Changes in microbial community structure and carbon cycling due to anthropogenic sediment resuspension

Bottom trawling is a widespread anthropogenic activity that disturbs coastal sediments, releasing organic and inorganic matter into the water column and altering biogeochemical and microbial dynamics. In this study, we examined how repeated resuspension of the upper 5 cm of sediments influences organic matter dynamics, nutrient cycling, microbial physiology and diversity in the overlying water column. Each resuspension event released organic carbon and nutrients into the water column, initially dominated by particulate forms. These inputs clearly stimulated bacterial production, indicating rapid degradation of labile organic matter. Over successive resuspensions events, the amount of organic carbon release declined, suggesting progressive depletion of reactive sediment pools. Concurrently, nitrogen and phosphorus pools shifted from organic to inorganic forms, reflecting ongoing microbial organic matter degradation. Resuspension also changed the microbial community composition by introducing sediment-associated taxa, mainly sulphur-cycling groups such as Desulfobacterales, into the overlying water column. However, the water column bacterial community consistently returned to its initial structure over time. Overall, our findings show that repeated sediment disturbance enhances microbial activity and accelerates organic matter turnover, providing new insights into the ecological impacts of bottom trawling and sediment disturbance.