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  • 1.
    Algesten, Grete
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Sobek, Sebastian
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Tranvik, Lars J
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Contribution of sediment respiration to summer CO2 emission from boreal and subarctic lakes2005In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 50, no 4, 529-535 p.Article in journal (Refereed)
    Abstract [en]

    We measured sediment production of carbon dioxide (CO(2)) and methane (CH(4)) and the net flux of CO(2) across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were made in situ under ambient light conditions. The flux of CO(2) between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m(-2) day(-1) from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated to dissolved organic carbon (DOC) concentration in the water (r(2) = 0.61). The net flux of CO(2) across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed layer (r(2) = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration. Lakes with DOC concentrations <5.6 mg L(-1) had net consumption of CO(2) in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic (<2.6 mg L(-1)) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources.

  • 2.
    Berggren, Martin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Department of Forest Ecology and Management, SLU, Umeå.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nutrient constraints on metabolism affect the temperature regulation of aquatic bacterial growth efficiency2010In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 60, no 4, 894-902 p.Article in journal (Refereed)
    Abstract [en]

    Inorganic nutrient availability and temperature are recognized as major regulators of organic carbon processing by aquatic bacteria, but little is known about how these two factors interact to control bacterial metabolic processes. We manipulated the temperature of boreal humic stream water samples within 0–25°C and measured bacterial production (BP) and respiration (BR) with and without inorganic nitrogen + phosphorus addition. Both BP and BR increased exponentially with temperature in all experiments, with Q 10 values varying between 1.2 and 2.4. The bacterial growth efficiency (BGE) showed strong negative relationships with temperature in nutrient-enriched samples and in natural stream water where community-level BP and BR were not limited by nutrients. However, there were no relationships between BGE and temperature in samples where BP and BR were significantly constrained by the inorganic nutrient availability. The results suggest that metabolic responses of aquatic bacterial communities to temperature variations can be strongly dependent on whether the bacterial metabolism is limited by inorganic nutrients or not. Such responses can have consequences for both the carbon flux through aquatic food webs and for the flux of CO2 from aquatic systems to the atmosphere.

  • 3.
    Berggren, Martin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ström, L
    Laudon, H
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lake secondary production fueled by rapid transfer of low molecular weight organic carbon from terrestrial sources to aquatic consumers2010In: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 13, no 7, 870-880 p.Article in journal (Refereed)
    Abstract [en]

    Ecology Letters (2010) Abstract Carbon of terrestrial origin often makes up a significant share of consumer biomass in unproductive lake ecosystems. However, the mechanisms for terrestrial support of lake secondary production are largely unclear. By using a modelling approach, we show that terrestrial export of dissolved labile low molecular weight carbon (LMWC) compounds supported 80% (34-95%), 54% (19-90%) and 23% (7-45%) of the secondary production by bacteria, protozoa and metazoa, respectively, in a 7-km(2) boreal lake (conservative to liberal estimates in brackets). Bacterial growth on LMWC was of similar magnitude as that of primary production (PP), and grazing on bacteria effectively channelled the LMWC carbon to higher trophic levels. We suggest that rapid turnover of forest LMWC pools enables continuous export of fresh photosynthates and other labile metabolites to aquatic systems, and that substantial transfer of LMWC from terrestrial sources to lake consumers can occur within a few days. Sequestration of LMWC of terrestrial origin, thus, helps explain high shares of terrestrial carbon in lake organisms and implies that lake food webs can be closely dependent on recent terrestrial PP.

  • 4.
    Bergström, Ann-Kristin
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Phytoplankton responses to nitrogen and phosphorus enrichment in unproductive Swedish lakes along a gradient of atmospheric nitrogen deposition2008In: Aquatic Biology, Vol. 4, 55-64 p.Article in journal (Refereed)
    Abstract [en]

    Lake sampling and in situ nutrient enrichment enclosure experiments with nitrogen (N) and phosphorus (P) were conducted in unproductive Swedish lakes along a gradient of increasing atmospheric N-deposition. The regional and seasonal patterns of nutrient limitation of phytoplankton were clearly related to the amounts of N-deposition and N-inputs the lakes received. In areas of low N-deposition in northern Sweden, N-limitation of phytoplankton was evident throughout the summer season due to high catchment N-retention and very low dissolved inorganic N (DIN) inputs during the early summer. High N-deposition in the south was accompanied by high lake DIN-concentrations during the early summer and subsequent P-limitation of phytoplankton. However, P-limitation did not persist over the summer and, as a consequence of a declining DIN-pool, the lakes switched to dual- and co-limitation by N and P, and then to N-limitation. Generally, the lakes were N-limited rather than P-limited during the summer. We conclude that N-limitation is probably a natural state of the unproductive lakes studied, but P-limitation of variable intensity and duration has been induced by elevated atmospheric N-deposition.

