Can fine sediment addition promote carbon stabilization in coastal wetland soils? A laboratory experiment

Abstract

Scientists are increasingly exploring soil carbon (C) stabilization processes that protect soil organic C from microbial decomposition. Mineral-associated organic matter (MAOM) is considered one of the most protected pools of soil C, but remains understudied in wetland soils relative to upland soils. Using complementary intact soil core and bottle incubation studies, this research investigated how fine sediment addition, in the form of dredged sediment, impacts soil respiration and MAOM pools in coastal wetland soils that vary by soil organic matter (SOM) content and particle size. We hypothesized fine sediment additions would reduce soil respiration and increase MAOM pools, with the greatest response to fine sediment addition being in the high SOM soil. Contrary to our prediction, addition of fine sediments to high SOM intact soil cores did not change respiration rate, but CO₂ production rate decreased by 21% in low SOM cores, and the mass of MAOM-C increased by 23% after receiving fine sediment additions. In the bottle study of high SOM soils only, the response to fine sediment addition varied by initial soil particle size. Specifically, the largest soil particles (>2 mm) showed a 1727% increase in MAOM-C, which coincides with a 49% decrease in CH₄ production rate. Overall, soil C protection resulting from fine sediment addition differed by soil type and SOM texture, suggesting initial soil properties (e.g., existing mineral sediment content, nutrient availability, and degree of decomposition) influence C stabilization through fine sediment addition, and these properties should be considered when choosing potential coastal restoration sites.