River Network Change and Its Ecological Effects in Shenzhen Region in Recent 30 Years
近30 年来深圳河网变化及其生态效应分析

Based on the topographic map data(in the late of the 1960s and 1980s),rivers general investigation data(in 2003) and remote sensing data(MMS in 1980;TM in 1988,2005) of Shenzhen region,the temporal and spatial changes of river networks and the relationship between river networks and urbanization ratio were analyzed.According to the above results,ecological effects of river networks change in Guanlan River basin,based on the four indicators of vegetation coverage(Vc),biological resources value(Br),ecosystem services value(Es) and ecological capital(Ec),were discussed.The results showed that:(1) the river network structure appeared as a trend from comprehension to simplicity,and the development of river branches were restricted strongly in recent 30 years.The length was shortened by 355.4 km,and the number of rivers reduced 378,while the drainage density decreased from 0.84 km/km2 to 0.65 km/km2.The major area,where the river networks decreased or disappeared,is located in the circle area with the town as the center and the radius of 1-2 km.There were 4 different types of change characteristics of river networks in all 9 drainages of Shenzhen according to urbanization ratio in the main drainage and whether or not it flows into sea directly.(2) There was significant correlation between urban expansion and river networks reduction,especially with river branches decreasing when the urban land ratio was less than 30%;while it was above 30%,the effects became weak.(3) The ecological functions of Guanlan River basin became weaker remarkably,of which Br decreased most(about 41%),Vc was second(24%).The ecological capital per unit area decreased from 22.79 million yuan/km2 to 2.34 million yuan/km2,while total capital reduced 3136 million yuan in 2000-2005.(4) Changing river networks and urbanization were the main reasons for the degradation of ecological functions,and they had different contribution ratios for decline of the four indexes,of which they were respectively 23.1% and 35.8% for Vc,25.1% and 32.7% for Br,7.7% and 56.2% for Es,and 10.6% and 52.2% for Ec.The paper provided an empirical case to recover river networks in the last several periods,and a quantitative expression of river networks change.