Organic Carbon Accumulation And Carbon Cycling Simulating In Typical Wetland Ecosystems

Organic carbon (C) cycling in wetland ecosystems plays a very important role in global organic C cycling and climate change. The characteristics of organic C accumulation in wetland ecosystems can pridive information not only of the source, history and present condition of organic C, but also the impact of climate change on organic C cycling, It is important to understand the mechanism involed in accumulation and the process of organic C cycling in typical wetlands. Improving our ability to simulate C sequestration is of prime importance. Content, composition and density of organic C and the variabilities in typical wetland sediment profiles were investigated in temperate Sanjiang Plain and subtropical Dongting Lake zone in China. Fractionation and incubation methods were also employed to elucidate the key environmental factors and mechanisms of organic C accumulation. A model was developed to simulate organic C cycling in wetlands. The model of organic C cycling was based on plant physiological and ecological datamatter and dynamics of organic mater decomposition and transformation. The model was validated using observed data of plant biomass and CO₂ flux from a field expriment station in Sanjiang Plain, and using organic C density data from Sanjiang Plain and Dongting Lake. The results are summarized as follows:(1) There was distinct organic C layers (OL) in the sediment profiles of the Sanjing Plain wetlands. The thickness of OL varied between and within the different wetland types. In contrast, no stable OL was found in the profiles from the Dongting Lake floodplain. Organic C content in sediment profiles differed from one type to another. There was also great variability in OL for the same type of wetland under the same climate zone. Organic C content decreased with the increasing depth of sediment profiles.(2) Llight fraction (LF, SD<1.7) was the main fraction of organic C accumulated in wetlands in temperate zone. The ratio of LF to total organic C decreased with increasing depth of OL. The degree of organic C decomposition increased with increasing depth, which indicated the natural sedimentation of organic C in temperate zone. However, the ratio presented the state of striation in the profiles in subtropical zone, which resulted from the discontinuous flooding.