A Tentative Analysis About The Bait Casting Ponds Ecosystem Of Bishan County

Based on the data of ecological surveys made in 2003.11²004.12 in fish ponds of Jingmei fish farm of Chongqing, the abiotic environments, primary and secondary production, energy conversion efficiency and energy flow in the bait casting ponds ecosystem were described and discussed in the paper.1 The abiotci environments of the experimental pondsThe average values of pH were 6.8 in two experimental ponds, which was constant in the year. The transparency changed from 0.20 to 0.45, and it was in accordance with the trend of intensive fishponds. The COD got to the level of fertilized fishponds. It showed there were a large number of organic crumbs, and resulted in caused lower content of DO.The contents of N, P nutrient ion in baiting casting pond were abundant. The total contents of effective nitrogen were 2.701 mg·L^-1 for A pond, 2.370 mg·L^-1 for B pond. The content of NH⁴+-N, NO₃^--N and NO₂^--N in A pond were about 68.07%, 21.44%, 10.95% of total effective nitrogen , and those in B pond were about 62.60%, 25.65%, 11.75% of one, respectively. The NH⁴+-N was main form of effective nitrogen because the value of pH was less than 7 in the year, which had no harm to fish. However, the content of NO₂^--N was higher, which caused negative impact on health of fish. The content of soluble reactive phosphorus exceeded greatly one of fertilized fishponds. It resulted in low N/P value.2 Phytoplankton and primary productivity of the experimental pondsThe composition of phytoplankton was similar in the two ponds, with flagellates, especially Euglena, predominanted. The abundance of phytoplankton varied significantly with climatic. It occurred two peak values in whole year, and ones occurred in April and September, respectively, for pond A; ones in April and July, respectively, for pond B. The mean production of phytoplankton in two ponds was 23.932 mg-L'1, 47.070 mg-L'1, respectively. The analyses of correlation were suggested that the linearity equation (Y=0.3171X-14.495 ( n=13,r=0.908,p<0.01 ) ; Y=l.3331X-153.78 (n=12,r=0.809,p<0.01) )could be used to fit the relation between the productionof phytoplankton (Y.mg·L^-1) and the content of chlorophyll (X,ug·L^-1) in two ponds.The primary productivity of phytoplankton was in accordance with the trend of abundance, and vertical distribution was significantly dissymmetry. The average primary productivity of pond A was 4.28gO₂·m^2d-1, which was less than the prevalent one of freshwater pond. It was 4.28gO₂·m^2d-1 in pond B, which reached the moderate one of freshwater pond. The average P/B values of two ponds were 1.14 and 1.12, respectively. The analyses of correlation were suggested that there were positive correlation between the primary productivity (Pg gO₂·m^2d-1) , the biomass of phytoplankton, chlorophyll (chla, ug·L^-1) .water temperature (T, ℃) , and soluble reactive phosphorus (X, mg·L^-1) in pond A. The regression equation were P_G=4.3609B+5.2122 (n=13, r=0.678, 0.012·m^2d-1) , water temperature (T, ℃ , and soluble reactive phosphorus (X, mg-L"1) in pond B. The regression equation were, PG =13.257T⁰.254 (n=11, r=0.587, 0.01-2 for pond A, 4.86 g·m^-2 for pond B, respectively. The total productivity of protozoan and rotifer accounted for 91.50% in pond A and 99.49% in pond B, respectively.The biomass and production of zoobenthos were very low, and the average production of two ponds were 3.92 kJ·m^-2 and 4.16 kJ·m^-2, respectively. Water earthworm and chironomidae were the main zoobenthos.The production offish in the two ponds were 4.79 g·m^-2·d^-1 and 4.37 g·m^-2·d^-1, respectively, and which remain with higher yield. However, the single yield of silver carp and bighead carp was low.4 Analysis of energy flow in the experimental pondsThe utilization rate of the solar radiation energy by the gross production of phytoplankton were 0.63% for pond A and 0.88% for pond B, respectively ; the utilization rate of the yield of silver carp and bighead carp by the net primary production of phytoplankton were 7.20% for pond A and 7.55% for pond B, respectively ; the ecological conversion efficiency of the solar radiation energy to fish...