Pollution and Prevention Measures of Shiyan Reservoir in Shenzhen City

Shiyan Reservoir was the main water supply reservoir of Baoan District in Shenzhen City and was polluted for a long time. 8 water samples at different depths from every branch and near the dam were collected, and tested by Shenzhen Water Quality Testing Center. The water quality of the Shiyan Reservoir was assessed by using a single water quality parameter model (contrast to the second criterion of environmental quality standards for surface water) and an eutrophication assessment model. The results indicate that pollutants are found in all samples according to single water quality model, and twelve items totally (respectively total nitrogen, total phosphorus, ammoniacal nitrogen, BOD5, fecal coliforms, dissolved oxygen, permanganate index, volatile hydroxybenzene, Fe, Mn,pH and petrolic) exceed the criterions. The amount of TN is far higher than the standard. The first three most serious polluted samples are from Shiyan River and Shenkengli Branch, Mabu Branch and Shiyan Lake Hot Springs Hotel. The whole water quality of the reservoir belongs to a mesotrophic state but several samples are eutrophic. Phosphor was the limiting nutrition element in the reservoir. Some pollutants show a gradual sediment trend, i.e. Fe,Mn, increasing with water depth. Without putting the reservoir under environmental control, water quality in the deeper water area will become under the national standard first, and in turn affects water quality of the whole reservoir. In the paper, three methods to solve the water pollutant are given: physical disposal, chemical disposal and biologic technique. The corresponding measures for every branch with different pollutant characteristic are also suggested.