  • 5. Buffam, I
    et al.
    Kohler, S
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bishop, K
    Photochemical and microbial processing of dissolved organic matter in streams and soilwater1996In: The Biological Bulletin, ISSN 0006-3185, E-ISSN 1939-8697, Vol. 191, no 2, 330-331 p.Article in journal (Refereed)
  • 6.
    Jansson, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Berggren, Martin
    Laudon, Hjalmar
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bioavailable phosphorus in humic headwater streams in boreal Sweden2012In: Limnology and Oceanography, ISSN 0024-3590, Vol. 57, no 4, 1161-1170 p.Article in journal (Refereed)
    Abstract [en]

    Bioavailable phosphorus (BAP) concentrations were determined nine times between April and October 2010 in two humic boreal headwater streams draining forest-and mire-dominated catchments. BAP was analyzed in a bioassay in which natural P-limited bacterioplankton grew with natural P as the sole P source. In both streams, approximately 90% of the BAP occurred as dissolved species (passing a 0.2-mu m filter), consisting partly of low-molecular-weight forms (passing a filter with nominal cutoff at 1 kDa) and partly of high-molecular-weight forms (passing a 0.2-mu m filter but not a 1-kDa filter). Concentrations of total dissolved BAP varied between 1 mu g L-1 and 14 mu g L-1, with the highest values in the middle of the summer. Compared to the forest stream, BAP concentrations were generally higher in the mire stream, where it occasionally amounted to nearly 50% of total P. Molybdate reactive phosphorus overestimated BAP considerably. Most of the BAP was in forms other than free orthophosphate. Temporal BAP variations showed no relationships with dissolved organic carbon (C) or iron but were positively related to air temperature and negatively related to the absorbance ratio (a254 : a365) of organic compounds in the water, indicating connections between terrestrial export of BAP and temperature-dependent terrestrial C metabolism. Concentrations of BAP can relieve stream bacteria from P limitation, and a significant share of BAP exported to streams can reach and be used in downstream lakes.

  • 7.
    Jansson, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Blomqvist, Peter
    Isaksson, A
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Impact of allochthonous organic carbon on microbial food web carbon dynamics and structure in Lake Örträsket1999In: Archiv für Hydrobiologie, ISSN 0003-9136, Vol. 144, no 4, 409-428 p.Article in journal (Refereed)
    Abstract [en]

    Bacterial utilization of allochthonous organic carbon and the subsequent fate of the bacterial production in the pelagic food web were estimated in Lake Örträsket, a large humic lake in northern Sweden. Bacterial production relied mainly on allochthonous DOC and exceeded primary production in the epilimnion. Bacterial productivity was clearly stimulated during high flow episodes, increasing the input of bacteria degradable organic material to the lake. Bacterioplankton were exploited mainly by mixotrophic flagellates which probably used bacteria as a source of carbon, phosphorus and nitrogen. The possibly extremely low availability of inorganic P during periods with high bacterial production may have allowed the mixotrophs to outcompete obligate autotrophs and help them become dominant phytoplankters during large parts of the summer. The results from Lake Örträsket indicated that the total production depended on bacterial energy mobilization from allochthonous organic carbon compounds and that heterotrophic mobilized energy was linked via mixotrophs to higher levels in the food chain.

  • 8.
    Jansson, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Blomqvist, Peter
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nutrient limitation of bacterioplankton, autotrophic and mixotrophic phytoplankton, and heterotrophic nanoflagellates in Lake Örträsket1996In: Limnology and Oceanography, ISSN 0024-3590, Vol. 41, no 7, 1552-1559 p.Article in journal (Refereed)
    Abstract [en]

    Enrichment experiments with P and N were conducted in humic Lake Örträsket in northern Sweden. The composition of the microplankton community showed a dominance by bacterioplankton, followed by mixotrophic sind potentially mixotrophic phytoplankton, heterotrophic nanoflagellates, and autotrophic phytoplankton. Bacterioplankton was P limited for most of the ice-free period, and phytoplankton biomass and primary production mostly increased after enrichment with N, but not with P. The dominant group of phytoplankton, the mixotrophic flagellates, was stimulated by N bur not by P, while obligate autotrophic species were stimulated only by P+N. It is suggested that N limitation in mixotrophic species is induced by grazing of P-rich bacteria. The results suggest that primary productivity in humic lakes can be limited by N and indicate the importance of phagocytosis as a means of nutrition in phytoplankton. A link is suggested to exist in humic lakes whereby heterotrophic bacterioplankton, which use humic compounds as their principal energy source, can transfer energy and nutrients to potentially autotrophic organisms, with subsequent utilization by other components of the food web.

  • 9.
    Jansson, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Hickler, T.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Links between terrestrial primary production and bacterial production and respiration in lakes in a climate gradient in subarctic Sweden2008In: Ecosystems, Vol. 11, 367-376 p.Article in journal (Refereed)
    Abstract [en]

    We compared terrestrial net primary production (NPP) and terrestrial export of dissolved organic carbon (DOC) with lake water heterotrophic bacterial activity in 12 headwater lake catchments along an altitude gradient in subarctic Sweden. Modelled NPP declined strongly with altitude and annual air temperature decreases along the altitude gradient (6ºC between the warmest and the coldest catchment). Estimated terrestrial DOC export to the lakes was closely correlated to NPP. Heterotrophic bacterial production (BP) and respiration (BR) were mainly based on terrestrial organic carbon and strongly correlated with the terrestrial DOC export. Excess respiration over PP of the pelagic system was similar to net emission of CO2 in the lakes. BR and CO2 emission made up considerably higher shares of the terrestrial DOC input in warm lakes than in cold lakes, implying that respiration and the degree of net heterotrophy in the lakes were dependant not only on terrestrial export of DOC, but also on characteristics in the lakes which changed along the gradient and affected the bacterial metabolization of allochthonous DOC. The study showed close links between terrestrial primary production, terrestrial DOC export and bacterial activity in lakes and how these relationships were dependant on air temperature. Increases in air temperature in high latitude unproductive systems might have considerable consequences for lake water productivity and release of CO2 to the atmosphere, which are ultimately determined by terrestrial primary production.

