbon-rich permafrost areas draining into the Arctic are affected by global warming.

  • 4. Andersen, Hans Estrup
    et al.
    Blicher-Mathiesen, Gitte
    Thodsen, Hans
    Mejlhede Andersen, Peter
    Larsen, Søren E.
    Stålnacke, Per
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Smedberg, Erik
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Identifying Hot Spots of Agricultural Nitrogen Loss Within the Baltic Sea Drainage Basin2016In: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932, Vol. 227, no 1Article in journal (Refereed)
    Abstract [en]

    Agricultural management practices are among the major drivers of agricultural nitrogen (N) loss. Legislation and management incentives for measures to mitigate N loss should eventually be carried out at the individual farm level. Consequently, an appropriate scale to simulate N loss from a scientific perspective should be at the farm scale. A data set of more than 4000 agricultural fields with combinations of climate, soils and agricultural management which overall describes the variations found in the Baltic Sea drainage basin was constructed. The soil-vegetation-atmosphere model Daisy (Hansen et al. 2012) was used to simulate N loss from the root zone of all agricultural fields in the data set. From the data set of Daisy simulations, we identified the most important drivers for N loss by multiple regression statistics and developed a statistical N loss model. By applying this model to a basin-wide data set on climate, soils and agricultural management at a 10 x 10 km scale, we were able to calculate root-zone N losses from the entire Baltic Sea drainage basin and identify N loss hot spots in a consistent way and at a level of detail not hitherto seen for this area. Further, the root-zone N loss model was coupled to estimates of nitrogen retention in catchments separated into retention in groundwater and retention in surface waters allowing calculation of the coastal N loading.

  • 5. Anderson, Leif G.
    et al.
    Björk, Göran
    Holby, Ola
    Jutterström, Sara
    Mörth, Carl Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark.
    Semiletov, Igor
    Stranne, Christian
    Stöven, Tim
    Tanhua, Toste
    Ulfsbo, Adam
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Shelf-Basin interaction along the East Siberian Sea2017In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 13, no 2, p. 349-363Article in journal (Refereed)
    Abstract [en]

    Extensive biogeochemical transformation of organic matter takes place in the shallow continental shelf seas of Siberia. This, in combination with brine production from sea-ice formation, results in cold bottom waters with relatively high salinity and nutrient concentrations, as well as low oxygen and pH levels. Data from the SWERUS-C3 expedition with icebreaker Oden, from July to September 2014, show the distribution of such nutrient-rich, cold bottom waters along the continental margin from about 140 to 180 degrees E. The water with maximum nutrient concentration, classically named the upper halocline, is absent over the Lomonosov Ridge at 140 degrees E, while it appears in the Makarov Basin at 150 degrees E and intensifies further eastwards. At the intercept between the Mendeleev Ridge and the East Siberian continental shelf slope, the nutrient maximum is still intense, but distributed across a larger depth interval. The nutrient-rich water is found here at salinities of up to similar to 34.5, i.e. in the water classically named lower halocline. East of 170 degrees E transient tracers show significantly less ventilated waters below about 150 m water depth. This likely results from a local isolation of waters over the Chukchi Abyssal Plain as the boundary current from the west is steered away from this area by the bathymetry of the Mendeleev Ridge. The water with salinities of similar to 34.5 has high nutrients and low oxygen concentrations as well as low pH, typically indicating decay of organic matter. A deficit in nitrate relative to phosphate suggests that this process partly occurs under hypoxia. We conclude that the high nutrient water with salinity similar to 34.5 are formed on the shelf slope in the Mendeleev Ridge region from interior basin water that is trapped for enough time to attain its signature through interaction with the sediment.

  • 6.
    Andersson, Rina Argelia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Meyers, Philip
    Department of Earth and Environmental Sciences, The University of Michigan, Ann Arbor, Michigan, U.S.A..
    Zebür, Yngve
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Impacts of paleohydrological changes on n-alkane biomarker compositions of a Holocene peat sequence in the eastern European Russian Arctic2011In: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 42, no 9, p. 1065-1075Article in journal (Refereed)
    Abstract [en]

    Coupled analyses of n-alkane biomarkers and plant macrofossils from a peat plateau deposit in the northeast European Russian Arctic were carried out to assess the effects of past hydrology on the molecular contributions of plants to the peat. The n-alkane biomarkers accumulated over 9.6 kyr of local paleohydrological changes in this complex peat profile in which a succession of vegetation changes occurred during a transition from a wet fen to a relatively dry peat plateau bog. This study shows that the contribution of the n-C31 alkane from rootlets to peat layers rich in fine and dark roots is important. The results further indicate that the n-alkanePaqandn-C23/n-C29 biomarker proxies that have been useful to reconstruct past water table levels in many peat deposits can be misleading when the contributions of Betulaand Sphagnum fuscum to the peat are large. Under these conditions, the C23/(C27+ C31) n-alkane ratio seems to correct for the presence of BetulaandS. fuscum and provides a better description for the relative amounts of moisture. The average chain length (ACL) n-alkane proxy also appears to be a good paleohydrology proxy in having larger values during dry and cold conditions in this Arctic bog setting.

  • 7.
    Andersson, Rina Argelia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Meyers, Philip
    Department of Earth and Environmental Sciences, The University of Michigan, Ann Arbor, Michigan, U.S.A..
    Hornibrook, Edward
    Bristol Biogeochemistry Research Centre & Cabot Institute, School of Earth Sciences, University of Bristol, Queens Road, Bristol BS8 1RJ, United Kingdom.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Mörth, Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Elemental and isotopic carbon and itrogen records of organic matter accumulation in a Holocene permafrots peat sequence in the East European Russian ArcticManuscript (preprint) (Other academic)
    Abstract [en]

    A peat deposit from the East European Russian Arctic, spanning nearly 10,000 years, was investigated to reconstruct past environmental conditions and to study soil organic matter (SOM) degradation using analyses of bulk elemental and stable isotopic compositions and plant macrofossil remains. The peat accumulated initially in a wet fen that transformed into a peat plateau bog following aggradation of permafrost in the late Holocene (~2,500 cal a BP). Total organic carbon (TOC) and total nitrogen (N) concentrations are different in the bog peat compared to the fen peat, with lower values in the moss-dominated bog peat layers.  Lower concentrations of total hydrogen (H) are associated with degraded vascular plant residues.  The atomic ratios of bulk elemental parameters indicate better preservation of organic matter in peat deposits dominated by bryophytes relative to vascular plants.  The presence of permafrost in the peat plateau stage and water-saturated conditions at the bottom of the fen stage appear to be associated with better preservation of organic plant material.  δ15N values suggest N isotopic fractionation was driven primarily by microbial decomposition while differences in δ13C values appear to be associated mainly with changes in plant assemblages rather than diagenesis.  Positive shifts in both δ15N and δ13C values coincide with a local change to drier conditions as a result of the onset of permafrost and frost heave of the peat surface.  This pattern suggests that permafrost aggradation not only resulted in changes in vegetation but also aerated the underlying fen peat, which enhanced microbial denitrification, causing the observed 15N-enrichment.

  • 8.
    Andrén, Margareta
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stockmann, Gabrielle
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sturkell, Erik
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Guðrúnardóttir, Helga Rakel
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Keller, Nicole Simone
    Odling, Nic
    Dahrén, Börje
    Broman, Curt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Balic-Zunic, Tonci
    Hjartarson, Hreinn
    Siegmund, Heike
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Freund, Friedemann
    Kockum, Ingrid
    Coupling between mineral reactions, chemical changes in groundwater, and earthquakes in Iceland2016In: Journal of Geophysical Research - Solid Earth, ISSN 2169-9313, E-ISSN 2169-9356, Vol. 121, no 4, p. 2315-2337Article in journal (Refereed)
    Abstract [en]

    Chemical analysis of groundwater samples collected from a borehole at Hafralaekur, northern Iceland, from October 2008 to June 2015 revealed (1) a long-term decrease in concentration of Si and Na and (2) an abrupt increase in concentration of Na before each of two consecutive M 5 earthquakes which occurred in 2012 and 2013, both 76km from Hafralaekur. Based on a geochemical (major elements and stable isotopes), petrological, and mineralogical study of drill cuttings taken from an adjacent borehole, we are able to show that (1) the long-term decrease in concentration of Si and Na was caused by constant volume replacement of labradorite by analcime coupled with precipitation of zeolites in vesicles and along fractures and (2) the abrupt increase of Na concentration before the first earthquake records a switchover to nonstoichiometric dissolution of analcime with preferential release of Na into groundwater. We attribute decay of the Na peaks, which followed and coincided with each earthquake to uptake of Na along fractured or porous boundaries between labradorite and analcime crystals. Possible causes of these Na peaks are an increase of reactive surface area caused by fracturing or a shift from chemical equilibrium caused by mixing between groundwater components. Both could have been triggered by preseismic dilation, which was also inferred in a previous study by Skelton et al. (2014). The mechanism behind preseismic dilation so far from the focus of an earthquake remains unknown.

