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Table 4

The classification of nitrogen and phosphorus index

NPI ≤ 1.01.0 < NPI ≤ 2.0NPI > 2.0
Water quality grade Qualified Small amount exceeding standard Several times exceeding the standard 
NPI ≤ 1.01.0 < NPI ≤ 2.0NPI > 2.0
Water quality grade Qualified Small amount exceeding standard Several times exceeding the standard 
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