Nitrous oxide and methane emissions from the restored mangrove ecosystem of the Cienaga Grande de Santa Marta, Colombia

摘要

Most studies on emission of the greenhouse gases nitrous oxide (N_2O) and methane (CH_4) have been carried out in temperate areas so there is generally a lack of data from subtropical and tropical climates. A large part of the subtropical and tropical coastal wetlands consists of mangrove ecosystems, which have potential to act as sources of N_2O and CH_4. We measured N_2O and CH_4 emissions during 11 months in the brackish lagoon system Cienaga Grande de Santa Marta (CGSM) on the Caribbean coast of Colombia. The area has been seriously influenced by human disturbance which resulted in approximately 60% mangrove mortality but the ecosystem is now being rehabilitated. In addition to N_2O and CH_4 emissions at four sampling sites, we also measured temperature, salinity, pH, dissolved oxygen (DO), redox potential, nitrite (NO_2~-), nitrate (NO_3~-), ammonium (NH_4~+) and organic material in the water and/or the sediment. We found the mangrove sediments of CGSM to be a source of N_2O and CH_4 but there was large variability of the emissions on both temporal and spatial scale with N_2O and CH_4 fluxes in the range 35 -1180 μg m~(-2) h~(-1) and 0-31570 μg m~(-2) h~(-1), respectively. Correlations between N_2O fluxes and the water variables showed that salinity significantly contributed towards decreased emission of N_2O (r = -0.38). By contrast, water concentrations of NO_3~- were correlated with increased emission of N_2O (r = 0.54). Emission of CH_4 was negatively correlated with DO in the water (r = -0.34) and there was a positive correlation between organic matter and CH_4 emission (r = 0.75). It was found that untreated wastewater discharged into the Magdalena River and in turn, the lagoon system may have resulted in a substantially higher emission of both N_2O and CH_4 as the wastewater contributes substrate to the processes in the form of N and organic matter. With better treatment of wastewater, it is possible that emission of both gases would be lower, especially at the sites closest to Magdalena River.