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Rapid urbanization has destroyed urban water systems and led to blackened and odorous rivers. The heavily polluted rivers are always facing eutrophication and heavy metal pollution, while the combined effects of these environmental factors on the microbial diversity and distribution of the river microbial communities have not been adequately reported, especially the archaeal communities. In this study, we investigated the community structure and microbial distribution of sediment archaeal communities from an urban blackened and odorous river basin of the Zhang river, in Nanling, China. Results showed that the archaeal community from the eight sediment sites have average values of Shannon and Chao1 at 3.4921 and 232.7202, respectively. The community diversity and richness were different among samples. Halobacterota and Euryarchaeota were the most abundant phylum and Crenarchaeota also took up a considerable amount of the archaeal community. To reveal the main environmental drivers of the distribution of archaeal communities in sediment, the environmental physicochemical factors (total nitrogen, total phosphorus, oxidation/reduction potential, nitrate nitrogen, ammonia nitrogen, pH and total organic carbon) and heavy metals (Cr, Ni, Cu, Zn, As, Cd, Pb and Hg) in sediment were determined. A redundancy analysis (RDA) revealed that Eh was the most prominent influencing factor, and As was the most influential heavy metal on the microbial distribution of archaeal communities. Furthermore, a variance partitioning analysis (VPA) was used to identify the impacts of physicochemical factors and heavy metals on the archaeal community distribution. Results showed that heavy metals have higher effects on archaeal community distribution than physicochemical factors. The present study suggested that the heavy metal pollution should be paid more attention in the microbial distribution in heavily polluted urban rivers, and also should be taken into consideration for improving the efficacies of ecological evaluation and remediation.

Dissolved effluent organic matter (dEfOM) from wastewater treatment plants (WWTPs) is bound to encounter photo- and bio-degradation as discharged into the receiving water body. However, the comprehensive variations of dEfOM by photo- and bio-degradation are not well unveiled because of its compositional heterogeneity. In this work, dissolved organic carbon (DOC) concentrations, UV-Vis and fluorescent spectra combined with fluorescence regional integration (FRI) analysis were used to investigate the changes in bulk dEfOM and its fluorescent components during photo- and bio-degradation processes in the receiving water body. Results showed that 48.49%-69.62% of the discharged dEfOM was decomposed by ultra violet (UV)-irradiation and indigenous microbes, while the others (33%-45%) were recalcitrant and stable in the receiving water body. Specifically, the photo- and bio-degradation of chromophoric, fluorescent dEfOM and its components were found to follow the single or double exponential kinetic model, and the differences in photo- and bio-degradability of each components shifted its composition. Furthermore, results of bio-degradation after UV-irradiated dEfOM indicated that there was overlapping of photo- and bio-degradable fractions in dEfOM, and photoreactions could improve the self-production of natural organic matter in the receiving water body. These results could improve the understanding the fate of discharged dEfOM in the receiving water body, and we proposed some cost-effective strategies for discharging WWTPs effluent.

Although more attention has been paid to plastic pollution in marine ecosystems, research on the influence of plastic in freshwater ecosystems remains limited. To help fill this information gap, this article represents an investigation of the effects of virgin polyvinyl chloride (v-PVC) microplastics (MPs) and UV-aged polyvinyl chloride (a-PVC) MPs on the growth and chlorophyll content of the freshwater algae, Chlamydomonas reinhardtii (C. reinhardtii) at different periods (0, 24, 48, 72 and 96 h). The results suggest that both virgin and aged PVC MPs have negative effects on the growth of C. reinhardtii in the range of 10 mg/L to 200 mg/L, which leads to the reduction of chlorophyll-a level in the cells. Furthermore, a-PVC MPs were more toxic than v-PVC MPs, as shown by the a-PVC MPs' lower EC50 values after 96 h (63.66 mg/L for a-PVC MPs and 104.93 mg/L for v-PVC MPs). The inhibition effect of both kinds of PVC was also testified by the enhancement of enzymatic activity of superoxide dismutase (SOD) and malondialdehyde (MDA) in algae. Meanwhile, a-PVC MPs obviously had a higher toxicity than v-PVC MPs. The aging process that affected the surface characteristics of a-PVC was identified using Fourier transform infrared (FTIR) and Zetasizer. The carbonyl groups formed on the surface and the increased zeta potential of the a-PVC MPs affected the interaction between the microplastics and the algae, which increased the toxicity of aged microplastics. The research results presented here provide more evidence of the risks microplastics bring into the freshwater ecosystem.

