Greenhouse gas emissions from coastal freshwater wetlands in Veracruz Mexico: Effect of plant community and seasonal dynamics

Wetlands play an important role in modulating atmospheric concentrations of Greenhouse Gases (GHGs), such as methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2). Despite the fact that similar to 30% of wetlands in the world occur in tropical latitudes, little is known about GHG emissions from these ecosystems and the variables that control such emissions. We investigated the CH4, N2O and CO2 emissions in tropical freshwater marshes (FM) and swamps (FS) on the coastal plain of Veracruz, Mexico. GHGs were measured every two months using the closed chamber technique from April 2010 to February 2012 (CH4 and N2O) and during the last year for CO2. The ranges of the emissions were 20-2000 mg C-CH4 m(-2) d(-1), -2-16 mg N-N2O m(-2) d(-1) and 0.5-18 g C-CO2 m(-2)d(-1). There were not significant differences in the emissions between FM and FS (P = 0.314, 0.528 and 0.213 for CH4, N2O, and CO2, respectively). However, significant differences (P < 0.001) in CH4 and CO2 emissions were found in the different seasons. During the rainy and windy seasons, the water level was higher than during dry season, this enhanced reduced conditions in the soils and caused significantly higher (P < 0.05) CH4 emissions (>364 mg m(-2) d(-1)) than during dry season (<150 mg m(-2) d(-1)). The opposite was observed for CO2 emissions, during dry season, wetland soils were more aerobic and CO2 fluxes increased (FM: 11 +/- 2, FS: 12 +/- 1 g m(-2) d(-1)). N-N2O emissions (FM: 1.5 +/- 0.96, FS: 2.4 +/- 0.9 mg m(-2) d(-1)) were similar during different climatic season (P = 0.056). Based on the global warming potential, CH4 was the main contributor to total GHGs emission during the rainy and windy seasons (75-93%), while CO2 was predominant during the dry season (79.6%) and N2O contributed with less than 7% in the three seasons. Water level and redox potential were found to be main factors influencing GHG emissions in these wetlands. (C) 2015 Elsevier Ltd. All rights reserved.