A stream-to-sea experiment reveals inhibitory effects of freshwater residency on organic-matter decomposition in the sea

Abstract

One billion tons of carbon are annually transported to the global ocean, and the fate of this carbon hinges notonly on marine processing rates, but also on freshwater processing during downstream transport. Using acotton-strip assay, we assessed the decomposition of organic matter in marine and freshwater sites and simu-lated its downstream transport from freshwater to the sea by translocating cotton strips approximately half-waythrough the freshwater incubation period. We observed faster decomposition in the sea relative to the streamand interestingly, an inhibitory effect of stream incubation on subsequent decomposition in the sea. Totalnitrogen content and∂15N in the cotton strips were both greater in the strips incubated entirely in the sea,suggesting greater microbial activity in the marine habitat. Our results lend needed insights into global carboncycling, the factors that govern organic-carbon processing, and highlight the importance of connections thatexist among some of Earth’s major ecosystems