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Reduction of zooplankton communities in small lake outlets in relation to abiotic and biotic factors

Czerniawski R., Domagała J.

Oceanological and Hydrobiological Studies

2013

Vol. 42, No. 2

123-131

The aim of this study was to answer the following questions: (1) which environmental variables, biotic (fish predation) or abiotic factors, have a greater influence on the rate of zooplankton changes in lake outlet sections and (2) which plankters suffer the greatest reduction in the outlet section. Samples were collected in two locations at each of 18 lakes. The first site was right at the outflow; the second site was 0.2 km downstream from the outflow. At downstream sites the percentage contribution of Rotifera in zooplankton species number and abundance was higher than in the outflow, whilst the percentage contribution of Cladocera and Copepoda (except nauplii) in the zooplankton species number and abundance was lower at downstream sites than in outlets. The most important variables affecting the rate of zooplankton reduction in the lake outlets are the biomass of cyprinids and hydrological parameters along the outlet, such as discharge, current velocity, and depth. The most dramatic reductions involved daphnids, adult copepods, small cladocerans, and copepodites, while the reduction in the abundance of rotifers and nauplii was statistically insignificant.

Potamozooplankton communities in three different outlets from mesotrophic lakes located in lake-river system

Czerniawski R., Domagała J.

Oceanological and Hydrobiological Studies

2012

Vol. 41, No. 1

46-56

Qualitative and quantitative composition of potamozooplankton was studied in three outlets from mesotrophic lakes. The greatest taxonomic and quantitative similarity of zooplankton occurred between the outflows of the second and third lake, located in the lake-river system. The farther the lake was located in the lake-river system, the greater was the quantity of zooplankton in the outflow. Within a short distance between the outflow and the downstream section, there was a strong reduction of cladocerans’ communities, followed by copepods, while the communities of rotifers were reduced in relatively small quantities. The hydrological conditions and transparency had a strong impact on the rate of changes in the zooplankton community.