  • 9.
    Barrientos, Natalia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen
    Lear, Caroline
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl-Magnus
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mg/Ca ratios in late Quaternary benthic foraminifera from the central Arctic OceanManuscript (preprint) (Other academic)
  • 10.
    Barrientos, Natalia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Miller, Clint
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Johansson, Carina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Post-recovery dissolution of calcareous microfossils in sediments from a highly productive Arctic marine environmentManuscript (preprint) (Other academic)
  • 11. Berggren, A. -M
    et al.
    Aldahan, A.
    Possnert, G.
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Steen-Larsen, H. C.
    Storm, A. Sturevik
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Murad, A.
    Variability of Be-10 and delta O-18 in snow pits from Greenland and a surface traverse from Antarctica2013In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 294, p. 568-572Article in journal (Refereed)
    Abstract [en]

    To examine temporal variability of Be-10 in glacial ice, we sampled snow to a depth of 160 cm at the NEEM (North Greenland Eemian Ice Drilling) drilling site in Greenland. The samples span three years between the summers of 2006 and 2009. At the same time, spatial variability of Be-10 in glacial ice was explored through collection of the upper similar to 5 cm of surface snow in Antarctica during part of the Swedish-Japanese traverse from Svea to Syowa station during the austral summer in 2007-2008. The results of the Greenlandic 1 Be snow suggested variable concentrations that apparently do not clearly reflect the seasonal change as indicated by the delta O-18 data. The Be-10 concentration variability most likely reflects also effects of aerosol loading and deposition pathways, possibly in combination with post-depositional processes. The Antarctic traverse data expose a negative correlation between Be-10 and delta O-18, while there are weaker but still significant correlations to altitude and distance to the coast (approximated by the distance to the 70th latitude). These relationships indicate that geographical factors, mainly the proximity to the coast, may strongly affect 1 Be concentrations in snow in Queen Maud Land, Antarctica.

  • 12.
    Björkvald, Louise
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Buffam, Ishi
    Laudon, Hjalmar
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hydrogeochemistry of Fe and Mn in small boreal streams: The role of seasonality, landscape type and scale2008In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, Vol. 72, no 12, p. 2789-2804Article in journal (Refereed)
    Abstract [en]

    Stream water from a stream network of 15 small boreal catchments (0.03–67 km2) in northern Sweden was analyzed for unfiltered (total) and filtered (<0.4 μm) concentrations of iron (Fetot and Fe<0.4) and manganese (Mntot and Mn<0.4). The purpose was to investigate the temporal and spatial dynamics of Fe, Mn and dissolved organic carbon (DOC) as influenced by snow melt driven spring floods and landscape properties, in particular the proportion of wetland area. During spring flood, concentrations of Fetot, Fe<0.4, Mntot, Mn<0.4 and DOC increased in streams with forested catchments (<2% wetland area). In catchments with high coverage of wetlands (>30% wetland area) the opposite behavior was observed. The hydrogeochemistry of Fe was highly dependent on wetlands as shown by the strong positive correlation of the Fetot/Altot ratio with wetland coverage (r2 = 0.89, p < 0.001). Furthermore, PCA analysis showed that at base flow Fetot and Fe<0.4 were positively associated with wetlands and DOC, whereas they were not associated during peak flow at spring flood. The temporal variation of Fe was likely related to varying hydrological pathways. At peak discharge Fetot was associated with variables like silt coverage, which highlights the importance of particulates during high discharge events. For Mn there was no significant correlation with wetlands, instead, PCA analysis showed that during spring flood Mn was apparently more dependent on the supply of minerogenic particulates from silt deposits on the stream banks of some of the streams. The influence of minerogenic particulates on the concentration of, in particular, Mn was greatest in the larger, lower gradient streams, characterized by silt deposits in the near-stream zone. In the small forested streams underlain by till, DOC was of greater importance for the observed concentrations, as indicated by the positive correlation of both Fetot and Fe<0.4 with DOC (r2 = 0.77 and r2 = 0.76, p < 0.001) at the smallest headwater forest site. In conclusion, wetland area and DOC were important for Fe concentrations in this boreal stream network, whereas silt deposits strongly influenced Mn concentrations. This study highlights the importance of studying stream water chemistry from a landscape perspective in order to address future environmental issues concerning mobility of Fe, Mn and associated trace metals.

  • 13.
    Björkvald, Louise
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Giesler, R.
    Laudon, H.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Landscape variations in stream water SO42- and delta S-34(SO4) in a boreal stream network2009In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 73, no 16, p. 4648-4660Article in journal (Refereed)
    Abstract [en]

    Despite reduced anthropogenic deposition during the last decades, deposition sulphate may still play an important role in the biogeochemical cycles of S and many catchments may act as net sources of S that may remain for several decades. The aim of this study is to elucidate the temporal and spatial dynamics of both SO42- and delta S-34(SO4) in stream water from catchments with varying percentage of wetland and forest coverage and to determine their relative importance for catchment losses of S. Stream water samples were collected from 15 subcatchments ranging in size from 3 to 6780 ha, in a boreal stream network, northern Sweden. In forested catchments (2% wetland cover) S-SO42- concentrations in stream water averaged 1.7 mg L-1 whereas in wetland dominated catchments (30% wetland cover) the concentrations averaged 0.3 mg L-1. A significant negative relationship was observed between S-SO42- and percentage wetland coverage (r(2) = 0.77, p  0.001) and the annual export of stream water SO42- and wetland coverage (r(2) = 0.76 p  0.001). The percentage forest coverage was on the other hand positively related to stream water SO42- concentrations and the annual export of stream water SO42- (r(2) = 0.77 and r(2) = 0.79, respectively). The annual average delta S-34(SO4) value in wetland dominated streams was +7.6%omicron. and in streams of forested catchments +6.7%omicron. At spring flood the delta S-34(SO4) values decreased in all streams by 1%omicron to 5%omicron. The delta S-34(SO4) values in all streams were higher than the delta S-34(SO4) value of +4.7%omicron in precipitation (snow). The export of S ranged from 0.5 kg S ha(-1) yr(-1) (wetland headwater stream) to 3.8 kg S ha(-1) yr(-1) (forested headwater stream). With an average S deposition in open field of 1.3 kg S ha(-1) yr(-1) (2002-2006) the mass balance results in a net export of S from all catchments, except in catchments with 30% wetland. The high temporal and spatial resolution of this study demonstrates that the reducing environments of wetlands play a key role for the biogeochemistry of S in boreal landscapes and are net sinks of S. Forested areas, on the other hand were net sources of S.

  • 14.
    Björkvald, Louise
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Geokemi.
    Laudon, Hjalmar
    Borg, Hans
    Department of Applied Environmental Science (ITM).
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Trace metals and sulphur isotopes in samll boreal streams: the influence of landscape type2008In: 2008 Ocean Sciences Meeting: From the watershed to the global ocean, 2008, p. 1-Conference paper (Refereed)
    Abstract [en]

    The transport of trace metals (TM) and dissolved organic carbon (DOC) from headwater streams to the sea is influenced by various landscape elements. Our focus was to investigate the influence of major landscape elements on observed concentrations of dissolved metals (e.g. As, Cd, Co, Fe, Pb), DOC, sulphate, and sulphur isotope composition in streams, north- eastern Sweden, a coastal region characterized by peat wetlands and coniferous forests.

    Stream water samples collected from 10 streams (0.13 to 67 km2) in a boreal stream network reveal that landscape type (i.e. coverage of wetland and forest) is significant for river chemistry. Streams with different catchment characteristics responded differently to hydrological episodes. In forested streams, concentrations of TM, Fe and DOC increased, while they decreased in wetland influenced streams. Furthermore, Fe and Pb correlated positively with wetland coverage. Moreover, significantly lower average sulphate concentrations, but higher isotope values, were observed in wetland streams.

    This study emphasises the importance of understanding stream water chemistry from a landscape perspective in order to identify potential environments where climate change may induce enhanced metal mobilization in the future.

