umu.sePublications
Change search
Refine search result
12 1 - 50 of 53
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 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.
    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.
    Ågren, Anneli
    Tranvik, Lars J
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Role of lakes for organic carbon cycling in the boreal zone2004In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 10, no 1, 141-147 p.Article in journal (Refereed)
    Abstract [en]

    We calculated the carbon loss (mineralization plus sedimentation) and net CO2 escape to the atmosphere for 79 536 lakes and total running water in 21 major Scandinavian catchments (size range 437–48 263 km2). Between 30% and 80% of the total organic carbon that entered the freshwater ecosystems was lost in lakes. Mineralization in lakes and subsequent CO2 emission to the atmosphere was by far the most important carbon loss process. The withdrawal capacity of lakes on the catchment scale was closely correlated to the mean residence time of surface water in the catchment, and to some extent to the annual mean temperature represented by latitude. This result implies that variation of the hydrology can be a more important determinant of CO2 emission from lakes than temperature fluctuations. Mineralization of terrestrially derived organic carbon in lakes is an important regulator of organic carbon export to the sea and may affect the net exchange of CO2 between the atmosphere and the boreal landscape.

  • 3. Berggren, Martin
    et al.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Soares, Ana R. Alves
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Toward an ecologically meaningful view of resource stoichiometry in DOM-dominated aquatic systems2015In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 37, no 3, 489-499 p.Article in journal (Refereed)
    Abstract [en]

    Research on nutrient controls of planktonic productivity tends to focus on a few standard fractions of inorganic or total nitrogen (N) and phosphorus (P). However, there is a wide range in the degree to which land-derived dissolved organic nutrients can be assimilated by biota. Thus, in systems where such fractions form a majority of the macronutrient resource pool, including many boreal inland waters and estuaries, our understanding of bacterio-and phytoplankton production dynamics remains limited. To adequately predict aquatic productivity in a changing environment, improved standard methods are needed for determining the sizes of active (bioavailable) pools of N, P and organic carbon (C). A synthesis of current knowledge suggests that variation in the C:N:P stoichiometry of bioavailable resources is associated with diverse processes that differentially influence the individual elements across space and time. Due to a generally increasing organic nutrient bioavailability from C to N to P, we hypothesize that the C:N and N:P of bulk resources often vastly overestimates the corresponding ratios of bioavailable resources. It is further proposed that basal planktonic production is regulated by variation in the source, magnitude and timing of terrestrial runoff, through processes that have so far been poorly described.

  • 4.
    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.

  • 5.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Seasonal dynamics of bacteria and mixotrophic flagellates as related to input of allochthonous dissolved organic carbon2009In: International association of theoretical and applied limnology, vol 30, pt 6: proceedings / [ed] Jones, J & Faaborg, J, Stuttgart: Schweizerbart , 2009, 923-928 p.Conference paper (Refereed)
  • 6.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Seasonal dynamics of bacteria and mixotrophic flagellates as related to input of allochthonous dissolved organic carbon: internal and external sources to the CO2 emission from a subarctic lake2009In: Verhandlungen / Internationale Vereinigung für Theoretische und Angewandte Limnologie, ISSN 0368-0770, Vol. 30, no 6, 923-928 p.Article in journal (Refereed)
  • 7.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The use of TN:TP and DIN:TP ratios as indicators for phytoplankton nutrient limitation in oligotrophic lakes affected by N deposition2010In: Aquatic Sciences, ISSN 1015-1621, E-ISSN 1420-9055, Vol. 72, no 3, 277-281 p.Article in journal (Refereed)
    Abstract [en]

    The stoichiometric composition of lake water chemistry affects nutrient limitation among phytoplankton. I show how TN:TP and DIN:TP ratios vary in oligotrophic lakes of Europe and the USA affected by different amounts of N deposition, and evaluate whether the DIN:TP ratio is a better indicator than the TN:TP ratio for discriminating between N and P limitation of phytoplankton. Data were compiled from boreal and low to high alpine lakes, and comprise epilimnetic lake water chemistry data (106 lakes) and results from short-term nutrient bioassay experiments (28 lakes). A large share (54%) of the oligotrophic lakes in the study had low TN:TP mass ratios (<25). DIN:TP ratios showed higher variability than TN:TP ratios. Variability in DIN:TP ratios was related to N deposition, but also to catchment characteristics. Data from short-term bioassay experiments with separate addition of N and P showed that the DIN:TP ratio was a better indicator than the TN:TP ratio for N and P limitation of phytoplankton. Phytoplankton shift from N to P limitation when DIN:TP mass ratios increase from 1.5 to 3.4. High DIN:TP ratios, indicating P limitation of phytoplankton, were generally found in alpine lakes with low to moderate N deposition and in boreal lakes with high to very high amounts of N deposition.

  • 8.
    Bergström, Ann-Kristin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Algesten, G
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sobek, S
    Tranvik, L J
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Emission of CO2 from hydroelectric reservoirs in northern Sweden2004In: Archiv fur Hydrobiologie, Vol. 159, 25-42 p.Article in journal (Refereed)
  • 9.
    Bergström, Ann-Kristin
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Bigler, Christian
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Stensdotter, U.
    Lindström, E.S.
    Composition and dispersal of riverine and lake phytoplankton communities in connected systems with different water retention times2008In: Freshwater Biology, Vol. 53, 2520–2529- p.Article in journal (Refereed)
    Abstract [en]

    1. Lake phytoplankton community structure may be influenced by both internal factors (predation, competition, resource constraints) and external ones, such as dispersal of materials and cells between connected habitats. However, little is known about the importance of cell dispersal for phytoplankton community structure in lakes.

    2. We investigated the abundance and dispersal of phytoplankton cells between connected rivers and lakes, and analysed whether similarities in phytoplankton community composition between rivers and lakes were primarily related to cell import rates or to characteristics of the local habitat. We focused on lakes along a gradient of theoretical water retention times (TWRT). Two data sets from Swedish lakes were used; a seasonal study of two connected boreal forest lakes, differing in TWRT, and a multi-lake study of 13 lakes with a continuous range of TWRTs.

    3. Phytoplankton cells were transported and dispersed in all investigated rivers. In the seasonal study, cell import rates and similarities in phytoplankton community composition between the lake and its inlet(s) were much higher in the lake with a shorter TWRT. Phytoplankton community structure in different habitats was associated with total organic carbon (TOC). This indicates that local habitat characteristics may be important in determining lake phytoplankton community composition, even in the presence of substantial cell import.

    4. The multi-lake study also showed a negative relationship between TWRT and similarities in phytoplankton community composition between inlets and lakes. Moreover, similarity in community structure was related to both cell import rates from inlet to lake and differences in habitat characteristics between inlet and lake. However, the variable most strongly correlated with community structure was TOC, indicating that species sorting rather than a mass effect was the most important mechanism underlying the correlation between community structure and retention time.

