The impacts of drainage and reclamation on wetlands water resources in the Sanjiang plain, China

Wetlands are a special natural complex with transitional characters between water and land; they have both water and land ecosystem´s characters. In this unique and multifunctional ecosystem, water is the most active factor which could not only influence plant growth, population distribution and soil formation, but also control the development and evolvement of wetlands together with thermal condition. The direct impacts of drainage and agricultural reclamation changed regional water balance, and the wetlands hydrology and water cycle have been greatly changed, especially influencing the surface water and runoff of wetlands. The Sanjiang plain is the largest and most concentrated wetlands distribution region in China in history, the total area is about 1.088×10⁷ hm² with rich wetland resources and biodiversity. Before 1949, the Sanjiang plain was a large untraveled wild plant and waterfowl habitat, and also was a huge fresh water resource reservoir. From 1950 on, the government of China began to reclaim the wetlands in Sanjiang plain, built the commodity grain base of Northeast China, and developed the industry of grain processing. Up to now, there are 54 farms controlling 5.24×10⁶ hm² agriculture field. The wetlands areas are reduced to 83.5×10⁴hm², and become drier and drier by losing water in the mean time. The human activities and agriculture reclamation made a great change on the environment, especially on water balance change, so it is extremely urgent to study and protect the wetlands ecosystem and wetland resource in the Sanjiang plain. This paper is the research result according to the long-term observation of the experiment station of wetlands in the Sanjiang plain, Chinese academy of sciences. We focus on the hydrology change before and after wetlands reclamation, study on surface water resource, evapotranspiration and run off, on both wetlands and agriculture field- - , analyzing the reason that causes seasonal drought, waterlogging and degeneration of wetlands in the Sanjiang plain. The research result shows that the surface water level largely dropped due to human agricultural activities which mainly involved the intense influence of drainage system on runoff processes. The regional climate became drought and waterlogging frequently after large-scale reclamation and agriculture drainage, so it should be paid enough attention.