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Fishpond management and ecological stability of fishponds -as a key water habitats of the Třeboň region
Pechar, Libor
Fishponds have an important role in the hydrological system of the Třeboň region and generally they represent the most common type of stagnant water habitat in the Czech Republic. Most of the fishponds are several hundred years old, and have therefore lost most of their man-made character. The period of intensification of fish production started in the 1930s, when liming and fertilization of the fishponds became a common practice. Since the 1930s, fish production has increased from a mean of about 50 kg ha-1 to more than 500 kg ha-1. Common carp, Cyprinus carpio L. has been the main cultivated fish species. Management for higher fish stock densities, accompanied by higher nutrient loads result in increasing trophic levels, ultimately reaching a state of 'hypertrophy'. The main symptoms of this state are the massive development of phytoplankton and cyanobacterial ' algal blooms', great fluctuations in oxygen concentrations, pH, which, in turn, destabilise the fish pond ecosystem.
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Fytoplankton aluviálních tůní
Pithart, David ; Kylbergerová, Magdalena ; Pechar, Libor ; Hrbáček, Jaroslav ; Fiala, Dan ; Bílý, Michal ; Rulík, M.
Phytoplankton of alluvial pools at Lužnice alluvium have been investigated by following methodological approaches: seasonal course of phytoplankton in two pools, extensive sampling (quarterly) of 30 pools, and phytoplankton diurnal vertical migration studies in several pools. Prevailing dominance of phytoflagellates, especially Cryptophyceae and Euglenophyceae and low contribution of coccal forms as Chlorococcales and Cyanophyte has been found as a main feature of phytoplankton community. This is caused by poor mixing of water column (large relative depth, wind protectio), where th ecoccal forms sediment out and are outcompeted by motile forms, able to determinate the position within the water column.
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Funkce allochtonní organické hmoty v tůni aluvia horní Lužnice
Dvořák, Jan ; Pechar, Libor
Large amounts of leaf litter enter into the pool ecosystem from the canopy of riparian woody plants every year. If the leaf litter is spread out over bottom in a dense layer it becomes a medium for nutrient exchange between the benthic and pelagic zones of the water body. Leaf litter processing was studied in material closed in nylon mesh-bags laid out on the bottom surface from the time of leaf abscission in November 1989 until the next autumn when the bottom was covered by a new leaf layer (exposure time was 372 days). The residual matter becomes deposited in bottom sediments storing the rest of the original nutrient content in an enriched form as immobilization products in the bottom deposits.
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Fenomén tůně: úvod do morfologie, hydrologie a limnologie
Pithart, David ; Pechar, Libor ; Hrbáček, Jaroslav
Small size of pools result in large interaction with the surrounding terrestrial ecosystem. 1.Wind protection caused by banks and vegetation results in stable water column. 2. Shading of vegetation restrict the amount of light, reaching the water surface. 3. Inflows of underground water may influence the water chemistry substantially. 4. Bottom processes influence the whole water volume in larger extent compared to large lakes.
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