    5. Overall, our data suggest that local habitat characteristics may play a key role in determining community similarity in this set of lakes covering a large range of habitat connectedness. Due to the strong co-variations between cell dispersal and TOC, it was hard to unequivocally disentangle the different mechanisms; hence, there is a need for further studies of the role of dispersal for phytoplankton community structures.

  • 10.
    Bergström, Ann-Kristin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Blomqvist, P
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of atmospheric nitrogen deposition on nutrient limitation and phytoplankton biomass in unproductive Swedish lakes2005In: Limnology & Oceanography, Vol. 50, 987-994 p.Article in journal (Refereed)
  • 11.
    Bergström, Ann-Kristin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull Mathisen, Carolyn
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Daniel
    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.
    Nitrogen deposition and warming  – effects on phytoplankton nutrient limitation in subarctic lakes2013In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 19, no 8, 2557-2568 p.Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to predict the combined effects of enhanced nitrogen (N) deposition and warming on phytoplankton development in high latitude and mountain lakes. Consequently, we assessed, in a series of enclosureexperiments, how lake water nutrient stoichiometry and phytoplankton nutrient limitation varied over the growingseason in 11 lakes situated along an altitudinal/climate gradient with low N-deposition (<1 kg N ha1yr1) in northern subarctic Sweden. Short-term bioassay experiments with N- and P-additions revealed that phytoplankton inhigh-alpine lakes were more prone to P-limitation, and with decreasing altitude became increasingly N- andNP-colimited. Nutrient limitation was additionally most obvious in midsummer. There was also a strong positivecorrelation between phytoplankton growth and water temperature in the bioassays. Although excess nutrients wereavailable in spring and autumn, on these occasions growth was likely constrained by low water temperatures. Theseresults imply that enhanced N-deposition over the Swedish mountain areas will, with the exception of high-alpinelakes, enhance biomass and drive phytoplankton from N- to P-limitation. However, if not accompanied by warming,N-input from deposition will stimulate limited phytoplankton growth due to low water temperatures during largeparts of the growing season. Direct effects of warming, allowing increased metabolic rates and an extension of thegrowing season, seem equally crucial to synergistically enhance phytoplankton development in these lakes.

  • 12.
    Bergström, Ann-Kristin
    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.
    Atmospheric nitrogen deposition has caused nitrogen enrichment and eutrophication of lakes in the northern hemisphere2006In: Global Change Biology, Vol. 12, 1-9 p.Article in journal (Refereed)
  • 13.
    Bergström, Ann-Kristin
    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.
    Bacterioplankton production in humic Lake Örträsket in relation to input of bacterial cells and input of allochthonous organic carbon2000In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 39, no 2, 101-115 p.Article in journal (Refereed)
    Abstract [en]

    In order to compare riverine bacteria input with lake water bacterial production and grazing loss with output loss, a bacterial cell budget was constructed for humic Lake Ortrasket in northern Sweden. The riverine input of bacterial cells in 1997 represented 29% of the number of bacterial cells produced within the layer of the lake affected by inlet water. A large share of the in situ lake bacterial production was consumed by grazers, mainly flagellates, which stresses the importance of bacteria as energy mobilizers for the pelagic food web in the lake. The bacterial production in Lake Ortrasket, which is almost entirely dependent on humic material as an energy source, was clearly stimulated by high flow episodes which brought high amounts of little degraded material into the lake. During base flow condition the bacterial production in the inlet rivers was high, which led to an input of more degraded material to the lake. This material did not stimulate the lake bacterial production. Internal factors that determined the utilization of the allochthonous DOC in the lake were the retention time and the exposure to light and high temperatures. Thus, the potential for in situ production of bacteria in Lake Ortrasket was to a large extent a function of how precipitation and runoff conditions affected terrestrial losses and river transport of humic material.

  • 14.
    Bergström, Ann-Kristin
    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.
    Blomqvist, P
    Drakare, S
    The influence of water colour and effective light climate on mixotrophic phytoflagellates in three small Swedish dystrophic lakes2000In: Verhandlungen / Internationale Vereinigung für Theoretische und Angewandte Limnologie, ISSN 0368-0770, Vol. 27, no 4, 1861-1965 p.Article in journal (Refereed)
  • 15.
    Bergström, Ann-Kristin
    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.
    Drakare, Stina
    Blomqvist, Peter
    Occurrence of mixotrophic flagellates in relation to bacterioplankton production, light regime and availability of inorganic nutrients in unproductive lakes with differing humic contents2003In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 48, no 5, 868-877 p.Article in journal (Refereed)
    Abstract [en]

    1. Field data from five unproductive Swedish lakes were used to investigate the occurrence of mixotrophic flagellates in relation to bacterioplankton, autotrophic phytoplankton, heterotrophic flagellates and abiotic environmental factors. Three different sources of data were used: (i) a 3-year study (1995-97) of the humic Lake Örträsket, (ii) seasonal measurements from five lakes with widely varying dissolved organic carbon (DOC) concentrations, and (iii) whole lake enrichment experiments with inorganic nutrients and organic carbon. 2. Mixotrophic flagellates usually dominated over autotrophic phytoplankton in Lake Örträsket in early summer, when both bacterial production and light levels were high. Comparative data from the five lakes demonstrated that the ratio between the biomasses of mixotrophic flagellates and autotrophic phytoplankton (the M/A-ratio) was positively correlated to bacterioplankton production, but not to the light regime. Whole lake carbon addition (white sugar) increased bacterial biomass, and production, reduced the biomass of autotrophs by a factor of 16, and increased the M/A-ratio from 0.03 to 3.4. Collectively, the results indicate that the dominance of mixotrophs among phytoplankton was positively related to bacterioplankton production. 3. Whole lake fertilisation with nitrogen (N) and phosphorus (P) demonstrated that the obligate autotrophic phytoplankton was limited by N. N-addition increased the biomass of the autotrophic phytoplankton but had no effect on mixotrophic flagellates or bacteria, and the M/A-ratio decreased from 1.2 to 0.6 after N-enrichment. Therefore, we suggest that bacteria under natural conditions, by utilising allochthonous DOC as an energy and carbon source, are able to outcompete autotrophs for available inorganic nutrients. Consequently, mixotrophic flagellates can become the dominant phytoplankters when phagotrophy permits them to use nutrients stored in bacterial biomass. 4. In Lake Ortrasket, the biomass of mixotrophs was usually higher than the biomass of heterotrophs during the summer. This dominance could not be explained by higher grazing rates among the mixotrophs. Instead, ratios between mixotrophic and heterotrophic biomass (the M/H-ratio) were positively related to light availability. Therefore, we suggest that photosynthesis can enable mixotrophic flagellates to outcompete heterotrophic flagellates.

  • 16.
    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.

