Analysis of Algal Blooms in Da-ning River of Three Gorges Reservoir
三峡水库支流大宁河水华特征研究

According to the survey conducted from Apr. to Jun. 2007 and from Apr. to May. 2008, the changes of water quality, forms and distributions of nutrient salts and characters of algal blooms in Da-ning River of Three Gorges Reservoir (TGR) were studied. The results indicated that the concentrations of nitrogen and phosphorus nutrient were abundant during sensitive period of algal blooms in Da-ning River.Total nitrogen (TN) and total phosphorus (TP) values are 0.84-3.21 mg/L and 0.011-0.531 mg/L respectively, and the nutrients' concentrations become high gradually from upstream to downstream. Total dissolved nitrogen (TDN) is the major form of TN accounting for 84% , and total dissolved phosphorus (TDP) is dominant (TDP/TP = 60% ). Algal blooms bring phosphorus nutrient bio-concentration. The rates of TN and TP are all in excess of 16, which show eutrophication is limited by phosphorus. Potassium permanganate index and dissolved oxygen (DO) are at low levels and change stably. But chlorophyll a (Chl-a) becomes frequently, the value is 1.41-219.04 mg·m~(-3).Significant positive correlations are all observed by correlation analysis between Chl-a and the main parameters ( r_(Chla-TP) = 0.453,r_(Chla-potassium permanganate index) = 0.641, r_(Chla-DO)= 0.584, r_(Chla-pH) = 0.409, p <0.01), but significant negative correlations are observed between Chl-a and Secchi depth (SD) ( r_(Chla-SD) = - 0.392,p < 0.01) .The pH is fluctuated by multiparameter esp. in algal blooms. Widespread algae are observed by microscope during sensitive period of algal blooms in Da-ning River accounting for 8 phylum 82 genus 124 species, which Bacillariophyta and Chlorophyta are dominant, and then Cyanophyta and Pyrrophyta. Three whole watershed algal blooms break out in Da-ning River during the period, and the highest values of algal density are 14-1 427 times as many as the normal values. The dominant species of algal blooms are mostly involved with O. borgei, C. microporum, Chlorococcum humicola, P. morum and C. vulgaris of Chlorophyta; P. plewonectes and T. oblonga of Euglenophyta; Cyclotella, Stephanodiscus astraea and Navicula of Bacillariophyta; P. elpatiewskyi of Pyrrophyta. Multi-algal species blooms are observed in the same time and place, and there are few algae in the estuary of Da-ning River to Changjiang River.