| Inner Mongolia Hetao Irrigation District is the important agricultural production base in Northern China. However, due to rapid agricultural development in the irrigation area, the abuse use of fertilizer and pesticide, which causes water resource to suffer severe threats. The area boasts rich wetland resources that show unique advantages in treating agricultural pollution. Therefore, it is urgent to understand the wetland conditions in Hetao area, analyze, hydrology, vegetation and other characteristics of wetlands and discuss removing a large amount of N, P and other nutrients in farms of Hetao Irrigation District through transforming natural wetlands and constructing artificial wetlands, thereby reducing the pollution pressure caused by agricultural pollution load on Wuliangsu Sea and the Yellow River.This paper takes natural and artificial wetlands in Inner Mongolia Hetao Irrigation District as the research object. With the methods of satellite remote sensing interpretation, field survey on vegetation and water quality monitoring, etc., statistical analysis is conducted on the existing wetland resources in the Hetao Irrigation District to analyze the features of hydrology, water and vegetation and evaluate the purification potential of wetland to solve farm return water pollution. Then, water purification test is carried out on the farm return water from transformed natural wetlands and newly-built artificial vegetation. Main results include:1. There are a lot of wetland resources in Hetao Irrigation District. Satellite remote sensing interpretation shows the quantity of wetlands is about 875, covering an area of 700 km2, of which 333.48km2 is an area of Wuliangsu Sea. The wetland landscape takes on a tendency to fragments while the area of Wuliangsu Sea is relative more stable.2. Wetlands in Hetao Irrigation District consist of simple plants and vegetations. Most wetlands are covered with reeds, water bamboo and other emergent plants. Submerged plants in lake-like wetlands mainly produce P.crispus, mainz algae, bamboo malaianus, etc. But its distribution shows regional characteristics. The primary productivity of reeds, the typical vegetation in wetlands, reaches 1.7kg/m2 while that of submerged plants is 4.156kg/m2.3. The water pollution in Hetao Irrigation District is mainly caused by agricultural non-point source pollution. Annual discharges of N and P in the irrigation district caused by over use of fertilization reaches 86194t and 56715t respectively. Agricultural non-point source pollution accounts for more than 60% of the overall water pollution in the irrigation area.4. Among numerous wetland types in the irrigation district, except a small amount is unusable due to water source, other types of natural wetlands boast potential for purifying pollution. However, for transformation of natural wetlands, artificial transformation should be made for topographic and hydrological conditions.5. Hetao Irrigation District has a huge potential for water purification. After measurement, it can remove at least 6000t nitrogen and 1300t phosphorus annually.6. When utilizing wetlands in Hetao Irrigation District or other regions with similar climatic conditions, it is necessary to pay attention to plant growth rhythm and seasonal variations and give full play to wetlands’ ecological and physical functions in different periods of time. At the same time artificial wetlands and natural wetlands should be combined reasonably and complement each other. |
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