  • 17.
    Bergström, Ann-Kristin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Daniel
    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.
    Vrede, Tobias
    N-limited consumer growth and low nutrient regeneration N:P ratios in lakes with low N deposition2015In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Vol. 6, no 1, 9Article in journal (Refereed)
    Abstract [en]

    Nutrient limitation of primary producers and their consumers can have a large influence on ecosystem productivity. The nature and strength of nutrient limitation is driven both by external factors (e.g., nutrient loading) and internal processes (e.g., consumer-driven nutrient regeneration). Here we present results from a field study in 10 low productive headwater lakes in northern subarctic Sweden, where nitrogen (N) deposition is low and phytoplankton is primarily N-limited. We assessed the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of seston and zooplankton and estimated the N:P ratio of consumer-driven nutrient regeneration. Based on stoichiometric models, the estimated elemental imbalances between seston and zooplankton suggest that zooplankton were mainly N-limited and regenerated nutrients with low N:P ratios (median 11.9, atomic ratio). The predicted N:P regeneration ratios were consistent with results from phytoplankton nutrient limitation bioassays in mid-summer, i.e., the N:P regeneration was predicted to be low when phytoplankton were N-limited, and high when phytoplankton were P-limited. During other seasons, when water discharge was high, nutrient loading from the surrounding catchments apparently had the strongest effect on phytoplankton nutrient limitation. We propose that lakes with higher N:P ratios than the open ocean is an effect of N deposition, that N-limitation of consumers and phytoplankton is further enhanced by low nutrient regeneration N:P ratios, and that in the absence of N deposition, lake and ocean N:P stoichiometry are similar.

  • 18. Blomqvist, Peter
    et al.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Drakare, Stina
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Brydsten, Lars
    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).
    Effects of additions of DOC on pelagic biota in a clearwater system: results from a whole lake experiment in northern Sweden2001In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 42, no 3, 383-394 p.Article in journal (Refereed)
    Abstract [en]

    An oligotrophic clearwater lake, initially characterized by a pronounced dominance of autotrophic phytoplankton and mostly by one species, the green alga Botryococcus, was subject to additions of dissolved organic carbon in the form of white sugar (sucrose) during two consecutive years. The hypothesis tested was that it is organic carbon per se, and not other possible effects of humic substances, that determines the differences in structure of the planktonic ecosystem between humic and clearwater lakes. The additions of DOC resulted in a significant increase in bacterial biomass and a decrease in the biomass of autotrophic phytoplankton. The biomass of mixotrophic and heterotrophic flagellates instead increased significantly, whereas no effects were found to propagate to higher trophic levels. As a result of the changes among biota, total planktonic biomass also decreased to a level typical of nearby humic lakes. We suggest that it is the carbon component of humic material and its utilization by bacterioplankton that determines the structure and function of the pelagic food web in humic lakes.

  • 19.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    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.
    Nitrogen effects on aquatic food web efficiency in the pelagic zone of unproductive lakes along a gradient of dissolved organic carbonManuscript (preprint) (Other academic)
    Abstract [en]

    Atmospheric nitrogen (N) deposition and terrestrial dissolved organic carbon (DOC) loadings are increasing in northern boreal lakes. However, consequences of increased N availability on food web efficiency (FWE) and consumer growth in N limited unproductive boreal lakes are unclear. Here, we performed in situ mesocosm experiments in late summer (2011; 2013) in six unproductive boreal Swedish lakes, paired across a DOC gradient, with one lake in each pair fertilized with N (2011: reference year; 2012, 2013: impact years). We assessed how zooplankton growth and FWE were affected by changes in pelagic energy mobilization (PEM), food chain length (PP:BP, i.e. phytoplankton: bacterial production ratio), and food quality (seston stoichiometry) in response to N fertilization. Although PP, PEM and PP:BP increased in low and medium DOC lakes after N fertilization, consumer growth and FWE in the low DOC lake were reduced, potentially due to a reduction in phytoplankton food quality (increased C:P; N:P). At high DOC, N fertilization caused modest increases in PP and PEM, with marginal changes in PP:BP and phytoplankton food quality, which combined led to a slight increase in zooplankton growth and FWE. We conclude that the background lake DOC level is critical in order to infer effects of enhanced inorganic N availability on pelagic productivity and FWE. In clear lakes increased N deposition will decrease FWE due to mismatches in food quality demand and supply. In humic lakes this mismatch will not occur, wherefore and zooplankton production and FWE will increase slightly following enhanced N deposition.

  • 20.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    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.
    Phytoplankton response to whole lake inorganic N fertilization along a gradient in dissolved organic carbon2017In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 98, no 4, 982-994 p.Article in journal (Refereed)
    Abstract [en]

    Global change has increased inorganic nitrogen (N) and dissolved organic carbon (DOC; i.e. ‘browning’) inputs to northern hemisphere boreal lakes. However, we do not know how phytoplankton in nutrient poor lake ecosystems of different DOC concentration respond to increased N availability. Here, we monitored changes in phytoplankton production, biomass and community composition in response to whole lake inorganic N fertilization in six boreal unproductive Swedish lakes divided into three lake pairs (control, N enriched) at three DOC levels (low, medium, high), with one reference year (2011) and two impact years (2012, 2013). We found that phytoplankton biomass and production decreased with DOC concentration before N fertilization. Further, phytoplankton community composition also differed with respect to DOC, with a dominance of non-flagellated autotrophs at low DOC towards an increasing dominance of flagellated autotrophs with increased lake DOC concentration. The N fertilization increased phytoplankton biomass and production in all lakes, but did not affect phytoplankton community composition. However, the net response in biomass and production to N fertilization declined with increasing DOC, implying that the lake DOC concentration is critical in order to infer phytoplankton responses to N fertilization, and that the system switches from being primarily nutrient limited to becoming increasingly light limited with increased DOC concentration. In conclusion, our results show that browning will reduce phytoplankton production and biomass and influence phytoplankton community composition, whereas increased inorganic N loadings from deposition, forestry or other land use will primarily enhance phytoplankton biomass and production. Together, any change in the landscape that enhances inorganic N availability will increase phytoplankton production and biomass, but the positive effects of N will be much weaker or even neutralized in browner lakes as caused by light limitation.

