| ·In order to study the water environment which included physiochemical features and biological factors in Lake Changyang, an investigation had been conducted during July2011to June2012. The major contents of this paper were as the follows:time-space distribution of physico-chemical factors; comprehensive assessment on trophic state of the lake in Changyang water system; community structure of phytoplankton and it’s relationship with trophic state; community structure of zooplankton and it’s relationship with trophic state; suggestions presented in relation to fishery resources and reasonable exploitation of these resources based on the above resersh. The results are as follows.·On the average the water is2.85meter deep. The average water temperature, Secchi degree and dissolved oxygen were17.8℃,63cm, and7.85mg/L, respectively. Mean pH value was7.82. The mean concentration of CODMn, TP, PO4--P, TN, NH4+(NH3)-N, NO2--N, NO3--N and chlorophyll-a were6.00mg/L,0.132mg/L,0.046mg/L,2.40mg/L,0.063mg/L,0.051mg/L,0.573mg/L and25.78mg/m3, separately. The results showed that Lake Changyang was in the state of light eutrophication and moderate eutrophication evaluated by trophic status index (TLI). In the winter the water quality was in the state of light eutrophication, and with the coming of the spring, the water quality became worse gradually, which was in the state of moderate eutrophication. Very significantly positive linear relationship was exist in chlorophyll-a and TLI (r=0.909, p<0.01). As a complicated lake ecological system, the results of PCA (Principal Component Analysis) showed that WT, TN, and DO were the main impact factors to the water environment, and other physico-chemical factors played an comprehensive role to the lake.·Results showed that8classes including299species had been found in the lake. Chlorophyta had132species (44.15%of the total species), and Bacillariophyta and Cyanophyta had66species (22.07%) and48species (16.05%), respectively. The biomass and quantity of phytoplankton ranged from6.87mg/L to13.56mg/L and1.46×106cells/L to23.15×106cells/L, separately. Chlorophyta was lagest in the quantity of phytoplankton. The maximum of biomass is Bacillariophyta but not Chlorophyta. The biomass in the order of size was:Autumn>Spring>Summer>Winter, but the largest quantities of phytoplankton appeared in Summer. The seasonal succession of phytoplank was slightly different from the PEG (Plankton Ecology Group) model, because of filter-feeding fishes’ grazing on zooplankton. Thirty dominant species existed, and all of them were pollution indicators. Results showed that diversity and evenness of phytoplankton were in good status in the lake. The water quality is between oligotrophic and moderate pollution assessed by biodiversity index and pollution indicators. Very significantly positive linear relationship was exist in density and TLI (r=0.820, p<0.01), and TLI had a significant correlation with the biomass (r=0.691, p<0.05)·One hundred and twenty nine species of zooplankton have been founded in the lake. Protozoa, rotifer and cladocera had43species,69species and11species, separately. The annual average density of zooplankton was35492ind./L, and protozoa and rotifer was accounted for90%and10%, respectively. The mean biomass of zooplankton was5.97mg/L, dominated by rotifer for77%and protozoa for16%. It is very obvious that so many small-size species of zooplankton appeared because of fishes’grazing. The analysis result of the predominance index showed that there were35dominant species. And the species of oligosaprobic zone and β-mesosaprobic zone rotifer was accounted for60%. The water quality of Lake Changyang was in oligosaprobic or mesosaprobic state indicated by indicators and predominance index. The biomass and density of zooplankton had significant or highly significant correlation with DO and pH, and no significant correlation with TLI index analyzed by correlation analysis. Biodiversity index gave a negative indication of water quality, which was attributable to the alteration of community structure of zooplankton by fishes’grazing probably.·The potential fishery productive capacity estimated by biomass of aquatic organisms. The potential production of phytoplankton, zooplankton, zoobenthos, organic detritus and bacteria were123155.1kg,216934.9kg,26356.3kg,170045kg, and totaled546491.3kg, respectively. If the stocking weight and catch weight of silver carp and bighead carp were supposed to be lkg and3kg,151thousand silver carp and167thousand bighead carp can be farmed reasonably in Lake Changyang. The theoretical number of silver carp and bighead carp decreased by60thousand and42thousand compared with the actual fish stocking number. The expected production of silver carp was363279.8kg coincided with the real production. The output of bighead carp was expected to401922.7kg, which was more than the actual production. The reasonable output of fishes was102.8kg/666.7m2. Suggestions based on research offered as follows:reducing the number of silver carp and bighead carp slightly; continuing to control the area of cage culture; improving the conditions of the leisure fisheries and doing a lot of publicity to enhance own competitive advantage;"green" development. |
PDF Full Text Request