Sanjiang Plain in northeast China's Heilongjiang Province is a vast, low lying alluvial floodplain of about 54,000 square kilometers between the Songhua, Heilongjiang and Wusuli rivers. It is the largest fresh water wetlands in China, and one of the world's three major black-soil belts.
Supported by CAS, a project was started in 2002 to study the cycling of elements in typical marsh ecosystem in Sanjiang Plain, and after two years study, staged progress has been achieved. In January 2005, a panel of experts organized by the CAS headquarters made a mid-term assessment, in which the project won universal acclaim from the experts.
Headed by Prof. Liu Jingshuang, vice director of the Northeast Institute of Geography & Agricultural Ecology, CAS, the research team has made efforts to explore the transfer, transformation, build-up and decomposition of such elements as carbon (C), nitrogen (N) and phosphorus (P) in the complicated marsh ecosystem of water bodies, soils and plants, and their exchange with the outside environment.
Their objectives are to explain the fundamental rules concerning the related geochemical processes in the ecosystem, revealing the internal mechanism's influence imposed by human activities on the cycling of C, N, P and other elements in the ecosystem. Based on a clear understanding of the inter-relations between the cycling of the matters and the landscape and functions of the marshes, researchers are expected to offer suggestions for optimal readjustment and managerial modes to maintain the stability and healthy development of the ecosystem.
Until now, the research team has conducted 16 simulation experiments and field observations, collecting more than 5,000 samples and more than 17,000 data.
Through the experiments, researchers have made a clear picture on the following issues:
The water equilibrium of the hydrological system in the wetland and its N- and P-flux are determined; the characteristics in the amassment and decomposition of C, N and P elements in the plants of the wetland are initially revealed; the impacts of external input of N and P elements and the change in the water table on the plant bio-diversity, its density and water quality are explained; the inter-dependence between the variances in C/N and C/P and the wetland's N or P cycling, with the aid of the N isotope-tracking tests, the N transfer among the subsystems and within a subsystem as well as its relations with different environmental factors in the wetland ecosystem are exposed; the rules in releasing the C (or N) containing gases and the influence imposed from other factors under the sway of natural and human activities are developed. Furthermore, the scientists also make clear that the water amount has a more remarkable impact on the wetland than nutrients themselves and based on this, they suggest that water discharge from farmlands cannot lead the latter to eutrophication. They also succeeded in initially establishing a multi-cameral model for depicting the C-, N- and P- cycling in the wetland ecosystem.