  • 15.
    Bohlin, Hanna
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Holm, Nils
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Point source influences on the carbon and nitrogen geochemistry of sediments in the Stockholm archipelago, Sweden2006In: The Science of the Total Environment, Vol. 366, p. 337-349Article in journal (Refereed)
  • 16.
    Bohlin, Hanna
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holm, Nils G.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Point source influences on the carbon and nitrogen geochemistry of sediments in the Stockholm inner archipelago, Sweden2006In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 366, no 1, p. 337-349Article in journal (Refereed)
    Abstract [en]

    This study reports analyses of carbon and nitrogen content, and δ15N and δ13C in sediments of the Höggarnsfjärden Bay near Stockholm. Samples have been taken upstream, near, and downstream of a point source of processed leach water from a garbage dump. The surface sediment at the upstream and downstream sites has δ15N and δ13C close to the expected background of the area, even though a contribution from the leach water can be observed downstream of the point source. The sediment close to the outflow is strongly influenced by the carbon and nitrogen in the leach water.

  • 17.
    Brink, Jenni
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Humborg, Christoph
    Department of Applied Environmental Science (ITM).
    Sahlberg, J.
    Rahm, Lars
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Weathering rates and origin of inorganic carbon as influenced by river regulation in the boreal sub-arctic region of Sweden2007In: Hydrology and Earth System Sciences, Vol. 4, p. 555-588Article in journal (Refereed)
  • 18. Buffam, I.
    et al.
    Laudon, H.
    Temnerud, J.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Bishop, K.
    Landscape-scale variability of acidity and dissolved organic carbon during spring flood in a boreal stream network2007In: Journal of Geophysical Research: Biogeosciences, Vol. 112Article in journal (Refereed)
  • 19. Buffam, Ishi
    et al.
    Laudon, Hjalmar
    Seibert, Jan
    Stockholm University.
    Mörth, Carl Magnus
    Stockholm University.
    Bishop, Kevin
    Spatial heterogeneity of the spring flood acid pulse in a boreal stream network2008In: Science of the Total Environment, Vol. 407, no 1, p. 708-722Article in journal (Refereed)
  • 20. Campeau, Audrey
    et al.
    Wallin, Marcus B.
    Giesler, Reiner
    Löfgren, Stefan
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Schiff, Sherry
    Venkiteswaran, Jason J.
    Bishop, Kevin
    Multiple sources and sinks of dissolved inorganic carbon across Swedish streams, refocusing the lens of stable C isotopes2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 9158Article in journal (Refereed)
    Abstract [en]

    It is well established that stream dissolved inorganic carbon (DIC) fluxes play a central role in the global C cycle, yet the sources of stream DIC remain to a large extent unresolved. Here, we explore large-scale patterns in delta C-13-DIC from streams across Sweden to separate and further quantify the sources and sinks of stream DIC. We found that stream DIC is governed by a variety of sources and sinks including biogenic and geogenic sources, CO2 evasion, as well as in-stream processes. Although soil respiration was the main source of DIC across all streams, a geogenic DIC influence was identified in the northernmost region. All streams were affected by various degrees of atmospheric CO2 evasion, but residual variance in delta C-13-DIC also indicated a significant influence of in-stream metabolism and anaerobic processes. Due to those multiple sources and sinks, we emphasize that simply quantifying aquatic DIC fluxes will not be sufficient to characterise their role in the global C cycle.

  • 21.
    Chawchai, Sakonvan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Chulalongkorn University, Thailand.
    Chabangborn, Akkaneewut
    Stockholm University, Faculty of Science, Department of Geological Sciences. Chulalongkorn University, Thailand.
    Fritz, Sherilyn
    Valiranta, Minna
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Blaauw, Maarten
    Reimer, Paula J.
    Krusic, Paul J.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lowemark, Ludvig
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hydroclimatic shifts in northeast Thailand during the last two millennia - the record of Lake Pa Kho2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 111, p. 62-71Article, review/survey (Refereed)
    Abstract [en]

    The Southeast Asian mainland is located in the central path of the Asian summer monsoon, a region where paleoclimatic data are still sparse. Here we present a multi-proxy (TOC, C/N, delta C-13, biogenic silica, and XRF elemental data) study of a 1.5 m sediment/peat sequence from Lake Pa Kho, northeast Thailand, which is supported by 20 AMS C-14 ages. Hydroclimatic reconstructions for Pa Kho suggest a strengthened summer monsoon between BC 170-AD 370, AD 800-960, and after AD 1450; and a weakening of the summer monsoon between AD 370-800, and AD 1300-1450. Increased run-off and a higher nutrient supply after AD 1700 can be linked to agricultural intensification and land-use changes in the region. This study fills an important gap in data coverage with respect to summer monsoon variability over Southeast Asia during the past 2000 years and enables the mean position of the Intertropical Convergence Zone (ITCZ) to be inferred based on comparisons with other regional studies. Intervals of strengthened/weaker summer monsoon rainfall suggest that the mean position of the ITCZ was located as far north as 35 degrees N between BC 170-AD 370 and AD 800-960, whereas it likely did not reach above 17 degrees N during the drought intervals of AD 370-800 and AD 1300-1450. The spatial pattern of rainfall variation seems to have changed after AD 1450, when the inferred moisture history for Pa Kho indicates a more southerly location of the mean position of the summer ITCZ.

  • 22.
    Chawchai, Sakonvan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Chabangborn, Akkaneewut Nut
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kylander, Malin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Loewemark, L.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Blaauw, M.
    Klubseang, W.
    Reimer, P. J.
    Fritz, S. C.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lake Kumphawapi - an archive of Holocene palaeoenvironmental and palaeoclimatic changes in northeast Thailand2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 68, p. 59-75Article in journal (Refereed)
    Abstract [en]

    The long-term climatic and environmental history of Southeast Asia, and of Thailand in particular, is still fragmentary. Here we present a new C-14-dated, multi-proxy sediment record (TOC, C/N, CNS isotopes, Si, Zr, K, Ti, Rb, Ca elemental data, biogenic silica) for Lake Kumphawapi, the second largest natural lake in northeast Thailand. The data set provides a reconstruction of changes in lake status, groundwater fluctuations, and catchment run-off during the Holocene. A comparison of multiple sediment sequences and their proxies suggests that the summer monsoon was stronger between c. 9800 and 7000 cal yr BP. Lake status and water level changes around 7000 cal yr BP signify a shift to lower effective moisture. By c. 6500 cal yr BP parts of the lake had been transformed into a peatland, while areas of shallow water still occupied the deeper part of the basin until c. 5400-5200 cal yr BP. The driest interval in Kumphawapi's history occurred between c. 5200 and 3200 cal yr BP, when peat extended over large parts of the basin. After 3200 cal yr BP, the deepest part of the lake again turned into a wetland, which existed until c. 1600 cal yr BP. The observed lake-level rise after 1600 cal yr BP could have been caused by higher moisture availability, although increased human influence in the catchment cannot be ruled out. The present study highlights the use of multiple sediment sequences and proxies to study large lakes, such as Lake Kumphawapi in order to correctly assess the time transgressive response to past changes in hydroclimate conditions. Our new data set from northeast Thailand adds important palaeoclimatic information for a region in Southeast Asia and allows discussing Holocene monsoon variability and ITCZ movement in greater detail.

  • 23.
    Claesson, Lillemor
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Geologi.
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Geologi.
    Graham, Colin
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Geokemi.
    The timescale and mechanisms of fault sealing and water-rock interaction after an earthquake2007In: Geofluids, Vol. 7, p. 427-440Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    Hydrogeochemical monitoring of a basalt-hosted aquifer, which contains Ice Age meteoric water and is situated

    at 1220 m below sea level in the Tjornes Fracture Zone, northern Iceland, has been ongoing since July 2002.

