Temporal and spatial dynamic changes and driving forces analysis of wetland landscape of Chang-Zhu-Tan urban agglomeration

Abstract: Urban wetland is an important ecological base of urban agglomeration, and is crucial to the ecological environment of the city. In this study, we selected Chang-Zhu-Tan urban agglomeration as the study area. The time series Landsat data and phenology characteristics, as well as the random forest algorithm with object-oriented method were employed to get wetland landscape data of Chang-Zhu-Tan urban agglomeration. Then, the Markov matrix, landscape pattern index, and mass migration method were used to analyze the spatial and temporal changes characteristics of wetland landscape. And we also analyzed the driving forces of wetland degradation by logistics regression model. The results showed that: 1) The major wetland type was paddy field, followed by river and pond, and lake and sedge marsh areas were relatively small, and the areas of these wetland types were 3008.32, 179.98, 48.20, 4.96, and 4.85 km2, respectively. Wetlands were mainly distributed outside the city suburbs, hills and valleys, or areas with relatively dense irrigation facilities. Wetlands were mainly distributed in the northwest and southwest of the study area, and the area in the northeast and southeast was relatively small. 2) The total wetland area of Chang-Zhu-Tan urban agglomeration during 2000-2015 was decreased by about 231.12 km2. Among them, the reduction of paddy field was the most intense, which reached 227.38 km2. There was a great deal of conversion between wetlands and non-wetland landscape types, as well as the conversion between wetland types. 3) In the past 16 years, the coordinates of the centers of mass of the 4 wetland types have been shifted obviously. The migration of the mass centers of the river and pond was the most obvious, while the center of mass of the lake was relatively stable. The center of mass of the lake moved eastward firstly and then northward. 4) The mean patch area of the river in the study area was the largest, followed by paddy fields, lakes, ponds and sedge marsh. The landscape fragmentation of paddy field, ponds and sedge marsh was higher than other wetland types, the patch shape of sedge marsh and ponds was the most complicated, and the aggregation index of paddy field and ponds was relatively higher than others. The landscape patch number, shape index and Shannon diversity index of study area were obviously increased, while the aggregation index decreased significantly. 5) The reduction of precipitation and increasing of temperature coupled with the high intensity of human disturbance were the main reasons to wetland degeneration in recent years in Chang-Zhu-Tan urban agglomeration. The change of temperature in study area was gentle, and it had a relatively less significant influence on wetland area change than precipitation. Among the social economic factors affecting the wetland change of Chang-Zhu-Tan urban agglomeration during 2000-2015, the most important was the urbanization rate index, and Wald statistic (reflecting contribution rate) was 9.82. Another major economic factor was GDP (gross domestic product) per capita, with Wald statistic of 9.27. The resident population was also an important factor of wetland change, with Wald statistic of 7.85.