THE PRIMARY PRODUCTIVITY OF PHYTOPLANKTON IN SALINE-ALKALINE PONDS

The primary productivity of phytoplankton in saline-alkaline ponds in Zhaodian Fish Farm, Gaoqing county, Shandong Province, has been estimated by means of dark and light bottles method, during the season of fish growth during from April to September in 1997. The results showed that the primary productivity was 9 42? 21 gO2/(m2穌),daily P/B ratio was 0.24?.18, the available utilization rate of light energy was 1.53%, range from 0.20 to 3.15%. The primary productivity in control ponds without fish was significant fewer than that of fish-culture ponds. The primary production of phytoplankton occur two peak values, one occurs in spring, the other occurs in the late summer, the highest productive layer is the surface above 25cm. The analyses of correlation were suggested that phytoplankton biomass, transparency depth, water temperature, salinity are important ecological factors influenced the primary productivity of phytoplankton in saline-alkaline ponds in Gaoqing. As far as experimental ponds are concerned, limit effects of phosphorus to productivity was more important than that of nitrogen. The conversion efficiency of solar radiation to gross primary productivity ranged from 0.88% to 1.23%. The net primary productivity to yield of silver carp, bighead and tilapia varied from 6.6%-14.1%. The ecological conversion efficiency of solar radiation to fish yield was 0.028%-0.059%.