    Based on hydrogeochemical changes following an earthquake of magnitude (Mw) 5.8 on 16 September 2002, we

    constrained the timescales of post-seismic fault sealing and water–rock interaction. We interpret that the earthquake

    ruptured a hydrological barrier, permitting a rapid influx of chemically and isotopically distinct Ice Age

    meteoric water from a second aquifer. During the two subsequent years, we monitored a chemical and isotopic

    recovery towards pre-earthquake aquifer compositions, which we interpret to have been mainly facilitated by

    fault-sealing processes. This recovery was interrupted in November 2004 by a second rupturing event, which was

    probably induced by two minor earthquakes and which reopened the pathway to the second aquifer. We conclude

    that the timescale of fault sealing was approximately 2 years and that the approach to isotopic equilibrium

    (from global meteoric water line) was approximately 18% after >10^4 years. Key words: earthquake, fault sealing, hydrogeochemistry, Iceland, Tjornes Fracture Zone, water–rock interaction

  • 24.
    Conley, Daniel J.
    et al.
    GeoBiosphere Science Centre, Department of Geology, Lund University, Sweden.
    Humborg, Christoph
    Stockholm University, Stockholm Resilience Centre.
    Smedberg, Erik
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Rahm, Lars
    Department of Water and Environmental Studies, Linköping University, Sweden.
    Papush, Liana
    Department of Water and Environmental Studies, Linköping University, Sweden.
    Danielsson, Åsa
    Department of Water and Environmental Studies, Linköping University, Sweden.
    Clarke, Annemarie
    Department of Marine Ecology, National Environmental Research Institute, Denmark.
    Pastuszak, Marianne
    Sea Fisheries Institute, Poland.
    Aigars, Juris
    Institute of Aquatic Ecology, University of Latvia, Latvia.
    Ciuffa, Daniele
    Department of Biology, University of Rome, Italy.
    Mörth, Carl-Magnus
    Stockholm University, Stockholm Resilience Centre.
    Past, present and future state of the biogeochemical Si cycle in the Baltic Sea.2008In: Journal of Marine Systems, Vol. 73, 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 DSi 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.

  • 25. Cory, Neil
    et al.
    Buffam, Ishi
    Laudon, Hjalmar
    SUBBjorkvald, Louise
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Koehler, Stephan
    Bishop, Kevin
    Particulate aluminium in boreal streams: Towards a better understanding of its sources and influence on dissolved aluminium speciation2009In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 24, no 9, p. 1677-1685Article in journal (Refereed)
    Abstract [en]

    The adverse impacts of the inorganic labile monomeric Al (Al-i) fraction on aquatic organisms have meant that Al (Al-tot) determination and even speciation has become a routine part of environmental monitoring and assessment. However, if samples are not filtered prior to analysis then particulate Al (Al-tot(p)) could influence the determination of Al-tot, and therefore the determination of the more toxicologically important (Al-i), both when it is measured analytically or modelled from Al-tot. This paper shows that the Al/DOC ratio in unfiltered samples can identify the Al-tot(p) fraction, and thus improve the speciation of Al-i. These findings are based on data from a study in a 67 km(2) catchment in northern Sweden during the snowmelt-driven spring flood of two consecutive years. Filtered and unfiltered samples were studied to determine the spatial and temporal patterns in Al-tot(p). The concentrations of Al-tot(p) were greatest in larger downstream sites where significant silt deposits are located. The sites with no silt in their drainage area showed a mean difference between filtered (Al-tot(f)) and unfiltered (Al-tot(uf)) samples of 6%, while sites with silt deposits had a mean difference of 65%. The difference between filtered and unfiltered samples was greatest at peak flow. Spikes in Al-tot(p) did not behave consistently during fractionation with a cation exchange column, resulting in increases in either measured Al-i(f) or non-labile monomeric Al (Al-o(f)). Al-tot(p) spikes were associated with sharp increases in the Al:DOC ratio. The baseflow Al:DOC ratio could be used to model filtered Al-tot from DOC with a Spearman rho of 0.75. 

  • 26.
    Dahlgren Strååt, Kim
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sobek, Anna
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Smedberg, Erik
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Undeman, Emma
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Modeling total particulate organic carbon (POC) flows in the Baltic Sea catchment2016In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 128, no 1-2, p. 51-65Article in journal (Refereed)
    Abstract [en]

    The largest input source of carbon to the Baltic Sea catchment is river discharge. A tool for modeling riverine particulate organic carbon (POC) loads on a catchment scale is currently lacking. The present study describes a novel dynamic model for simulating flows of POC in all major rivers draining the Baltic Sea catchment. The processes governing POC input and transport in rivers described in the model are soil erosion, in-stream primary production and litter input. The Baltic Sea drainage basin is divided into 82 sub-basins, each comprising several land classes (e.g. forest, cultivated land, urban areas) and parameterized using GIS data on soil characteristics and topography. Driving forces are temperature, precipitation, and total phosphorous concentrations. The model evaluation shows that the model can predict annual average POC concentrations within a factor of about 2, but generally fails to capture the timing of monthly peak loads. The total annual POC load to the Baltic Sea is estimated to be 0.34 Tg POC, which constitutes circa 7-10 % of the annual total organic carbon (TOC) load. The current lack of field measurements of POC in rivers hampers more accurate predictions of seasonality in POC loads to the Baltic Sea. This study, however, identifies important knowledge gaps and provides a starting point for further explorations of large scale POC mass flows.

  • 27.
    Dahlgren Strååt, Kim
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Undeman, Emma
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Future export of particulate and dissolved organic carbon from land to coastal zones of the Baltic Sea2018In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 177, p. 8-20Article in journal (Refereed)
    Abstract [en]

    The Baltic Sea is a semi-enclosed brackish sea in Northern Europe with a drainage basin four times larger than the sea itself. Riverine organic carbon (Particulate Organic Carbon, POC and Dissolved Organic Carbon, DOC) dominates carbon input to the Baltic Sea and influences both land-to-sea transport of nutrients and contaminants, and hence the functioning of the coastal ecosystem. The potential impact of future climate change on loads of POC and DOC in the Baltic Sea drainage basin (BSDB) was assessed using a hydrological-biogeochemical model (CSIM). The changes in annual and seasonal concentrations and loads of both POC and DOC by the end of this century were predicted using three climate change scenarios and compared to the current state. In all scenarios, overall increasing DOC loads, but unchanged POC loads, were projected in the north. In the southern part of the BSDB, predicted DOC loads were not significantly changing over time, although POC loads decreased in all scenarios. The magnitude and significance of the trends varied with scenario but the sign (+ or -) of the projected trends for the entire simulation period never conflicted. Results were discussed in detail for the middle CO2 emission scenario (business as usual, a1b). On an annual and entire drainage basin scale, the total POC load was projected to decrease by ca 7% under this scenario, mainly due to reduced riverine primary production in the southern parts of the BSDB. The average total DOC load was not predicted to change significantly between years 2010 and 2100 due to counteracting decreasing and increasing trends of DOC loads to the six major sub-basins in the Baltic Sea. However, predicted seasonal total loads of POC and DOC increased significantly by ca 46% and 30% in winter and decreased by 8% and 21% in summer over time, respectively. For POC the change in winter loads was a consequence of increasing soil erosion and a shift in duration of snowfall and onset of the spring flood impacting the input of terrestrial litter, while reduced primary production mainly explained the differences predicted in summer. The simulations also showed that future changes in POC and DOC export can vary significantly across the different sub-basins of the Baltic Sea. These changes in organic carbon input may impact future coastal food web structures e.g. by influencing bacterial and phytoplankton production in coastal zones, which in turn may have consequences at higher trophic levels.

  • 28.
    Eriksson Hägg, Hanna
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mörth, Carl- Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Rodriguez Medina, Miguel
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Scenario Analysis on Human Protein consumption and Climate change effects on riverine N export to the Balitc SeaManuscript (preprint) (Other academic)
  • 29.
    Eriksson Hägg, Hanna
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Mörth, Carl-Magnus
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Medina, Miguel Rodriguez
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Wulff, Fredrik
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Scenario Analysis on Protein Consumption and Climate Change Effects on Riverine N Export to the Baltic Sea2010In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 44, no 7, p. 2379-2385Article in journal (Refereed)
    Abstract [en]

    This paper evaluates possible future nitrogen loadings from 105 catchments surrounding the Baltic Sea. Multiple regressions are used to model total nitrogen (TN) flux as a function of specific runoff (0), atmospheric nitrogen deposition, and primary emissions (PE) from humans and livestock. On average cattle contributed with 63%, humans with 20%, and pigs with 17% of the total nitrogen PE to land. Compared to the reference period (1992-1996) we then evaluated two types of scenarios for year 2070. i) An increased protein consumption scenario that led to 16% to 39% increased mean TN flux (kg per km(-2)). ii) Four climate scenarios addressing effects of changes in river discharge. These scenarios showed increased mean TN flux from the northern catchments draining into the Gulf of Bothnia (34%) and the Gulfs of Finland and Riga (14%), while the mean TN flux decreased (-27%) for catchments draining to the Baltic Proper. However, the net effect of the scenarios showed a possible increase in TN flux ranging from 3-72%. Overall an increased demand for animal protein will be instrumental for the Baltic Sea ecosystem and may be a major holdback to fulfill the environmental goals of the Baltic Sea Action Plan.

