Study On The Primary Productivity Of The Tian'e-zhou And Hei-wa-wu Oxbows Of The Yangtze River And Its Relationships With Several Ecological Factors

By investigating the main environmental factors, the primary productivity of phytoplankton, aquatic vascular plant(AVP)and its primary productivity of the Tian'e-zhou and Hei-wa-wu Oxbows, the relationship between the primary productivity and the main environmental- factors has been analyzed, and the difference of the aquatic plant's radiation energy transformation rate of the two Oxbows has been compared.1.The main environmental factors: (l)The average annual temperature of the two Oxbows was 16.0℃, the annual total radiation level was 445.2 kJ·cm^-2·a^-1. (2)The average annual values of the water indicators of Tian'e-zhou Oxbows: the water temperature was 21.07℃, the pH was 7.76, the transparency was 110.5cm, the ammonia nitrogen was 0.10 mg·L^-1,the total phosphorus was 0.07 mg·L^-1,the COD_Mn was 2.3 mg·L^-1, and the suspended substance was 22.88 mg·L^-1 respectively; and those of Hei-wa-wu Oxbows were 22.28℃, 7.78, 146.3cm, 0.215 mg·L^-1, 0.065 mg·L^-1 3.33 mg·L^-1,and 19.22 mg·L^-1 respectively (3)During the abundant water season, the surface water quality of the Tian'e-zhou and Hei-wa-wu Oxbows all reached class I of surface water standard. During the low water season, the water quality of the Tian'e-zhou Oxbow still maintained class I of surface water standard, but that of the Hei-wa-wu Oxbow declined to class II. The comparison of the water quality between the two Oxbows and Shishou section at the same time indicated that the two Oxbow's nutrition indicator such as ammonia nitrogen, total phosphorus etc were better than those of Shishou.2.The primary productivity of phytoplankton: (1)the average daily productivity of phytoplankton of Tian'e—zhou Oxbows was 1.41 gO₂·(m²Â·d)^-1 and that of Hei-wa-wu Oxbows was 1.76 gO₂·(m²Â·d)^-1, both of the two Oxbows belonged to the Medium type when classified by the water nutrition type; (2)the season variation of the productivity of phytoplankton showed that the productivity reached the top in summer and the bottom in winter, and in spring and autumn , they were in middle. For the vertical distribution, the highest productivity of phytoplankton reached when the transparency was at 0.5 times; (3) the Tian'e-zhou and Hei-wa-wu Oxbows' annual productivity of phytoplankton and the transformation rate of radiation energy were 7.214E+10kJ, 0.083% and 6.834E+10kJ,0.104% respectively.3.The AVP and its primary productivity: (1) there were 28 species of AVP in Tian'e--zhou and Hei-wa-wu Oxbows, belonging to 15 families, 12 of which were emerging plants; 4 were floating— leaved plants; 11 were submerged plants. The major genera were Potamogeton, Vallisneria, Phragmites, Zizania, Ceratophyllum, and Hydrilla verticillata; (2) The annual productivity of Tian'e-zhou Oxbow's AVP was 9.244E+7 kJ, the transformation rate of radiation energy was 0.101 %, and those of Hei-wa-wu Oxbow's were 2.308E+11 kJ and 0.944% separately.4. The analysis of the relationship between Tian'e-zhou and Hei-wa-wu Oxbows' primary productivity of phytoplankton and the main environmental factors indicated: (1) the indicators of two Oxbows such as the transparency, water temperature, ammonia nitrogen, total phosphorus and so on showed positive linear correlation to the productivity of water column of phytoplankton, but the correlation was not significant, for the indicator of COD_Mn, which showed negative linear correlation to the water column of productivity of phytoplankton, and the correlation was not significant too; (2) The major differences between the living environment of the two Oxbow's AVP were the river terrain conditions, the mode of the fishery production and the differences between the hydrologic condition and water quality; (3) The annual aquatic primary productivity of the Tian'e-zhou Oxbow was 7.224E+10 kJ, the radiation energy transformation rate was 0.0834%, and those of Hei-wa-wu Oxbows were 2.992E+11 kJ and 0.4550% respectively. (4) The main environmental factors influenced the two Oxbows' aquatic primary productivity and the rates of the transformation were the differences of the biomass of the self-support lives and the content of the nutrients.5. Summary: the essential environmental factors influenced the Tian'e-zhou and Hei-wa-wu Oxbows were the change of the hydrologic condition and the damage of the aquatic biological resource and its structure.