The Response Of Zooplankton Community To Nutrient Loading Induced Bu Hydrological Process

We investigated the zooplankton, nutrient and phytoplankton variations inLiuxihe Reservoir during2012.4-2013.3, and also an enclosure experiment withdifferent intensity of man-made vertical mixing was designed, to get betterunderstanding of the effects of nutrient induced by hydrological process onzooplankton community. When water-level started to upraise, TP concentration washighest in surface layer, then decreased with settling of suspended matters which wasenhanced by water level continuous uprising, but when water-level started droppingTP concentration increased comparing to the end of the water-level uprising period.Zooplankton biomass wasn’t correlated with phytoplankton standing crop, butpositively correlated with TP (R2=0.20P=0.023). The ratio of zooplankton tophytoplankton in the field was low and varied between0.2-0.01, but higher inmesocosm (0.05-0.36). Field study and enclosure experiment both showed thatzooplankton community was predominated by Phyllodiaptomus tunguidus and smallsized cladocerans such as Diaphnasoma, Bosmina and Bosminopsis. Copepods werein dominance most of the time but when zooplankton biomass was in peakcladocerans became dominate, and large sized cladocerans Daphnia galeata wasnever in dominance.These results indicated zooplankton responded strongly to nutrient loadingincreasing in surface layer which was induced by hydrological process. Even whenlarge sized grazing cladocerans wasn’t in dominance, zooplankton biomass could stillrespond strongly to increasing nutrient loading but only last a short time, while largesized invertebrate predator-Leptodora richardi was also improved by zooplanktonbiomass increasing, which enhanced the predatory pressure weaking the response ofzooplankton to nutrient loading.