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Träfflista för sökning "WFRF:(Bertilsson S.) srt2:(2000-2004)"

Sökning: WFRF:(Bertilsson S.) > (2000-2004)

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  • Bertilsson, S, et al. (författare)
  • Photochemical transformation of dissolved organic matter in lakes
  • 2000
  • Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 45:4, s. 753-762
  • Tidskriftsartikel (refereegranskat)abstract
    • In a survey of photochemical transformation of dissolved organic matter (DOM) in lake water, we found photochemical production of dissolved inorganic carbon (DIC) and low molecular weight carboxylic acids (oxalic, malonic, formic, and acetic acid), upon simulated solar ultraviolet (UV) radiation exposure of filter-sterilized surface water from 38 investigated lakes. Given the large variability in water chemistry of the studied systems, we suggest that these photoproducts are universally produced in sunlight exposed lake water. The measured production of carboxylic acid carbon corresponded to 34.4% (median) of the produced DIC. The production of DIC and carboxylic acids during 8 h of mild UV irradiation corresponded to an average of 4.7% (SD 2.9) of the total dissolved organic carbon pool. Hence, photochemical degradation could be a major sink for DOM in the surface layer of lakes. All photoreaction rates were strongly correlated to the total radiation absorbed during UV exposure (r(2) > 0.8), which depends mainly on amount of colored DOM in the water. The variability in DIC production after normalizing for absorbed radiation energy could partly be attributed to general water chemistry parameters (e.g., pH, iron concentration, conductivity).
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  • Bertilsson, S, et al. (författare)
  • Size-selective predation on pelagic microorganisms in Arctic freshwaters
  • 2003
  • Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 25:6, s. 621-631
  • Tidskriftsartikel (refereegranskat)abstract
    • Herbivorous zooplankton may have a pronounced influence on pelagic microorganisms in Arctic freshwaters. We quantified experimentally the size-selective feeding of several zooplankton groups on pelagic microorganisms in high Arctic tundra systems. Our experiments and field study focused on dominant herbivores in Arctic freshwaters, including the cladoceran Dophnia, the copepod Diaptomus and the anostracan Branchinecta, and their effects on prey ranging in size from bacteria to large phytoplankton. Grazing experiments showed that Dophnia were effective predators on all types of prey, whereas Diaptomus grazed preferentially on larger phytoplankton with low clearance rates for bacterial cells. Further analysis by flow cytometry indicated that Diaptomus grazed selectively on the largest bacteria. In contrast to the results obtained in the controlled experiments, Arctic lakes and ponds with a zooplankton community dominated by Dophnia had a higher bacterial production and abundance than systems not dominated by this grazer. This may indicate that the stimulatory effect of grazers on bacterial growth is more pronounced in natural systems, or that factors other than zooplankton grazing are more important in regulating bacterial abundance and production in natural systems. Although Arctic waters differ considerably from temperate systems with respect to temperature and light regime, herbivore-prey dynamics as well as the bacterial response to temperature appear to be similar between the climatic regions.
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