Methane Cycling and Flux in Mangrove Ecosystems: A Comparison of Natural and Impacted Coastal Lagoons on the Yucatan Peninsula, Mexico

Tropical and subtropical wetlands are thought to be the dominant natural source of methane to the atmosphere, and mangrove ecosystems cover approximately 170,000 square kilometers of tropical and sub-tropical land, and dominating approximately 75 percent of the coastline between 25 degrees N and 25 degrees S. Previous studies have shown extremely wide ranges of methane flux from mangrove ecosystems, and have indicated that anthropogenic disturbances such as pollution, sewage discharge, and alteration of freshwater influx can have significant impacts on methane flux from mangrove ecosystems. Due to rapid population growth in tropical and sub-tropical areas and increasing impacts to coastal zones, it is important to obtain information regarding both natural and anthropogenic factors influencing methane cycling and flux within mangrove ecosystems, and to create a better estimate of the contribution of mangrove ecosystems to the global methane budget. Sampling for this study was conducted in three tropical coastal lagoons surrounded by mangrove vegetation located on the Yucatan Peninsula, Mexico. The three lagoons, Chelem, Celestun, and Terminos have similar vegetation and underlying geology, and are affected by similar seasonal patterns of temperature and precipitation. Significant differences in groundwater discharge and type and extent of anthropogenic impacts exist between the three lagoons. Chelem has moderate to low pollution and little to no ground water discharge. Celestun has very little pollution and large ground water discharges, while Terminos has relatively high impacts from pollution and human disturbance and varying ground water discharge. Previously reported data from these lagoons show distinct differences in methane concentrations in the sediment and water from Chelem in comparison to the concentrations measured in Celestun. Data collected over three seasons from Chelem and Celestun will be presented, providing information about seasonal variability in sediment and water methane concentrations and estimated methane flux to the atmosphere from these mangrove ecosystems. Additionally, methane concentrations in sediment profiles and surface waters of the three lagoons will be compared in order to examine differences in methane cycling and flux potentially related to human impacts.