Wetlands Changes And Its Driving Forces In China Between 1978 And 2008

Wetlands are considered as the most productive ecosystem on earth. People have paid more and more attention to its environmental and ecological value. Wetland conservation is increasingly becoming a global hotspot. In the context of global climate changes and rapid economic development, the factors that influence the spatial and temporal distribution of China’s wetlands are greatly complicated. In this paper, considering relevance with wetlands change and data availability, we chose 12 impact factors as independent variables, including three natural factors and nine social economic factors(average temperature, average humidity, cumulative precipitation, population, gross regional domestic product, agricultural production value, cultivated land acreage, grain production, effective irrigation area, reservoir capacity, drainage area and saline-alkali management area). The driving mechanism of wetland change from 1978 to 2008 was studied with the method of Geographically Weighted Regression(GWR) on the basis of four years of wetland remote sensing mapping data(1978, 1990, 2000, 2008) and three years of land use data(1990, 2000, 2005). GWR, as a local linear regression method, can not only effectively reflect regional disparity of driving factors influencing wetlands, but present results intuitively.It is also known that wetland protection often contradicts with cultivated land development and economic growth. It is important to ascertain the spatial and temporal conversion feature for coordinating the relationship between the two aspects. Considering the rich wetland resources, unique geographical location and climate conditions in Xinjiang, and the rapid development of economy of Shandong, this contradiction is especially prominent in these two provinces. This paper analyzed 30 years of wetlands change and its relationship with cultivated land development and economic growth in Xinjiang and Shandong since 1978, in order to reflect the differences between western and eastern of China. The results showed that:(1) The main influencing factors of various types of wetlands are different. Inland wetlands were closely associated with average temperature, cumulative precipitation, activities related to farming irrigation and so on. Economic development and water infrastructure had a huge impact on artificial wetlands. Moreover, coastal wetlands had a close relationship with population, fishery industry and so on. The main factors influencing the same type of wetlands changed as time goes on, and there were also obvious differences in the degree of the influence over the space. For inland wetlands, cumulative precipitation had significant effects in the northwest arid region from 1978 to 1990, and average temperature had significantly positive correlation with inland wetlands in the north areas where snow and permafrost distribute from 1990 to 2000. Both of them can increase the wetlands water supplies to expand the wetlands area. The influence of drainage area on inland wetlands was significant in the southeast coastal area, while that of cultivated land acreage, effective irrigation area and grain production was significant in the north, especially in regions such as northeast three provinces and the Inner Mongolia autonomous region. Due to these factors, inland wetlands sharply declined because of drainage, reclamation and increasing demand of water in agriculture. Regarding to artificial wetlands, it had a consistent change trend with economic development in China from 1978 to 2008, in which economic development moved from south to north and from east to west, and artificial wetlands increased accordingly in those areas. During the past 30 years, the reduction of coastal wetlands was mainly caused by fisheries development, tideland reclamation, oilfield development, infrastructure and water conservancy facilities construction. Among these factors, fishery production mainly affected Jiangsu province and Zhejiang province, tidal land reclamation had a great influence in Fujian province and Guangdong province, and oilfield development had a significant effect on the areas around the Bohai Sea. At the same time, the population growth rate is faster in coastal area than in other regions, resulting that wetlands were occupied by a large number of artificial facilities.(2) Overall, wetland resources in Xinjiang have experienced three stages: sharply dropped- slightly increased- slightly reduced. Most of the reduced wetlands distribute along rivers or lakes, and inland wetland is the major type of decreasing wetlands. Artificial wetlands continued to increase since 1990. The volatility of wetlands change of the southern area is more drastic than the northern. And the reduction characteristic changes from concentrated to scattered and uniform over the time. The impact of climate change on wetlands in Xinjiang is more significant from 1990 to 2000. Warm and wet climate resulted in short-term increase of wetlands in parts of Xinjiang, such as Yarkand River. Cultivated development has always been a key factor affecting wetlands change. From 1978 to 1990, there were 1193.44 square kilometers wetlands converted to cultivated land, followed by significantly reducing in the next two periods, in contrast, the area of cultivated land converted to wetland from 1990 to 2008 showed an increasing trend, indicating that wetlands reclamation weakened and conceded cultivated land gradually increased. The main types of wetlands converted to cultivated land are inland swamps and flooding wetland. In the past 30 years, it primarily occurred in Ili Kazak Autonomous Prefecture, Aksu Prefecture, Kashi Prefecture, Altay region and so on. Frequent conversion between wetlands and cultivated land mainly occurred in the north and west part of Xinjiang, especially in Ili Kazak Autonomous Prefecture and Aksu Prefecture. Xinjiang wetland resources are closely related to water resources and cultivated land development, and the influence of human factors is growing as time goes on.(3) In the past 30 years, the total wetlands were growing in Shandong province, but the main increased wetland was artificial wetland. In fact, the natural wetlands have shown severe recession state: inland wetlands significantly reduced and coastal wetlands have continued to decrease since 1990. Seawater farm, salt pan, reservoir and pond increased the most among artificial wetlands. After nearly 30 years of development and transformation, the wetland structure of Shandong province has changed dramatically. Inland wetlands proportion dropped from 53% in 1978 to 12% in 2008, while artificial wetlands are from 16% in 1978 to 66% in 2008, the proportion of coastal wetlands shrunk to 22%. The main factors influencing the wetlands change in Shandong province are cultivated land development, fishery and salt industry and water conservancy facilities construction. Compared with human activities, the impact of climatic factors was not very significant. Coastal wetlands loss is due to the construction of artificial wetlands or grassland reclamation. Inland wetlands were mainly converted to cultivated lands and artificial wetlands.Wetlands change and its driving forces vary over time and space. In the protection process, we need to pay attention to local conditions and overall development. This study basically reflect the driving forces of wetlands change in China and typical provinces from 1978 to 2008, which could provide helpful policy support for management and rational utilization of wetlands at national scale.