Study of primary production of phytoplankton and the environmental factors in C haohu Lake water

Primary productivity was measured by the oxygen method．When there was no algal bloom，the lake water appeared clean and there was no difference between the upper and lower part of the lake water．The dissolved oxygen(DO)approached saturate around 7．0 mg/L．The average productivity rate was 0.2—0.6 g O2/m3d，and slightly larger than respiration rate．During the period of heavy algal bloom in late September 1987，the productivity even reached 1.6g O/m3 d．The average net productivity was 0.22g O2/m3 d，equivalent to 0.07 g C／m3d．Meanwhile，the respiration rate was also high and pH reached 9—10．The variation of water temperature，pH and DO，at various depths of the lake，are not large due tO its shallowness and turbulent mixing．