A comparative study of the physical and chemical characteristics of different nutrient reservoirs along the Yangtze River watershed in China

An annual study had been conducted on the physical and chemical factors, as well as water quality assessment, of 4 different types of reservoirs along the Yangtze River watershed in China during the period of 2006-2008. The reservoir water temperature range during the year was 5.5-31.0°C, an average of 16.5°C; There was obvious temporal and spatial variation in DO, DO was sufficient in all water levels. It was stable and was maintained at 6.5 mg / L or above; DIN horizontal distribution and seasonal change was evident, but there was no water layer distribution; PO₃-P was extremely deficient, and P was the main limiting factor of nutrient salts; TN value in the winter was 3-5 times of that in the summer and the spring, except for the value of 0.392 mg/L in Jinsha River, the other three reservoirs were 0.700 mg/L or more, indicating that the water had been polluted by N in varying degrees; N/P was relatively large, the variation range was 7.6-142.6, with an average value of about 38.0; the variation range of ALK and TH was 1.0-2.6 mmol/L, which was classified as soft water. Thermocline appeared at about 10 m in all reservoirs, the difference between the upper and lower temperatures could reach 10°C. In accordance with the relevant composite trophic state index (TSIc), combined with the reservoir nutrient type to draw the criteria for the classification, evaluation on the water quality of four reservoirs was conducted. The results were: Jinsha River was mesotrophic, Daoguan River was eutrophic, Xujia River and Taoyuan River were meso-eutrophic.