  • 10.
    Jansson, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Biomass and structure of planktonic communities along an air temperature gradient in subarctic Sweden2010In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 55, no 3, 691-700 p.Article in journal (Refereed)
    Abstract [en]

    1. Air temperature will probably have pronounced effects on the composition of plankton communities in northern lake ecosystems, either via indirect effects on the export of essential elements from catchments or through direct effects of water temperature and the ice-free period on the behaviour of planktonic organisms.

    2. We assessed the role of temperature by comparing planktonic communities in 15 lakes along a 6 °C air temperature gradient in subarctic Sweden.

    3. We found that the biomass of phytoplankton, bacterioplankton and the total planktonic biomass were positively related to air temperature, probably as a result of climatic controls on the export of nitrogen from the catchment (which affects phytoplankton biomass) and dissolved organic carbon (affecting bacterioplankton biomass).

    4. The structure of the zooplankton community, and top down effects on phytoplankton, were apparently not related to temperature but mainly to trophic interactions ultimately dependent on the presence of fish in the lakes.

    5. Our results suggest that air temperature regimes and long-term warming can have strong effects on the planktonic biomass in high latitude lakes. Effects of temperature on the structure of the planktonic community might be less evident unless warming permits the invasion of fish into previous fishless lakes.

  • 11.
    Jansson, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Carbon dioxide supersaturation promotes primary production in lakes2012In: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 15, no 6, 527-532 p.Article in journal (Refereed)
    Abstract [en]

    Ecology Letters (2012) Abstract A majority of the worlds lakes are supersaturated with respect to carbon dioxide (CO2). By experimental manipulation of the CO2 concentration in supersaturated boreal lakes, we demonstrate that phytoplankton primary production was up to 10 times higher in supersaturated lake water in comparison with water with CO2 at equilibrium concentrations and that CO2, together with nutrients, explained most of the variation in pelagic primary production and phytoplankton biomass over a wide variety of unproductive lakes. These results suggest that phytoplankton can be co-limited by CO2 and nutrients in unproductive lakes. As import of terrestrial organic carbon and its subsequent microbial mineralisation in lakes is a driving force of CO2-supersaturation our results suggest that lake productivity and carbon cycling may respond to variations in terrestrial organic carbon export, (e.g. caused by land use or climate change) in ways not described before.

  • 12.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Fe and Al sedimentation and their importance as carriers for P, N and C in a large humic lake in northern Sweden1997In: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932, Vol. 99, no 1-4, 283-295 p.Article in journal (Refereed)
    Abstract [en]

    The sedimentation of organic, amorphous oxides, crystalline oxides and crystalline silicate species of Fe and Al was investigated in humic Lake Ortrasket. The covariation with C, N and P sedimentation also was studied. The results showed a strong temporal variation in the occurrence of different Fe species. During high discharge, such as in spring, Fe mostly occurred as crystalline Fe-silicate species, while the amorphous form dominated at other times of the year. Al generally sedimented as crystalline Al-silicate species (95%). Amorphous Fe species showed a strong relation with organic C and N, suggesting an association between organic material and amorphous Fe oxides. P was not as strongly related to amorphous Fe, probably as a result of apatite or clay bound-P species sedimentation.

  • 13.
    Jonsson, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Algesten, Grete
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Bishop, Kevin
    Sobek, Sebastian
    Tranvik, Lars J.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Integrating aquatic carbon fluxes in a boreal catchment carbon budget2007In: Journal of Hydrology, Vol. 334, no 1-2, 141-150 p.Article in journal (Refereed)
    Abstract [en]

    In this paper, we assess the extent to which the export of terrestrially fixed carbon to aquatic systems and the aquatic metabolism of this carbon affect the overall accumulation of organic carbon in a boreal catchment. We estimated the contribution of stocks and processes in aquatic environments to the carbon balance of a boreal catchment in northern Sweden. We used published data concerning the net ecosystem exchange (NEE) of CO2 in terrestrial environments, and calculations of loss of terrestrial carbon to surface water and the turnover of terrestrial carbon in aquatic systems. The NEE of terrestrial environments was estimated to be 139 g C/m2 of catchment area per year. The export of terrestrially fixed carbon to aquatic systems was 8.6 g C/m2/yr, resulting in a net accumulation of organic carbon in terrestrial systems of 131 g C/m2/yr. Almost 45% of the terrestrial export was mineralized in streams and lakes and evaded as CO2, while most of the remaining (approximately 55%) terrestrial export was transported to the sea as organic carbon or as dissolved inorganic carbon emanating from soil respiration. The sedimentation of organic carbon and input of organic carbon via aquatic primary production were insignificant when compared to the mineralization and river transport of terrestrial organic carbon. Aquatic fluxes were small compared to the terrestrial NEE, which we consider to be largely a consequence of the studied catchment being subject to intensive forestry resulting in a large annual accumulation of carbon in growing tree biomass.