  • 21.
    Deininger, Anne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Faithfull, Carolyn L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Oceanography, University of Hawai'i, Honolulu, USA.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaus, Marcus
    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.
    Pelagic food web response to whole lake N fertilization2017In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, no 4, 1498-1511 p.Article in journal (Refereed)
    Abstract [en]

    Anthropogenic activities are increasing inorganic nitrogen (N) loadings to unproductive boreal lakes. In many of these lakes phytoplankton are N limited, consequently N fertilization may affect ecosystem productivity and consumer resource use. Here, we conducted whole lake inorganic N fertilization experiments with six small N limited unproductive boreal lakes (three control and three N enriched) in an area receiving low N deposition with one reference and two impact years. Our aim was to assess the effects of N fertilization on pelagic biomass production and consumer resource use. We found that phytoplankton primary production (PP) and biomass, and the PP: bacterioplankton production ratio increased after fertilization. As expected, the relative contribution of phytoplankton derived resources (autochthony) that supported the crustacean zooplankton community increased. Yet, the response in the consumer community was modest with autochthony only increasing in one of the three major zooplankton groups and with no effect on zooplankton biomass. In conclusion, our findings imply that newly available phytoplankton energy derived from N fertilization was not efficiently transferred up to zooplankton, indicating a mismatch between producer energy supply and consumer energy use with potential accumulation of phytoplankton biomass as the result.

  • 22. Drakare, Stina
    et al.
    Blomqvist, Peter
    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.
    Primary production and phytoplankton composition in relation to DOC input and bacterioplankton production in humic Lake Örträsket2002In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 47, no 1, 41-52 p.Article in journal (Refereed)
    Abstract [en]

    1. The biomass and production of picophytoplankton, large phytoplankton and heterotrophic bacterioplankton were measured in humic Lake Örträsket, northern Sweden during four consecutive summers. 2. High flow episodes, carrying fresh dissolved organic carbon (DOC) into the lake, always stimulated heterotrophic bacterial production at the expense of primary production. Primary production never exceeded bacterial production for approximately 20 days after such an episode had replenished epilimnial DOC. We suggest that allochthonous DOC is an energy source that stimulates bacterioplankton that, because of their efficient uptake of inorganic nutrients, are then able to outcompete phytoplankton. After the exhaustion of readily available DOC, phytoplankton were able to dominate epilimnion production in Lake Örträsket. 3. Biomass production was higher when dominated by phytoplankton than by bacterioplankton, despite a similar utilization of nutrients in the epilimnion throughout the summer. We propose that different C : N : P ratios of bacterioplankton and phytoplankton permit the latter to produce more carbon (C) biomass per unit of available inorganic nutrients than bacterioplankton.

  • 23. Drakare, Stina
    et al.
    Blomqvist, Peter
    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.
    Relationships between picophytoplankton and environmental variables in lakes along a gradient of water colour and nutrient content2003In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 48, no 4, 729-740 p.Article in journal (Refereed)
    Abstract [en]

    1. Biomass and production of picophytoplankton, phytoplankton and heterotrophic bacterioplankton were measured in seven lakes, exhibiting a broad range in water colour because of humic substances. The aim of the study was to identify environmental variables explaining the absolute and relative importance of picophytoplankton. In addition, two dystrophic lakes were fertilised with inorganic phosphorus and nitrogen, to test eventual nutrient limitation of picophytoplankton in these systems. 2. Picophytoplankton biomass and production were highest in lakes with low concentrations of dissolved organic carbon (DOC), and DOC proved the factor explaining most variation in picophytoplankton biomass and production. The relationship between picophytoplankton and lake trophy was negative, most likely because much P was bound in humic complexes. Picophytoplankton biomass decreased after the additions of P and N. 3. Compared with heterotrophic bacterioplankton, picophytoplankton were most successful at the clearwater end of the lake water colour gradient. Phytoplankton dominated over heterotrophic bacteria in the clearwater systems possibly because heterotrophic bacteria in such lakes are dependent on organic carbon produced by phytoplankton. 4. Compared with other phytoplankton, picophytoplankton did best at intermediate DOC concentrations; flagellates dominated in the humic lakes and large autotrophic phytoplankton in the clearwater lakes. 5. Picophytoplankton were not better competitors than large phytoplankton in situations when heterotrophic bacteria had access to a non-algal carbon source. Neither did their small size lead to picophytoplankton dominance over large phytoplankton in the clearwater lakes. Possible reasons include the ability of larger phytoplankton to float or swim to reduce sedimentation losses and to acquire nutrients by phagotrophy.

  • 24. Elser, JJ
    et al.
    Andersen, T
    Baron, J
    Bergström, A-K
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Jansson, M
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Kyle, M
    Nydick, KR
    Steger, L
    Hessen, DO
    Shifts in lake N:P stoichiometry and nutrient limitation driven by atmospheric nitrogen deposition2009In: Science, ISSN 0036-8075, Vol. 326, 835-837 p.Article in journal (Refereed)
    Abstract [en]

    Human activities have more than doubled the amount of nitrogen (N) circulating in the biosphere. One major pathway of this anthropogenic N input into ecosystems has been increased regional deposition from the atmosphere. Here we show that atmospheric N deposition increased the stoichiometric ratio of N and phosphorus (P) in lakes in Norway, Sweden, and Colorado, United States, and, as a result, patterns of ecological nutrient limitation were shifted. Under low N deposition, phytoplankton growth is generally N-limited; however, in high–N deposition lakes, phytoplankton growth is consistently P-limited. Continued anthropogenic amplification of the global N cycle will further alter ecological processes, such as biogeochemical cycling, trophic dynamics, and biological diversity, in the world’s lakes, even in lakes far from direct human disturbance.

  • 25.
    Faithfull, Carolyn
    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.
    Vrede, Tobias
    Effects of nutrients and physical lake characteristics on bacterial and phytoplankton production: a meta-analysisManuscript (preprint) (Other academic)
    Abstract [en]

    We performed a meta-analysis compromising of field (300 studies) and experimental data (249 studies) from a wide range of lake trophic states and locations. We examined the effects of nitrogen (N), phosphorus (P), carbon (dissolved organic matter) (C (DOM)), temperature, latitude, and lake morphometry on the absolute and relative rates of primary production (PPr) and bacterial production (BP). We compared areal and volumetric rates of PPr, BP and BP:PPr, and differences between experimental and natural systems. Both field studies and experimental results showed tight agreement with regard to N and P as predictors of volumetric PPr and BP respectively. This was despite the large variation in study length, size and nutrient addition rates in experimental systems, and indicates that bacteria and phytoplankton do not seem to be competing for the same nutrients. Areal production measurements were more difficult to model and were more dependent on physical lake characteristics than nutrients. Temperature was positively correlated with PPr, but not with BP. BP:PPr was stable across experiments regardless of N, P, DOM, or glucose additions. In contrast, BP:PPr ratios varied greatly in the field data set and were highest in systems with low total N and at high latitudes. This pattern was driven by reduced PPr, not increased BP, therefore experimenters may need to manipulate PPr to change BP:PPr. Collectively, our results indicate that increased temperatures and N availability due to climate change will lead to higher PPr and lower BP:PPr, potentially decreasing the importance of energy mobilized through the microbial food web on a global scale.