Lacustrine sediment played important roles in migration and transformation of its water soluble organic matter (WSOM), and the source and composition of WSOM would affect water trophic status and the fate of pollutants. However, we know little about the pathway of WSOM transformation and its driving bacterial communities in lacustrine sediment. In the present study, we investigated the spatial distribution patterns of sediment WSOM and its fluorescent fractions across Lake Chaohu using fluorescence spectroscopy, and explored WSOM compositional structure through our proposed calculated ratios. In addition, we also analyzed sediment bacterial community using Illumina sequencing technology, and probed the possible pathway of sediment WSOM transformation under the mediate of indigenous bacteria. Our results showed that the inflowing rivers affected the spatial distribution patterns of WSOM and its five fractions (including tyrosine-, tryptophan-, fulvic acid-, humic acid-like substances and soluble microbial productions), and sediment WSOM originated from fresh algae detritus or bacterial sources. In parallel, we also found that Proteobacteria (mainly γ-Proteobacteria and δ-Proteobacteria), Firmicutes (mainly Bacilli), Chloroflexi, Acidobacteria, Planctomycetes and Actinobacteria dominate sediment bacterial community. Furthermore, these dominant bacteria triggered sediment WSOM transformation, specifically, the humic acid-like substances could be converted into fulvic acid-like substances, and further degraded into aromatic protein-like and SMP substances. In addition, our proposed ratios (P-L:H-L, Ar-P:SMP and H-L ratio), as supplementary tool, were effective to reveal WSOM composition structure. These results figured out possible pathway of WSOM transformation, and revealed its microbial mechanism in lacustrine sediment.

As the emerging contaminants, the behavior and fate of microplastics (MPs) were highly related to the interactions with surrounding organic matters. However, information on the effects of molecular sizes of organic matters on the interaction is still lacking. In this study, the bulk algal-derived organic matter (AOM) samples were obtained and further fractionated into high molecular weight (HMW-, 1kDa-0.45 μm) and low molecular weight (LMW-,1 kDa) fractions. The interaction between MPs [polyethylene (PE) and polystyrene (PS)] and these MW-fractionated AOMs were characterized by dissolved organic carbon, fluorescence and absorbance spectroscopy, and fourier transform infrared (FTIR) analysis. Results showed that presence of AOM could effectively inhibit the release of additives from MPs. Further analysis found that the inhibition extents decreased in the order of HMW- bulk LMW-AOM. The absorbance and fluorescence spectroscopy showed that aromatic protein-like substances in HMW fraction exhibited higher adsorption affinity to MPs than the bulk and LMW counterparts. The strong sorption of aromatic substances may offer more binding sites for additives to inhibit the release of organic substances. Moreover, two dimensional FTIR correlation spectroscopy revealed that the HMW non-aromatic substances were preferentially adsorbed onto PS, which led to an enhanced adsorption capacity to additives by forming H-bonding. Therefore, the MW- and component-dependent heterogeneities of AOM samples must be fully considered in evaluating the environmental behavior of MPs.

Increasing discharge of plastic debris into aquatic ecosystems and the worsening ecological risks have received growing attention. Once released, plastic debris could serve as a new substrate for microbes in waters. The complex relationship between plastics and biofilms has aroused great interest. To confirm the hypothesis that the presence of plastic in water affects the composition of biofilm in natural state, in situ biofilm culture experiments were conducted in a lake for 40 days. The diversity of biofilm attached on natural (cobble stones (CS) and wood) and plastic substrates (Polyethylene terephthalate (PET) and Polymethyl methacrylate (PMMA)) were compared, and the community structure and composition were also analyzed. Results from high-throughput sequencing of 16S rRNA showed that the diversity and species richness of biofilm bacterial communities on natural substrate (observed species of 1353~1945, Simpson index of 0.977~0.989 and Shannon–Wiener diversity index of 7.42~8.60) were much higher than those on plastic substrates (observed species of 900~1146, Simpson index of 0.914~0.975 and Shannon–Wiener diversity index of 5.47~6.99). The NMDS analyses were used to confirm the taxonomic significance between different samples, and Anosim (p = 0.001, R = 0.892) and Adonis (p = 0.001, R = 808, F = 11.19) demonstrated that this classification was statistically rigorous. Different dominant bacterial communities were found on plastic and natural substrates. Alphaproteobacterial, Betaproteobacteria and Synechococcophycideae dominated on the plastic substrate, while Gammaproteobacteria, Phycisphaerae and Planctomycetia played the main role on the natural substrates. The bacterial community structure of the two substrates also showed significant difference which is consistent with previous studies using other polymer types. Our results shed light on the fact that plastic debris can serve as a new habitat for biofilm colonization, unlike natural substrates, pathogens and plastic-degrading microorganisms selectively attached to plastic substrates, which affected the bacterial community structure and composition in aquatic environment. This study provided a new insight into understanding the potential impacts of plastics serving as a new habitat for microbial communities in freshwater environments. Future research should focus on the potential impacts of plastic-attached biofilms in various aquatic environments and the whole life cycle of plastics (i.e., from plastic fragments to microplastics) and also microbial flock characteristics using microbial plastics in the natural environment should also be addressed.

Riparian wetland controls the transfer of terrestrial dissolved organic matter (DOM) to surface water bodies. However, the effects of land use on riparian soil DOM quality and its contribution to aquatic environment are largely unknown. In this study, the amount and composition of water-extracted soil organic matter (WSOM) in riparian wetlands were determined to evaluate the effect of land uses on spatial patterns of WSOM and streamwater quality on Chongming Island, China. The fluorescent properties of WSOM and fluvial DOM were analyzed using EEM spectra-combining PARAFAC model and accurate MS and MS/MS identification. Our findings showed no differences in the riparian WSOC contents between land use types (agricultural land, natural wetland, commercial land and industrial land). However, the fluorescent WSOM and its humic-like (Comp.1 and Comp.2) and microbial degradation (Comp.4) components significantly varied under different land uses (P

Wastewater effluent makes up an increasingly large percentage of surface water supplies, but the impacts of discharge of effluent organic matter (EfOM) on receiving riverine and lacustrine dissolved organic matter (DOM) is still largely unknown. In the present study, we investigated variations of DOM quantity and quality along wastewater treatment plants (WWTPs)-river-lake continuum during drought periods, and made a tentative discussion on its implications for watershed environmental management. We used dissolved organic carbon (DOC) concentrations, UV absorption coefficients and excitation-emission-matrixs (EEMs) fluorescence spectroscopy combined with fluorescence regional integration (FRI) to characterize EfOM and riverine and lacustrine DOM along WWTPs-river-Chaohu Lake continuum. Our results showed that changes in DOM quantity and quality in receiving waterbodies were related to EfOM discharged from WWTPs and external input of DOM along inflowing river. Specifically, we found that the ratio of protein-like/humic-like notably decreased (P 0.05), and %humic-like increased (P 0.01) along WWTPs-river-lake continuum. Furthermore, the recent autochthonous contribution index (BIX) and the humification index (HIX) values showed that these variations of DOM composition were attributed to microbial degradations in receiving waterbodies. We concluded that the changes of DOM quantity and quality along WWTPs-river-lake continuum had important implications for DOM behaviors, and offered some novel ideas for watershed environmental management.

Riparian wetlands play important roles in the enhancement of water quality by controlling nonpoint source pollution and protecting aquatic ecosystems. In the present study, we surveyed and identified vegetation types in riparian wetlands, evaluated how vegetation types influence spatial patterns of water-extracted soil organic matter (WSOM) from riparian wetland, and probed the impacts of riparian fluorescent WSOM on fluorescent dissolved organic matter (FDOM) and water trophic states in river ecosystems. We used absorption and excitation-emission-matrix (EEM) fluorescence spectroscopy to characterize the optical properties of riparian WSOM and riverine DOM from Chongming Island, China, the largest alluvial plain island in the world. Our results showed that fifty-eight spermatophytes in riparian wetland were clustered into five vegetation types, including warm coniferous forest (WCF), deciduous broad leaf forest (DBF), evergreen broad leaf forest (EBF), aquatic plants (AP) and herbaceous plants (HP). Absorption spectra revealed the effects of vegetation types on riparian chromophoric WSOM quantity. Although no difference in water-extracted soil organic carbon (WSOC) contents was observed, deciduous broad leaf forest (DBF) and evergreen broad leaf forest (EBF) fed more fluorescent WSOM quantity than did the other vegetation (AP, HP and WCF), and deciduous broad leaf forest (DBF) and aquatic plants (AP) provided more humic-like (RC.1 and RC.2) and fulvic-like (RC.3) substances into riparian wetland (P