Table 1.
The criteria of surface water quality for lakes or reservoir (CNEPA, 2002)
| Items | Surface water quality classification |
||||
| Class I | Class II | Class III | Class IV | Class V | |
| Water temperature (°C) | Maximum week increase≤1; maximum week decrease≤2 | ||||
| pH | 6~9 | ||||
| DO (mg/L) | Saturation≥90% | ≥6 | ≥5 | ≥3 | ≥2 |
| CODMn (mg/L) | ≤2 | ≤4 | ≤6 | ≤10 | ≤15 |
| CODCr (mg/L) | ≤15 | ≤15 | ≤20 | ≤30 | ≤40 |
| BOD5 (mg/L) | ≤3 | ≤3 | ≤4 | ≤6 | ≤10 |
| TN (mg/L) | ≤0.2 | ≤0.5 | ≤1.0 | ≤1.5 | ≤2.0 |
| NH3-N (mg/L) | ≤0.15 | ≤0.5 | ≤1.0 | ≤1.5 | ≤2.0 |
| NO2-N (mg/L) | ≤0.06 | ≤0.1 | ≤0.15 | ≤1.0 | ≤1.0 |
| TP (mg/L) | ≤0.01 | ≤0.025 | ≤0.05 | ≤0.1 | ≤0.2 |
| Chlorophyll a | ≤0.001 | ≤0.004 | ≤0.01 | ≤0.03 | ≤0.065 |
| Transparency (m) | ≥15 | ≥4 | ≥2.5 | ≥1.5 | ≥0.5 |
| Escherichia coli (L−1) | ≤200 | ≤2000 | ≤10000 | ≤20000 | ≤40000 |
DO: dissolved-oxygen; CODMn: Chemical oxygen demand by K2MnO4 oxidation method; CODCr: Chemical oxygen demand by chromium oxidation method; BOD5: Biological oxygen demand; TN: Total nitrogen; TP: Total phosphorus