  • 26.
    Faithfull, Carolyn
    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.
    Vrede, Tobias
    Swedish University of Agricultural Sciences, Uppsala.
    Effects of nutrients and physical lake characteristics on bacterial and phytoplankton production: A meta-analysis2011In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 56, no 5, 1703-1713 p.Article in journal (Refereed)
    Abstract [en]

    We performed a meta-analysis comprising field (300 studies) and experimental data (249 studies) from a widerange of lake trophic states and locations. We examined the effects of nitrogen (N), phosphorus (P), carbon(dissolved organic matter [DOM]), temperature, latitude, and lake morphometry on the absolute and relative ratesof phytoplankton primary production (PPr) and secondary bacterial production (BP). Areal and volumetric rates ofPPr, BP, and BP : PPr were compared, and we analyzed differences between experimental and natural systems. Bothfield studies and experimental results showed agreement with regard to N and P as predictors of volumetric PPr andBP, respectively, despite the large variation in study duration, size, and nutrient addition rates in experimentalsystems. This indicates that bacteria and phytoplankton do not seem to be competing for the same nutrients. Arealmeasurements were more difficult to predict and were more dependent on physical lake characteristics thannutrients. Temperature was positively correlated with PPr, but not with BP. BP: PPr was stable across experimentsregardless of N, P, DOM, or glucose additions. In contrast, BP : PPr ratios varied greatly in the field data set andwere highest in systems with low total N and at high latitudes. This pattern was driven by reduced PPr, not BP;therefore, experimenters may need to manipulate PPr to change BP: PPr. Collectively, our results indicate thatincreased temperatures and N availability will lead to higher PPr and lower BP : PPr, potentially decreasing theimportance of energy mobilized through the microbial food web on a global scale.

  • 27.
    Faithfull, Carolyn
    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.
    Vrede, Tobias
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Pelagic energy mobilization across crossed gradients of phosphorus and dissolved organic carbon in a chemostat experiment2010In: INTERNATIONAL ASSOCIATION OF THEORETICAL AND APPLIED LIMNOLOGY, VOL 30, PT 9 / [ed] Jones J, Faaborg J, 2010, Vol. 30, no 9, 1411-1415 p.Conference paper (Refereed)
    Abstract [en]

    Pelagic production depends on biological energy mobilization based on both light energy mobilized by phytoplankton and imported energy bound as allochthonous organic carbon (AOC) and utilized by bacteria. Both autotrophic (phytoplankton) and heterotrophic (bacterioplankton) production form the basis of pelagic energy mobilization (PEM) in lakes (JANSSON et al. 2003). The relative importance of these two energy mobilization pathways changes with respect to phosphorus (P) and AOC availability (KARLSSON et al. 2002, JANSSON et al. 2003). Whereas heterotrophic pelagic energy mobilization (PEMhet) increases with AOC (HESSEN 1998, JANSSON et al. 2000), both autotrophic (PEMaut) and heterotrophic production increase with P (DEL GIORGIO & PETERS 1994, NURNBERG & SHAW 1999), although the proportion each contributes to PEM may change with increasing total phosphorus (TP) concentration (ROTHHAUPT & CODE 1992, KRITZRERG et al. 2006). JANSSON et al. (2003) demonstrated from whole lake data from unproductive lakes that nutrient use efficiency (PEM/TP) is lower in heterotrophic systems than in autotrophic systems. Bacteria can use AOC as a carbon and energy source, thus uncoupling bacterial production from reliance on phytoplankton carbon (JONES 1992). Because bacteria have a higher affinity for P than phytoplankton, they can out compete phytoplankton at low concentrations of P, but would be expected to mobilize less carbon (C) per unit of P because bacteria contain approximately 10 times more P per unit C (by weight) than phytoplankton (VADSTEIN 2000). Consequently, it would be expected that less energy per unit P would be available for higher trophic levels in pelagic systems dominated by heterotrophy (JANSSON et al. 2003). A second explanation for PEM/TP being lower in heterotrophic than autotrophic systems is that although a high AOC input rate is correlated with a high TP input rate (MEILI 1992), P can be tightly bound to AOC and not always be available for bacterial and phytoplankton production (JONES 1998). An increase in the bioavailability of P may be caused by UV degradation of AOC, or eutrophication (COTNER & BIDDANDA 2002). In this study we examine how the relative contributions of heterotrophic and autotrophic production change with a range of AOC and P concentrations in a chemostat environment. We hypothesise that the proportion of pelagic energy mobilisation that is heterotrophic (%PEMhet) is positively correlated with the input rate of AOC and negatively related to the input rate of inorganic P at a given dissolved organic carbon (DOC) concentration. We also hypothesise that the nutrient use efficiency (PEM/TP) will decrease as heterotrophy increases.

  • 28.
    Faithfull, Carolyn
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Huss, Magnus
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Vrede, Tobias
    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.
    Bottom–up carbon subsidies and top–down predation pressure interact to affect aquatic food web structure2011In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 120, no 2, 311-320 p.Article in journal (Refereed)
    Abstract [en]

    Human impacts such as eutrophication, overexploitation and climate change currently threaten future global food and drinking water supplies. Consequently, it is important that we understand how anthropogenic resource (bottom–up) and consumer (top–down) manipulations affect aquatic food web structure and production. Future climate changes are predicted to increase the inputs of terrestrial dissolved organic carbon to lakes. These carbon subsidies can either increase or decrease total basal production in aquatic food webs, depending on bacterial competition with phytoplankton for nutrients. This study examines the effects of carbon subsidies (bottom–up) on a pelagic community exposed to different levels of top–down predation. We conducted a large scale mesocosm experiment in an oligotrophic clear water lake in northern Sweden, using a natural plankton community exposed to three levels of glucose addition (0, 420 and 2100 mg C l–1 total added glucose) and three levels of young-of-the-year perch Perca fluviatilis density (0, 0.56 and 2 individuals m–3). Bacterioplankton production doubled with glucose addition, but phytoplankton production was unaffected, in contrast to previous studies that have manipulated carbon, nutrients or light simultaneously. This suggests that carbon addition alone is not sufficient to reduce autotrophic production, at least in an oligotrophic lake dominated by mixotrophic phytoplankton. Larval perch grazing did not produce a classical trophic cascade, but substantially altered the species composition of crustacean zooplankton and ciliate trophic levels. Glucose addition increased the biomass of rotifers, thus potentially increasing energy transfer through the heterotrophic pathway, but only when fish were absent. This study illustrates that changes in community structure due to selective feeding by top-predators can determine the influence of bottom–up carbon subsidies.

