Effect of degradation of a black mangrove forest on seasonal greenhouse gas emissions.

Abstract

Mangroves play an essential role in the global carbon cycle. However, they are highly vulnerable to degradation with little-known effects on greenhouse gas (GHG) emissions. This study compared seasonal soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes from a black mangrove (Avicennia germinans) forest in the Tampamachoco coastal lagoon, Veracruz, Mexico, in areas subjected to different degrees of environmental degradation (full canopy, transitional and dead mangrove), caused by hydrological perturbation. Furthermore, we aimed at determining the environmental factors driving seasonal fluxes. There was a combined effect of seasonality and degradation on CH4 fluxes, highest during the rainy season in the dead mangrove (0.93 ± 0.18 mg CH4 m-2 h-1). CO2 fluxes were highest during the dry season (220 ± 23 mg CO2 m-2 h-1), with no significant differences among degradation levels. N2O fluxes did not vary among seasons or degradation levels (- 3.8 to 2.9 mg N2O m-2 h-1). The overall CO2-eq emission rate was 15.3 ± 2.7 Mg CO2-eq ha-1 year-1, with CO2 as the main gas contributing to total emissions. The main factors controlling CH4 fluxes were seasonal porewater salinity and the availability of NO2-, NO3-, and SO4-2 in the soil, favored by high water level and temperature in the absence of pneumatophores. The main determining factors controlling CO2 fluxes were water level, porewater redox potential, and soil Cl- and SO4-2 concentration. Finally, N2O fluxes were related to NO2-, NO3-, and SO4-2 soil concentrations. This study contributes to improving the knowledge of soil GHG fluxes dynamics in mangroves and the effect of degradation of these ecosystems on the coastal biogeochemical cycles, which may bring important insights for assessing accurate ways to mitigate climate change protecting and restoring these ecosystems.