  • 30.
    Eriksson Hägg, Hanna
    et al.
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Humborg, Christoph
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Swaney, D. P.
    Mörth, Carl-Magnus
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Riverine nitrogen export in Swedish catchments dominated by atmospheric inputs2012In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 111, no 1-3, p. 203-217Article in journal (Refereed)
    Abstract [en]

    We present the first estimates of net anthropogenic nitrogen input (NANI) in European boreal catchments. In Swedish catchments, nitrogen (N) deposition is a major N input (31-94%). Hence, we used two different N deposition inputs to calculate NANI for 36 major Swedish catchments. The relationship between riverine N export and NANI was strongest when using only oxidized deposition (NOy) as atmospheric input (r(2) = 0.70) rather than total deposition (i.e., both oxidized and reduced nitrogen, NOy + NHx deposition, r(2) = 0.62). The y-intercept (NANI = 0) for the NANI calculated with NOy is significantly different from zero (p = 0.0042*) and indicates a background flux from the catchment of some 100 kg N km(-2) year(-1) in addition to anthropogenic inputs. This agrees with similar results from North American boreal catchments. The slope of the linear regressions was 0.25 for both N deposition inputs (NOy and NOy + NHx), suggesting that on average, 25% of the anthropogenic N inputs is exported by rivers to the Baltic Sea. Agricultural catchments in central and southern Sweden have increased their riverine N export up to tenfold compared to the inferred background flux. Although the relatively unperturbed northernmost catchments receive significant N loads from atmospheric deposition, these catchments do not show significantly elevated riverine N export. The fact that nitrogen export in Swedish catchments appears to be higher in proportion to NANI at higher loads suggests that N retention may be saturating as loading rates increase. In northern and western Sweden the export of nitrogen is largely controlled by the hydraulic load, i.e., the riverine discharge normalized by water surface area, which has units of distance time(-1). Besides hydraulic load the percent total forest cover also affects the nitrogen export primarily in the northern and western catchments.

  • 31.
    Eriksson Hägg, Hanna
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Swaney, Dennis
    Cornell University, US.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Riverine nitrogen export in Swedish catchments dominated by atmospheric inputsManuscript (preprint) (Other academic)
    Abstract [en]

    The net anthropogenic nitrogen input (NANI) approach addressing N loading from agricultural sources and the atmosphere were applied to 36 major Swedish catchments. We tested three alternatives of the empirical relationship between NANI and riverine N export using different ways of estimating atmospheric N deposition as the major N input (31-94 %) in these catchments. The relationship between riverine N export and NANI was strongest for the NANI calculation using NOy (r2 linear =0.704, r2 exponential =0.723) compared to NOy + net NHx (r2 linear =0.623, r2 exponential =0.670) and total NOy + NHx deposition (r2 linear =0.615, r2 exponential =0.658). The y-intercept (NANI= 0) of the linear and exponential regression models were between 40-160 kg N km-2 year-1 indicating a natural background flux from the catchment without anthropogenic inputs of some 100 kg N km-2 year-1. This agrees with similar results from North American boreal catchments. The slope of the three linear regressions varies from 0.24 (NOy + Net NHx) to 0.25 (NOy and NOy+ NHx), suggesting that in average 25% of the human inputs of nitrogen are exported by the rivers to the Baltic Sea. Agricultural catchments, in the middle and southern Sweden, have increased their riverine N export up to an order of magnitude compared to the inferred natural background flux as an effect of anthropogenic loading. Although, the relatively unperturbed northernmost catchments receive significant N loads from atmospheric deposition these catchments do not show any significant elevated riverine N export. The fact that nitrogen export in Swedish catchments appears to be higher in proportion to NANI at higher loads suggests that N retention could be saturating as loading rates increase. Such nonlinear or threshold responses have significant implications for nutrient management.

  • 32.
    Eriksson Hägg, Hanna
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Wällstedt, Teresia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Claremar, Björn
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Future nutrient load scenarios for the Baltic Sea due to climate and lifestyle changes2014In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 43, no 3, p. 337--351Article in journal (Refereed)
    Abstract [en]

    Dynamic model simulations of the future climate and projections of future lifestyles within the Baltic Sea Drainage Basin (BSDB) were considered in this study to estimate potential trends in future nutrient loads to the Baltic Sea. Total nitrogen and total phosphorus loads were estimated using a simple proxy based only on human population (to account for nutrient sources) and stream discharges (to account for nutrient transport). This population-discharge proxy provided a good estimate for nutrient loads across the seven sub-basins of the BSDB considered. All climate scenarios considered here produced increased nutrient loads to the Baltic Sea over the next 100 years. There was variation between the climate scenarios such that sub-basin and regional differences were seen in future nutrient runoff depending on the climate model and scenario considered. Regardless, the results of this study indicate that changes in lifestyle brought about through shifts in consumption and population potentially overshadow the climate effects on future nutrient runoff for the entire BSDB. Regionally, however, lifestyle changes appear relatively more important in the southern regions of the BSDB while climatic changes appear more important in the northern regions with regards to future increases in nutrient loads. From a whole-ecosystem management perspective of the BSDB, this implies that implementation of improved and targeted management practices can still bring about improved conditions in the Baltic Sea in the face of a warmer and wetter future climate

  • 33. Eriksson Hägg, Hanna
    et al.
    Pastuszak, M.
    Löfgren, S.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Nitrogen budgets of the Polish agricuture 1960-2000: Implications for riverine nitrogen loads to the Baltic Sea from transitional countries2007In: Biogeochemistry, ISSN 0168-2563, Vol. 85, p. 153-168Article in journal (Refereed)
  • 34. Fehr, Manuela A.
    et al.
    Andersson, Per S.
    Halenius, Ulf
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Iron enrichments and Fe isotopic compositions of surface sediments from the Gotland Deep, Baltic Sea2010In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 277, no 3-4, p. 310-322Article in journal (Refereed)
    Abstract [en]

    Recent sediments from the Gotland Deep display enrichments in reactive Fe, associated with elevated Fe/Al ratios and light Fe isotopic signatures of the bulk sediments that are indicative of euxinic (anoxic and sulfidic) conditions. These enrichments can be explained by the Fe shuttle model where benthic Fe is transported from the shelf to the euxinic basin and transferred to the sediments by pyrite precipitation in the sulfidic water. The data provide evidence that the Fe shuttle at present results in accumulations of Fe that are larger compared to Fe enrichments during the Litorina Sea stage in the Gotland Deep probably caused by an increase of the benthic Fe flux from the shelf to the basin. The derived Fe enrichments are also larger compared to those in recent Black Sea sediments, which likely reflects the larger shelf to basin ratio of the Gotland Deep compare to the Black Sea. The Fe isotope data show no correlation with the organic C content of the samples indicating that the negative Fe isotope signatures are not associated with organic materials, as was suggested as an alternative explanation for the origin of the isotopically light Fe in sediments from the Litorina Sea stage. Conversely, pyrites carry the negative Fe isotopic signature of the sediments, which supports the Fe shuttle model. Variations in the abundance and Fe isotopic signature of reactive Fe and pyrite with depth suggest that syngenetically formed pyrite in the sulfidic water column has a less negative Fe isotopic composition compared to diagenetically produced pyrite.

  • 35. Fehr, Manuela A.
    et al.
    Andersson, Per S.
    Halenius, Ulf
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Iron isotope variations in Holocene sediments of the Gotland Deep, Baltic Sea2008In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 72, no 3, p. 807-826Article, review/survey (Refereed)
    Abstract [en]

    Holocene sediments from the Gotland Deep basin in the Baltic Sea were investigated for their Fe isotopic composition in order to assess the impact of changes in redox conditions and a transition from freshwater to brackish water on the isotope signature of iron. The sediments display variations in delta Fe-56 (differences in the Fe-56/Fe-54 ratio relative to the IRMM-14 standard) from -0.27 +/- 0.09 parts per thousand to +0.21 +/- 0.08 parts per thousand. Samples deposited in a mainly limnic environment with oxygenated bottom water have a mean delta Fe-56 of +0.08 +/- 0.13 parts per thousand, which is identical to the mean Fe isotopic composition of igneous rocks and oxic marine sediments. In contrast, sediments that formed in brackish water under periodically euxinic conditions display significantly lighter Fe isotope signatures with a mean delta Fe-56 of -0.14 +/- 0.19 parts per thousand. Negative correlations of the delta Fe-56 values with the Fe/Al ratio and S content of the samples suggest that the isotopically light Fe in the periodically euxinic samples is associated with reactive Fe enrichments and sulfides. This is supported by analyses of pyrite separates from this unit that have a mean Fe isotopic composition of -1.06 +/- 0.20 parts per thousand for delta Fe-56. The supply of additional Fe with a light Fe isotopic signature can be explained with the shelf to basin Fe shuttle model. According to the Fe shuttle model, oxides and benthic ferrous Fe that is derived from dissimilatory iron reduction from shelves is transported and accumulated in euxinic basins. The data furthermore suggest that the euxinic water has a negative dissolved delta Fe-56 value of about -1.4 parts per thousand to -0.9 parts per thousand. If negative Fe isotopic signatures are characteristic for euxinic sediment formation, widespread euxinia in the past might have shifted the Fe isotopic composition of dissolved Fe in the ocean towards more positive delta Fe-56 values.

