## 2 Materials and Methods
### Flux and Meteorological Measurements  
Based on the vegetation and wind patterns, a 5-m flux tower was installed in the center of the wetland park in 2019 (Figure 1). As the mangrove stands grew, the tower was adjusted to 10 m in June 2020. An eddy covariance (EC) system was mounted on the top of the tower. The system consisted of a close-path infrared gas analyzer (GGA, ABB-Los Gatos Research, Mountain View, CA, USA) and a three-dimensional sonic anemometer (WindMaster Pro, Gill Instruments, Lymington, UK). The H\({}_{2}\)O, CO\({}_{2}\), and CH\({}_{4}\) flux measurements were recorded by a CR3000 datalogger at a 10 Hz frequency. The environmental variables were measured above the canopy and averaged over 30 min on a CR1000 datalogger. These measurements include air temperature (T\({}_{\rm a}\)) and relative humidity (RH) (HMP155, Vaisala Inc., Helsinki, Finland), wind speed (WS), and wind direction (WD) (03002, RM Young, Inc. Traverse City, MI, USA). Soil temperature (T\({}_{\rm s}\)), soil moisture (SWC), and soil salinity (Hydra Prob II, Campbell Scientific Inc., Logan, UT, USA) were measured 5 cm below the soil surface. A water-level probe (CS456, Campbell Scientific Inc., Logan, UT, USA) was installed below the water surface inside a 1-m tube, and the water level and water temperature were measured every 30 min. Data were collected from 2019 to 2022 in this study.  
Additional meteorological data, including rainfall and sunshine duration, were obtained from a nearby (within 1 km) standard meteorological station (Shijuchong). The solar radiation data were collected from the Guangzhou national meteorological station (23\({}^{\circ}\)08\({}^{\prime}\) N, 113\({}^{\circ}\)19\({}^{\prime}\) E). The 4-day leaf area index (LAI) data from 2019 to 2022 were extracted from the MCD15A3H product (250 m) (available online at [[http://www.glass.umd.edu/LAI/MODIS/250m/](http://www.glass.umd.edu/LAI/MODIS/250m/)]([http://www.glass.umd.edu/LAI/MODIS/250m/](http://www.glass.umd.edu/LAI/MODIS/250m/)), accessed on 20 January 2023). The data were first quality assured based on the product quality control (QC) flag, and were then excluded for outliers considering the weak LAI seasonality of mangroves. Thereby, the low-quality (QC > 32 or LAI < 0.2) LAI data were removed. The preprocessed LAI data were then linearly interpolated to a daily timescale, and the time-series data were smoothed based on a Savitzky-Golay filtering approach [28]. The filtering used cubic polynomials to reconstruct LAI data in a 91-day (3-month) time window. The specific time window was selected as it produced low-noise and plausible LAI time series [28].  
Figure 1: A illustration of the study site and the EC system including **(a)** the location of the Nansha Wetland Park, **(b)** the location of the EC system, and **(c)** the footprint of 90% flux source area for EC observation (blue for the 5-m tower, red for the 10-m tower).  
The footprints of flux observation varied with the heights of the tower. The footprint of the 5-m tower ranged from 100 m to 200 m [29], which covered approximately 60% of the mangrove stands and 40% of the open waters and fish ponds. The footprint extended to the surrounding of 500-600 m when the tower was raised to a height of 10 m, with an underlying surface of 50% mangrove stands and almost 50% open waters and fish ponds.