engleski

The influence of anthropogenic stressors on littoral benthic macroinvertebrate communities in man-made lakes

Reservoirs are heavily modified lentic waters, usually derived from lotic habitats. They are complex systems that represent a transitional ecosystem between lakes and rivers with substantial ecological impact on not only the remaining lotic habitat but also the surrounding terrestrial ecosystem. Specific macroinvertebrate communities, usually consisting of high ratios of resilient euryvalent taxa, inhabit these artificial lentic habitats. Our goal was to test how anthropogenic abiotic factors such as land cover, water fluctuations, and littoral zone depth (slope) influence benthic macroinvertebrate community composition. Macroinvertebrate communities were studied at 15 reservoirs located in the Pannonian ecoregion of Croatia. Prior to sampling at each reservoir, sites with both “more natural” and “less natural” shorelines were selected. The sampling site covered 25 m of lakeshore length up to a distance of 10 m towards the open water, or to a point where the depth of water surpasses 1 m, depending on the steepness of the shore. Four levels of depth were defined: 0 to 0.25 m, 0.25 m to 0.50 m, 0.50 m to 0.75 m and 0.75 m to 1.00 m and ten samples were collected using a 25 × 25 cm benthos hand net (500 μm mesh) at each site. Non-metric Multidimensional Scaling Analysis (nMDS) of littoral benthic macroinvertebrate community similarities between reservoirs showed clustering of locations with similar water level fluctuations. One group consisting of reservoirs with water fluctuation above, and the other one with water fluctuation less than one meter. Differences in community composition between these two groups of reservoirs are due to the macroinvertebrate community’s ability to adapt to rather harsh conditions of habitats that remain after the water is withdrawn or abruptly inundated. Land cover of the catchment area was examined in relation to the macroinvertebrate community species richness, abundance and alpha diversity. Increased ratios of intensive agricultural surfaces in the catchment area were positively correlated with species richness and alpha diversity (p<0.05). We assume that the nutrient intake in reservoirs coming from the catchment area provided additional food sources that supported more diverse communities but was not as excessive as to cause disturbances in terms of algal blooms. A positive correlation between species richness and deeper parts of the littoral zone was found (p<0.05). This is because, in deeper parts, there are fewer disturbances associated with water fluctuation, wind power, daily temperature ranges, which makes this habitat more stable for macroinvertebrates.

reservoir ecology

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