  • 36.
    Fransner, Filippa
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gustafsson, Erik
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Tedesco, Letizia
    Vichi, Marcello
    Hordoir, Robinson
    Roquet, Fabien
    Stockholm University, Faculty of Science, Department of Meteorology .
    Spilling, Kristian
    Kuznetsov, Ivan
    Eilola, Kari
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. University of Helsinki, Finland.
    Nycander, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Non-Redfieldian Dynamics Explain Seasonal pCO2 Drawdown in the Gulf of Bothnia2018In: Journal of Geophysical Research - Oceans, ISSN 2169-9275, E-ISSN 2169-9291, Vol. 123, no 1, p. 166-188Article in journal (Refereed)
    Abstract [en]

    High inputs of nutrients and organic matter make coastal seas places of intense air‐sea CO2 exchange. Due to their complexity, the role of coastal seas in the global air‐sea CO2 exchange is, however, still uncertain. Here, we investigate the role of phytoplankton stoichiometric flexibility and extracellular DOC production for the seasonal nutrient and CO2 partial pressure (pCO2) dynamics in the Gulf of Bothnia, Northern Baltic Sea. A 3‐D ocean biogeochemical‐physical model with variable phytoplankton stoichiometry is for the first time implemented in the area and validated against observations. By simulating non‐Redfieldian internal phytoplankton stoichiometry, and a relatively large production of extracellular dissolved organic carbon (DOC), the model adequately reproduces observed seasonal cycles in macronutrients and pCO2. The uptake of atmospheric CO2 is underestimated by 50% if instead using the Redfield ratio to determine the carbon assimilation, as in other Baltic Sea models currently in use. The model further suggests, based on the observed drawdown of pCO2, that observational estimates of organic carbon production in the Gulf of Bothnia, derived with the method, may be heavily underestimated. We conclude that stoichiometric variability and uncoupling of carbon and nutrient assimilation have to be considered in order to better understand the carbon cycle in coastal seas.

  • 37.
    Fransner, Filippa
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nycander, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Geological Sciences.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Meier, H. E. Markus
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish Meteorological and Hydrological Institute, Sweden.
    Hordoir, Robinson
    Gustafsson, Erik
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Deutsch, Barbara
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Tracing terrestrial DOC in the Baltic Sea - a 3-D model study2016In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 30, no 2, p. 134-148Article in journal (Refereed)
    Abstract [en]

    The fate of terrestrial organic matter brought to the coastal seas by rivers, and its role in the global carbon cycle, are still not very well known. Here the degradation rate of terrestrial dissolved organic carbon (DOCter) is studied in the Baltic Sea, a subarctic semi-enclosed sea, by releasing it as a tracer in a 3-D circulation model and applying linear decay constants. A good agreement with available observational data is obtained by parameterizing the degradation in two rather different ways; one by applying a decay time on the order of 10 years to the whole pool of DOCter, and one by dividing the DOCter into one refractory pool and one pool subject to a decay time on the order of 1 year. The choice of parameterization has a significant effect on where in the Baltic Sea the removal takes place, which can be of importance when modeling the full carbon cycle and the CO2 exchange with the atmosphere. In both cases the biogeochemical decay operates on time scales less than the water residence time. Therefore only a minor fraction of the DOCter reaches the North Sea, whereas approximately 80% is removed by internal sinks within the Baltic Sea. This further implies that DOCter mineralization is an important link in land-sea-atmosphere cycling of carbon in coastal- and shelf seas that are heavily influenced by riverine DOC.

  • 38.
    Gdaniec, Sandra
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden; Université Paris-Saclay, France.
    Roy-Barman, Matthieu
    Foliot, Lorna
    Thil, Francois
    Dapoigny, Arnaud
    Burckel, Pierre
    Garcia-Orellana, Jordi
    Masqué, Pere
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Andersson, Per S.
    Thorium and protactinium isotopes as tracers of marine particle fluxes and deep water circulation in the Mediterranean Sea2018In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 199, p. 12-23Article in journal (Refereed)
    Abstract [en]

    Pa-231, Th-230 and Th-232 were analyzed in unfiltered seawater samples (n = 66) and suspended particles (n = 19) collected in the Mediterranean Sea during the MedSeA-GA04-S cruise along the GEOTRACES section GA04S and used to investigate mechanisms controlling the distribution and fractionation of Pa and Th in an ocean margin environment. Pa-231 and Th-230 are particle reactive radionuclides and are often used as tracers of processes such as boundary scavenging, particle transport and ocean circulation. The depth profiles of total Pa-231 and Th-230 concentrations in the Mediterranean Sea displayed non-linear shapes. Higher total Th-232 concentrations were observed at the straits and in deep waters pointing at lithogenic sources. Fractionation factors F-Th/Pa ranged from 1.4 to 9. Application of a box-model illustrated that 94% of the Pa-231 and almost all of the Th-230 (99.9%) produced in the Mediterranean Sea is removed to the sediment by scavenging. The negligible export of Th-230 to the Atlantic Ocean, leads to a reevaluation of the mean settling speed of the filtered particles, which is now estimated to 500-1000 m/y. The low F-Th/Pa fractionation factors are attributed to the efficient scavenging and lack of transport of Pa-231 to the Atlantic Ocean.

  • 39. Giesler, R
    et al.
    Björkvald, Louise
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Laudon, H
    Mörth, Carl-Magnus
    Stockholm University, Stockholm Resilience Centre.
    Spatial and seasonal variations in stream water d34S-dssiolved organic matter in Northern Sweden2009In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 43, no 2, p. 447-452Article in journal (Refereed)
    Abstract [en]

    The discharge of terrestrial dissolved organic matter (DOM) by streams is an important cross-system linkage that strongly influences downstream aquatic ecosystems. Isotopic tracers are important tools that can help to unravel the source of DOM from different terrestrial compartments in the landscape. Here we demonstrate the spatial and seasonal variation of delta S-34 of DOM in 70 boreal streams to test if the tracer could provide new insights into the origin of DOM. We found large spatial and seasonal variations in stream water delta S-34-DOM values ranging from -5.2 parts per thousand to + 9.6 parts per thousand with an average of +4.0 +/- 0.6 (N=62; average and 95% confidence interval). Large seasonal variations were found in stream water delta S-34-DOM values: for example, a shift of more than 10 parts per thousand during the spring snowmelt in a wetland-dominated stream. Spatial differences were also observed during the winter base flow with higher delta S-34-DOM values in the fourth-order Krycklan stream at the outlet of the 68 km(2) compared to the small (<1 km(2)) headwater streams. Our data clearly show that the delta S-34-DOM values have the potential to be used as a tracer to identify and generate new insights about terrestrial DOM sources in the boreal landscape.

  • 40. Giesler, Reiner
    et al.
    Björkvald, Louise
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Laudon, Hjalmar
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Unravelling the origin of stream water DOM using δ34S-DOMIn: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851Article in journal (Refereed)
  • 41. Giesler, Reiner
    et al.
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Karlsson, Jan
    Karlsson, E. M.
    Jantze, Elin J.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Catchment-scale dissolved carbon concentrations and exportestimates across six subarctic streams in northern Sweden2014In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 11, p. 525-537Article in journal (Refereed)
    Abstract [en]

    Climatic change is currently enhancing permafrostthawing and the flow of water through the landscape in subarcticand arctic catchments, with major consequences forthe carbon export to aquatic ecosystems. We studied streamwater carbon export in several tundra-dominated catchmentsin northern Sweden. There were clear seasonal differencesin both dissolved organic carbon (DOC) and dissolved inorganiccarbon (DIC) concentrations. The highest DOC concentrationsoccurred during the spring freshet while the highestDIC concentrations were always observed during winterbaseflow conditions for the six catchments considered in thisstudy. Long-term trends for the period 1982 to 2010 for oneof the streams showed that DIC concentrations has increasedby 9% during the 28 yr of measurement while no clear trendwas found for DOC. Similar increasing trends were alsofound for conductivity, Ca and Mg. When trends were discretizedinto individual months, we found a significant linearincrease in DIC concentrations with time for September,November and December. In these subarctic catchments, theannual mass of C exported as DIC was in the same orderof magnitude as DOC; the average proportion of DIC to thetotal dissolved C exported was 61% for the six streams. Furthermore,there was a direct relationship between total runoffand annual dissolved carbon fluxes for these six catchments.These relationships were more prevalent for annual DIC exportsthan annual DOC exports in this region. Our results alsohighlight that both DOC and DIC can be important in highlatitudeecosystems. This is particularly relevant in environmentswhere thawing permafrost and changes to subsurfaceice due to global warming can influence stream water fluxesof C. The large proportion of stream water DIC flux also hasimplications on regional C budgets and needs to be consideredin order to understand climate-induced feedback mechanismsacross the landscape.

