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Allochthonous Carbon - a major driver of bacterioplankton production in the subarctic Northern Baltic Sea
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).
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Food and Environmental Sciences, Division of Microbiology and Biotechnology, University of Helsinki, Helsinki, Finland. (Arcum)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
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2016 (English)In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 71, no 4, 789-801 p.Article in journal (Refereed) Published
Abstract [en]

Heterotrophic bacteria are, in many aquatic systems, reliant on autochthonous organic carbon as their energy source. One exception is low-productive humic lakes, where allochthonous dissolved organic matter (ADOM) is the major driver. We hypothesized that bacterial production (BP) is similarly regulated in subarctic estuaries that receive large amounts of riverine material. BP and potential explanatory factors were measured during May–August 2011 in the subarctic Råne Estuary, northern Sweden. The highest BP was observed in spring, concomitant with the spring river-flush and the lowest rates occurred during summer when primary production (PP) peaked. PLS correlations showed that ∼60 % of the BP variation was explained by different ADOM components, measured as humic substances, dissolved organic carbon (DOC) and coloured dissolved organic matter (CDOM). On average, BP was threefold higher than PP. The bioavailability of allochthonous dissolved organic carbon (ADOC) exhibited large spatial and temporal variation; however, the average value was low, ∼2 %. Bioassay analysis showed that BP in the near-shore area was potentially carbon limited early in the season, while BP at seaward stations was more commonly limited by nitrogen-phosphorus. Nevertheless, the bioassay indicated that ADOC could contribute significantly to the in situ BP, ∼60 %. We conclude that ADOM is a regulator of BP in the studied estuary. Thus, projected climate-induced increases in river discharge suggest that BP will increase in subarctic coastal areas during the coming century.

Place, publisher, year, edition, pages
Springer, 2016. Vol. 71, no 4, 789-801 p.
Keyword [en]
Allochthonous organic matter, carbon utilization, bacterioplankton production, Sub-arctic estuary, Baltic Sea
National Category
Research subject
Earth Sciences with Specialization Environmental Analysis
URN: urn:nbn:se:umu:diva-117966DOI: 10.1007/s00248-015-0714-4ISI: 000373683000001OAI: diva2:910124
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Available from: 2016-03-08 Created: 2016-03-08 Last updated: 2016-08-15Bibliographically approved
In thesis
1. Bacterioplankton in the Baltic Sea: influence of allochthonous organic matter and salinity
Open this publication in new window or tab >>Bacterioplankton in the Baltic Sea: influence of allochthonous organic matter and salinity
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Climate change is expected to increase the precipitation ~30% in higher latitudes during the next century, increasing the land runoff via rivers to aquatic ecosystems. The Baltic Sea will receive higher river discharges, accompanied by larger input of allochthonous dissolved organic matter (DOM) from terrestrial ecosystems. The salinity will decrease due to freshwater dilution. The allochthonous DOM constitute a potential growth substrate for microscopic bacterioplankton and phytoplankton, which together make up the basal trophic level in the sea. The aim of my thesis is to elucidate the bacterial processing of allochthonous DOM and to evaluate possible consequences of increased runoff on the basal level of the food web in the Baltic Sea. I performed field studies, microcosm experiments and a theoretical modeling study.

Results from the field studies showed that allochthonous DOM input via river load promotes the heterotrophic bacterial production and influences the bacterial community composition in the northern Baltic Sea. In a northerly estuary ~60% of bacterial production was estimated to be sustained by terrestrial sources, and allochthonous DOM was a strong structuring factor for the bacterial community composition. Network analysis showed that during spring the diversity and the interactions between the bacteria were relatively low, while later during summer other environmental factors regulate the community, allowing a higher diversity and more interactions between different bacterial groups. The influence of the river inflow on the bacterial community allowed “generalists” bacteria to be more abundant than “specialists” bacteria.   

Results from a transplantation experiment, where bacteria were transplanted from the northern Baltic Sea to the seawater from the southern Baltic Sea and vice versa, showed that salinity, as well as the DOM composition affect the bacterial community composition and their enzymatic activity. The results showed that α-proteobacteria in general were favoured by high salinity, β-proteobacteria by low salinity and terrestrial DOM compounds and γ-proteobacteria by the enclosure itself. However, effects on the community composition and enzymatic activity were not consistent when the bacterial community was retransplanted, indicating a functional redundancy of the bacterial communities. 

Results of ecosystem modeling showed that climate change is likely to have quite different effect on the north and the south of the Baltic Sea. In the south, higher temperature and internal nutrient load will increase the cyanobacterial blooms and expand the anoxic or suboxic areas. In the north, climate induced increase in riverine inputs of allochthonous DOM is likely to promote bacterioplankton production, while phytoplankton primary production will be hampered due to increased light attenuation in the water. This, in turn, can decrease the production at higher trophic levels, since bacteria-based food webs in general are less efficient than food webs based on phytoplankton. However, complex environmental influences on the bacterial community structure and the large redundancy of metabolic functions limit the possibility of predicting how the bacterial community composition will change under climate change disturbances.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2016. 23 p.
Bacterioplankton production; bacterial community structure; allochthonous organic matter; carbon utilization; dissolved organic carbon composition; bacterioplankton ecological function; bacterial diversity; bacterial network; Baltic Sea estuary; food web; climate change.
National Category
Research subject
biology, Environmental Science
urn:nbn:se:umu:diva-117977 (URN)978-91-7601-412-7 (ISBN)
Public defence
2016-04-01, KB3B1, Linnaeus väg 6 (Chemical Biological Center, KBC), Umeå, 10:00 (English)
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Available from: 2016-03-11 Created: 2016-03-08 Last updated: 2016-03-10Bibliographically approved

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Figueroa, DanielaRowe, OwenPaczkowska, JoannaAndersson, Agneta
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