Salinity reduces coastal marsh respiration more than photosynthesis

Abstract

A paradigm in carbon cycling science predicts that sea-level rise will enhance carbon accumulation in an apparent negative carbon-climate feedback1,2. However, ecosystems exposed to combinations of stressors and subsidies – such as saltwater intrusion and sea-level rise – may adapt, transition to an alternative state, or experience a decline in functions, such as carbon storage, thereby altering their response trajectories to environmental changes3,4. Climate change is increasing salinity in coastal ecosystems worldwide yet the effects on ecosystem metabolism remain uncertain4-8. Here, we synthesized gross ecosystem productivity (GEP), ecosystem respiration [CO2 and CH4 (ERCO2 and ERCH4)], and net ecosystem productivity (NEP) from diverse coastal marshes exposed to experimental additions and observational gradients in salinity. Increases in salinity generally caused decreases in median GEP, ERCO2, and ERCH4 but increases in GEP and NEP from ~5 to 10 ppt. Increased saltwater intrusion can stimulate or stress wetlands based on relative exposure and acclimation to increased salinities, and we detected positive NEP where salinity increases had greater negative effects on ERCO2 and ERCH4 than GEP. Although increases in NEP are detectable at low salinities, saltwater intrusion and climate-driven disturbances may reduce carbon storage capacity of coastal ecosystems as productivity declines toward higher salinities.

The paleo-ecological application of mollusks in the calculation of saltwater encroachment and resultant changes in depositional patterns driven by the Anthropocene Marine Transgression

“…Increasing salinity triggers changes in: the distribution and type of plant communities (Ellison and Stoddart, 1991;Ellison, 1993;Ross et al, 2000), plant productivity (Blum and Roberts, 2009;Wilson et al, 2018;Charles et al, 2019), organic carbon storage (Neubauer et al, 2013;Doughty et al, 2016;Meeder et al, 2021) and sulfur availability (Sutter et al, 2014;Poulin et al, 2017;Chambers et al, 2019). The combined effects of these changes are a reduction in rates of vertical sediment accumulation, peat collapse, and the formation of inundation ponds in South Florida (Chambers et al, 2015;Meeder et al, 2017;Servais et al, 2019;Wilson et al, 2018;Kominoski et al, 2021). Ultimately, these changing patterns in sediment production and accumulation are preserved in the stratigraphic record (Meeder and Parkinson, 2018).…”