Modeling ecosystem respiration, gross primary productivity, and net ecosystem exchange of a Southern Hemisphere salt marsh

NAHUEL BAUTISTA ; MARIA I GASSMANN ; CLAUDIO F. PÉREZ

Encuentro; 2020 AmeriFlux Annual Meeting; 2020

Natural land conservation can mitigate the effects of climate change by removing greenhouse gases from the atmosphere, which has motivated the study of methane and carbon dioxide (CO2) fluxes in different ecosystems. Among many environments, marshes have shown a great capacity for CO2 sequestration and biomass production. In this research, carbon and biomass budgets were estimated for a salt marsh located in southeastern Buenos Aires (Argentina). Carbon dioxide fluxes were measured from March to December 2018 with the eddy covariance technique. After filtering poor turbulence periods, and evaluating the quality of the measured data, the series presented about 50% of missing values. Different gap-filling techniques, including Lloyd & Taylor and Q10 models for ecosystem respiration (Reco), the Michaelis-Menten hyperbolic model for Gross Primary Productivity (GPP), and Look-Up tables, all combined with Mean Diurnal Variation, were evaluated. Reco models showed better estimates with near-surface soil temperature as a predictor variable, but they underestimated and overestimated respiration values for high and low temperatures respectively. GPP models parameters followed an annual cycle with lower and higher Photosynthesis Saturation Rate in winter and spring respectively. Deterministic models presented higher mean bias and absolute error than Look-Up tables when estimating half-hourly Net Ecosystem Exchange values. Regardless of the methodology used, the CO2 budget was 5.5 ton ha-1 from May to December 2018, while conclusive values were not met for March and April, due to the excessive amount of missing data (more than 85%). On the other hand, the biomass produced during the study showed an increasing linear relationship with gross primary production, which agrees with previous results for another site in the marsh.