Effect of fish stocking with bait on phytoplankton and water quality in Panjiakou Reservoir enclosures
投饵养鱼对潘家口水库围隔中浮游植物及水质的影响

Field enclosure experiments were carried out in Panjiakou Reservoir from August,2009 to October,2009,to study the impacts of fish stocking with bait on phytoplankton and water quality. The results showed that in Panjiakou Reservoir the phytoplankton density was maintained at 2.6×106cells·L-1 in the experimental period,and the ratio of nitrogen to phosphorus was 112,so the reservoir was categorized as a "phosphorus-limited" reservoir. The phytoplankton densities in enclosures with bait only and with both fish stocking and bait were significantly higher than those in the controlled enclosure and the reservoir water,and the phytoplankton density in the bait only enclosure was significantly higher than that in the fish enclosures,with that in the bighead carp (Aristichthy novilis) monocultured enclosure being the lowest. Bighead carp and carp (Cyprinus carpio) could effectively restrain the growth of Cyanophyta,and change the dominant species of phytoplankton from Cyanophytato Chlorophyta in the fish enclosures. Fish stocking with bait significantly increased the turbidity,CODMn and total phosphorus. The concentrations of total nitrogen and dissolved oxygen in enclosures with bait only and with both fish stocking and bait were significantly lower than those in the controlled enclosure and the reservoir water. In bait only and fish stocking with bait enclosures,significant positive correlations between phytoplankton density and the turbidity,CODMn,total phosphorus were found.