Analysis of bacterial biodiversity and ecological risk evaluation of organophosphorus in Lianhuan Lake

PLOS One | https://doi.org/10.1371/journal.pone.0332712 September 26, 2025 5 / 20 2.3.2 Analysis of the eutrophication index. This study used the trophic level index (TLI) to assess the eutrophication of water samples [29]. The trophic state index is computed by utilizing a specific formula: TLI(Chl – a) = 10(2.5 + 1.086ln(Chl – a)) (1) TLI(TP) = 10(9.436 + 1.624ln(TP)) (2) TLI(TN) = 10(5.453 + 1.694ln(TN)) (3) TLI(SD) = 10(5.118 – 1.94ln(SD)) (4) TLI(COD Mn) = 10(0.109 + 2.661ln(COD Mn)) (5) TLI(∑) = ∑m j=1 Wj × TLI (j) (6) Chl.a is measured in mg/m3 and SD is measured in m. All other indicators are measured in mg/L. The trophic status par- tition criterion is based on the TLI scores. The range of Oligotropher is TLI < 30. The range of Mesotropher is 30 ≤ TLI ≤ 50. The range of light eutropher is 50 < TLI ≤ 60; Middle eutropher is 60 < TLI ≤ 70. The range of Hyper eutropher is TLI > 70. 2.3.3 Analysis of water quality index. The water quality index is determined by the utilization of the weighted arithmetic mean technique, where each parameter is allocated a certain weight depending on its importance in assessing the total water quality. The weights were derived from expert consensus and prior research on the development of the water quality index (Table 2). The water quality index was calculated using the following formula [30]: WQI = ∑n i=1 CiPi ∑n i=1 Pi (7) Where WQI is the water quality index, Pi is the weight assigned to each parameter, and Ci is the measured value of each parameter.

The Water quality is based on the WQI scores. The range of Bad is WQI < 25. The range of Low is 25 ≤ WQI ≤ 50. The range of Moderate is 50 < WQI ≤ 70; Good is 70 < WQI ≤ 90. The range of Excellent is WQI > 90. Table 2. Normalized values and weights for WQI. Water quality indicators Unit Weight (pi) Normalization factor (Ci) 100 90 80 70 60 50 40 30 20 10 0 pH – 1 7 7-8 7-8.5 7-9 6.5-7 6-9.5 5-10 4-11 3-12 2-13 1-14 EC μS/cm 1 <750 <1000 <1250 <1500 <2000 <2500 <3000 <5000 <8000 <12000 >12000 TN mg/L 2 <0.1 <0.2 <0.35 <0.5 <0.75 <1 <1.25 <1.5 <1.75 ≤2 >2 NH3-N mg/L 3 <0.01 <0.05 <0.1 <0.2 <0.3 <0.4 <0.5 <0.75 <1 ≤1.25 >1.25 TP mg/L 1 <0.01 <0.02 <0.05 <0.1 <0.15 <0.2 <0.25 <0.3 <0.35 ≤0.4 >0.4 CODMN mg/L 3 <1 <2 <3 <4 <5 <8 <10 <12 <14 ≤15 >15 https://doi.org/10.1371/journal.pone.0332712.t002