CAUSES AND CONTROL COUNTERMEASURES OF EUTROPHICATION IN CHAOHU LAKE, CHINA

Chaohu Lake, located in the central Anhui Province, is one of the five largest fresh lakes in China. Now it is one of the three most eutrophication lakes in China. The deterioration of its water quality has influenced the sustainable development of society, economy and environment of Hefei City, the capital of Anhui Province. A series of measures have been carried out to control its eutrophication, but it is still serious. On the basis of the lake water quality data from 1984 to 2003, the causes of the eutrophication of Chaohu Lake are analyzed. Studies indicated that the suitable natural conditions and human activities played a crucial role in the process of the eutrophication of Chaohu Lake. A great amount of industrial, agricultural and domestic sewage discharged into the lake is the main cause of eutrophication in the lake. Land use, soil erosion and shoreline collapse destroyed the watershed eco-environment and the terrestrial ecosystem of Chaohu Lake. And the building of Yuxi Gate extends the sluggish of the nutritious substance and speeds up the process of the eutrophication. From the view of systematic engineering and watershed ecology, a series of the countermeasures have been put forward to control the eutrophication.

The effects of co-cultivation of pearl mussels and fishes on water pollution control in middle or small sized water

Our field experiments showed that the cultivation of pearl mussels formed a new biocoene composed of filamentous algae, protozoa, porifera and coelenterate. It effectively reduced nitrogen, phosphorus, chemical oxygen demand and biochemical oxygen demand in the water by 67.3%, 73.2%, 38.1% and 15.5%, respectively, during May to September 1998 when the water eutrophication was developing. This could control water eutrophication and produce pearls, shellfish meat and shells. This is an economical and effective way to control water eutrophication by using the ultra strong filtering capability of freshwater pearl mussels.

System： Pattern of Phosphorus Sequestration in Different Depths of Sediment

The present study investigated potential effectiveness of certain chemical candidates for controlling internal phosphorus loading, and for delineating inactivation pattern in sediment depths of an eutrophic pond under simulated mesocosm condition. Chemical administration （@ 30 mg/dm3） resulted in phosphate precipitation from water column concomitant with inactivation in sediments, under specific pH range and/or redox regime. The alum-lime combination dosing wrought the maximum reduction in orthophosphate （65.6%） and soluble reactive phosphate （71.9%） in water plus the utmost increment in sediment-P （0.257 ppm）. The inactivated P forms typically exhibited a downhill concentration gradient with highest sequestration in the uppermost sediment stratum. Ironbound P displayed the highest mobility while calcium- and aluminum- bound P behaved almost immune to internal feedback dynamics. The combo-treatment was established as the most effective phosphate scavenging and confiscating agent, to be adopted as chemical remediation regime for de-eutrophication, restoration and rehabilitation of the water body.

Water Environment Pollution in Three-Gorge Reservoir Area and Treatment Technology

After the erection of Three-Gorge Reservoir, the water environment in the reservoir area will be turned into water bodies like lakes, and the self-clarification ability of water will also be much slower than ever. Now, the quality of water in most segments in upper reaches of Yangtze River cannot meet the requirements of l-ll class Environment Quality Standard (GHZB1-1999). In Yangtze River, dialing River and Wujiang River, the main indexes such as colon bacillus, nonionic ammonia, chemical oxygen demand (COD), petroleum, phenol, total phosphorus (TP), heavy metal, etc., have exceeded the standard limits. The water bodies of the reservoir area are facing serious risk of eutrophicationm. To solve that problem, a countermea-sure of multi-spot diverted treatment and separate discharge is recommended. For doing this, lots of small-scale wastewater treatment facilities employing updated activated sludge treatment technologies are to be set up. Up to now, a number of sewage treatment technologies to control eutrophication of water have been developed, which include processes of sequencing batch activated sludge (SBR), absorbing bio-degradation (AB), oxidation channel, package intermittent aeration system (PIAS), intermittent cycle extended aeration system (ICEAS), UNITANK and so on. The Effective one to be applied in the reservoir area should convey the requirements of ecological agriculture, forestry and urban planning, and be accompanied by legal support for appropriate exploitation of natural resources.