Carbon dynamics, processes and factors regulating greenhouse gas emissions from wetlands

Abstract

Wetlands are prominent ecosystems lying at the interphase between terrestrial and aquatic ecosystems storing nearly 20-30% of the global carbon pool and are considered as the first ecosystem to experience the impact of climate change. Carbon storage in wetlands depends on the balance between carbon input and output influenced by several environmental and micro-meteorological factors such as temperature, moisture, pH, redox conditions, topography, geological position, the hydrological regime and type of vegetation. Globally rice paddies share a significant portion of the wetlands functioning as a major sink or source of carbon micromanaging the emissions of major greenhouse gases. Studies conducted by the authors in selected paddy wetlands of Kerala, India, have established that they are net source of methane during the flooded paddy growth period (92.638 mg m-2 h-1), whereas they act as sink during the summer fallow period (-2.0176 mg m-2 h-1). The carbon dioxide fluxes in the paddy act as a source (-0.45 to 2.3 g m-2 h-1) during the entire study period. Seasonal carbon dioxide was higher in the summer fallow period than in the flooded cultivation period. Fallow period facilitates the aeration of soil, thereby resulting in net loss of soil organic carbon by oxidizing it to carbon dioxide. Highest nitrous oxide emission (0.76 mg m-2 h-1) was observed during the end of first crop season whereas lowest (-0.017 mg m-2 h-1) was during summer fallow months of April. During the study, the global warming potential determined for the paddy wetlands of Palakkad was 337.16 g m-2. Wetlands having considerable role in carbon sequestration levels and greenhouse gas (GHG) emissions have a potential bearing on the effective management for mitigating climate change.