[Ecosystem CO2 Exchange and Its Environmental Regulation of a Restored Wetland in the Liaohe River Estuary]

Abstract

Coastal wetlands are important carbon sinks， and they contribute to reducing the effects of global warming. This study used the eddy covariance method to detect the CO₂ flux in the restoration wetland of the Liaohe River estuary in 2021 and investigate the characteristics of ecosystem CO₂ exchange and its environmental control factors. The aim was to assess the carbon source/sink capacity of salt marshes in the restored area and to provide data support and theoretical basis for evaluating the effectiveness of ecological restoration projects. The study revealed "U" curves in spring and autumn， "V" curves in summer， and horizontal lines in winter for the average daily variation curve of net ecosystem CO₂ exchange （NEE） in the restored area. Its carbon sink efficiencies were -40.06， -63.62， 2.33， and 34.43 g·m^-2 in the spring， summer， autumn， and winter， respectively. In the restored area， the daily cumulative variation in NEE was "V" shaped， and the monthly cumulative changes in NEE， ecosystem respiration （R_eco）， and gross primary productivity （GPP） were obviously different. Photosynthetically active radiation （PAR） was an important regulation factor of daytime NEE in the restored area in 2021， and they displayed a rectangular hyperbolic relationship. PAR could explain 53% of the variation in the daytime NEE. Air temperature （T_a） was the main control factor of R_eco，night， and there was an exponential relationship between them. When T_a < 5.5 ℃， the temperature sensitivity of ecosystem respiration （Q₁₀） was 2.19， and T_a could explain 42% of the variation in the R_eco，night； when T_a ≥ 5.5 ℃， the Q₁₀ was 1.81， and T_a could explain 51% of the variation in the R_eco，night. Additionally， there were significant linear negative correlations between NEE and both soil water content （SWC） and vapor pressure deficit （VPD）， whereas NEE was not significantly correlated with soil temperature （T_s） or relative humidity （RH）. In 2021， the restored wetland in the Liaohe River estuary acted as a CO₂ sink， and the total net carbon sequestration was -66.89 g·m^-2. The restored salt plays a role as an important carbon sink and has long-term carbon sequestration potential.

Keywords: CO2 fluxes; coastal blue carbon; eddy covariance （EC）; net ecosystem CO2 exchange; salt marsh; wetland restoration.