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Abstract Terrestrial organic matter (tOM) plays a critical role in aquatic ecosystems, influencing carbon processes and greenhouse gas emissions. Here, we investigate the impact of tOM on methane production in littoral and pelagic sediments from the Mississippi River headwaters using a microcosm approach. Contrary to our expectations, tOM addition universally increased methane production across lentic sediments, with no significant difference between littoral and pelagic zones. Methane production was influenced by select sediment microorganisms, primarily methanogens and lignocellulose degrading bacteria, which responded similarly across different sediment habitats. The study highlights the role of cytochrome-containing methanogens and their syntrophic relationships with fermentative bacteria, emphasizing the significance of microbial community structure in sediment methane dynamics. Our findings suggest that increasing tOM loads to freshwater systems could have broader implications for methane emissions, driven by specific microbial interactions. Author Contribution StatementHMS and TLH conceived the study and obtained the funds. HMS led fieldwork and microcosm set-up. HMS and LAD analyzed gas samples and HMS performed the data analysis and graphical representation of the results. HMS wrote the first draft of the manuscript, and all authors contributed significantly to the preparation of the final draft. Scientific Significance StatementAs human activities and climate change increase the amount of organic material entering lakes and rivers, understanding the effects this has on greenhouse gas emissions is crucial. Our study reveals that adding terrestrial organic matter to freshwater sediments universally boosts methane production, a potent greenhouse gas. Through the exploration of microbial communities responsible for this process, our research highlights how changes in terrestrial organic matter export to aquatic systems could increase methane emissions from sediments. Data Availability StatementAdditional Supporting Information can be found in the online version of this article, including an extended version of methods and supplementary tables. Sequencing data associated with this paper is available on NCBI, BioProject PRJNA1164797. 

The microbial communities of lake sediments have the potential to serve as valuable bioindicators and integrators of watershed land-use and water quality; however, the relative sensitivity of these communities to physio-chemical and geographical parameters must be demonstrated at taxonomic resolutions that are feasible by current sequencing and bioinformatic approaches. The geologically diverse and lake-rich state of Minnesota (USA) is uniquely situated to address this potential because of its variability in ecological region, lake type, and watershed land-use. In this study, we selected twenty lakes with varying physio-chemical properties across four ecological regions of Minnesota. Our objectives were to (i) evaluate the diversity and composition of the bacterial community at the sediment-water interface and (ii) determine how lake location and watershed land-use impact aqueous chemistry and influence bacterial community structure. Our 16S rRNA amplicon data from lake sediment cores, at two depth intervals, data indicate that sediment communities are more likely to cluster by ecological region rather than any individual lake properties ( e . g ., trophic status, total phosphorous concentration, lake depth). However, composition is tied to a given lake, wherein samples from the same core were more alike than samples collected at similar depths across lakes. Our results illustrate the diversity within lake sediment microbial communities and provide insight into relationships between taxonomy, physicochemical, and geographic properties of north temperate lakes.