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 8 / 20 MEC is the concentration of a chemical actually measured in an environmental sample. PNEC is the maximum concen- tration of a chemical substance predicted from experimental data or modeling to have no significant adverse effects on the environment and organisms. LC50 is the semi-lethal concentration, EC50 is the half-maximal effective concentration. In PNEC calculations, the value of the safety factor AF is usually based on the type and amount of toxicity data available. When acute toxicity data (e.g., EC50 and LC50) are used for PNEC calculations, a higher safety factor is usually chosen, and here AF takes the value 1000. ECOSAR provides the values for LC50 and EC50. According to the technical guide of risk evaluation prepared by the European Commission, RQ > 1 suggests high ecological risk, 0.1 < RQ < 1 suggests an intermediate ecological risk, and RQ < 0.1 suggestsa relatively low ecological risk. 3. Results and discussion 3.1 Water quality characteristics analysis Statistical analysis of water-quality data from five sampling sites (Table 5) showed that Lianhuan Lake overall meets class V water quality (GB 3838−2002) and was mildly eutrophic. TLI values at sites W1–W5 were 54.21, 54.74, 54.66, 51.00, and 57.80, respectively, all indicating slight eutrophication; The water quality grades of sites W1, W2, and W3 were clas- sified as Class IV, while W4 and W5 remain at Class V. WQI scores range from 42.73 to 53.64, classifying W1 and W4

as moderate quality and W2, W3, and W5 as low quality. IWQI values between 65 and 80 further confirm minor pollution at all sites. These results reflect the influence of intensive agriculture, dense population, and urban runoff in the lake’s catchment. Consistent with other shallow-lake studies, Shi et al. [34] similarly found that Mei Lake’s water bodies were mildly eutro- phic due to surrounding agricultural and anthropogenic activities. Comparable dynamics have been observed in Taihu Lake [35], where seasonal nutrient pulses drove TLI and WQI fluctuations alongside genus-level microbial shifts, and in Poyang Lake [36], where increases in TLI corresponded with marked changes in bacterial community composition. These studies underscore the sensitivity of shallow lakes to nutrient loading and the value of integrated indices (TLI, WQI, IWQI) for rapid assessment and cross-system comparisons, highlighting the need for watershed management strategies priori- tizing phosphorus control and pH stabilization. 3.2. The analysis of Alpha diversity Microbial diversity was assessed by calculating Shannon, Chao1, ACE and Simpson indices from Operational Taxonomic Unit (OTU) clustering results. The Shannon index integrated species richness and evenness, with higher values indicat- ing a more diverse and evenly distributed community. The Chao1 estimator projected total species richness, with larger values reflecting greater richness. The ACE estimator, based on species-abundance data, emphasized rare species pres-

ence, so higher ACE values corresponded to increased richness and rarity. Finally, the Simpson index quantified domi- nance—lower Simpson values denoted higher diversity [37]. The alpha diversity index (Table 6) indicated that bacterial diversity and abundance were generally higher in sediment samples compared to water samples. In the water samples, W3 had high bacterial diversity and abundance, and the Table 5. Comprehensive water quality analysis of Lianhuan. Sampling Number Water quality level TLI Eutrophication level WQI Water quality IWQI Water quality W1 Ⅳ 54.21 light eutropher 50.91 Moderate 80 Minor pollution W2 Ⅳ 54.74 light eutropher 48.18 Low 77.5 Minor pollution W3 Ⅳ 54.66 light eutropher 49.09 Low 80 Minor pollution W4 Ⅴ 51.00 light eutropher 53.64 Moderate 77.5 Minor pollution W5 Ⅴ 57.80 light eutropher 42.73 Low 65 Minor pollution https://doi.org/10.1371/journal.pone.0332712.t005