Using Landsat images to quantify different human threats to the Shuangtai Estuary Ramsar site, China

Abstract

Multiple human activities can impose significant negative effects on wetland ecosystem. This study aimed to identify and quantify the human threats on the Shuangtai Estuary Ramsar site (SERS) by means of detecting wetland landscape changes using Landsat images from 1988 to 2014. Land-cover changes induced by agricultural reclamation, urban expansion, petroleum industry, aquaculture, and the increases in transportation land were identified using an object-oriented classification method and a decision tree. Human-triggered wetland conversions and landscape metrics-characterized wetland changes were documented in order to assess the protection effectiveness after this wetland was listed as a national nature reserve (1988) and a Ramsar site with international importance (2005). Results indicate that wetlands area at this Ramsar site decreased from 127,526 ha in 1988–117,805 ha in 2005, 113,705 ha in 2014 at an annual averaged loss rate of 531.6 ± 72 ha/yr. The only two vegetated wetland types, Phragmites australis and Suaeda heteroptera, have lost 4788 ha and 12,856 ha, respectively. Aquaculture ponds increased by 9715 ha, and almost all were transformed from natural wetlands. The landscape metrics used in this study show notable fragmentation trend of wetland as a result of the expansion of transportation lands. Multiple human activities occupied large areas of various wetland types. Compared to agricultural reclamation and urbanization, wetland changes at the study site were affected primarily by the development of aquaculture and petroleum industry. Obvious wetland loss and fragmentation determined by the analysis of Landsat images suggests that the protection effect has been relatively low in spite of the fact that the SERS is a national natural reserve and Ramsar site. As an internationally critical rest habitat for migration waterfowl, ecological degradation of the SERS and severe human threats create great challenges for ecosystem managements. This study also indicates that the protection effectiveness of other costal wetland should also be assessed using remote sensing to objectively track the conservation or restoration of these areas.