  • 14.
    Jonsson, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sedimentation and mineralisation of organic carbon, nitrogen and phosphorous in a large humic lake, northern Sweden1997In: Archiv für Hydrobiologie, ISSN 0003-9136, Vol. 141, 45-65 p.Article in journal (Refereed)
    Abstract [en]

    Lake Örträsket is a large (7.3 km2) and deep (64 m) humic (DOC 10 mg-L-1) lake in northern Sweden. Sediment trap data (gross sedimentation) and sediment core data (net sedimentation) has been used to calculate sedimentation and mineralisation of carbon, nitrogen, phosphorus, iron, aluminium and total particulate matter (TPM). Yearly gross sedimentation of nitrogen and organic carbon was higher than yearly net sedimentation caused by an annual sediment mineralisation of 54 % and 32 % of gross sedimentation, respectively. Annual gross sedimentation of phosphorus, iron, aluminium and TPM equalled annual net sedimentation and no significant sediment mineralisation of these elements was calculated. The annual retention (input-output) of organic carbon and nitrogen approximately equalled net sedimentation. Sediment mineralisation of nitrogen resulted in an accumulation of nitrate in the water column of the lake during periods of lake stratification. Approximately 2/3 of the nitrogen mineralised in and lost from the sediment was transported out of the lake (as nitrate) via the outlet during turnover in spring and autumn. Remaining 1/3 was assumed to be lost through sediment denitrification, equalling a denitrification rate of about 1 mgN-m-2-y-1.

  • 15.
    Jonsson, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sources of carbon dioxide supersaturation in clearwater and humic lakes in northern Sweden2003In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 6, no 3, 224-235 p.Article in journal (Refereed)
    Abstract [en]

    Partial pressure (pCO(2)) and flux to the atmosphere of carbon dioxide (CO2) were studied in northern alpine and forest lakes along a gradient of dissolved organic carbon (DOC) content (0.4-9.9 mg L-1). Sixteen lakes were each sampled three times over the course of the ice-free season, and an additional 35 lakes were sampled once at midsummer. pCO(2) data were acquired in the field by a headspace equilibration technique. Most lakes were supersaturated with CO2 along the entire DOC gradient, with relatively small seasonal differences. pCO(2) was positively correlated to DOC content, reflecting a close dependence between allochthonous DOC in-put and heterotrophic respiration in the lakes. Fluxes of CO2 to the atmosphere were estimated from the pCO(2) measurements. Benthic respiration was indicated to be important for CO2 emission in lakes with high DOC concentrations. In lakes with low DOC concentrations, pelagic mineralization alone was sufficient to account for a large part of the estimated fluxes.

  • 16.
    Jonsson, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Meili, Markus
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Whole-lake mineralization of allochthonous and autochthonous organic carbon in a large humic lake (Örträsket, N. Sweden)2001In: Limnology and Oceanography, ISSN 0024-3590, Vol. 46, no 7, 1691-1700 p.Article in journal (Refereed)
    Abstract [en]

    Organic carbon mineralization was studied. in a large humic lake (Lake Örträsket) in northern Sweden during a well-defined summer stratification period following high water flow during snowmelt. Several independent methods including plankton counts, measurements of bacterioplankton and phytoplankton production, stable isotope monitoring, sediment trapping, and mass balance calculations were used. Total organic carbon mineralization showed a summer mean of 0.3 g C m(-2) d(-1) and was partitioned about equally between water and sediment. In the water column, organic matter was mineralized by bacteria (60%) and protozoan and metazoan zooplankton (30%), as well as by photooxidation (10%). Most of the mineralized organic carbon was of allochthonous origin. Primary production in the lake contributed at most 5% of the total organic carbon input and about 20% of the total organic carbon mineralization. Total carbon mineralization in. the epilimnion and metalimnion agreed well with an estimate of CO2 evasion from the stratified lake, while CO2 accumulation in the hypolimnion matched the O-2 consumption and resulted in a very negative delta C-13 of DIC before autumn overturn (-23 parts per thousand). Isotopic compositions of DIC and POC confirmed the dominant influence of terrestrial organic input on the cycling of both organic and inorganic carbon in the lake.

  • 17.
    Jonsson, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Ström, Lena
    Åberg, Jan
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Composition and variations in the occurrence of dissolved free simple organic compounds of an unproductive lake ecosystem in northern Sweden2007In: Biogeochemistry, Vol. 82, no 2, 153-163 p.Article in journal (Refereed)
    Abstract [en]

    Low molecular weight organic carbon compounds are potentially important carbon and energy substrates to heterotrophic production in the aquatic environment. We studied the occurrence of dissolved free amino acids (AA), monosaccharides (CHO), and carboxylic acids (CA) in the subarctic Lake Diktar-Erik. The lake is unproductive with slightly humic water, and receives water via one major inlet stream draining a birch forest environment. The concentration of dissolved organic carbon (DOC) in the inlet stream was strongly correlated with the discharge. This relationship changed from season to season, indicating changes in the sources of the DOC entering the stream. AA and CHO each accounted for an average of less than 0.5% of the DOC. After high discharge events during the ice-free period, AA and CHO occurred in especially high concentrations. CA occurred in higher concentrations during the ice-free period, when it generally accounted for 20–30% of the DOC pool. The CA content relative to the total DOC pool was strongly inversely correlated with overall DOC concentration, and at low DOC levels the relative content of CA was high and vice versa. This followed a seasonal trend, with CA accounting for a smaller proportion of the DOC in winter and a larger part in spring/early summer. A conservative estimate suggested that the studied simple organic carbon compounds potentially could cover 30% of the bacterial gross production in the lake and therefore potentially also was an important source of CO2 that occur in supersaturated concentrations in the lake.

