On Changes in Landscape Pattern of Coastal Wetland around the Pearl River Estuary in Past Two Decades

Coastal wetland data in the years of 1986, 1995 and 2005 of the Pearl River Estuary was extracted from the matic maps and remote sensing images respectively by using GIS and RS. Some indexes of landscape pattern, such as landscape diversity index, landscape contagion index and landscape fractal dimensions were chosen to describe the spatial pattern of the Pearl River Estuary coastal zone in the past two decades at both landscape and patch type level. The result shows that: (1) Among all the wetland types, the area of shallow waters accounted for the largest proportion, that was 61.67﹪ in 1986, 62.42﹪ in 1995 and 73.40﹪ in 2005. The area of aquaculture water landscape increased the most, while paddy fields decreased the most. (2) Affected by human factors, the total area of wetland in the Pearl River Estuary coastal zone continued to decline. From 1986 to 1995, it decreased 20 821 hm2, and from 1995 to 2005 decreased 55 708 hm2, accounting for 5.3﹪ and 14.2﹪ of the total studied area respectively. (3) The changes of wetland landscape were of temporal heterogeneity, and the distribution of that had significant spatial heterogeneity. The landscape contagion index of each wetland type decreased to a great extent, while the landscape fractal dimensions increased distinctively during the two periods. In terms of landscape diversity index it showed a decrease after an increase. (4) The centroid of the wetland in the Pearl River Estuary coastal zone moved northwards from 1986 to 1995 by a linear distance of 0.4 km, and moved southeastwards from 1995 to 2005 by 6.1 km. By comparison between the wetland area decreasing speed and the centroid displacing speed, it can be concluded that the degradation of the wetlands is accelerated.