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Ellimination of unwanted fish species from dam reservoirs - Possibilities, efficiency and economic evaluation.
Jůza, Tomáš ; Blabolil, Petr ; Čech, Martin ; Draštík, Vladislav ; Holubová, Michaela ; Hůda, J. ; Kočvara, Luboš ; Kolařík, Tomáš ; Muška, Milan ; Peterka, Jiří ; Prchalová, Marie ; Říha, Milan ; Sajdlová, Zuzana ; Tušer, Michal ; Vašek, Mojmír ; Vejřík, Lukáš ; Kubečka, Jan
spontaneous development of populations and the influence of human interventions. For situations where a certain part of the fish population needs to be caught, within the project 'Biomanipulation as a tool for improving the water quality of reservoirs', we tested the available approaches in terms of their effectiveness and difficulty. The target species of catches were mainly cyprinid fish (bream, bleak, roach, rudd, white bream), which feed mainly\non zooplankton and tend to form very large populations. Among the most effective methods of catch during spawning are catches using electrofishing boats and fyke nets. In the non-spawning period, it is possible to carry out mass catches using trawl nets. Catches are effective both before spawning (in April) and during the summer. However, with repeated catches in the same places, their effectiveness decreases as a result of the fish being spooked. The efficiency of the catches partially improves again if the catches are repeated with a break of approximately 1–2 weeks. Catches also vary according to the stocking density of a given water body. With effective catches, the cost of catching 1 kg of fish is in the range of CZK 15–50.
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Content of iron and quality of organic matter as a factor affecting stabilization of carbon and nutrients in fresh water ecosystems.
Osafo, Nana O. A. ; Jan, Jiří ; Porcal, Petr ; Borovec, Jakub
The effect of watershed geochemistry, in terms of soil pH, Fe concentration and organic matter quality, on the stability of organic carbon and nutrients level in freshwater sediments of shallow lakes was studied. Twelve fishponds were divided into two groups based on the typical soil pH: i) watershed with acidic soils (pH 5.1 – 6.3) rich in Fe called H_Fe and ii) watershed with neutral pH soils (pH 6.8 – 7.6) poor in Fe called L_Fe. The parameters of the water column, pore water and sediment chemical extractions were compared. A higher concentration of hydrated Fe oxides, together with the aromatic character of organic substances were shown to highly contribute to the overall stabilization of the sediment. Conversely, low Fe concentrations were accompanied by lower mineralization of sediments and a higher risk for the aquatic ecosystem in terms of nutrient release or the development of anoxic conditions.
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