According to China's Environmental Quality Standard for Surface Water (GB3838-2002), water quality above Class III (that is, Class I, Class II, including Class III) can be used as source water, while water quality below Class III (that is, Class IV and Class V) cannot be used as source water.

According to the water body of Taihu Lake, samples were taken in Xueyan, Tongli, East Taihu Lake and Yixing, and the test items included six indicators, including chemical oxygen demand, total nitrogen, total phosphorus, water temperature, pH and chromaticity. From the results, COD greatly exceeds the water quality requirements of Class V water bodies, and the water quality in Tongli and Yixing exceeds the standard by more than 3 times, indicating that the water quality is very poor. The contents of total nitrogen and total phosphorus, the key indicators leading to eutrophication, are also not optimistic. The lowest total nitrogen content in the snow weir is 0.3mg/L, which is Grade II water quality. The worst water samples come from Tongli and Yixing, which are close to Grade IV water quality. The total phosphorus content has a great influence on eutrophication. From the results, the water samples in Tongli and Yixing have reached or exceeded the V water quality standard, and the degree of eutrophication is very high. The water samples of Xueyan and East Taihu Lake are close to Class III water quality standards.

According to the above analysis, the water body of Taihu Lake is already below Class III and Class III standards, and the water quality is poor. It is reported that Microcystis (a typical cyanobacteria that releases microcystins) becomes the dominant species when the total nitrogen and total phosphorus in the lake exceed 0.5 mg/ L and 0.08 mg/ L, respectively. Taihu Lake is a shallow water lake with thorough illumination and high nitrogen and phosphorus content, which is easy to breed cyanobacteria, mainly Microcystis.

Attached Table: Test Results of Taihu Lake Water Samples

sampling point

index

Xueyan

Tongli

Wuxi (East Taihu Lake)

Yixing

Chemical oxygen demand (mg/L)

58.3

154.8

60.7

124.4

Total nitrogen (mg/L)

0.3

1.4

0.6

1.3

Total phosphorus (mg/L)

0. 19

0.45

0. 15

0.84

Water temperature (? c)

28.2

28.6

28.5

28.7

Patient History

6.5

6.6

6.5

6.8

Standard limit value of basic project of surface water environmental quality standard unit: mg/L.

Serial number I Category II Category III Category IV Category V

Man-made variation of ambient water temperature at 1 (℃) should be limited to: weekly average maximum temperature rise ≤ 1, and weekly average maximum temperature drop ≤2.

2 p H value (dimensionless) 6-9

3 chemical oxygen demand (CODcr) ≤1515 20 30 40

4 Total phosphorus (TP) (calculated as P) ≤ 0.02 (0.0 1) 0. 1 (0.025) 0.2 (0.05) 0.3 (0. 1) 0.4 (lake).

5 Total nitrogen (TN) (in terms of N in lakes and reservoirs) ≤ 0.2 0.5 1.0 1.5 2.0.