Patterns of terrestrial anthropogenic impacts on coastal wetlands in three city clusters in China
三大沿海城市群滨海湿地的陆源人类活动影响模式

Coastal wetlands are increasingly affected by terrestrial anthropogenic impacts associated with urbanization along the worlds' coastlines. There is a strong need to balance utilization and protection of coastal wetland resources via understanding of patterns of coastal wetland changes in response to terrestrially derived anthropogenic impacts. This study was carried out to characterize impacts of wetland reclamation (a direct anthropogenic impact) and contaminant influxes of nutrients and non-point inorganic contaminants (an indirect anthropogenic impact) on coastal wetlands in the three largest city clusters in China between 1990 and 2000 using a GIS-based approach. The three coastal city clusters were 1) the city cluster surrounding the Bo Sea (BSS), the Yangtze River Delta city cluster (YRD), and the Pearl River Delta city cluster (PRD). Thirty-eight TM or ETM+ Landsat images from 1990 and 2000 were assembled and nutrient influxes were generated from the Global NEWS2 and Global Nutrient Export WaterSheds2 models by the Workgroup of UNESCO's Intergovernmental Oceanographic Commission for each city cluster. Non-point contaminants were estimated from impervious area in the coastal cities according to the world impervious area map for 2000 produced by the US National Oceanic and Atmospheric Administration (US NOAA). The "intensity" of contaminant loading was calculated by normalizing both nutrient loads and non-point contaminant loads between 0-1.Results indicated that although wetland reclamation for agricultural land use was predominant in all three city clusters (over 50% of the area), wetland reclamation to urban land use (directly from wetland reclamation and indirectly from wetland-derived agricultural land) increased along with urban population between 1990 and 2000. The PRD area showed the largest conversion of coastal wetlands to urban land while the BBS area showed the largest conversion to agricultural land use. Over 60% of the BBS and PRD areas were contaminated above a mid-level of intensity, whereas 44.7% of the YRD area received contaminants at mid-level intensity or above.Integrating the two factors with weights (0.5 for land use/cover change and 0.25 for influxes of nutrients and non-point contaminants, respectively), the combined impact intensity was highest in the PRD area, with an average index of 0.79 and 78% of its area influenced by two anthropogenic impacts at mid-level intensity or above. Combined impact was lower in the BSS (0.65) and YRD (0.63) areas with approximately 30% of these areas at mid-level impact intensity or above. Spatial analyses were very useful for illustrating the nature and extent of terrestrially-derived anthropogenic impacts on coastal wetlands and should be useful for assessing development impacts on estuaries and coastal wetlands in many areas.