## 4 Discussion  
In recent years, studies have reported that freshwater lakes are important natural sources of CH\({}_{4}\) emission into the atmosphere [2; 32]. In this study, the CH\({}_{4}\) emission flux shows very large temporal variations at Hong Lake, with a range from 0.10 to 59.75 mg m\({}^{-2}\) h\({}^{-1}\) during 2021-2022 (Figure 4). The CH\({}_{4}\) emissions in Hong Lake were high and comparable to Dong Lake of the largest Chinese urban lake (0.06-5.53 mg m\({}^{-2}\) h\({}^{-1}\)) [33] and the largest shallow eutrophic lake Taihu in the Chinese subtropical region (0.006-0.37 mg m\({}^{-2}\) h\({}^{-1}\) for the diffusion emission) [34]. This could be attributed to the three pathways of CH\({}_{4}\) release, namely: diffusion, ebullition, and plant transport. For example, [PERSON] et al [33] highlighted that there was no grown vegetation in their observation site, while [PERSON] et al. [34] indicated that the CH\({}_{4}\) flux only included diffusion. Generally, ebullition is a major pathway for CH\({}_{4}\) release from lake sediments to the atmosphere [35]. However, our results did not measure the ebullition of CH\({}_{4}\), which could limit the analysis in the three pathways of CH\({}_{4}\) emission. [PERSON] et al. [36] indicated that the macrophyte-covered littoral zones were the \"hotspots\" of CH\({}_{4}\) emission in Lake Taihu, ranging from \(-1.7\) to 131 mg m\({}^{-2}\) h\({}^{-1}\) from August 2003 to August 2004, emphasizing the importance of vegetation for the CH\({}_{4}\) emission. In addition, [PERSON] et al. [37] also reported that the CH\({}_{4}\) emission in the swamps in the Okavango Delta, Botswana, varied between 0.24 and 293 mg m\({}^{-2}\) h\({}^{-1}\), and indicated that high CH\({}_{4}\) emission could probably be regulated by high temperature in the tropical wetlands. Hence, the CH\({}_{4}\) emission fluxes in the present study were significantly higher than the results of [PERSON] et al. [33] and [PERSON] et al. [34], but significantly lower than the results of [PERSON] et al. [36] and [PERSON] et al. [37]. The CH\({}_{4}\) emission fluxes measured in Hong Lake were within the range reported for other subtropical/tropical wetlands. The results showed an obvious difference in the CH\({}_{4}\) emission in the lake in different regions. In our study, the maximal CH\({}_{4}\) emission occurred in the summer (July and August) and autumn (September), which is consistent with previous studies [36; 38; 39]. However, there was a significant difference in the temporal variation of CH\({}_{4}\) emission between the KKs and NNs, e.g., maximal CH\({}_{4}\) emissions in July and August for the KKs, while in September for the NNs (Figure 4). The significant difference of CH\({}_{4}\) emission was ascribed to ecological determinants, e.g., climate (temperature), water depth, and vegetation types. During two growing seasons, we found that CH\({}_{4}\) emission fluxes increased exponentially with the air and water temperatures (Figure 6a,b). The results are in agreement with the observations in previous studies, which revealed that temperature could obviously affect the seasonal CH\({}_{4}\) emission in lakes and peatlands [33; 38; 40; 41]. It is well-established that methanogenic microbial communities of lake sediments increase exponentially with temperature between 2 \({}^{\circ}\)C and 30 \({}^{\circ}\)C [42; 43; 44]. This could explain the maximum CH\({}_{4}\) emission in July and August in the KKs (Figure 4); namely, temperature was a key factor on the CH\({}_{4}\) emission for the open water. In addition, we analyzed the sensitivity of CH\({}_{4}\) emission fluxes to water temperature. The \(Q_{10}\) was 3.94, suggesting that the CH\({}_{4}\) emission  
Figure 7: The correlation between CH\({}_{4}\) emission fluxes and DO concentration in Hong Lake. from Hong Lake will continue to strengthen under the scenarios of future climate change, thus contributing to climate warming.