## 3 Results and Discussion
### Carbon Exchange between Natural and Managed Mangroves
The proportion of CH\({}_{4}\) to NEE is lower from mangroves in Hongkong and Yunxiao, China (Table 2), and resulted in a cooling effect with GWP100 of \(-\)2812\(--\)2357 eq-CO\({}_{2}\) m\({}^{-2}\) a\({}^{-1}\) and \(-\)3830 eq-CO\({}_{2}\) m\({}^{-2}\) a\({}^{-1}\), respectively (Table 2). However, the CH\({}_{4}\) fluxes from mangroves in Sundarban, India, and Nansha, China, were relatively high and contributed to a warming effect with GWP100 values of 1204 eq-CO\({}_{2}\) m\({}^{-2}\) a\({}^{-1}\) and 151-1283 eq-CO\({}_{2}\) m\({}^{-2}\) a\({}^{-1}\), respectively (Table 2). The CH\({}_{4}\) fluxes depend on the biogeochemical processes of CH\({}_{4}\) production, oxidation, and emission, which are influenced by substrate availability [67], air temperature [68; 69], water table depth [56], salinity [60; 70] etc. Compared to the intermittently flooded mangrove sites in Fujian and Hong Kong, the mangroves in the Nansha mangrove park perennially flood by manual control, which may facilitate CH\({}_{4}\) emissions [21]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sites** & **NEE** & **GPP** & **Re** & **CH\({}_{4}\)** & **GWP100** & **References** \\ \hline \multicolumn{8}{c}{Natural} \\ \hline Hongkong, China * & \(-\)758 to \(-\)890 & \(-\)2741 to \(-\)2827 & 1983 to 1937 & 11.3 to 12.1 & \(-\)2812 to \(-\)2357 & [24; 47] \\ Yunxiao\_1, China * & \(-\)540 to \(-\)857 & \(-\)1762 to \(-\)1919 & 1238 to 1337 & – & – & [23] \\ Yunxiao\_2, China * & \(-\)1076 & \(-\)2197 & 1121 & 3.1 & \(-\)3830 & [13] \\ Gaoqiao, China * & \(-\)692 to \(-\)738 & \(-\)1698 to \(-\)1890 & 1027 to 1214 & – & – & [23] \\ Sundarban, India * & \(-\)249 & \(-\)1271 & 1022 & 56.7 & 1204 & [71; 72] \\ Pichavaram, India * & \(-\)345 & \(-\)2305 & 1072 & – & – & [73] \\ Quintana, Mexico * & \(-\)709 & \(-\)2473 & 1764 & – & – & [74] \\ Florida, USA * & \(-\)1170 & \(-\)2233 & 1063 & – & – & [40] \\ Hinchinbrook, Australia ** & \(-\)1621 & \(-\)3703 & 2082 & – & – & [48] \\ Missionary Bay, Australia ** & \(-\)1171 & \(-\)2940 & 1769 & – & – & [48] \\ \hline \multicolumn{8}{c}{Restored} \\ \hline Leizhou, China * & \(-\)1105 & \(-\)2009 & 904 & – & – & [65] \\ Sawi Bay, Thailand ** & \(-\)1023 & \(-\)4504 & 3481 & – & – & [48] \\ Nansha, China * & \(-\)195 to 82 & \(-\)1195 to \(-\)1527 & 1143 to 1703 & 23.2 to 26.3 & 151 to 1283 & This study \\ (14-year-old) & & & & & & \\ \hline \multicolumn{8}{c}{Disturbed} \\ \hline Matang, Malaysia ** & \(-\)745 & \(-\)4153 & 3408 & – & – & [48] \\ Beihai, China * & \(-\)106 & \(-\)341 & 235 & – & – & [75] \\ \hline \multicolumn{8}{c}{Note: GWP100 (eq-CO\({}_{2}\) m\({}^{-2}\) year\({}^{-1}\)) is the global carbon potential induced by CH\({}_{4}\) and CO\({}_{2}\) for the time horizon of 100 years in unit of CO\({}_{2}\), which were calculated based on the equation GWP100 = 28 \(\times\) CH\(4\times\) 16/12 + NEE \(\times\) 44/12. The units of NEE, GPP and CH\({}_{4}\) are g C m\({}^{-2}\) a\({}^{-1}\). * The annual fluxes were based on the eddy covariance technique. ** The annual fluxes were based on the summation method.** \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of the NEE, GPP, Re, CH\({}_{4}\), and GWP100 values of natural and managed mangroves.