Krystian Obolewski

Effects of lateral connectivity on zooplankton community structure in floodplain lakes

Hydrological conditions are responsible for the changes in lateral connectivity between the main river channel and the floodplain lakes, a factor controlling zooplankton abundance and diversity. We tested the hypothesis that the degree of connectivity between the aquatic habitats and the river channel governs the zooplankton densities and community structure. Abundances, community composition and species diversity of zooplankton were analysed against the gradient of lakes’ connectivity and the water quality parameters under a natural flood pulse in the Biebrza River (North-Eastern Poland). Our findings revealed that the water level fluctuations directly affect the availability of nutrients, aeration, what in turn controls the densities and biovolumes of zooplankton communities. Along with the increase in the lake isolation, the taxonomic diversity of zooplankton decreased, while the eudomination of taxa indicative of advanced trophy (Rotifera) was observed. Qualitative parameters, as number of species, diversity and richness, were significantly higher at mean water levels, which supports the intermediate disturbance hypothesis. The sensitivity of the zooplankton community to variable hydrological conditions and lateral connectivity gradient demonstrates its potential as an unexploited indicator of any habitat changes in the aquatic ecosystems.

Connectivity restoration of floodplain lakes: an assessment based on macroinvertebrate communities

Successful rehabilitation programmes of river–floodplain systems require understanding of environmental impacts of restoring hydrological connectivity. The present study is based on a field experiment carried out between 2008 and 2013 in a floodplain of a lowland river in northern Poland, in which two oxbow lakes isolated in the 1920s were reconnected to the main river channel. Water and macroinvertebrate samples were collected three to four times a year from six sites (nxa0=xa0114). After reconnection, water quality in the oxbow lakes improved and diversity and abundance of macrozoobenthos increased, especially the density of Oligochaeta, Malacostraca, Trichoptera, Bivalvia and Gastropoda, while the density of Diptera decreased. Water flow and physico-chemical variables were the most important factors explaining their variance. A direct inflow of water into the reconnected oxbow lakes occurred only during the first 2xa0years of the study, followed by silting and overgrowing of the inlet to the upper arm. We propose that creating semi-lotic side channels connected to the river with one arm and only occasionally flushed with fresh river water is one of the most effective restoration strategies. However, at the whole river scale, the maintenance of diversified hydrological connections is the optimal solution.

Rearing river lamprey Lampetra fluviatilis (L.) larvae under controlled conditions as a tool for restitution of endangered populations

A method for actively protecting river lamprey and increasing the number of river lamprey populations is presented as protocol of rearing stocking material. The objective of the study was to accommodate lamprey larvae during the most critical life period under controlled conditions until they reach a sufficient size, which will increase their chances to survive in the natural environment. The eggs obtained from wild breeders were incubated in Weiss’s jars at the water temperature of 12xa0°C. The larvae were reared in tanks set up in closed recirculating aquaculture systems. During the rearing period, the water temperature was 20xa0°C and the density of larvae was 150 individuals per 1xa0dm2 of bottom. In the initial rearing phase, the main focus was on the type of feeds and the nourishment method. It was determined that the most suitable feed type was Artemia nauplii combined with Hikari dry food. Additionally, the type of substrate was tested under controlled conditions. In this case, the optimum one was composed of sand of the grain size between 0.3 and 0.5xa0mm. The experiment proved that it is possible to successfully conduct river lamprey larvae rearing under controlled conditions. The growth rates are comparable to or better than those achieved under natural conditions. After 30xa0days of the rearing period, the lamprey larvae were 25xa0mm long. The results create a possibility to develop a technology for the restitution of river lamprey and other lamprey species, which are endangered throughout the world.