Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 11

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
The data obtained within the framework of a survey of macrozoobenthos and fish communities in Czech streams of the Danube and Elbe river basins were evaluated with respect to the relation between biodiversity and level of water (organic pollution) and/or physical habitat quality (heterogeneity, substrate, riparian vegetation, canalisation). The diversity of macrozoobenthos species was the highest at the water quality corresponding to betamesosaprobity (saprobiological index SI ≈ 2,0) and oligosaprobity (SI ≈ 1,0) in lowland and highland streams respectively, declining both towards lower and higher saprobic (≈ trophic) levels. The response of macrozoobenthos to habitat quality deterioration was less considerable with rising degradation in highland streams than in lowland ones. Fish assemblage followed a similar trend, namely: the highest biodiversity in betamezosaprobity in both lowland and highland streams. In comparison with the assemblage of benthic macroinvertebrates, fish community response was more pronounced both regarding water quality and habitat degradation. Both fish and macrozoobenthos biodiversity were influenced more by water quality than by physical habitat degradation.
Background. Fish embryos and larvae are frequently subject to chronic- and damaging exposure of cyanotoxins released by live and decomposing cyanobacteria Whereas the majority of former studies dealt with the embryotoxicological effects of pure toxins and extracts, we focused on the evaluation of toxic effects of crude cyanobacterial biomass in our study. Materials and methods. Samples of crude cyanobacterial biomass—intended for embryotoxicological tests with eggs of Japanese medaka, Oryzias latipes (strain Q2d-rR.YHNI)—were collected from natural bodies of water in the Czech Republic. Those samples consisted predominantly of: Microcystis aeruginosa, M. flos-aquae, Woronichinia naegeliana, Anabaena sigmoidea, and Aphanizomenon flos-aquae. In the preliminary optimization experiments, various numbers of fertilized medaka eggs (from 1 to 6 per one 10-mL well on a six well polypropylene plate) were hatched under standard conditions. Because of the highest hatching rates, 4 eggs per 10 mL well were selected as an optimal treatment. The embryotoxicological tests were performed according to the OECD 212 guideline in two concentrations (extracts of crude cyanobacterial biomass: 40 and 200 mg · L–1dry weight). Fertilized eggs in stage 6 to 8 (some 2–3 h after fertilization) were introduced into test wells, and hatching performance, duration of embryonic development as well as lethal and sublethal effects were monitored. Results. The hatching rates (treatment with 4 eggs per 10 mL well), achieved in the majority of experimental treatments with cyanobacterial biomass, were significantly different from the control group. Also hatching onset was considerably delayed due the presence of cyanobacterial biomass. The embryotoxicological impacts were more pronounced in higher concentrations of cyanobacterial biomass (200 mg · L–1) compared to lower concentrations (40 mg · L–1). Whilst deformities were not recorded in the control, their highest incidence amounted to 11.8% and 40.9% in 40 and 200 mg · L–1 of cyanobacterial biomass, respectively. Conclusion. Cyanotoxicity significantly affected examined parameters (hatching rates, duration of embryonic development, and morphological deformities occurrence) in medaka embryos. The study proved significant embryotoxic effects upon Japanese medaka at environmentally relevant levels of cyanobacteria commonly occurring in surface waters in Europe.
Background. Fish pond management can substantially modify the hydrological regime and ecological quality of receiving waters (usually rivers, canals, and ponds downstream in an interconnected system) with potentially positive or negative impacts on watershed functioning. To evaluate these effects with respect to carp pond management, the environmental impacts of semi-intensive farming on discharged water quality were monitored at four differently managed carp ponds, differing in trophic status (two eutrophic and two hypertrophic ponds). Materials and Methods. Fundamental determinants of pond inflow and outflow water quality were monitored monthly from April to October 2009. Water temperature, pH, and dissolved oxygen concentration and saturation were measured in situ whilst hydrochemical and microbiological parameters were assessed in the laboratory. Results. Compared to the inflow water, in the effluents there was a significant decline in numbers of bacterial loading indicators (Escherichia coli, enterococci, faecal coliform and mesophilic bacteria) in the outflow water. In ponds with the poor quality inflow water (downstream of water treatment plant discharges), a significant decrease was also registered in nutrients (N-NH4, N-NO3, total nitrogen, P-PO4, and total phosphorus) and organic loads? (five-day biological oxygen demand, chemical oxygen demand) of pond effluents. At the pond supplied with good quality river water, however, the same determinants showed that effluent water quality worsened significantly. Total organic carbon and suspended solids increased in effluents of ponds with high fish biomass stocked. Conclusion. The results demonstrate that, during the growing season, properly managed carp ponds represent ecosystems with high self-cleaning ability. They may play an important role in the nutrient balance, storage and trapping in agricultural landscape with high population density.
Extreme discharge rate increases in small streams caused by sudden extreme precipitation events are classifi ed as small-scale pulse-type disturbances. Small highland brooks in agricultural landscapes (arable land and meadows) are frequently characterised by extremely low flows during normal conditions, plus the rare appearance of high-flow events that periodically may reset their ecosystems. We studied two small highland brooks to assess the impact of extreme discharge rates (flow pulses) upon periphyton, macrozoobenthos, and fish assemblages. No distinct changes were recorded in composition of periphyton assemblage or fish (brown trout, Salmo trutta m. fario) occurrence following such flow pulses. Cyanobacteria, however, were absent following a flow pulse, while growth appeared to be boosted in green algae (Chlorophyceae). Similarly, there was no negative response observed in macrozoobenthos communities, with density, diversity, taxa richness, and saprobic indices remaining either more-or-less unchanged or considerably enhanced following high-discharge episodes. These observations were confi rmed through Sörensen’s similarity indices, which indicated no signifi cant change in either periphyton or macrozoobenthos following such episodes.
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.