| Summary: | Water eutrophication is associated with an increase in the organic carbon content (both
particulate and dissolved forms), which may affect the functioning of the zooplankton
community. Mesotrophic and eutrophic lakes in the Masurian Lake District (Poland) were
selected to evaluate the relationship between the organic carbon level and the zooplankton
community. The lakes differed significantly in most environmental variables. RDA analysis
was performed to evaluate the impact of environmental variables on zooplankton. The
variables that significantly explained the variance in the zooplankton community abundance
(Monte Carlo permutation test) included dissolved and particulate organic carbon, Secchi
disc visibility, soluble reactive phosphorus and total nitrogen. The response of
zooplankton to an increasing level of organic carbon is functional rather than
quantitative. In the mesotrophic system, the results of the redundancy analysis indicated
relatively strong positive relationships between dissolved organic carbon and zooplankton
biomass, and negative correlations between chlorophyll a and zooplankton biomass.
The above suggests that indirect organic carbon utilization by zooplankton could partly
compensate for the poor feeding conditions of planktonic animals (decreased phytoplankton
availability). In the eutrophic lake, elevated organic carbon levels are partly limited by
zooplankton, which is suggested by the positive relationship between particulate organic
matter and the total zooplankton biomass (RDA results). The positive relationship between
the biomass of copepods and organic carbon in particulate and dissolved forms implies that
copepods benefit from the increased heterotrophic carbon flow that is activated in the
eutrophic lake.
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