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 not only on marine processing rates, but also on freshwater processing during downstream transport. Using a cotton‐strip assay, we assessed the decomposition of organic matter in marine and freshwater sites and simulated its downstream transport from freshwater to the sea by translocating cotton strips approximately half‐way through the freshwater incubation period. We observed faster decomposition in the sea relative to the stream and interestingly, an inhibitory effect of stream incubation on subsequent decomposition in the sea. Total nitrogen 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 carbon cycling, the factors that govern organic‐carbon processing, and highlight the importance of connections that exist among some of Earth's major ecosystems.

Intrinsic and extrinsic drivers of organic matter processing along phosphorus and salinity gradients in coastal wetlands

“…and salinity as drivers of breakdown. This finding supports previous studies that have shown salinity increasing the breakdown of litter (Frainer & Tiegs, 2022;Hu et al, 2019;Stagg et al, 2018;Trevathan-Tackett et al, 2021). Similarly, our data show that in addition to breakdown rates, salinity has a strong effect on the nutrient makeup of litter, even stronger than environmental chemistry, but breakdown rates were only affected by litter chemistry in a single species.…”