The　characteristics　of　dissolved　organic　matter　in　river　sediments,　affected　by　microorganisms,　are　of　great　significance　to　water　management　strategies.　Based　on　three-dimensional　excitation　and　emission　matrix　fluorescence,　ultravioletevisible　spectroscopy,　and　high-throughput　sequencing　technology,　this　study　jointly　analyzed　the　composition　and　transformation　mechanisms　of　dissolved　organic　matter　as　well　as　the　microbial　community　structure　in　sediments　of　the　Beiyun　River,　the　main　river　within　a　basin　with　extreme　water　shortages.　Moreover,　we　evaluated　N　and　P　contents　in　sediments　to　identify　parameters　to　reflect　potential　eutrophication　risks.　Our　results　demonstrated　that　the　content　of　dissolved　organic　matter　in　sediments　was　between　30.2　and　49.9　g/kg　in　the　Tongzhou　area　of　the　Beiyun　River.　Humic　substances　were　the　largest　components　of　dissolved　organic　matter　in　the　sediments,　followed　by　protein-like　substances　and　soluble　microbial　byproducts.　Furthermore,　the　proportion　of　humic　matter　decreased　from　upstream　to　downstream.　The　proportion　of　carbonyl,　carboxyl,　hydroxyl,　and　ester　substituents　on　the　aromatic　structures　of　dissolved　organic　matter　was　significantly　higher　in　the　upstream,　whereas　the　proportion　of　substances　with　aliphatic　chain　substituents　on　their　aromatic　structures　was　relatively　low.　The　variation　in　downstream　sediment　microbial　communities　was　much　greater　than　that　in　the　upstream　(analyzed　at　the　phylum　level).　Proteobacteria　was　the　most　abundant　phylum　(47.97%),　which　was　closely　related　to　the　aromaticity　of　the　dissolved　organic　matter　in　sediments.　The　N　and　P　contents　in　the　sediments　of　the　Beiyun　River　were　high　and　exhibited　active　transformation.　The　maximum　fluorescence　intensity　of　fulvic-acid-like　components　in　the　sediments　[F-max(C4)]　can　indirectly　reflect　the　potential　risk　of　eutrophication　in　the　Beiyun　River.　Therefore,　our　results　provide　a　theoretical　basis　for　the　assessment　of　water　quality　and　pollution　control　in　the　Beiyun　River　and　other　water-deficient　regions　worldwide.　(C)　2020　Elsevier　Ltd.　All　rights　reserved.