The Study On The Wetlands Evolution And Its Driving Force In The Yellow River Delta

Wetland, forest and sea are called three ecosystems on the earth. The study on wetlands has become an emphasis subject and study field because of vital importances in the healthy development of the earth's environment. Due to its remarkable primordial, vulnerability and scarcity, the Yellow River Delta Wetland (YRDW) has various ecological function and economical and social value, and plays a very important role internationally. In recent years, it has attracted many domestic and international researchers to study it. But there are few studies on its driving force of wetland evolution. Supported by computer and maths methods, combining with findings from field surveys and the collected data , using four-period TM remote sensing data, the evolution process, driving force and trends were studied in this paper. The main content is as follows:(1) On the basis of findings from field surveys and data analysis, the author makes use of ERDAS8.5 software to interpret four-period remote sensing data and gains four-temporal data base of wetland resourse in 1985, 1996, 2000 and 2004. Making use of Arcview3.3 to superimpose and analyse the data base, a conversion probability matrix of wetlands was catulated in YRD (in Dongying City) and a regulation of spacial structure evolution was drawn: in this 19 years, salt fields and shrimpfields turn out greatly in natural wetlands and artifical wetlands such as meadow, foreshore, swamp, sandy beach, paddy fields and saline alkali lands, while other non-wetlands, such as building lands, oil fields and arid lands, keep few turning out, and the total area has a trend of increasing. Landscape keeps a fluctuating situation of"turning out and turning in greatly".(2) By comparing the changing area rate between wetlands and non-wetlands from1985 to 2004, and calculating the evolution rate through the dynamic degree of land use in the YRD(in Dongying City), the rule of temporal evolution was drawn: From 1985 to 2004, the total area of wetlands is decreasing while the area of non-wetlands is increasing; the total area of natural wetlands is gradully reducing, especially foreshore and meadow; the total area of artificial wetlands is growing especically salt fields and shrimpfields. In the three periods from 1996 to 2000, the rate of evolution in YRD wetlands is biggest, especially salt fields and shrimpfields; the evolution rappid of wetlands is bigger than that of non-wetlands, and the evolution rappid of natural wetlands is dropping; the most active natural wetlands and artifical wetlands are foreshore, saltfields and shrimpfields respectively.(3) In the 19 years from 1985 to 2004, the total area of wetlands is gradually reducing in the YRD, especially the natural wetlands are degenerating, so that ecological function is weakened. The areas of the swamp and shallow are reducing so that the function of hydrographic pondage is lowering year by year and ecological system of wetlands, which is destroied even carries out converse succession, causes the function of degrading pollutant to drop; water deterioration in YRD causes biological multiplicity to be disturbed and destroied to some degree; the reduction of river and lake surface causes the function of climatic adjustment to drop; wetland's losing and degeneration cause the function of nitrogen fixation to be destroied severely.(4) On macroscopic view, the primary reasons for the evolution of the YRDW (in Dongying city) was natural factors in its earlier period, and gradually has permeated the more and more strong mankind's influences in its later period; On microscopic view, the evolution power of the YRDW is disturbed by mankind's activities, so that the whole wetland system carries straightforward and converse succession. Although the negative influences such as flow blocks and sediment accumulations were weakening, the natural driving forces such as climatic change, sea-level rising and storm tidal damaging have a trend of aggravating, and the intensity of mankind's driving force increased steadily.Therefore, on the basis of various driving forces gradually increasing, its loss and degeneration would become a basic trendency, which would mainly manifest in its ecological characteristic, the space-time structure, the function and its evolution. This study can not only provide the decision basis for the wetlands protection and administration in the YRD, but also offer references for protection, expoitation and utilization effectively in the rescources and environment of this delta, and provide theoretical instructions and technical supportions for the research of global climatic change and biodiversity protection specially birds protection. This study has universal resource-environment significances.