The study of wetlands change in Yellow River delta Based on RS and GIS

Abstract

In recent years, the water and sediment were dropped significantly in Yellow River, the average annual water and sediment discharge was 143.5 X 108 m3 and 3.75 X 108 t respectively, accounting for 29.2% and 31.2% of the 1950-1969 values. In addition, the day of flow depletion was also increased continuously and there was 21 years of flow depletion from 1972 to 1998. Especially in 1997 the day of flow depletion was up to 226 days in the section below Lijin Hydraulic Station. In the new hydrological environment the Yellow River delta eco- environment must be changed. Based on Remote Sensing and Geographic Information System (RS & GIS) technology, we study what and how the Yellow River delta wetlands changed in the new hydrologic conditions in recent years using the Landsat TM/ETM+ image of 1996, 2000 and 2004. The results show that the area of the wetlands in Yellow River Delta was increased and from 1996 to 2004 the area of the wetlands has been increased 22838.55 hm2 and the increase rate was 2854.82 hm2/y. The area of the nature wetlands and the artificial wetlands were increased as a whole, but their change character was different. The area of the nature wetlands was increased quickly from 1996 to 2000, which is related to that the national park of Yellow River delta was changed in 1996 and from 2000 to 2004 it was increased tardily. On the contrary, the area of the artificial wetlands was decreased tardily from 1996 to 2000 and from 2000 to 2004 it was increased quickly. In the mean time the area of river, bottomland and paddy field was decreased and the area of swampland, reed marsh, reservoir, saline and acequia was increased. To scrutinize the dynamic changes of wetlands, the simulation for transformation of the wetland types has been carried out by means of the ecological Markov Process. The results showed that the whole transfer velocity of the wetlands is 2.99 % from 1996 to 2000 and the transfer among the wetland types is simple, but from 2000 to 2004 the transfer velocity of the wetlands is 6.95% and the transfer among the different wetland types is complex correspondingly. Moreover the reason of the wetlands changing has been analyzed in this paper. Firstly, the reciprocity between the decrease of the water and sediment and the regulating water and sediment is the main reason of the wetlands change. Aiming at the decrease of the water and sediment entering the Yellow River, the water and sediment regulation is an important measure which has positive impact on the Yellow River Delta Wetlands. Secondly, the process of the agriculture exploitation, city building and wetlands protection is also an important factor of the wetlands change. In order to resolve the problems of the excessive exploitation, wetlands pollution and so on, many protection measures, such as strengthening the management of the Yellow River, doing better program and dynamic monitoring, keeping harmony between the exploitation and recovery of the wetlands and paying attention to the wetland pollution, were carried out. Thirdly, the climate change and storm surge disaster are explicit factors of the wetlands change. This study has significance for building and protecting of eco-environment in Yellow River delta.