Soil Carbon Stocks Vary Across Geomorphic Settings in Australian Temperate Tidal Marsh Ecosystems
Connor Gorham, Paul S. Lavery, Jeffrey J. Kelleway, Cristian Salinas, Óscar Serrano
Abstract
Abstract Tidal marshes rank among the ecosystems with the highest capacity to sequester and store organic carbon (C org ) on earth. To inform conservation of coastal vegetated ecosystems for climate change mitigation, this study investigated the factors driving variability in carbon storage. We estimated soil C org stocks in tidal marshes across temperate Western Australia and assessed differences among geomorphic settings (marine and fluvial deltas, and mid-estuary) and vegetation type ( Sarcocornia quinqueflora and Juncus kraussii ) linked to soil biogeochemistry. Soil C org stocks within fluvial and mid-estuary settings were significantly higher (209 ± 14 and 211 ± 20 Mg C org ha −1 , respectively; 1-m-thick soils) than in marine counterparts (156 ± 12 Mg C org ha −1 ), which can be partially explained by higher preservation of soil C org in fluvial and mid-estuary settings rich in fine-grained (< 0.063 mm) sediments (49 ± 3% and 47 ± 4%, respectively) compared to marine settings (23 ± 4%). Soil C org stocks were not significantly different between S. quinqueflora and J. kraussii marshes (185 ± 13 and 202 ± 13 Mg C org ha −1 , respectively). The higher contribution of tidal marsh plus supratidal vegetation in fluvial (80%) and intermediate (76%) compared to marine (57%) settings further explains differences in soil C org stocks. The estimated soil C org stocks in temperate Western Australia’s tidal marshes (57 Tg C org within ~ 3000 km 2 extent) correspond to about 2% of worldwide tidal marsh soil C org stocks. The results obtained identify global drivers of soil C org storage in tidal marshes and can be used to target hot spots for climate change mitigation based on tidal marsh conservation.