Objective: The purpose of the study is to investigate the status of eutrophication, the polluted situation of algae and microcystins in different water bodies of X County in the Huai River Basin.
Method: Superficial water and sediment samples were taken from S River, Y River and a representative ditch in May 2010 (median-water period) and August (high water period ). Chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), chlorophyll a (Chl a) and algal density were detected by the recommended methods of national standard microcystin-LF/LR/LW/RR/YR in water (dissolved form), algal cells and sediments were detected by solid phase extraction and HPLC.
Results: Water pollutions in rivers and ditches of X County were serious, and total nitrogen and total phosphorus significantly exceed to the national standard for surface water quality. Most indexes of the water quality ranged from grade III to worse than grade V of national standard. Total nitrogen (4.78 mg/L) was most serious pollutions in the mainstream of S river, the water quality in high water period was better than in median-water period (P < 0.05). However, water quality in inner river Y and ditch in high water period was worse than in median-water period. Maximum chlorophyll a in ditch water reached 648.4 mg/ m3. The percent of cyanobacteria in various water bodies was less than 10% in median-water period, increased sharply to 40% and became dominant species in high water period. The maximum percentage of cyanobacteria was 44% in ditch. Microcystin-RR was the main toxin detected in water (dissolved form), algal cells and sediments. Maximum MC-RR in water and sediments reached 17.731 microg/L and 0.802 microg/g, respectively. The detected frequencies and concentrations of MC-LF/LR/LW/YR in most samples were low.
Conclusion: Water bodies in X County were between middle eutrophication and hyper-eutrophication. Microcystin-RR of sediments in high water period were significant higher than in median-water period (P < 0.05).