# Characteristics of Carbon Fluxes and Their Environmental Control in Chenhu Wetland, China
## 3 Results and Discussion
### Dynamics of CO\({}_{2}\) Flux over Various Temporal Scales
#### 3.2.2 Seasonal Variations in NEE  
As illustrated in Figure 4a, the NEE exhibited significant negative values from April to September, particularly during the summer months. In contrast, NEE values predominantly approached zero during the winter, early spring, and late autumn, a phenomenon largely attributable to the surface vegetation. The mean monthly total NEE was recorded at \(-\)1.77 molCO\({}_{2}\cdot\)m\({}^{-2}\cdot\)month\({}^{-1}\), with considerable fluctuations ranging from \(-\)7.78 molCO\({}_{2}\cdot\)m\({}^{-2}\cdot\)month\({}^{-1}\) in May to 2.32 molCO\({}_{2}\cdot\)m\({}^{-2}\cdot\)month\({}^{-1}\) in January. Throughout the growing season, spanning from April to September, the cumulative monthly respiratory losses of CO\({}_{2}\) reached a peak of 34.06 molCO\({}_{2}\cdot\)m\({}^{-2}\), while approximately 60.65 molCO\({}_{2}\cdot\)m\({}^{-2}\) was sequestered as GPP. Consequently, the Chenhu wetland functioned as a net carbon sink, with a total of 26.59 molCO\({}_{2}\cdot\)m\({}^{-2}\) (Figure 4b). Figure 3: Diurnal variation of NEE in the Chenhu Wetland during 2022 ((a) growing season; (b) non-growing season). During the first half of 2022, the value of \(\mathrm{R_{eco}}\) generally exhibited a predominantly upward trajectory, peaking in July at a maximum of 6.84 molCO\({}_{2}\cdot\)m\({}^{-2}\cdot\)month\({}^{-1}\). Following this peak, a declining trend was observed, with \(\mathrm{R_{eco}}\) reaching a minimum of 1.18 molCO\({}_{2}\cdot\)m\({}^{-2}\cdot\)month\({}^{-1}\) by December. Concurrently, the GPP values increased progressively alongside the growth of vegetation, such as reeds, from the onset of the growing season, achieving a peak of 12.37 molCO\({}_{2}\cdot\)m\({}^{-2}\cdot\)month\({}^{-1}\) in May, followed by a subsequent decline. The lowest recorded GPP value occurred in January, at 0.03 molCO\({}_{2}\cdot\)m\({}^{-2}\cdot\)month\({}^{-1}\). In 2022, the Chenhu wetland ecosystem demonstrated CO\({}_{2}\) absorption during the growing season, amounting to 26.59 molCO\({}_{2}\cdot\)m\({}^{-2}\), while exhibiting CO\({}_{2}\) emissions during the non-growing season, totaling 5.39 molCO\({}_{2}\cdot\)m\({}^{-2}\). The annual NEE, \(\mathrm{R_{eco}}\), and GPP values were recorded at \(-\)21.20, 49.61, and 70.81 molCO\({}_{2}\cdot\)m\({}^{-2}\), respectively. The annual NEE value is closely aligned with the average NEE of Asian wetlands, which is \(-\)19.68 molCO\({}_{2}\cdot\)m\({}^{-2}\cdot\)year\({}^{-1}\)[32], suggesting that the Chenhu wetland functions predominantly as a carbon sink. The overall carbon uptake of the ecosystem is influenced by the interplay between photosynthetic assimilation and the efflux of ecosystem respiration [2]. Furthermore, the ratio of \(\mathrm{R_{eco}}\) to GPP serves as an indicator of the relative contributions of the carbon exchange processes to the total annual exchange [33]. The annual \(\mathrm{R_{eco}}\)/GPP ratio for the Chenhu wetland was calculated to be 0.70, which is lower than the average \(\mathrm{R_{eco}}\)/GPP ratio of 0.83 observed in the FLUXNET ecosystem [34]. Consequently, the Chenhu wetland ecosystem is characterized by relatively low ecosystem respiration and a high net uptake of CO\({}_{2}\) through plant photosynthesis, resulting in significant CO\({}_{2}\) storage within the wetland ecosystem throughout the carbon exchange process. The carbon exchange dynamics within wetland ecosystems demonstrate considerable spatial heterogeneity, which can be attributed to variations in wetland types, climatic conditions, geographical factors, and management practices [35]. When compared to other subtropical wetlands in China, as depicted in Figure 5 and detailed in Table 1, the annual CO\({}_{2}\) absorption of the Chenhu wetland is marginally higher than that of the Chongxi wetland (18.75 molCO\({}_{2}\cdot\)m\({}^{-2}\)) [36] and the Beihai wetland (19.48 molCO\({}_{2}\cdot\)m\({}^{-2}\)) [31].