AME prepress abstract  -  DOI: https://doi.org/10.3354/ame01858

Increased water color affects freshwater plankton communities in a mesocosm study

Karen Lebret*, Silke Langenheder, Noemi Colinas, Örjan Östman, Eva S. Lindström

*Email: karen.lebret@gmail.com

ABSTRACT: Increases in water colour (brownification) have been observed in aquatic systems in the northern hemisphere, partly caused by increased loading of organic carbon from terrestrial origins. We investigated the effect of increase in water color on the composition, structure and function of lake plankton communities (bacteria, phytoplankton, and zooplankton) conducting a mesocosm experiment in three medium colored lakes (average absorbance at 420 nm: 0.034 cm-1), with different nutrient concentrations and phytoplankton community composition. To simulate an increase in water colour, we added humic substances (Huminfeed®) at three different concentrations. The additions significantly affected the water colour of the mesocosms, but had no measurable effect on total organic carbon concentrations, thus change in light conditions was the main effect of our treatment on the plankton communities. The increase in water colour did not significantly affect the measured functions (productivity, respiration) and biomass of the plankton communities (bacteria, phytoplankton and zooplankton), but led to changes in the relative abundances of some phytoplankton taxa and to lesser extent the bacterial community (differences in relative abundance). The treatments had no significant effect on zooplankton biomass or composition. Our study suggests that increases in water color favour low light adapted phytoplankton species, which in turn also can affect bacterial composition, whereas the change in light climate had no clear impact on the functioning of plankton communities in weakly humic lakes.