Document Type

Article

Journal/Book Title/Conference

Journal of Geophysical Research: Biogeosciences

Volume

130

Issue

7

Publisher

Wiley-Blackwell Publishing, Inc.

Publication Date

7-10-2025

First Page

1

Last Page

13

Abstract

Sea level rise and more frequent and larger storms will increase saltwater flooding in coastal terrestrial ecosystems, altering soil-atmosphere CO2 and CH4 exchange. Understanding these impacts is particularly relevant in high-latitude coastal soils that hold large carbon stocks but where the interaction of salinity and moisture on greenhouse gas flux remains unexplored. Here, we quantified the effects of salinity and moisture on CO2 and CH4 fluxes from low-Arctic coastal soils from three landscape positions (two Wetlands and Upland Tundra) distinguished by elevation, flooding frequency, soil characteristics, and vegetation. We used a full factorial laboratory incubation experiment of three soil moisture levels (40%, 70%, or 100% saturation) and four salinity levels (freshwater, 3, 6, or 12 ppt). Salinity and soil moisture were important controls on CO2 and CH4 emissions across all landscape positions. In saturated soil, CO2 emissions increased with salinity in the lower elevation landscape positions but not in the Upland Tundra soil. Saturated soil was necessary for large CH4 emissions. CH4 emissions were greatest with low salinity, or after 11 weeks of incubation when SO42− was exhausted allowing for methanogenesis as the dominant mechanism of anaerobic respiration. In partially saturated soil, greater salinity suppressed CO2 production in all soils. CH4 fluxes were overall quite low, but increased between 3 and 6 ppt in the Tundra. In the future, a small increase in floodwater salinity may increase CO2 production while suppressing CH4 production; however, where water is impounded, CH4 production could become large, particularly in the landscapes most likely to flood.

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