[Driving Factors Analysis for Spatial-Temporal Distribution of Organic Pollutants in the Yangtze River Delta Based on the Optimal-scale Geographical Detector].

Site contamination has caused serious harm to human health and the ecological environment, so understanding its spatial and temporal distribution patterns is the basis for contamination assessment and site remediation. For this reason, this study analyzed the spatial-temporal distribution patterns of organic pollutants and their driving factors in the Yangtze River Delta based on site sampling data using the optimal-scale geographical detector. The analysis results showed that:① There was a significant scale effect in the spatial distribution of organic pollutants in the Yangtze River Delta, and its optimal geographic detection scale grid was 8 000 meters. ② The main control factor of the spatial distribution of pollutants in the Yangtze River Delta originated mostly from the biological field, followed by the chemical field. ③ At the depth of 0-20 cm of soil, the explanatory power of sucrase content, urease content, microbial nitrogen amount, total nitrogen content, and cation exchange amount were stronger for the spatial distribution of organic pollutants. At the soil depth of 20-40 cm, the factors with stronger explanatory power on the spatial distribution of organic pollutants were soil moisture, population, and total nitrogen content. With the deepening of soil depth, the explanatory power of the factors of the hydrodynamic field increased. ④ Population, total nitrogen content, and polyphenol oxidase content had stronger explanatory power for the spatial distribution of organic pollutants in the spring. The spatial distribution of organic pollutants was more complex in autumn, and the factors showed stronger enhanced-nonlinear and enhanced-bi phenomena.

Responses of microbial communities subjected to hydrodynamically induced disturbances in an organic contaminated site.

Organic contaminated sites have gained significant attention as a prominent contributor to shallow groundwater contamination. However, limited knowledge exists regarding the impact of hydrodynamic effects on microbially mediated contaminant degradation at such sites. In this study, we investigated the distribution characteristics and community structure of prokaryotic microorganisms at the selected site during both wet and dry seasons, with a particular focus on their environmental adaptations. The results revealed significant seasonal variations (P < 0.05) in the α-diversity of prokaryotes within groundwater. The dry season showed more exclusive OTUs than the wet season. The response of prokaryotic metabolism to organic pollution pressure in different seasons was explored by PICRUSt2, and enzymes associated with the degradation of organic pollutants were identified based on the predicted functions. The results showed that hormesis was considered as an adaptive response of microbial communities under pollution stress. In addition, structural equation models demonstrated that groundwater level fluctuations can, directly and indirectly, affect the abundance and diversity of prokaryotes through other factors such as oxidation reduction potential (ORP), dissolved oxygen (DO), and naphthalene (Nap). Overall, our findings imply that the taxonomic composition and functional properties of prokaryotes in groundwater in organic contaminated sites is influenced by the interaction between seasonal variations and characteristics of organic pollution. The results provide new insights into microbiological processes in groundwater systems in organic contaminated sites.

Significant roles of core prokaryotic microbiota across soil profiles in an organic contaminated site: Insight into microbial assemblage, co-occurrence patterns, and potentially key ecological functions.

Extreme environmental disturbances induced by organic contaminated sites impose serious impacts on soil microbiomes. However, our understanding of the responses of the core microbiota and its ecological roles in organic contaminated sites is limited. In this study, we took a typical organic contaminated site as an example and investigated the composition and structure, assembly mechanisms of core taxa and their roles in key ecological functions across soil profiles. Results presented that core microbiota with a considerably lower number of species (7.93%) than occasional taxa presented comparatively high relative abundances (38.04%) yet, which was mainly comprised of phyla Proteobacteria (49.21%), Actinobacteria (12.36%), Chloroflexi (10.63%), and Firmicutes (8.21%). Furthermore, core microbiota was more influenced by geographical differentiation than environmental filtering, which possessed broader niche widths and stronger phylogenetic signals for ecological preferences than occasional taxa. Null modelling suggested that stochastic processes dominated the assembly of the core taxa and maintained a stable proportion along soil depths. Core microbiota had a greater impact on microbial community stability and possessed higher functional redundancy than occasional taxa. Additionally, the structural equation model illustrated that core taxa played pivotal roles in degrading organic contaminants and maintaining key biogeochemical cycles potentially. Overall, this study deepens our knowledge of the ecology of core microbiota under complicated environmental conditions in organic contaminated sites, and provides a fundamental basis for preserving and potentially utilizing core microbiota to maintain soil health.

Responses of abundant and rare prokaryotic taxa in a controlled organic contaminated site subjected to vertical pollution-induced disturbances.

Soil microbiota as the key role mediates the natural attenuation process of organic contaminated sites, and therefore illuminating the mechanisms underlying the responses of abundant and rare species is essential for understanding ecological processes, maintaining ecosystem stability, and regulating natural attenuation well. Here, we explored the distributional characteristics, ecological diversities, and co-occurrence patterns of abundant and rare prokaryotic subcommunities using 16S rRNA high-throughput sequencing in vertical soil profiles of a controlled organic contaminated site. Results showed that abundant prokaryotic taxa were widespread across all soil samples, whereas rare counterparts were unbalancedly distributed. Rare subcommunity had more taxonomic groups and higher α- and ß-diversities than abundant subcommunity. Both of these two subcommunities surviving in the organic polluted site possessed the potential of degrading organic contaminants. Abundant subcommunity was little affected by abiotic factors and mainly shaped by soil depth, while rare one was sensitive to environmental disturbances and presented a non-depth-dependent structure. Co-occurrence analysis revealed that rare taxa were more situated at the center of the network and more inclined to cooperate with non-abundant species than abundant taxa, which might play crucial roles in enhancing the resilience and resistance of prokaryotic community and maintaining its structure and stability. Overall, our results suggest that abundant and rare prokaryotic subcommunities present different responses to physicochemical factors and pollution characteristics along vertical soil profiles of organic contaminated sites undergoing natural attenuation.