Ecological parameter reductions, environmental regimes, and characteristic process diagram of carbon dioxide fluxes in coastal salt marshes

Abstract

We investigated the ecological parameter reductions (termed “similitudes”) and characteristic patterns of the net uptake fluxes of carbon dioxide (CO2) in coastal salt marshes using dimensional analysis method from fluid mechanics and hydraulic engineering. Data collected during May–October, 2013 from four salt marshes in Waquoit Bay and adjacent estuary, Massachusetts, USA were utilized to evaluate the theoretically-derived dimensionless flux and various ecological driver numbers. Two meaningful dimensionless groups were discovered as the light use efficiency number (LUE = CO2 normalized by photosynthetically active radiation) and the biogeochemical number (combination of soil temperature, porewater salinity, and atmospheric pressure). A semi-logarithmic plot of the dimensionless numbers indicated the emergence of a characteristic diagram represented by three distinct LUE regimes (high, transitional, and low). The high regime corresponded to the most favorable (high temperature and low salinity) condition for CO2 uptake, whereas the low regime represented an unfavorable condition (low temperature and high salinity). The analysis identified two environmental thresholds (soil temperature ~ 17 °C and salinity ~ 30 ppt), which dictated the regime transitions of CO2 uptake. The process diagram and critical thresholds provide important insights into the CO2 uptake potential of coastal wetlands in response to changes in key environmental drivers.

Salt Marsh Light Use Efficiency is Driven by Environmental Gradients and Species‐Specific Physiology and Morphology

“…Measurements of net photosynthesis have shown optimum temperatures for S. alterniflora between 30°C and 35°C (Giurgevich & Dunn, 1979) and <30°C for J. roemerianus (Giurgevich & Dunn, 1978). Ishtiaq and Abdul‐Aziz (2020) found optimal soil temperatures for S. alterniflora LUE (NEE/PAR) above 17°C in gas chamber experiments. Also, productivity for S. alterniflora increases with warming temperatures (Charles & Dukes, 2009; Kirwan & Blum, 2011).…”

“…In the marsh literature, these differences are less clear due to the lack of canopy level measurements. Leaf‐level light response curves for S. alterniflora in a Virginia marsh have shown photo‐saturation effects (Kathilankal, Mozdzer, Fuentes, McGlathery, et al., 2011), while Ishtiaq and Abdul‐Aziz (2020) found no saturation of NEE to incident PAR in closed gas chamber measurements. Discrepancies in the relationships between production and radiation can be scale‐dependent across biome types, and comparisons between leaf‐level and canopy level LUE APAR are difficult (Medlyn, 1998).…”

“…Studies of salt marsh LUE are sparse in the literature (Feagin et al., 2020; Ishtiaq & Abdul‐Aziz, 2020; Knox, Windham‐Myers, et al., 2018; M. Wu et al., 2015). However, improvements have been made adapting satellite GPP models to tidal marshes by estimating LUE through vegetation indices (M. Wu et al., 2015), parameterizing LUE scalars for tidal wetlands (Feagin et al., 2020), and creating simplified tide‐filtered vegetation indices to model GPP (Tao et al., 2018).…”

“…Studies of salt marsh LUE are sparse in the literature (Feagin et al, 2020;Ishtiaq & Abdul-Aziz, 2020;Knox, Windham-Myers, et al, 2018;M. Wu et al, 2015).…”