On Wetland Change And The Influencing Factors In Huai River Basin

Wetland is an important territorial resource and natural resource, with important ecological functions and abundant biodiversity, and one of the vital natural resources to human survival and development. However, for nearly half a century, along with the economic development and the continuous increasing of population, unreasonable use of wetland has caused a series ecological and social problems, such as worldwide ground loss of wetland, dramatic decrease of wetland ecological functions and ecological effectiveness, serious pollution of wetland water, sharp decline of biodiversity, increase of natural disaster and so on. Therefore, wetland protection allows no delay, and it should be the social responsibility of all citizens around the world. Wetland change is the combined result of human activity and natural process. Study of the growth and decline process of wetland and its mechanism in the landscape level is of an important meaning to protect and use the wetland resources reasonably.Huai River Basin is an important agriculture zone and densely populated zone. It has various types of wetland, including many large lakes, criss-crossing rivers and a lot artificial wetland. In addition, it has certain amount of shallow swamps and costal shoals. The wetland plays an important role in supply ecological service, such as hydrological regulation, water supply, water purification and so on. But unreasonable use of wetland have occupied too much water and caused serious wetland pollution, resulting in the decline of wetland water and self-purification capacity. Therefore understanding the regularity of wetland change in Huai River Basin and its influencing factors is of import reference value for the rational allocation of water resources, improving water equality and wetland protection.Wetland eco-systems are vulnerable to environment change, especially many human activities. Wetland change rate tends to have some significant difference in different area in landscape scale because of the spatial heterogeneity of the types and intensity of human activity, which leads to appearing of wetland change hotspots. Hotspots of decrease of wetland led by human activity are usually the wetland which has the highest productivity and is most sensitive to human activity in the specific area, which are should be protected with high priority. Identify the hotspots of wetland change will help to reveal the characteristics and its cause of the spatial pattern of the hotspots of wetland change, and will promote further understanding of the rule of wetland change under the coupling effect of natural factors and human activities, and will be of important practical meaning to lay down effective wetland protection and restoration measures.Using remote sensing and spatial analysis technology, this paper studied the wetland change in Huai River Basin. We explored the spatial pattern of wetland change hotspot and its influencing factors through quantitative analysis of the influence to wetland change by factors like climate, topography, population, economy and traffic accessibility etc. The result showed that:(1) Natural wetland increased a small amount, net increase of which accounts for1.16%and0.27%of the total wetland area and total basin surface area in Huai River Basin in1995, respectively. Costal wetland and river wetland increased significantly, but lakes and swamps decreased significantly. Seasonal rise of the floodplain may cause the massive growth of river wetland, and the increase of costal wetland was mainly caused by the fast silting of costal beach in east Jiangsu. Lakes and swamps mainly converted to other type wetland. The total amount of artificial wetland increased significantly, along with a big amount artificial wetland converted to other landscape element. Net increase of artificial wetland accounts for21.38%and4.86%of the total wetland area and total basin surface area in Huai River Basin in1995, respectively. Paddy field had the most dramatic transfer process, higher than other wetland types in both transfer in and out, and mainly transferred with dry land and construction land. Reservoirs and ponds mainly transferred in and out paddy field and dry land.(2) Among the non-wetland landscape elements in Huai River Basin, dry land, grassland and unused land reduced, and forest land and construction land expanded, among which, dry land had highest reduction rate (about20562.96km2) and construction land had highest expansion rate(about7167.35km2). For dry land, paddy field and construction land, any one of the three landscape elements, the other two were always the main transform objects in both transferring in and out. Forest land also had some expansion, and grassland was its main source of expansion, and dry land was the main landscape element to which forest land transferred.(3) In landscape level, landscape fragmentation decreased in Huai River Basin, and patch shape became more complicated. The predominant landscape types reduced, and evenness and diversity increased. Landscape pattern of wetland had some change, which were an increase of landscape fragmentation, becoming more complicated of patch shape, a decrease of connectivity, agglomeration and contagion degree, no obvious predominant wetland type, and an increase of diversity and evenness of wetland types. In class level, dry land, wetland and construction land were always the main landscape elements within Huai River Basin. Fragmentation of dry land construction land decreased, and connectivity was enhanced, which were opposite to that of wetland. The scale change of each wetland type had no significant correlation with its fragmentation, aggregation and contagion degree, but largest patch index presented consistency with the scale change of wetland. Patch shape of natural wetland became simpler, but that of artificial wetland became more complicated.(4) Spatial distribution of each wetland type change hotspots was different. The number of natural wetland hotspots was relatively small, and the hotspots had relatively dispersive spatial distribution. Artificial wetland increase hotspots had the most concentrate spatial distribution and the widest distribution space, and were usually continuous and concentrated. Artificial wetland decrease hotspots had the second widest distribution space, and were concentrated or spotted.(5) Wetland change in the watershed scale was the coupling effect of natural geographical conditions and human activities, and each type wetland had different sensitivity to each influencing factor. In Huai River Basin, the restriction effect of physical geographical background like temperature and elevation was the primary factor leading to spatial differentiation of wetland change hotspots. Temperature has an promoter effect on the occurrence of each type of wetland change hotspots. While elevation shows the strongest effects on the occurrence of hotspots of artificial wetland increase and natural wetland decrease, and the absolute value of β coefficient are1.562and0.524respectively. Social-economy and accessibility had significant effect to the occurrence of wetland change hotspots, but it was relatively less important.