THESIS
2002
xvii, 156 leaves : ill. ; 30 cm
Abstract
As a typical species in freshwater zooplankton, Daphnia magna plays a very important role in trophic transfer from phytoplankton to fish and in trace element recycling in lake ecosystems. By employing the approach of bioenergetic-based kinetic model, my study investigated the assimilation efficiency under different food concentrations, efflux rate constants, uptake rate from the dissolved phase, and release contribution by excretion, egestion, molting and reproduction for Cd, Cr(IlI), Se(IV), and Zn in Daphnia. The influences of P or N addition on metal uptake in freshwater alga and subsequently trophic transfer in Daphnia were further examined....[
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As a typical species in freshwater zooplankton, Daphnia magna plays a very important role in trophic transfer from phytoplankton to fish and in trace element recycling in lake ecosystems. By employing the approach of bioenergetic-based kinetic model, my study investigated the assimilation efficiency under different food concentrations, efflux rate constants, uptake rate from the dissolved phase, and release contribution by excretion, egestion, molting and reproduction for Cd, Cr(IlI), Se(IV), and Zn in Daphnia. The influences of P or N addition on metal uptake in freshwater alga and subsequently trophic transfer in Daphnia were further examined.
The experiments demonstrated that food concentrations had a negative effect on metal AE in the animal. The efflux rate constant was independent of the food concentrations. The release routes (excretion, egestion, molting and reproduction) in Daphnia were obviously metal specific. For Cd and Zn, molting is a crucial process to eliminate metals from the body following dissolved uptake. Transfer to next generation is a dominant route for accumulated Se from water. The dissolved uptake study indicated that metal concentration factor in Duphnia increased linearly over 12 h exposure period. Relationship between the uptake rate and metal concentration displayed a linear positive power function. The environmental factors (e.g. pH, Ca
2+) and body size apparently affected the metal uptake rates in the animals. The exposure study suggests that Zn accumulation in Daphnia may mainly depend on the dissolved uptake, whereas dietary uptake is possibly dominant for the accumulation of Cd and Se.
Ambient phosphate addition significantly increased algal intracellular uptake of Cd and Zn, but decreased Se accumulation in freshwater alga Scenedesmus ohliquus. Nitrate addition did not obviously affect metal uptake in the alga. The AEs of Cd and Zn in Daphnia seemed to be independent of the nutrient status of algae under different incubation conditions, whereas P addition distinctly influenced the Se AE. Increasing P concentrations further decreased the efflux rate constant for Cd and Zn, but no effects were found on metal release contribution patterns in Daphnia.
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