Study On Community Characterstics Of Zooplankton And Its Ecological Effect In Urban Lakes Of Guangdong Province

Zooplankton is an important component of aquatic ecosystem. The distribution of zooplankton mostly influenced by food, predation, water temperature and macrophytes etc. Now knowledge on community characterstics and function of zooplankton in urban lakes of Guangdong Province remains scarce. In this thesis, Based on the field investigation and setting up demonstration project of restoration, species composition, abundance, and dominant species variation of zooplankton in urban lakes of Guangdong Province were studied and analyzed in relation to the environmental factors. The response of zooplankton community to eutrophication and ecological restoration in Huizhou West Lake were studied and the relationship between macrophyte, zooplankton and fish were discussed, and the food web structures and trophic relationships in demonstration area were studied using stable carbon and nitrogen isotopes.Zooplankton in 14 urban lakes of Guangdong Province were investigated in the year 2005.94 species of rotifers were identified, the largest fraction belonged to the following families: Brachiomidae(17)＞Lecanidae(15)＞Trichcercidae(14), 20 species of cladocerans and 15 species of copepods were observed. The abundance of zooplankton was 51.20-1450.00 ind·L^-1, and the average abundance was (427.29±38.36) ind·L^-1. The average abundance ofrotifers, cladoeerans, copepods and nauplius were(345.95±32.33)ind·L^-1, (5.89±0.97) ind·L^-1, (23.66±4.83) ind·L^-1 and (58.40±8.50) ind·L^-1. The relative abundance of rotifers, cladocerans and copepods were (79.63±2.48)%, (1.37±0.21)% and (5.58±1.07)%, the zooplankton population was primarily dominated by rotifers. The dominant species included Polyarthra trigla, Schizocerca diversicornis, Brachionus forficula, B. calyciflorus, B. angularis, Anuraeopsis fissa, Trichocerca capucina, Filinia longiseta, and Asplanchna brightwelli etc.The dominant species of rotifers in 14 urban lakes of Guangdong Province are tropical and subtropical species. The abundance of zooplankton was significantly positively correlated with chlorophyâ…¡a concentration (r=0.426, p＜0.01), among it the rotifer abundance was significantly correlated with chlorophyⅡαconcentration (r=0.534, p＜0.01) but the cladoceran abundance had no positive correlation with chlorophyⅡα. Fishes were found in every urban lake, the abundance of cladoceran and copepods were lower and the rotifer abundance was on the absolute predominance in those urban lakes that feed fish specially. But the relative abundance of cladoceran and copepods were more higher when there had macrophyte in lake. The zooplankton abundance had a significant positive correlation with concentrations of TN (r=0.286, p＜0.05), COD_Mn(r=0.289, p＜0.05), SS(r=0.404, p＜0.01) but had negative correlation with transparence and pH. Zooplankton distribution appears to broadly related to lake trophic.Investigation on the zooplankton of Huizhou West Lake which composed of five small connected lakelets were carried out for three times from January to September 2005. 55 species of zooplankton including 38 species of Rotifers, 10 species of Cladocerans and 7 species of Copepods were found. The abundance of zooplankton were between 147.3 and 726.2 ind·L^-1 and the abundance of Rotifer were on predominance. The dominant species mostly were the indicators of eutrophication and the distribution of zooplankton were related closely to the water quality combined with correlative analyse of abundance of zooplankton and chemical and physical index of water. In order to control the eutrophication and restore the water quality, an ecological restoration project was carried out including planktivorons and benthivorous fish removal and macrophyte restoration in December, 2004. We investigated the zooplankton of demonstration area and un-restored Pinghu from January to December, 2005. The results showed that, in demonstration area, the water quality was improved greatly, the number of zooplankton species increased and the abundance of large-sized species included cladocerans and copepods increased. But the abundance of rotifers decreased significantly. Accordingly the index of diversity enhanced, at the same time the preponderant species in demonstration area tended to change to clear water species. In the period of March to September, 2006, we investigated macrophyte, zooplankton and fish in demonstration lake area. The biomass of macrophyte increased gradually from 1.249 kg.m-2 in March to 9.167 kg·m^-2 in September and the catch offish per month dropped from 17.5 kg in March to 7.61 kg in September. The abundance of zooplankton in demonstration area was lower than Pinghu (un-restored lake), however large-sized zooplankton was more abundant in restored area. The body size of zooplankton mostly was between 0 mm and 0.2 mm both demonstration area and Pinghu and the percentage of body size larger than 0.6 mm in demonstration area was two time higher than that in Pinghu. The biomass of zooplankton had no significant difference.The average values ofδ¹³C andδ¹⁵N of submersed macrophytes respectively were (-20.1±0.3)%o and (5.9±0.3)%0 in demonstration area of Huizhou West Lake, Compared to macrophytes theδ¹³C values of periphyton and seston were lower and the values were -23.0‰and -28.0‰, respectively, and theδ¹⁵N values of periphyton and seston were 5.7‰and 5.5‰. Theδ^<sup>13C values had an order: macrophytes＞periphyton＞seston and theδ¹⁵N values were similar. The average values ofδ¹³C andδ¹⁵N oftilapia in demonstration area were (-23.8±0.6)%0 and (11.0±0.1)%0. By using aδ¹³C mass balance model, it is estimated that the contributions of periphyton to the diet oftilapia were 80%.