The Effect of Increased Loads of Dissolved Organic Matter on Estuarine Microbial Community Composition and Function.
Increased river loads are projected as one of the major consequences of climate change in the northern hemisphere, leading to elevated inputs of riverine dissolved organic matter (DOM) and inorganic nutrients to coastal ecosystems. The objective of this study was to investigate the effects of elevated DOM on a coastal pelagic food web from the coastal northern Baltic Sea, in a 32-day mesocosm experiment. In particular, the study addresses the response of bacterioplankton to differences in character and composition of supplied DOM. The supplied DOM differed in stoichiometry and quality and had pronounced effects on the recipient bacterioplankton, driving compositional changes in response to DOM type. The shifts in bacterioplankton community composition were especially driven by the proliferation of Bacteroidetes, Gemmatimonadetes, Planctomycetes, and Alpha- and Betaproteobacteria populations. The DOM additions stimulated protease activity and a release of inorganic nutrients, suggesting that DOM was actively processed. However, no difference between DOM types was detected in these functions despite different community compositions. Extensive release of re-mineralized carbon, nitrogen and phosphorus was associated with the bacterial processing, corresponding to 25-85% of the supplied DOM. The DOM additions had a negative effect on phytoplankton with decreased Chlaand biomass, particularly during the first half of the experiment. However, the accumulating nutrients likely stimulated phytoplankton biomass which was observed to increase towards the end of the experiment. This suggests that the nutrient access partially outweighed the negative effect of increased light attenuation by accumulating DOM. Taken together, our experimental data suggest that parts of the future elevated riverine DOM supply to the Baltic Sea will be efficiently mineralized by microbes. This will have consequences for bacterioplankton and phytoplankton community composition and function, and significantly affect nutrient biogeochemistry.
Centre for Ocean Life, Marine Biological Section, University of Copenhagen Helsingør, Denmark.
Sachia J
SJ
Traving
Umeå Marine Sciences Centre, Umeå UniversityHörnefors, Sweden; Department of Ecology and Environmental Science, Umeå UniversityUmeå, Sweden.
Owen
O
Rowe
Laboratory for Applied Statistics, Department of Mathematical Sciences, University of Copenhagen Copenhagen, Denmark.
Nina M
NM
Jakobsen
Laboratory for Applied Statistics, Department of Mathematical Sciences, University of Copenhagen Copenhagen, Denmark.
Helle
H
Sørensen
Marine Biological Section, University of Copenhagen Helsingør, Denmark.
Julie
J
Dinasquet
Centre for Ocean Life, National Institute of Aquatic Resources, Technical University of Denmark Charlottenlund, Denmark.
Colin A
CA
Stedmon
Umeå Marine Sciences Centre, Umeå UniversityHörnefors, Sweden; Department of Ecology and Environmental Science, Umeå UniversityUmeå, Sweden.
Agneta
A
Andersson
Centre for Ocean Life, Marine Biological Section, University of CopenhagenHelsingør, Denmark; Marine Biological Section, University of CopenhagenHelsingør, Denmark.
Lasse
L
Riemann
16S rRNA; Baltic Sea; bacterioplankton community composition; climate change; community functions; dissolved organic matter; extracellular enzymes; generalized linear models