  • 29.
    Faithfull, Carolyn
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Huss, Magnus
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Vrede, Tobias
    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.
    Bergstrom, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Transfer of bacterial production based on labile carbon to higher trophic levels in an oligotrophic pelagic system2012In: Canadian Journal of Fisheries and Aquatic Sciences, ISSN 0706-652X, E-ISSN 1205-7533, Vol. 69, no 1, 85-93 p.Article in journal (Refereed)
    Abstract [en]

    Additions of labile organic carbon (C) enhanced bacterial production (BP) and were associated with increases in crustacean zooplankton and planktivorous fish biomasses. This was shown in a mesocosm experiment where we traced the contribution of BP to zooplankton and fish using stable isotopes and labile glucose-C as a biomarker. BP increased with glucose-C addition, and all zooplankton and fish incorporated some glucose-C. However, the effect of labile-C addition on zooplankton was taxa-dependant, as although cladocerans incorporated the most labile-C, increased BP did not affect cladoceran biomass. Instead, calanoid copepod biomass increased with glucose addition. This suggests that the ability to selectively graze on high quality food, such as bacterial grazing protists capable of trophic upgrading, had a stronger positive effect on calanoid copepods biomass than unselective grazing on bacteria and protists had on cladoceran biomass. Higher BP was associated with increased survival and population growth of young-of-the-year perch (Perca fluviatilis) when stocked at high densities, which suggested that BP had a density-dependant positive effect on fish growth.

  • 30.
    Faithfull, Carolyn
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Huss, Magnus
    Vrede, Tobias
    Institutionen för vatten och miljö, Sveriges Lantbruksuniversitet, Uppsala.
    Karlsson, Jan
    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.
    Transfer of bacterial production based on labile carbon to higher trophic levels in an oligotrophic pelagic systemManuscript (preprint) (Other academic)
    Abstract [en]

    It is debatable whether bacterial production (BP) based on labile carbon (C) is an important energy subsidy for higher trophic levels in the pelagic zone of lakes. Increased BP may reduce phytoplankton and basal production through competition for phosphorus. However, enhanced BP can also be regarded  as an additional basal food resource used directly by unselective filter feeding (cladocerans) or indirectly through grazing on the microbial food web (cladocerans and copepods). In a mesocosm experiment we traced the contribution of BP to crustacean zooplankton and planktivorous fish using stable isotopes and labile glucose-C as a biomarker. BP increased with glucose-C addition and all zooplankton and fish incorporated some glucose-C. Although cladocerans incorporated the most glucose-C, increased BP did not affect cladoceran biomass. Instead, calanoid copepod biomass increased with glucose addition. This suggests that the ability to select high quality food such as bacterial grazing protists capable of trophic upgrading (i.e. de novo synthesis of fatty acids), had a stronger positive effect on calanoids, than unselective grazing on bacteria and protists had on cladoceran biomass. Higher BP was associated with increased survival and population growth of young-of-the-year perch when stocked at high densities, which suggested that BP had a density dependant effect on fish growth. Although the total amount of energy mobilized did not affect fish growth, energy mobilized through the microbial food chain increased calanoid copepod biomass; the favored prey species of planktivorous fish in this system.

  • 31.
    Faithfull, Carolyn L.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Deininger, Anne
    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.
    Food quantity and quality in unproductive clear water and humic lakes and consequences for pelagic mesozooplanktonManuscript (preprint) (Other academic)
    Abstract [en]

    1. Small oligotrophic humic lakes are the most common type of lake in the boreal zone and are predicted to become more abundant with climate change. Humic lakes generally have lower whole lake primary and consumer production than clear water lakes, but research is inconclusive as to what controls pelagic production in these lakes.

    2. We compared food quantity (primary production (PP) and phytoplankton biomass, pelagic energy mobilization, seston carbon (C)) and food quality (phytoplankton edibility, seston stoichiometry) for crustacean mesozooplankton in four humic (> 15 mg L-1 DOC) and four clear water lakes.

    3. We found that PP was over three times higher in clear water lakes, and was controlled by nutrient concentrations and temperature, whereas in humic lakes PP was dependant on light availability. Nevertheless, total food quantity (i.e. pelagic energy mobilization, seston C concentrations) was similar between lake types, even though food composition differed. In humic lakes bacterial production based on allochthonous C contributed three times more to total pelagic energy mobilization and seston C consisted of 20% less phytoplankton biomass.

    4. Food composition did not have any effect on total zooplankton biomass, however, cladoceran: copepod biomass ratios increased with DOC concentration, both in our lakes and in a subset of northern lakes from the Swedish lake monitoring program.

    5. Our results imply that increased DOC concentrations in boreal lakes will reduce PP and phytoplankton biomass and can alter food composition. However, browning of boreal lakes is unlikely to reduce pelagic energy mobilization or total zooplankton biomass, but can promote a higher dominance of cladocerans relative to copepods, which may have consequences for pelagic planktivorous predators.

  • 32.
    Faithfull, Carolyn L.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Mathisen, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wenzel, Anja
    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.
    Vrede, T.
    Food web efficiency differs between humic and clear water lake communities in response to nutrients and light2015In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 177, no 3, 823-835 p.Article in journal (Refereed)
    Abstract [en]

    This study demonstrates that clear and humic freshwater pelagic communities respond differently to the same environmental stressors, i.e. nutrient and light availability. Thus, effects on humic communities cannot be generalized from existing knowledge about these environmental stressors on clear water communities. Small humic lakes are the most numerous type of lake in the boreal zone, but little is known about how these lakes will respond to increased inflows of nutrients and terrestrial dissolved organic C (t-DOC) due to climate change and increased human impacts. Therefore, we compared the effects of nutrient addition and light availability on pelagic humic and clear water lake communities in a mesocosm experiment. When nutrients were added, phytoplankton production (PPr) increased in both communities, but pelagic energy mobilization (PEM) and bacterial production (BP) only increased in the humic community. At low light conditions, the addition of nutrients led to increased PPr only in the humic community, suggesting that, in contrast to the clear water community, humic phytoplankton were already adapted to lower ambient light levels. Low light significantly reduced PPr and PEM in the clear water community, but without reducing total zooplankton production, which resulted in a doubling of food web efficiency (FWE = total zooplankton production/PEM). However, total zooplankton production was not correlated with PEM, PPr, BP, PPr:BP or C:nutrient stoichiometry for either community type. Therefore, other factors such as food chain length, food quality, ultra-violet radiation or duration of the experiment, must have determined total zooplankton production and ultimately FWE.

