Eutrophication Study For Yuqiao Reservoir

Eutrophication has been recognized as the most common and severe environment hazard in Lake Ecosystem, which seriously threaten the reliability of drinking water supply and has caused serious damage to the ecological environment. As the only drinking water source of Tianjin, Yuqiao reservoir had experienced several algae blooms in recent years, which had adversely impacted on the safety of drinking water supply and reservoir management. Therefore, it is of great significance to conduct research on eutrophication for yuqiao reservoir.In this desertation, the eutrophication status of Yuqiao reservoir between 2004 and 2009 had been evaluated by employing the Carlson trophic status index method. The variation of trophic status after the water divertion from the Luanhe River in 1988 was analysied. Correlation analysis of induction factors for algae bloom by using the factor analysis method in annual and seasonal scale had been done with the focuses of total phosphorous, total nitrogen, total phosphorous and total nitrogen ratio, precipitation and temperature. This research found the key factors inducing algae growth in reservoir. The main conclusions and achievements are as the follows:(1) The trophic status and water quality of reservoir has developed gradually from oligotrophic to eutrophic during the period of 1988 to 2009, and very close to hypertrophic now.(2) The algae biomass of Yuqiao reservoir showed positive relationship with total phosphorous at signicant level of 5% according to the factor analysis. This finding illustrated that total phosphorous was the main control factor. While the algae biomass showed negative relationship with nitrogen including nitrate, nitrate, ammonia and total nitrogen. This meant that nitrogen was not the key factor to control algae bloom in current status. Temperature especially in summer had great impacts to algae growth. Algae blooms were more likely to occur at high temperature condition.(3) The research on induction factors of algae bloom demonstrated that: 1) phosphorous was the key factor of algae growth in Yuqiao reservoir and the primary source of phosphorous was rainfall runoff. The first rainfall in summer were largely determined the the time and scale of algae bloom in reservoir with the effects of the adsorption and release nitrogen and phosphorous from Potamogeton Crispus. 2) Similarly, the temperature in late spring and early summer had also directly impacted the time and scale of algae bloom in reservoir. 3) Base on the relationship of various form of dissolved inorganic nitrogen and algae growth, the nitrogen source being effectively used was nitrate. The concentration of chlorophyll-a showed negative relationship with the ratio of ammonia to total oxidation nitrogen ratio at significance of 0.05. 4) The concentration of chlorophyll-a illustrated the positive relationship with the ratio of TN to TP. The concentration of nutrients decreased significantly with the growth of algae which caused the ratio of TN to TP from above 29 down to 29 below. This phonaminon explained that low TN to TP ratio was the results not the causes of algae bloom in reservoir.