  • 42. Giesler, Reiner
    et al.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Karlsson, Jan
    Lundin, Erik J.
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Spatiotemporal variations of pCO(2) and delta C-13-DIC in subarctic streams in northern Sweden2013In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 27, no 1, p. 176-186Article in journal (Refereed)
    Abstract [en]

    Current predictions of climate-related changes in high-latitude environments suggest major effects on the C export in streams and rivers. To what extent this will also affect the stream water CO2 concentrations is poorly understood. In this study we examined the spatiotemporal variation in partial pressure of CO2 (pCO(2)) and in stable isotopic composition of dissolved inorganic carbon (delta C-13-DIC) in subarctic streams in northern Sweden. The selected watersheds are characterized by large variations in high-latitude boreal forest and tundra and differences in bedrock. We found that all streams generally were supersaturated in pCO(2) with an average concentration of 850 mu atm. The variability in pCO(2) across streams was poorly related to vegetation cover, and carbonaceous bedrock influence was manifested in high DIC concentrations but not reflected in either stream pCO(2) or delta C-13-DIC. Stream water pCO(2) values were highest during winter base flow when we also observed the lowest delta C-13-DIC values, and this pattern is interpreted as a high contribution from CO2 from soil respiration. Summer base flow delta C-13-DIC values probably are more affected by in situ stream processes such as aquatic production/respiration and degassing. A challenge for further studies will be to disentangle the origin of stream water CO2 and quantify their relative importance.

  • 43.
    Gustafsson, Erik
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Deutsch, Barbara
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Gustafsson, Bo G.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Carbon cycling in the Baltic Sea - The fate of allochthonous organic carbon and its impact on air-sea CO2 exchange2014In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 129, p. 289-302Article in journal (Refereed)
    Abstract [en]

    A coupled physical-biogeochemical model (BALTSEM) is used to estimate carbon fluxes in the Baltic Sea over the 1980-2006 period. Budget calculations for organic carbon indicate that of the total allochthonous organic carbon (TOCT) supplied to the system, on average 56% is mineralized, 36% is exported out of the system, and the remainder is buried. River discharge is the main source of dissolved inorganic carbon (DIC) to the Baltic Sea. However, model results indicate that in the Gulf of Bothnia (northern Baltic Sea), the contribution to the DIC stock by TOCT mineralization is of the same order as direct river input of DIC In the Kattegat and Danish Straits (southwestern Baltic Sea) on the other hand, net uptake of atmospheric CO2 comprises the major DIC source. Despite large variations within the system, with net outgassing from some sub-basins and net absorption in others, the Baltic Sea as a whole was estimated to be a net sink for atmospheric CO2. Mineralization of allochthonous dissolved organic carbon (DOCT) influences air-sea CO2 exchange. A sensitivity study indicates that depending on the labile fraction of DOCT, the contribution from CO2 absorption to total external DIC sources can amount to 10-25%.

  • 44.
    Gustafsson, Erik
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Björk, Göran
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of New Hampshire, USA.
    Andersson, Leif G.
    Geibel, Marc C.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sundbom, Marcus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Semiletov, Igor P.
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gustafsson, Bo G.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Carbon cycling on the East Siberian Arctic Shelf – a change in air-sea CO2 flux induced by mineralization of terrestrial organic carbon2017In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189Article in journal (Refereed)
    Abstract [en]

    Measurements from the SWERUS-C3 and ISSS-08 Arctic expeditions were used to calibrate and validate a new physical-biogeochemical model developed to quantify key carbon cycling processes on the East Siberian Arctic Shelf (ESAS). The model was used in a series of experimental simulations with the specific aim to investigate the pathways of terrestrial dissolved and particulate organic carbon (DOCter and POCter) supplied to the shelf. Rivers supply on average 8.5 Tg C yr−1 dissolved inorganic carbon (DIC), and further 8.5 and 1.1 Tg C yr−1 DOCter and POCter respectively. Based on observed and simulated DOC concentrations and stable isotope values (δ13CDOC) in shelf waters, we estimate that only some 20 % of the riverine DOCter is labile. According to our model results, an additional supply of approximately 14 Tg C yr−1 eroded labile POCter is however required to describe the observed stable isotope values of DIC (δ13CDIC). Degradation of riverine DOCter and POCter results in a 1.8 Tg C yr−1 reduction in the uptake of atmospheric CO2, while degradation of eroded POCter results in an additional 10 Tg C yr−1 reduction. Our calculations indicate nevertheless that the ESAS is an overall small net sink for atmospheric CO2 (1.7 Tg C yr−1). The external carbon sources are largely compensated by a net export from the shelf to the Arctic Ocean (31 Tg C yr−1), and to a smaller degree by a permanent burial in the sediments (2.7 Tg C yr−1).

  • 45.
    Gustafsson, Erik
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Geological Sciences.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gustafsson, Bo G.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Modelling the C-13 and C-12 isotopes of inorganic and organic carbon in the Baltic Sea2015In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 148, p. 122-130Article in journal (Refereed)
    Abstract [en]

    In this study, C-12 and C-13 contents of all carbon containing state variables (dissolved inorganic and organic carbon, detrital carbon, and the carbon content of autotrophs and heterotrophs) have for the first time been explicitly included in a coupled physical-biogeochemical Baltic Sea model. Different processes in the carbon cycling have distinct fractionation values, resulting in specific isotopic fingerprints. Thus, in addition to simulating concentrations of different tracers, our new model formulation improves the possibility to constrain the rates of processes such as CO2 assimilation, mineralization, and air-sea exchange. We demonstrate that phytoplankton production and respiration, and the related air-sea CO2 fluxes, are to a large degree controlling the isotopic composition of organic and inorganic carbon in the system. The isotopic composition is further, but to a lesser extent, influenced by river loads and deep water inflows as well as transformation of terrestrial organic carbon within the system. Changes in the isotopic composition over the 20th century have been dominated by two processes the preferential release of C-12 to the atmosphere in association with fossil fuel burning, and the eutrophication of the Baltic Sea related to increased nutrient loads under the second half of the century.

  • 46.
    Gustafsson, Erik
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Wällstedt, Teresia
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gustafsson, Bo G.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    External total alkalinity loads versus internal generation: The influence of nonriverine alkalinity sources in the Baltic Sea2014In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 28, no 11, p. 1358-1370Article in journal (Refereed)
    Abstract [en]

    In this study we first present updated riverine total alkalinity (TA) loads to the various Baltic Sea sub-basins, based on monthly measurements in 82 of the major rivers that represent 85% of the total runoff. Simulations in the coupled physical-biogeochemical BALTSEM (BAltic sea Long-Term large Scale Eutrophication Model) model show that these river loads together with North Sea water inflows are not sufficient to reproduce observed TA concentrations in the system, demonstrating the large influence from internal sources. Budget calculations indicate that the required internal TA generation must be similar to river loads in magnitude. The nonriverine source in the system amounts to about 2.4mmolm(-2) d(-1) on average. We argue here that the majority of this source is related to denitrification together with unresolved sediment processes such as burial of reduced sulfur and/or silicate weathering. This hypothesis is supported by studies on sediment processes on a global scale and also by data from sediment cores in the Baltic Sea. In a model simulation with all internal TA sources and sinks switched on, the net absorption of atmospheric CO2 increased by 0.78mol C m(-2) yr(-1) compared to a simulation where TA was treated as a passive tracer. Our results clearly illustrate how pelagic TA sources together with anaerobic mineralization in coastal sediments generate a significant carbon sink along the aquatic continuum, mitigating CO2 evasions from coastal and estuarine systems.

