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 9 / 20 distribution of each species was relatively uniform. This may be due to the fact that agricultural activities around W3 were relatively more frequent, and under the influence of agricultural runoff, the water body may have contained higher concen- trations of nutrients such as nitrogen and phosphorus, which triggered the phenomenon of eutrophication and led to the rapid reproduction of microbial populations. The higher bacterial abundance in sediments may be attributed to the fact that sediments were less influenced by water currents, offering a more stable environment, which served as a more suitable habitat for microorganisms [38]. Additionally, sediments typically contained a high concentration of organic matter (e.g., humus, plant debris) and mineral components, which supplied essential nutrients such as carbon, nitrogen, and other vital elements necessary for microbial communities. The research conducted by Li Ming’s team demonstrated that the level of species richness in the silt of the Songhua River was greater than that found in the water body [39]. The conclusion aligned closely with the findings of this investigation. 3.3. Analysis using Venn The Venn results (Fig 2) described the distribution of water samples, sediment samples, and water and sediment samples OTU distributions. Fig 2 showed that bacterial species richness in the sediments was significantly higher than in water, with 1246 OTUs

unique to sediments, 1808 OTUs shared by both habitats, and only 115 OTUs unique to water. The numbers of OTUs in sediment samples N1–N5 were 2950, 3024, 3006, 2957, and 3063, respectively; the number of OTUs common to all five sediment samples was 1246, accounting for 23.57% of the sediment OTUs. This was attributed to the fact that sediments offered a wider variety of substrates for microbial growth, including organic matter, minerals, and nutrients [40]. The num- bers of OTUs in water samples W1–W5 were 411, 341, 1603, 482, and 1353, respectively; the number of OTUs common to all five water samples was 115, representing 4.88% of the water OTUs. The microbial diversity in the water samples from monitoring sites W3 and W5 was greater, and the similarity between the two sites was also higher. The high envi- ronmental heterogeneity of lakes provides many habitats for bacteria. The OTU number of water sample and sediment were 2356 and 5287, the number of OTU shared by water and sediment samples was 1808. There were great differences between water environment and sediment environment. Bacteria in water were more affected by river flow than sedi- ment bacteria, and bacteria in water had greater migration rate and fusion rate. With the seasonal or hydrological period transition, the bacterial community structure also changed in the lakes, which was not only related to the turnover of the bacteria themselves, but also involved seasonal differences in environmental factors. The high number of species shared

between sediment and water samples may be due to the exchange and migration of microorganisms between the water column and sediments. Wu et al found that the number of OTUs in Xiangjiang River sediment samples was higher than water samples, this conclusion was consistent with the results of this investigation [41]. Table 6. Alpha Diversity index at water and sediment sampling sites. Sample Shannon Index Chao1 Index ACE Index Simpson Index W1 2.048 866.294 1228.489 0.27 W2 2.262 582.5 912.523 0.188 W3 4.794 2419.273 2979.378 0.029 W4 2.098 895.143 1234.312 0.256 W5 3.934 2101.944 2660.519 0.087 N1 6.284 154.797 4093.253 0.007 N2 6.341 4153.093 4135.809 0.008 N3 6.478 4045.18 4179.994 0.004 N4 6.338 4173.954 4175.893 0.006 N5 6.313 4407.745 4395.509 0.007 https://doi.org/10.1371/journal.pone.0332712.t006