  • 18.
    Jonsson, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Åberg, Jan
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Variations in pCO2 during summer in the surface water of an unproductive lake in northern Sweden2007In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, Vol. 59, no 5, 797-803 p.Article in journal (Refereed)
    Abstract [en]

    Unproductive lakes are generally supersaturated with carbon dioxide (CO2) and emit CO2 to the atmosphere continuously during ice-free periods. However, temporal variation of the partial pressure of CO2 (pCO2) and thus of CO2 evasion to atmosphere is poorly documented. We therefore carried out temporally high-resolution (every 6 h) measurements of the pCO2 using an automated logger system in the surface water of a subarctic, unproductive, lake in the birch forest belt. The study period was June–September 2004. We found that the pCO2 showed large seasonal variation, but low daily variation. The seasonal variation was likely mainly caused by variations in input and mineralization of allochthonous organic matter. Stratification depth probably also influenced pCO2 of the surface water by controlling the volume in which mineralization of dissolved organic carbon (DOC) occurred. In lakes, with large variations in pCO2, as in our study lake a high (weekly) sampling intensity is recommended for obtaining accurate estimates of the evasion of CO2.

  • 19.
    Jonsson, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Åberg, Jan
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Lindroth, Anders
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Gas transfer rate and CO2 flux between an unproductive lake and the atmosphere in northern Sweden2008In: Journal of Geophysical Research - Biogeosciences, Vol. 113, Art.no. G04006- p.Article in journal (Refereed)
    Abstract [en]

    Measurements of the gas transfer rate of CO2 between lake water and the atmosphere present a critical problem for the understanding of lake ecosystem carbon balances and landscape carbon budgets. We present calculations of the gas transfer rate of CO2 from direct measurements of the CO2 flux using an eddy covariance system and concurrent measurements of the concentration of CO2 in the surface water in a lake in boreal zone of northern Sweden. The measured gas transfer rate was different, and in general larger than, rates obtained with the most commonly used models for prediction of the gas transfer rate in lakes. The normalized gas transfer rate (k600EC) was well predicted from the wind speed at 10 m height if data were bin classed into wind classes of 1 m/s for winds above 1 m/s. Unbinned data were also correlated to wind speed but also to water temperature, water temperature/air temperature ratio and to incoming photosynthetic active radiation (PAR). These relationships could reflect effects of both physico-chemical reactions and biological activity.

  • 20.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Berggren, M.
    Ask, Jenny
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, H.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Response to Comment: Terrestrial support of pelagic consumers in unproductive lakes- Uncertainty and potential in assessments using stable isotopes2014In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 59, no 5, 1800-1803 p.Article in journal (Refereed)
  • 21.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ask, Jenny
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laudon, Hjalmar
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Terrestrial organic matter support of lake food webs: Evidence from lake metabolism and stable hydrogen isotopes of consumers2012In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 57, no 4, 1042-1048 p.Article in journal (Refereed)
    Abstract [en]

    We quantified the utilization of terrestrial organic matter (OM) in the food web of a humic lake by analyzing the metabolism and the consumers' stable isotopic (C, H, N) composition in benthic and pelagic habitats. Terrestrial OM inputs (3 g C m(-2) d(-1)) to the lake greatly exceeded autochthonous OM production (3 mg C m(-2) d(-1)) in the lake. Heterotrophic bacterial growth (19 mg C m(-2) d(-1)) and community respiration (115 mg C m(-2) d(-1)) were high relative to algal photosynthesis and were predominantly (> 85%) supported by terrestrial OM in both habitats. Consequently, terrestrial OM fueled most (85%) of the total production at the base of the lake's food web (i.e., the sum of primary and bacterial production). Despite the uncertainties of quantitatively estimating resource use based on stable isotopes, terrestrial OM clearly also supported around half the zooplankton (47%), macrozoobenthos (63%), and fish (57%) biomass. These results indicate that, although rates of terrestrial OM inputs were around three orders of magnitude greater than that of autochthonous OM production, the use of the two resources by higher trophic levels was roughly equal. The disproportionally low reliance on terrestrial OM at higher trophic levels, compared with its high rates of input and high support of basic biomass production in the lake, suggests that autochthonous resources could not be completely replaced by terrestrial resources and indicates an upper limit to terrestrial support of lake food webs.

  • 22.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Respiration of allochthonous organic carbon in unproductive forest lakes determined by the Keeling plot method2007In: Limnology and Oceanography, Vol. 52, no 2, 603-608 p.Article in journal (Refereed)
    Abstract [en]

    We carried out short-term (2 d) experiments in nine unproductive lakes in northern Sweden in order to investigate organic carbon sources supporting lake water respiration. Surface water was incubated in gas-tight bottles in the dark, and the concentration and isotopic composition (d13C) of dissolved inorganic carbon (DIC) were measured at the start and end of the incubations. Keeling plot analyses revealed that the d13C of the respired carbon was between -28.4% and -30.6% in the lakes and that the respired carbon was mainly of allochthonous organic carbon (AlloOC) origin. The respiration of AlloOC corresponded well with metabolic imbalances indicated by negative net ecosystem production (NEP) values in the lake waters. Keeling plot analysis of DIC accumulating in the hypolimnion of two lakes during summer stratification showed d13C values of around -26.6% for excess DIC, implying that the accumulation of DIC was mainly derived from respiration of AlloOC. Our data provide direct evidence that net heterotrophy of these lakes is caused by input and respiration of AlloOC. We conclude that the Keeling plot method is a powerful technique that enables characterization and quantification of the organic carbon sources contributing to respiration in aquatic systems.

  • 23.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Similar relationships between pelagic primary and bacterial production in clearwater and humic lakes2002In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 83, no 10, 2902-2910 p.Article in journal (Refereed)
    Abstract [en]

    We examined the relationship between planktonic primary production (PP) and bacterial production (BP) in 16 subarctic lakes along an altitude gradient extending from colored coniferous forest lakes to clearwater high alpine lakes. We tested the hypothesis that there was a shift from low to high PP:BP ratios along this gradient. The clearwater alpine lakes had low PP:BP ratios, generally well below 1.0, while the highest ratios were-found in the forest lakes. In contradiction to our hypothesis, the pelagic systems of the clearwater lakes were thus dominated by bacterial energy mobilization from external carbon sources. In this respect the alpine lakes were similar to highly humic lakes. We suggest that the relationship between C, N, and P plays a critical role in determining the PP:BP ratio, and that the N:P ratio in particular can be critical for development of PP or BP dominance in the pelagic systems of unproductive lakes.

  • 24.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bacterioplankton production in lakes along an altitude gradient in the subarctic north of Sweden2001In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 42, no 3, 372-382 p.Article in journal (Refereed)
    Abstract [en]

    We examined changes in bacterioplankton standing stock and production in subarctic lakes in the north of Sweden to elucidate their coupling to lake physical, chemical, and biological characteristics. Sixteen lakes situated along an altitude gradient extending from the coniferous forest to the high-alpine belt were studied during 1998 and 1999. The summer mean bacterial numbers and production varied substantially between the lakes, with a general trend toward decreasing values with increasing altitude. The results demonstrate that P probably restricted bacterial utilization of DOC in the coniferous forest lakes, while low DOC concentrations limited bacterial growth during the summer in the alpine lakes. The primary production of plankton was insufficient to support bacterial production in the lakes. High input of allochthonous DOC to the alpine lakes in spring was sufficient both to increase the bacterial production and to induce P-limitation. As a consequence, there was a tendency toward higher bacterial activity in the spring compared to the summer in the alpine lakes. The results indicate that most of the bacterial standing stock and production are supported by allochthonous DOC plus DOC from benthic production, and more or less limited by the phosphorus supply. We therefore suggest that bacteria populations in subarctic lakes may be indirectly affected by climate variations through its impact on the input of DOC and nutrients from the lake catchments.

  • 25.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Productivity of high-latitude lakes: climate effect inferred from altitude gradient2005In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 11, no 5, 710-715 p.Article in journal (Refereed)
    Abstract [en]

    Climate change is predicted to be dramatic at high latitudes. Still, climate impact on high latitude lake ecosystems is poorly understood. We studied 15 subarctic lakes located in a climate gradient comprising an air temperature difference of about 6&DEG; C. We show that lake water productivity varied by one order of magnitude along the temperature gradient. This variation was mainly caused by variations in the length of the ice-free period and, more importantly, in the supply of organic carbon and inorganic nutrients, which followed differences in terrestrial vegetation cover along the gradient. The results imply that warming will have rapid effects on the productivity of high latitude lakes, by prolongation of ice-free periods. However, a more pronounced consequence will be a delayed stimulation of the productivity following upon changes of the lakes terrestrial surroundings and subsequent increasing input of elements that stimulate the production of lake biota.

  • 26.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Meili, M
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Control of zooplankton dependence on allochthonous organic carbon in humic and clear-water lakes in northern Sweden2003In: Limnology and Oceanography, ISSN 0024-3590, Vol. 48, no 1, 269-276 p.Article in journal (Refereed)
    Abstract [en]

    We compared the stable carbon isotopic composition (delta(13)C) of crustacean zooplankton with that of potential carbon sources in 15 lakes in northern Sweden with different dissolved organic carbon (DOC) concentrations (2-9 mg L-1) to test the hypothesis that zooplankton depended more on allochthonous carbon in humic lakes than in clear-water lakes. Based on delta(13)C signature, we found that the pool of organic matter in the lakes was dominated by carbon of allochthonous origin over the whole DOC gradient. Zooplankton were generally depleted in C-13 compared to organic matter in the catchment, particulate organic matter in the lake water, and shallow surface sediment. However, the isotopic composition of zooplankton could not be explained without a significant contribution from both allochthonous and autochthonous carbon sources in all lakes. The relative importance of these two carbon sources did not relate to the concentration of, or proportion between, allochthonous and autochthonous organic carbon in the water. Instead, the proportion between allochthonous and autochthonous carbon in the crustacean zooplankton was consistent with a rather conservative use of the energy mobilized by bacterioplankton and phytoplankton in the lakes.

  • 27.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Meili, M
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    δ15N of zooplankton species in subarctic lakes in northern Sweden: Effects of diet and trophic fractionation2004In: Freshwater Biology, Vol. 49, 526-534 p.Article in journal (Refereed)
    Abstract [en]

    1. To assess the use of stable nitrogen isotopes (δ15N) for reconstructing trophic relationships in planktonic food webs, crustacean zooplankton species and pelagic dissolved and particulate matter were analysed in 14 subarctic lakes in northern Sweden. The lakes are situated along an altitudinal gradient and show a substantial variation in nutrient content and energy mobilization by bacterioplankton and phytoplankton.

    2. The δ15N of dissolved and particulate matter was comparatively low, suggesting efficient N recycling and low losses of depleted N from the pelagic zone of these unproductive lakes.

    3. Copepods had a systematically higher δ15N than cladocerans, with an average difference of 3.1–4.9‰ within lakes, implying different trophic positions of the two groups. Comparisons of nitrogen pools and energy fluxes suggest that the low cladoceran δ15N was a result of feeding on bacteria.

    4. The difference in δ15N between copepods and cladocerans declined with decreasing bacterioplankton production among lakes, due either to increasing trophic isotope fractionation or decreasing relative importance of bacteria in the diet of cladocerans.

  • 28. Kohler, S
    et al.
    Buffam, I
    Jonsson, A
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bishop, K
    Photochemical and microbial processing of stream and soilwater dissolved organic matter in a boreal forested catchment in northern Sweden2002In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 64, no 3, 269-281 p.Article in journal (Refereed)
    Abstract [en]

    Natural organic matter (NOM) from stream and soil water in a humic-rich headwater catchment in northern Sweden (initial total organic carbon (TOC) concentrations 10-40 mg C L-1) was rapidly degraded by light and microbial activity in an incubation experiment. Concentration losses were 33-50% after 12 days of exposure to 69 W m(-2) artificial PAR and 16 W m(-2) UV radiation. Natural, unshaded mid-day solar radiation in the region (68degreesN 18degreesE) during the month of june is 159 W m(-2) for PAR. In contrast to microbial organic carbon removal, TOC exponentially decreased upon radiation, which suggests that TOC is more rapidly oxidized by light than by ambient microbes. Further, rapid decline in TOC concentration implies the presence of a dominant pool of photo-labile compounds (p > 95%). A measured mass balance for carbon identified 50-75% of the degraded TOC as carbon dioxide after 12 days of exposure to light. The observed conversion of organic to inorganic carbon was accompanied by increases in pH and alkalinity, suggesting that photo-degradation of NOM potentially contributes to in-stream buffering capacity. The remaining refractory TOC changed in chemical character, including an altered molecular weight distribution with decreased average weight and a change in the proportions of humics as evidenced by absorbance ratios (A(254)/A(420)). Extrapolation of the experiment to natural headwater conditions show that photo-degradation is an important in-stream process that should be considered in calculations of carbon turnover in surface waters because of its influence on both TOC amount and character.

  • 29. MacIntyre, Sally
    et al.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Åberg, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Turney, Damon E.
    Miller, Scott D.
    Buoyancy flux, turbulence, and the gas transfer coefficient in a stratified lake2010In: Geophysical Research Letters, ISSN 0094-8276, Vol. 37, no L24604Article in journal (Refereed)
    Abstract [en]

    Gas fluxes from lakes and other stratified water bodies, computed using conservative values of the gas transfer coefficient k600, have been shown to be a significant component of the carbon cycle. We present a mechanistic analysis of the dominant physical processes modifying k600 in a stratified lake and resulting new models of k600 whose use will enable improved computation of carbon fluxes. Using eddy covariance results, we demonstrate that i) higher values of k600 occur during low to moderate winds with surface cooling than with surface heating; ii) under overnight low wind conditions k600 depends on buoyancy flux β rather than wind speed; iii) the meteorological conditions at the time of measurement and the inertia within the lake determine k600; and iv) eddy covariance estimates of k600 compare well with predictions of k600 using a surface renewal model based on wind speed and β.