  • 33.
    Faithfull, Carolyn
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wenzel, Anja
    Vrede, Tobias
    Institutionen för vatten och miljö, Sveriges Lantbruksuniversitet, Uppsala.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lower bacterial production and phytoplankton edibility reduces crustacean zooplankton biomass at low lightManuscript (preprint) (Other academic)
    Abstract [en]

    Anthropogenic changes in the nitrogen (N), phosphorus (P), and carbon (C) cycles have altered nutrient concentrations and the light climate in freshwaters globally. These factors influence phytoplankton (PPr) and bacterial production (BP), which constitute the basal energy resource for higher trophic levels in the pelagic zone of lakes. The light:nutrient hypothesis (LNH) predicts that although basal production will decrease at low light, seston C:nutrient ratios also decrease, thus increasing food quality for crustacean zooplankton, which tend to have relatively fixed C:nutrient ratios. We tested the LNH in a mesocosm experiment by examining the effects of N, P and C additions and shading on PPr, BP, seston C:nutrient ratios and zooplankton biomass in an oligotrophic clear water lake. We found that zooplankton biomass was strongly reduced in shaded treatments. Although PPr was unaffected by shading, BP decreased with shading. Bacteria can be an important energy and P source for zooplankton when mobilized through intermediate trophic levels, and correlations between BP, bacterial biomass, ciliates and zooplankton support this. Seston C:nutrient ratios were not affected by shading, possibly due to a high abundance of mixotrophic phytoplankton across treatments. Shading shifted the phytoplankton community towards low light adapted, but potentially less edible phytoplankton species, such as colony forming Dinobryon (Chrysophyta) and gymnoid (Dinoflagellata) taxa, which were negatively correlated with zooplankton biomass. Thus, the LNH may be inadequate when predicting changes in crustacean zooplankton biomass in response to light and nutrients in oligotrophic systems, where Daphnia is rare and mixotrophic phytoplankton are abundant.

  • 34.
    Faithfull, Carolyn
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wenzel, Anja
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Vrede, Tobias
    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.
    Testing the light: nutrient hypothesis in an oligotrophic boreal lake2011In: Ecosphere, ISSN 2150-8925, Vol. 2, no 11, 123- p.Article in journal (Refereed)
    Abstract [en]

    Anthropogenic changes in the nitrogen (N), phosphorus (P), and carbon (C) cycles have altered nutrient concentrations and the light climate in freshwaters globally. These factors affect phytoplankton (PPr) and bacterial production (BP), which constitute the basal energy resource for higher trophic levels in the pelagic zone of lakes. The light:nutrient hypothesis (LNH) predicts that although basal production decreases at low light, seston C:nutrient ratios also decrease, thus increasing food quality for crustacean zooplankton and potentially offsetting the negative effects of reduced food availability. We tested the LNH in an oligotrophic boreal lake by manipulating N, P, C and reducing light, and measuring PPr, BP, seston C:nutrient ratios and zooplankton biomass in 32 mesocosms. Low light strongly reduced zooplankton biomass in contrast to LNH predictions. PPr did not decrease with low light as predicted by the LNH, however, the phytoplankton community shifted towards low light adapted, but potentially less edible phytoplankton species, such as colony forming Dinobryon (Chrysophyta) and gymnoid (Dinoflagellata) taxa, which were negatively correlated with zooplankton biomass. Seston C:nutrient ratios did not decrease with reduced light, possibly due to the high abundance of mixotrophic phytoplankton across treatments. BP decreased with low light and correlations between BP, bacterial biomass, ciliates and zooplankton suggest that bacteria may be coupled with zooplankton biomass. Thus, the LNH was inadequate when predicting changes in crustacean zooplankton biomass in this typical oligotrophic boreal system, where Daphnia is rare and mixotrophic phytoplankton are abundant. Instead, alternative explanations, such as changes in phytoplankton edibility and energy transferred through the microbial food chain may need investigation to explain reduced zooplankton biomass in low light treatments.

  • 35. Isaksson, Anneli
    et al.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Blomqvist, Peter
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bacterial grazing by phagotrophic phytoflagellates in a deep humic lake in northern Sweden1999In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 21, no 2, 247-268 p.Article in journal (Refereed)
    Abstract [en]

    Bacterial grazing was measured from June to August 1995 in Lake Örträsket, a deep brown-water lake in northern Sweden. Mixotrophic chrysophytes were the dominating bacterivores at all times, grazing 3-14% of bacterial standing stock daily. The effects of altered nutrient supply and light availability on grazing activity and growth were studied in two mesocosm experiments. Incubation in the dark did not stimulate phagotrophy, which would otherwise be expected if bacteria were mainly being used as an energy source. Furthermore, clearance rates were not reduced after alleviation of nutrient limitation conditions. Rather, phagotrophy may work as a relatively fixed attribute of the mixotrophic community in this lake. When availability of dissolved nutrients is restricted, phagotrophy permits the mixotrophs to outcompete other phytoplankton, but they become less competitive at high nutrient concentrations. The relative share of mixotrophs in relation to total phytoplankton decreased considerably after enrichment with nitrogen + phosphorus.

  • 36.
    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
    Drakare, Stina
    Allochthonous organic carbon and phytoplankton/bacterioplankton production relationships in lakes2000In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 81, no 11, 3250-3255 p.Article in journal (Refereed)
    Abstract [en]

    Humic lakes with high inputs of allochthonous dissolved organic carbon have a pelagic food chain that, to a large extent, is based on bacterioplankton energy mobilization from allochthonous organic carbon compounds. This is in contrast to clear lakes in which total pelagic production is based mainly on phytoplankton photosynthesis. The energy economy in humic lakes may be less efficient than in clear lakes, because it is Likely that one more link is included in the food chain. Lake data from Scandinavia and North America demonstrate that shifts between food chains based on heterotrophic production and food chains based on primary production can take place at moderate increases or decreases in the concentration of dissolved organic carbon from allochthonous sources. Large variations in the loading of allochthonous organic carbon (e.g., due to climatic variations) may have considerable effects on the biostructure and productivity of lakes.

  • 37.
    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.

  • 38.
    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.
    Drakare, Stina
    Blomqvist, Peter
    Nutrient limitation of bacterioplankton and phytoplankton in humic lakes in northern Sweden2001In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 46, no 5, 653-666 p.Article in journal (Refereed)
    Abstract [en]

    1. Two small humic lakes in northern Sweden with concentrations of dissolved organic carbon (DOC) between 15 and 20 mg L-1 were fertilized with inorganic phosphorus (P) and inorganic nitrogen (N), respectively. A third lake was unfertilized and served as a control. In addition to this lake fertilization experiment, data from different regional surveys were used to assess the role of different limiting factors. 2. The P fertilization had no effects on bacterioplankton or phytoplankton, while phytoplankton were significantly stimulated by N fertilization. Inorganic nutrient limitation of bacterioplankton was a function of DOC concentration in water of the investigated region and nutrient-limited bacteria were found only in lakes with DOC concentrations less than around 15 mg L-1 3. The fertilization experiments demonstrated that the DOC-rich experimental lakes contained a bioavailable pool of P that was not utilized to its full potential under natural conditions. The overall mobilization of energy (bacterioplankton plus phytoplankton) in the experimental lakes was restricted by lack of inorganic N.