  • 47.
    Hirst, Catherine
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
    Andersson, Per S.
    Shaw, Samuel
    Burke, Ian T.
    Kutscher, Liselott
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
    Murphy, Melissa J.
    Maximov, Trofim
    Pokrovsky, Oleg S.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Porcelli, Don
    Characterisation of Fe-bearing particles and colloids in the Lena River basin, NE Russia2017In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 213, p. 553-573Article in journal (Refereed)
    Abstract [en]

    Rivers are significant contributors of Fe to the ocean. However, the characteristics of chemically reactive Fe remain poorly constrained, especially in large Arctic rivers, which drain landscapes highly susceptible to climate change and carbon cycle alteration. The aim of this study was a detailed characterisation (size, mineralogy, and speciation) of riverine Fe-bearing particles (> 0.22 mu m) and colloids (1 kDa-0.22 mm) and their association with organic carbon (OC), in the Lena River and tributaries, which drain a catchment almost entirely underlain by permafrost. Samples from the main channel and tributaries representing watersheds that span a wide range in topography and lithology were taken after the spring flood in June 2013 and summer baseflow in July 2012. Fe-bearing particles were identified, using Transmission Electron Microscopy, as large (200 nm(-1) mu m) aggregates of smaller (20-30 nm) spherical colloids of chemically-reactive ferrihydrite. In contrast, there were also large (500 nm(-1) mu m) aggregates of clay (illite) particles and smaller (100-200 nm) iron oxide particles (dominantly hematite) that contain poorly reactive Fe. TEM imaging and Scanning Transmission X-ray microscopy (STXM) indicated that the ferrihydrite is present as discrete particles within networks of amorphous particulate organic carbon (POC) and attached to the surface of primary produced organic matter and clay particles. Together, these larger particles act as the main carriers of nanoscale ferrihydrite in the Lena River basin. The chemically reactive ferrihydrite accounts for on average 70 +/- 15% of the total suspended Fe in the Lena River and tributaries. These observations place important constraints on Fe and OC cycling in the Lena River catchment area and Fe-bearing particle transport to the Arctic Ocean.

  • 48. Hong, Bongghi
    et al.
    Swaney, Dennis P.
    Mörth, Carl-Magnus
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Smedberg, Erik
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Hägg, Hanna Eriksson
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Humborg, Christoph
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Howarth, Robert W.
    Bouraoui, Faycal
    Evaluating regional variation of net anthropogenic nitrogen and phosphorus inputs (NANI/NAPI), major drivers, nutrient retention pattern and management implications in the multinational areas of Baltic Sea basin2012In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 227, p. 117-135Article in journal (Refereed)
    Abstract [en]

    The NANI/NAPI (net anthropogenic nitrogen/phosphorus input) Calculator Toolbox described in this paper is designed to address the consequences to Baltic Sea nutrient loads of the significant variation in agronomic practices and dietary preferences among European countries whose watersheds comprise the Baltic Sea basin. A primary objective of this work is to develop regional parameters and datasets for this budgeting tool. A previous version of the toolbox was applied to the entire contiguous United States to calculate NANI and its components (atmospheric N deposition, fertilizer N application, agricultural N fixation and N in net food and feed imports). Here, it is modified for application to the Baltic Sea catchments, where coastal watersheds from several countries are draining to international waters. A similar accounting approach is taken for calculating NAPI, which includes fertilizer P application, P in net food and feed imports and non-food use of P by human. Regional variation of NANI/NAPI parameters (agricultural fixation rates, human intake rates and livestock intake and excretion rates) are estimated, and their impact on the regional nutrient budget and the riverine nutrient flux is evaluated. There is a distinct north-to-south gradient in NANI and NAPI across the Baltic Sea catchments, and regional nutrient inputs are strongly related to riverine nutrient fluxes. Analysis of regional nutrient retention pattern indicates that, for some countries, compliance to the Baltic Sea Action Plan would imply enormous changes in the agricultural sector.

  • 49.
    Humborg, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Geibel, Marc C.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Anderson, Leif G.
    Björk, Göran
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Sundbom, Marcus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Deutsch, Barbara
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Gustafsson, Erik
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Gustafsson, Bo
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Ek, Jörgen
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Semiletov, Igor
    Sea-air exchange patterns along the central and outer East Siberian Arctic Shelf as inferred from continuous CO2, stable isotope, and bulk chemistry measurements2017In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 31, no 7, p. 1173-1191Article in journal (Refereed)
    Abstract [en]

    This large-scale quasi-synoptic study gives a comprehensive picture of sea-air CO2 fluxes during the melt season in the central and outer Laptev Sea (LS) and East Siberian Sea (ESS). During a 7 week cruise we compiled a continuous record of both surface water and air CO2 concentrations, in total 76,892 measurements. Overall, the central and outer parts of the ESAS constituted a sink for CO2, and we estimate a median uptake of 9.4 g C m(-2) yr(-1) or 6.6 Tg C yr(-1). Our results suggest that while the ESS and shelf break waters adjacent to the LS and ESS are net autotrophic systems, the LS is a net heterotrophic system. CO2 sea-air fluxes for the LS were 4.7 g C m(-2) yr(-1), and for the ESS we estimate an uptake of 7.2 g C m(-2) yr(-1). Isotopic composition of dissolved inorganic carbon (delta C-13(DIC) and delta C-13(CO2)) in the water column indicates that the LS is depleted in delta C-13(DIC) compared to the Arctic Ocean (ArcO) and ESS with an offset of 0.5% which can be explained by mixing of delta C-13(DIC)-depleted riverine waters and 4.0 Tg yr(-1) respiration of OCter; only a minor part (0.72 Tg yr(-1)) of this respired OCter is exchanged with the atmosphere. Property-mixing diagrams of total organic carbon and isotope ratio (delta C-13(SPE-DOC)) versus dissolved organic carbon (DOC) concentration diagram indicate conservative and nonconservative mixing in the LS and ESS, respectively. We suggest land-derived particulate organic carbon from coastal erosion as an additional significant source for the depleted delta C-13(DIC).

  • 50.
    Humborg, Christoph
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. University of Helsinki, Finland.
    Geibel, Marc C.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Sun, Xiaole
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    McCrackin, Michelle
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gustafsson, Bo
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. University of Helsinki, Finland.
    Sokolov, Alexander
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Norkko, Alf
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. University of Helsinki, Finland.
    Norkko, Joanna
    High Emissions of Carbon Dioxide and Methane From the Coastal Baltic Sea at the End of a Summer Heat Wave2019In: Frontiers in Marine Science, E-ISSN 2296-7745, Vol. 6, article id 493Article in journal (Refereed)
    Abstract [en]

    The summer heat wave in 2018 led to the highest recorded water temperatures since 1926 - up to 21 degrees C - in bottom coastal waters of the Baltic Sea, with implications for the respiration patterns in these shallow coastal systems. We applied cavity ring-down spectrometer measurements to continuously monitor carbon dioxide (CO2) and methane (CH4) surface-water concentrations, covering the coastal archipelagos of Sweden and Finland and the open and deeper parts of the Northern Baltic Proper. This allowed us to (i) follow an upwelling event near the Swedish coast leading to elevated CO2 and moderate CH 4 outgassing, and (ii) to estimate CH4 sources and fluxes along the coast by investigating water column inventories and air-sea fluxes during a storm and an associated downwelling event. At the end of the heat wave, before the storm event, we found elevated CO2 (1583 mu atm) and CH4 (70 nmol/L) concentrations. During the storm, a massive CO2 sea-air flux of up to 274 mmol m(-2) d(-1) was observed. While water-column CO2 concentrations were depleted during several hours of the storm, CH4 concentrations remained elevated. Overall, we found a positive relationship between CO2 and CH4 wind-driven sea-air fluxes, however, the highest CH4 fluxes were observed at low winds whereas highest CO2 fluxes were during peak winds, suggesting different sources and processes controlling their fluxes besides wind. We applied a box-model approach to estimate the CH4 supply needed to sustain these elevated CH4 concentrations and the results suggest a large source flux of CH4 to the water column of 2.5 mmol m(-2) d(-1). These results are qualitatively supported by acoustic observations of vigorous and widespread outgassing from the sediments, with flares that could be traced throughout the water column penetrating the pycnocline and reaching the sea surface. The results suggest that the heat wave triggered CO2 and CH4 fluxes in the coastal zones that are comparable with maximum emission rates found in other hot spots, such as boreal and arctic lakes and wetlands. Further, the results suggest that heat waves are as important for CO2 and CH4 sea-air fluxes as the ice break up in spring.

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