  • 30. Meili, Markus
    et al.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Seasonal dynamics of plankton and stable carbon isotopes (delta(13)C) in a large humic lake (Ortrasket, N. Sweden)2001In: INTERNATIONAL ASSOCIATION OF THEORETICAL AND APPLIED LIMNOLOGY, PROCEEDINGS, VOL 27, PT 4, 2001, 1940-1942 p.Conference paper (Refereed)
  • 31.
    Myrstener, Maria
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The effects of temperature and resource availability on denitrification and relative N2O production in boreal lake sediments2016In: Journal of Environmental Sciences(China), ISSN 1001-0742, E-ISSN 1878-7320, Vol. 47, 82-90 p.Article in journal (Refereed)
    Abstract [en]

    Anthropogenic environmental stressors (like atmospheric deposition, land use change, and climate warming) are predicted to increase inorganic nitrogen and organic carbon loading to northern boreal lakes, with potential consequences for denitrification in lakes. However, our ability to predict effects of these changes is currently limited as northern boreal lakes have been largely neglected in denitrification studies. The aim of this study was therefore to assess how maximum potential denitrification and N2O production rates, and the relationship between the two (relative N2O production), is controlled by availability of nitrate (NO3), carbon (C), phosphorus (P), and temperature. Experiments were performed using the acetylene inhibition technique on sediments from a small, nutrient poor boreal lake in northern Sweden in 2014. Maximum potential denitrification and N2O production rates at 4°C were reached already at NO3 additions of 106–120 μg NO3–N/L, and remained unchanged with higher NO3 amendments. Higher incubation temperatures increased maximum potential denitrification and N2O production rates, and Q10 was somewhat higher for N2O production (1.77) than for denitrification (1.69). The relative N2O production ranged between 13% and 64%, and was not related to NO3 concentration, but the ratio increased when incubations were amended with C and P (from a median of 16% to 27%). Combined, our results suggests that unproductive northern boreal lakes currently have low potential for denitrification but are susceptible to small changes in NO3 loading especially if these are accompanied by enhanced C and P availability, likely promoting higher N2O production relative to N2.

  • 32. Pers, C
    et al.
    Rahm, L
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Modelling dissolved organic carbon turnover in humic Lake Örträsket, Sweden2001In: Environmental Modelling and Assessment, ISSN 1420-2026, E-ISSN 1573-2967, Vol. 6, no 3, 159-172 p.Article in journal (Refereed)
    Abstract [en]

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

  • 33.
    Åberg, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Contributions of internal and external sources to the CO2 emission from a subarctic lake2005In: Verh. Internat. Verein. Limnol., Vol. 29, 577-579 p.Article in journal (Refereed)
  • 34.
    Åberg, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Importance of water temperature and thermal stratification dynamics for temporal variation of surface water CO2 in a boreal lake2010In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 115, no G02024, 10PP- p.Article in journal (Refereed)
    Abstract [en]

    Variation of the surface water CO2 concentration is likely to be the result of biological activity and physical processes as water mixing and gas exchange with the atmosphere. Here we have studied the variations in surface water CO2 during the ice-free period in the humic Lake Merasjärvi in northern Sweden. Meteorological, hydrological and limnological data were collected using data logging equipment permitting high time-resolution. The surface water of the lake was supersaturated with respect to CO2 throughout the study period. There were, however, considerable diurnal and longer-term temporal variations of the surface water CO2 concentrations. Partial least squares (PLS) models were used to link the logged CO2 data to the multivariate dataset. On the longer-term time scale (analyzed with 24h means of the logged data) high concentrations of surface water CO2 were best related to the depth and temperature of the upper warmer layer (epilimnion), and to erosion of the underlying colder layer (hypolimnion). The diurnal variation (analyzed with 30 minute means of the logged data) was best related to the thermal dynamics within the epilimnion, which regulated the surface water access to CO2 stores within this layer. Variables related to CO2 emission and photosynthesis (wind and PAR), showed only weak correlations to variations of the surface water CO2 concentration. Accordingly, the CO2 flux, measured with the eddy-covariance technique, was not correlated to the surface water CO2 concentration.

  • 35.
    Åberg, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Nääs, Klockar-Jenny
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Pelagic and benthic net production of dissolved inorganic carbon in an unproductive subarctic lake2007In: Freshwater Biology, Vol. 52, no 3, 549-560 p.Article in journal (Refereed)
    Abstract [en]

    1. Both the pelagic and benthic net dissolved inorganic carbon (DIC) productions were measured in situ on four occasions from June to September 2004, in the unproductive Lake Diktar-Erik in subarctic Sweden. The stable isotopic signal (δ13C) of respired organic material was estimated from hypolimnion water data and data from a laboratory incubation using epilimnion water.

    2. Both pelagic and benthic habitats were net heterotrophic during the study period, with a total net DIC production of 416 mg C m-2 day-1, of which the pelagic habitat contributed approximately 85%. The net DIC production decreased with depth both in the pelagic water and in the sediments, and most of the net DIC production occurred in the upper water column.

    3. Temporal variations in both pelagic and benthic DIC production were small, although we observed a significant decrease in pelagic net DIC production after the autumn turnover. Water temperature was the single most important factor explaining temporal and vertical variations in pelagic DIC production. No single factor explained more than 10% of the benthic net DIC production, which probably was regulated by several interacting factors.

    4. Pelagic DIC production, and thus most of the whole-lake net production of DIC, was mainly due to the respiration of allochthonous organic carbon. Stable isotope data inferred that nearly 100% of accumulated DIC in the hypolimnion water had an allochthonous carbon source. Similarly, in the laboratory incubation using epilimnion water, c. 85% of accumulated DIC was indicated to have an allochthonous organic carbon source.

1 - 35 of 35
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