  • 39.
    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.
    Lymer, David
    Vrede, Katarina
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bacterioplankton growth and nutrient use efficiencies under variable organic carbon and inorganic phosphorus ratios2006In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 52, no 2, 258-264 p.Article in journal (Refereed)
    Abstract [en]

    We carried out enclosure experiments in an unproductive lake in northern Sweden and studied the effects of enrichment with different dissolved organic carbon (glucose)/inorganic phosphorous (DOC/Pi) ratios on bacterioplankton production (BP), growth efficiency (BGE), nutrient use efficiency (BNUE), growth rate, and specific respiration. We found considerable variation in BP, BGE, and BNUE along the tested DOC/Pi gradient. BGE varied between 0.87 and 0.24, with the highest values at low DOC/Pi ratios. BNUE varied between 40 and 9 g C g P−1, with high values at high DOC/Pi ratios. More DOC was thus allocated to growth when bacteria tended to be C-limited, and to respiration when bacteria were P-limited. Specific respiration was positively correlated with bacterial growth rate throughout the gradient. It is therefore possible that respiration was used to support growth in P-limited bacteria. The results indicated that BP can be limited by Pi when BNUE is at its maximum, by organic C when BGE is at its maximum, and by dual organic C and Pi limitation when BNUE and BGE have suboptimal values.

  • 40.
    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.

  • 41.
    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.

  • 42.
    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.

  • 43.
    Karlsson, Jan
    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.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gudasz, Cristian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rodriguez, Patricia
    Hein, Catherine
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Terrestrial organic matter input suppresses biomass production in lake ecosystems2015In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 11, 2870-2876 p.Article in journal (Refereed)
    Abstract [en]

    Terrestrial ecosystems export large amounts of organic carbon (t-OC) but the net effect of this OC on the productivity of recipient aquatic ecosystems is largely unknown. In this study of boreal lakes, we show that the relative contribution of t-OC to individual top consumer (fish) biomass production, and to most of their potential prey organisms, increased with the concentration of dissolved organic carbon (DOC; dominated by t-OC sources) in water. However, the biomass and production of top consumers decreased with increasing concentration of DOC, despite their substantial use (up to 60%) of t-OC. Thus, the results suggest that although t-OC supports individual consumer growth in lakes to a large extent, t-OC input suppresses rather than subsidizes population biomass production.

  • 44. Lindström, E
    et al.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Community composition of bacterioplankton and cell transport in lakes in two different drainage areas2005In: Aquat. Sci., Vol. 67, 210-219 p.Article in journal (Refereed)
  • 45. Lindström, E S
    et al.
    Forslund, M
    Algesten, G
    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.
    External control of bacterial community structure in lakes2006In: Limnology and Oceanography, Vol. 51, 339-342 p.Article in journal (Refereed)
  • 46.
    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.

  • 47. 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.

  • 48.
    Seekell, David A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lapierre, Jean-Francois
    East Lansing, Michigan.
    Ask, Jenny
    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.
    Deininger, Anne
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rodriguez, Patricia
    Tierra del Fuego, Argentina.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The influence of dissolved organic carbon on primary production in northern lakes2015In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 60, no 4, 1276-1285 p.Article in journal (Refereed)
    Abstract [en]

    Dissolved organic carbon (DOC) concentrations in lakes are changing globally, but little is known about potential ecosystem impacts.We evaluated the relationship between DOC and whole-lake primary production in arctic and boreal lakes. Both light extinction (inhibits primary production) and nutrient availability (stimulates primary production) are positively and nonlinearly related to DOC concentration. These nonlinearities create a threshold DOC concentration (4.8mg L-1), below which the DOC-primary production relationship is positive, and above which the relationship is negative. DOC concentration varies maximally between regions, creating a unimodal relationship between primary production and DOC that emerges at broader scales because arctic lakes largely fall below the threshold DOC concentration, but boreal lakes fall above it. Our analysis suggests that the impact of DOC trends on lake primary production will vary across lakes and regions as a result of contrasting baseline conditions relative to the DOC threshold.

  • 49. Soares, Ana R. A.
    et al.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Moberg, Joanna M.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kritzberg, Emma S.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Berggren, Martin
    New insights on resource stoichiometry: assessing availability of carbon, nitrogen, and phosphorus to bacterioplankton2017In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, no 6, 1527-1539 p.Article in journal (Refereed)
    Abstract [en]

    Boreal lake and river ecosystems receive large quantities of organic nutrients and carbon (C) from their catchments. How bacterioplankton respond to these inputs is not well understood, in part because we base our understanding and predictions on "total pools", yet we know little about the stoichiometry of bioavailable elements within organic matter. We designed bioassays with the purpose of exhausting the pools of readily bioavailable dissolved organic carbon (BDOC), bioavailable dissolved nitrogen (BDN), and bioavailable dissolved phosphorus (BDP) as fast as possible. Applying the method in four boreal lakes at base-flow conditions yielded concentrations of bioavailable resources in the range 105-693 mu g CL-1 for BDOC (2% of initial total DOC), 24-288 mu g NL-1 for BDN (31% of initial total dissolved nitrogen), and 0.2-17 mu g PL-1 for BDP (49% of initial total dissolved phosphorus). Thus, relative bioavailability increased from carbon (C) to nitrogen (N) to phosphorus (P). We show that the main fraction of bioavailable nutrients is organic, representing 80% of BDN and 61% of BDP. In addition, we demonstrate that total C : N and C: P ratios are as much as 13-fold higher than C : N and C: P ratios for bioavailable resource fractions. Further, by applying additional bioavailability measurements to seven widely distributed rivers, we provide support for a general pattern of relatively high bioavailability of P and N in relation to C. Altogether, our findings underscore the poor availability of C for support of bacterial metabolism in boreal C-rich fresh-waters, and suggest that these ecosystems are very sensitive to increased input of bioavailable DOC.

  • 50. Sobek, Sebastian
    et al.
    Algesten, Grete
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    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.
    Tranvik, Lars J
    The catchment and climate regulation of pCO2 in boreal lakes2003In: Global Change Biology, Vol. 9, no 4, 630-641 p.Article in journal (Refereed)
    Abstract [en]

    The regulation of surface water pCO2 was studied in a set of 33 unproductive boreal lakes of different humic content, situated along a latitudinal gradient (57°N to 64°N) in Sweden. The lakes were sampled four times during one year, and analyzed on a wide variety of water chemistry parameters. With only one exception, all lakes were supersaturated with CO2 with respect to the atmosphere at all sampling occasions. pCO2 was closely related to the DOC concentration in lakes, which in turn was mainly regulated by catchment characteristics. This pattern was similar along the latitudinal gradient and at different seasons of the year, indicating that it is valid for a variety of climatic conditions within the boreal forest zone. We suggest that landscape characteristics determine the accumulation and subsequent supply of allochthonous organic matter from boreal catchments to lakes, which in turn results in boreal lakes becoming net sources of atmospheric CO2.

12 1 - 50 of 53
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf