Autochthonous organic matter input in reservoirs: Limited methane oxidation in sediments fails to suppress methane emission.

The interception of rivers leads to the accumulation of substantial organic matter in reservoirs, exerting a significant influence on greenhouse gas emissions. The diverse imported organic matter, coupled with sedimentary heterogeneity and intricate microbial processes, gives rise to seasonal variations in methane emissions from reservoirs. In this study, sediment cores were supplemented with terrestrial or autochthonous carbon to emulate reservoir carbon input across different seasons, thereby investigating methane emission potential and associated microbial mechanisms within the sediment cores. Results demonstrated that autochthonous organic matter enhanced sediment organic content, thereby providing more substrates for the methanogenic process and fostering the proliferation of methanogens (with a relative abundance of 47.17 % to 60.66 %). Notably, the dominant genera of Methanosaeta, Methanosarcina, and Candidatus Methanomethylicus were boost on the surface layer of sediment. Concurrently, the introduction of autochthonous organic carbon spurred an increase in methane-oxidizing microbe, reaching up to 5.59 %, with Methylobacter and Candidatus Methanoperedens as the predominant species, which led to a downward migration of the functional microbial group in the sediment. Under the priming impact of autochthonous carbon, however, the methane oxidation probably doesn't consume the substantial methane produced in sediment. Consequently, the sediment functions as a hotspot for methane release into the overlying water, highlighting the necessity to include summer as critical periods for integrated assessments, particularly during algae bloom.

Microbial processing of autochthonous organic matter controls the biodegradation of 17α-ethinylestradiol in lake sediments under anoxic conditions.

The decay of algal biomass and aquatic plants in freshwater lakes leads to the overproduction of autochthonous organic matter (OM) and the exhaustion of dissolved oxygen, impacting the microbial community and subsequent biodegradation of emerging contaminants in sediment. This study explored how the microbial processing of aquatic plant- and algal-derived OM (POM and AOM) mediates 17α-ethinylestradiol (EE2) biodegradation in the anoxic sediments of Lake Taihu in China. In four months of microcosm incubations, the increased concentrations of protein-like substances in AOM and POM exhibited temporary activation on microbial metabolic enzyme activity (fluorescein diacetate hydrolase and dehydrogenase) and significantly promoted the carbon mineralization with iron reduction (P < 0.001). These in turn increased the EE2 biodegradation efficiency to 77-90 ng g-1 in the anoxic sediment. However, a higher EE2 biodegradation of 109 ng g-1 was achieved with the humic acid augmentation containing more quinone-like compounds, showing a weaker substrate-priming effect but accelerated redox cycling of iron and organic substrates in the later period of incubation. The microbial analysis further revealed that the quinone-like compounds in OM were more closely associated with microbial electron transfer and strengthened their interspecies syntrophic cooperation favorable to contaminant biodegradation, even though the connective members exposed to protein-like components upregulated more functional genes related to organic carbon and xenobiotics metabolism and biodegradation. Our findings will help predict the fate of estrogens in various sedimentary environments under increasing eutrophication and further climate change scenarios.

Priming effect of autochthonous organic matter on enhanced degradation of 17α-ethynylestradiol in water-sediment system of one eutrophic lake.

Climate change and increasing eutrophication are expected to increase the release of autochthonous organic matter (OM) to sediments, where most contaminants are transformed or mineralized in freshwater lakes. This study sought to evaluate how cyanobacteria- and macrophyte-derived OM (COM and MOM) affected the microbial attenuation of 17α-ethinylestradiol (EE2) in the sediment from eutrophic Lake Taihu in China. In two months of water-sediment microcosm experiments, the input of COM and MOM both promoted EE2 degradation more strongly than humic acids, and the degradation efficiency was significantly and positively correlated with the cometabolism of increasing organic carbon in sediments (P < 0.001). The enhanced degradation was explained by responses of indigenous bacterial community to OM amendment as a priming effect. The immediate breakdown of biodegradable components such as proteinaceous substances in COM and MOM remarkably augmented the metabolic activity of bacteria in terms of the stimulated activity of extracellular enzymes including fluorescein diacetate and dehydrogenase, as well as the elevated production of proteins and polysaccharides in extracellular polymeric substances. In the meantime, the bacterial community composition was reshaped toward a more eutrophic state, leading to the clear upregulation of metabolic function genes of organic carbon and xenobiotics. Correlation-based network analysis further determined the strong facilitative coordination between the community members and the compositional variability of OM in the cometabolism. These results suggest that cyanobacterial blooms-dominated zones are potential hotspot areas for steroid estrogen attenuation, a finding of significance for the control and management of complex pollution in freshwater lakes.