Urban wetlands, although often overlooked, are hotspots for CH ₄ cycling. However, the understanding of anaerobic CH ₄ oxidation and microbial responses to different electron acceptors in urban wetlands remains limited. Here, we employed DNA-stable isotope probing (SIP) and metagenomic techniques to identify the core CH ₄ -oxidizing microbial groups in the presence of NO ₃ ^- , SO ₄ ^2- , or ferrihydrite (Fe(III)) in anoxic urban-lake sediments. The addition of NO ₃ ^- to sediment microcosms promoted CH ₄ oxidation, whereas SO ₄ ^2- and Fe(III) had minimal or inhibitory effects on CH ₄ oxidation rates in anoxic microcosms. The SIP-identified methanotrophs in response to the addition of CH ₄ comprised the Marine Benthic Group D (MBG-D), “ Candidatus Methylomirabilis Sh765B-TzT-35 and Z114MB74,” and the putatively aerobic methanotrophs Methylobacter and Methylocystis . The presence of NO ₃ ^- further enriched Methylocaldum , Methylomonas , ‘ Ca . Methylomirabilis Sh765B-TzT-35 and Z114MB74’, Methylococcaceae , and Methylospira . In contrast, SO ₄ ^2- and Fe(III) amendments notably shifted the dominant methanotrophs through the significant labeling of Methylocystis . Furthermore, metagenomic analysis of ¹³ C-labeled DNA showed enrichment of genes for oxidation of CH ₄ and its intermediates, as well as the reduction of NO ₃ ^- , SO ₄ ^2- , Fe(III), and fermentation. These results underscore the activity of NO ₃ ^- -dependent CH ₄ -oxidizing microorganisms and highlight their potential metabolic versatility in highly anthropogenically influenced urban wetlands. IMPORTANCE: Urban wetlands are critical ecosystems for CH ₄ cycling but are increasingly impacted by complex pollutants from urban development, such as nitrates, sulfates, and Fe(III) from industrial runoff, atmospheric deposition, and wastewater discharge. This study reveals how these pollutants act as electron acceptors, modulating microbial metabolic pathways and reshaping methanotrophic communities under anoxic conditions. By uncovering the microbial mechanisms driving CH₄ oxidation in urban wetland sediments, our findings provide a deeper understanding of how anthropogenic pollution alters biogeochemical cycles. These insights are crucial for developing targeted strategies to mitigate CH₄ emissions and improve greenhouse gas control in rapidly urbanizing regions.

Diesel spills in freshwater systems have adverse impacts on the water quality and the shore wetland. Microbial degradation is the major and ultimate natural mechanism that can clean the diesel from the environment. However, which, and how fast, diesel-degrading microorganisms could degrade spilled diesel has not been well-documented in river water. Using a combination of ¹⁴C-/³H--based radiotracer assays, analytical chemistry, MiSeq sequencing, and simulation-based microcosm incubation approaches, we demonstrated succession patterns of microbial diesel-degrading activities, and bacterial and fungal community compositions. The biodegradation activities of alkanes and polycyclic aromatic hydrocarbons (PAHs) were induced within 24 h after diesel addition, and reached their maximum after incubation for 7 days. Potential diesel-degrading bacteria Perlucidibaca, Acinetobacter, Pseudomonas, Acidovorax, and Aquabacterium dominated the community initially (day 3 and day 7), but later community structure (day 21) was dominated by bacteria Ralstonia and Planctomyces. The key early fungi responders were Aspergillus, Mortierella, and Phaeoacremonium by day 7, whereas Bullera and Basidiobolus dominated the fungal community at day 21. These results directly characterize the rapid response of microbial community to diesel spills, and suggest that the progression of diesel microbial degradation is performed by the cooperative system of the versatile obligate diesel-degrading and some general heterotrophic microorganisms in river diesel spills.