| Wetland has a variety of unique environmental functions and ecological benefits, and plays an important role in maintaining the earth’s ecological balance. While, it is also an ecologically fragile ecosystem of easy-to-change, improper way of development and utilization may cause ecosystem destruction and ecological function reduction even losen for wetland. As the global climate change, social and economic development and humans’ development and utilization of wetland resources, the type, area, space distribution, ecological function of wetland is changing. Therefore, we should strengthen the research on dynamic change of wetland, reveal the law of temporal-spatial evolution and prove the dynamic mechanism of wetland. It has an important scientific significance to rich the theory of wetland and a practical significance to rational development, utilization, protection and management of wetland resources for carrying out research on the information extraction and temporal-spatial evolution of wetland area.Dongping Lake is the second largest freshwater lake in Shandong province, and the first freshwater lake in Tai’an. It has a very important geographic location and ecological service function, but the related research is weak.Under the support of RS and GIS, this paper carried out research on the information extraction and temporal-spatial evolution of Dongping Lake wetland area taking TM,ETM data of1987,2000and2009as resources.The main contents and results are as follows:(1) Establishment of Dongping Lake wetland classification systemThe paper established the wetland classification system suitable for the study area, Refered to the wetland classification standard in the "Convention on wetlands" and "national wetland resources investigation technical regulations (for trial implementation2008)",followed the wetland classification principle, combined with the actual situation of Dongping Lake wetland. It contains natural and artificial wetland2categories, including lake, river, marsh, the Dutch field, reed marshes, beaches, natural ponds, rice field, pond and reservoir, pond culture10sub-categories.(2)Information extraction of Dongping Lake wetland areaThe paper carried out initial identification Dongping Lake wetland ecosystem type by density slice of NDVI and TM4gray-image.K-Ttransform humity component image of the study area. Proposed hierarchical classification extraction method for the Dongping Lake wetland information sperm extraction, building a water extraction model based on HSV transform, extracting vegetation information by density slice based on V value component of LBV transform, extracting other surface features information based on supervised classification.(3)Scale dynamic changes of Dongping Lake wetland areaFrom1987to2009, wetlands and large-scale increased in both in the study area, added pond breeding and rice field2kinds of new artificial wetland. Wetland areas were128.73square kilometers in1987, including127.74square kilometers for natural and0.99square kilometers for artificial wetland, and179.61square kilometers in2009, including161.18square kilometers for natural and18.43square kilometers for artificial wetland. In the2phases, natural wetland experienced a decrease after the first increase from127.74to167.6to161.18square kilometers, and artificial wetland experienced sustained growth from0.99to12.87to18.43square kilometers.In terms of wetland dynamic change, from1987to2000, annual growth rates of natural and artificial wetland were22.98percent and32.63percent, the new rates were33.63percent and34.34percent, depletion rates were10.65percent and1.17percent, respectively. From2000to2009, annual growth rates of natural and artificial wetland were-17.18percent and16.95percent, the new rates were19.96percent and39.07percent, depletion rates were37.06percent and22.12percent, respectively.In summary, we can draw from the contrast between the two periods, annual growth rate of natural and artificial wetland in first periods was greater than second periods.the new rate of natural wetland in first period was greater than second periods and the new rate of artificial wetland in first period was less than second period.depletion rate of both natural and artificial wetland in first period was less than second period. In terms of2periods, from1987to2000, annual growth of natural wetland was less than artificial; increasing levels of natural and artificial wetland was at the same level, depletion rate of natural wetland was greater than artificial wetland. From2000to2009, annual growth of natural and artificial was at the same level, new rate of natural wetland was less than artificial wetland, depletion rate of natural wetland was greater than artificial wetland.(4) Transfer process of Dongping Lake wetland areaThe paper calculated indexes of wetland component retention, move in or out contribution rate by using wetland transfer matrix. From1987to2009, maintaining and transferring characteristics of various types of wetlands were different. But maintaining areas were greater than transferring areas for each type of wetlands.Among it, from1987to2000, Dutch field had the highest component retention rate of96.25percent, lakes had the highest transferred in-contribution rate of53.92percent, and marsh had the highest transferred out-contribution rate of15.07percent. From2000to2009,lakes had the highest component retention and transferred-in contribution rate of94.04and16.80percent, reed marshes had the highest transferred out-contribution rate of19.02percent.We can see from the analysis of special transfer contribution rate, a common characteristic was that the cumulative contribution rate of natural succession transfer type was greater than transfer type humans dominated in2periods. The specific transfer contribution rate of the dominant component of natural succession metastatic decreased compared with the first period in the second period, respectively70.42percent and50.67percent. However the specific transfer contribution rate of the dominant component of the human-led metastatic increased, respectively25.05percent and42.43percent.Studies have shown that more than20years, the main driving factors of Dongping Lake wetland temporal-spatial evolution contained natural and man-made, and human disturbance is increasing, the impact of natural factors is weakening.By the dynamic monitoring of area and distribution in Dongping Lake wetland area for more than20years, we can accurately grasp the characteristics of temporal and spatial variation, and thus provide a scientific basis for wetland management, decision-making and wetland development and protection. |
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