Study On The Hydrochemistry And Primary Productivity In The Cage Culture Area In Wanzhou Region Of The Three Gorges Reservoir

The exeperiment was carried out at Wanzhou Region of the Three Gorges Reservoir from May.2005 to July.2006, analyze and reserach on Nitrogen, Phosphorus, other physical and chemical indicators,primary productivity.Six sampling stations were selected in the research. Station I was set 50 metres ahead the fist cage groups (from North to South), sationâ…¡,â…¢,â…£located at the district of the cage groups, sationâ…¥located at the south of the forth cage groups about 50 metres, sationâ…¤located at the other side of the cage groups district about 50 metres.The results are summarized as follows:1. Nitrogen and Phosphorus NutrientsAmong the stationâ… ,â…¡,â…¢,â…£,â…¤,â…¥, the average inorganic nitrogen contents reached 1.269 mg·L^-1,1.459 mg·L^-1,1.592 mg·L^-1,1.413 mg·L^-1,1.310 mg·L^-1,1.297 mg·L^-1respectively, in which NH₄⁺—N takes the marjority amounting to 49.88,51.25%,52.43%,54.51%,52.43%,50.27% respectively;Secondly, N0₃^-—N amounting to 40.35%,42.55%,40.56%,39.13%,41.75%,43.46% respectively; N0₂^-—N amounting to 9.78%,6.21%,7.01%,6.36%,5.82%,6.27% respectively. Contents of NH₄⁺—N,NO₃^-—N,NO₂^-—N,EN at cage district were higher than the other station, but did not reach significant level.Only contents of NH₄⁺—N, in which cage district was significantly higher than the other stations in December and January.The average contents of HPO₄^2- reached 0.086 mg·L^-1,0.1 mg·L^-1,0.097 mg·L^-1,0.12 mg·L^-1,0.099 mg·L^-1,0.097 mg·L^-1respectively.The average contents of Total Phosphorus reached 0.162 mg·L^-1,0.181 mg·L^-1,0.205 mg·L^-1,0.194 mg·L^-1,0.175 mg·L^-1,0.178 mg·L^-1. There was no significant difference between the cage district and the other stations. Its have reached eutrophication, and the cage distric was higher than other stations. The Nitrogen and Phosphorus ratio (N : P) were 12.31,12.22,11.32,10.28,10.25,10.56.2. The other physic-chemical indicatorsThe average transparency at each station was 69.1 cm,66.8 cm,65.4 cm,64.3 cm,64 cm,65.9 cm respectively,which reach high in winter and spring,low in summer. The sediment contents as the main factor had impact on transparency. Cage district was significantly lower than station I at 5% level,but has no significant difference with stationâ…¤,â…¥.The average of pH was 6.6,range 6.1～8.4,the largest share of 6.6,6.7.There has no significant difference between the cage districts with other stations.The average of DO at each station was 7.7 mg·L^-1,7.4mg·L^-1,7.5 mg·L^-1,7.3mg·L^-1,7.8 mg·L^-1,7.6 mg·L^-1respectively. Cage district's DO was significantly lower than other stations at 1% level.The average of temperature at each station was 21.8℃,20.8℃,21.2℃,21.1℃,21.8℃,21.0℃respectively. The maximum temperature was 29.4℃, the minimum temperature was 10.9℃. Cage district's temperature was significantly lower than other stations at 1% level.The average of conductivity at each station was 371.0μs·cm^-1,364.9μs·cm^-1,374.8μs·cm^-1,365.1μs·cm^-1,364.2μs·cm^-1,377.8μs·cm^-1 respectively. The maximum conductivity was 439μs·cm^-1, the minimum conductivity was 252μs·cm^-1.3. Phytoplankton primary productivityThe average gross primary productivity at stationâ…¡,â…¢,â…£was 0.799±0.678 gO₂·m^-2·d^-1, 0.945±0.761 gO₂·m^-2·d^-1, 0.815±0.755 gO₂·m^-2·d^-1 respectively, and the average P/R was 2.66,2.33,2.27 respectively.The average value of P/R was 0.852 gO₂·m^-2·d^-1, it was indicated that the microbial's activity weaker. The external inorganic nutrient input the water which weaked the water decomposition, material recycling rate became lower, primary productivity has not been fully utilized. Phytoplankton primary productivity was low in summer but high in spring. By analysis of variance, there has no significant difference between each station at 5% level.4. The relationship between primary productivity and other factorsThere has no significant correlation between phytoplankton biomass and primary productivity, significant negatively higer correlation was found between temperature and primary productivity, significant correlation was found between conductivity and primary productivity, both transparency and DO were found significant higer correlation with primary productivity.NH₄⁺—N (r=0.181, n=45),NO₃^-—N (r=0.001, n=45),NO₂^-—N (r=-0.288, n=45),EN (r=0.037, n=45),pH (r=-0.02, n=45) were found had no significant correlation with primary productivity.Both phosphate and phosphorous showed significant negatively higer correlation with primary productivity.5. ConclusionUnder feeding cage culture conditions, both nitrogen and phosphorus nutrients contents in cage district were higher than other stations, it have not reached significant. Primary productivity also has not reached significant difference among each station.but cage culture increace eutrophication trend.It was showed that feeding cage culture in river has not significant impact on the water quality. However, as the water nutrient concentrations have reached eutrophication, primary productivity has reached nutrition, develepment of feeding cage culture needs think twice.There are many factors affect primary productivity in river, various factors interaction each other.It's difficult to evaluate the single-factor method to description the impact of primary productivity.As this characteristic, the changes of cage culture nutrients and primary productivity in river are significantly different with ponds, lakes, Reservoir and other waters.