Quantifying the spatial characteristics of open-water conversion of tidal wetlands along China’s mainland coast using time-series water percent maps

Abstract

The conversion of tidal wetlands to open water has become a major concern for coastal managers worldwide. Collecting spatial information regarding the lost tidal wetlands resulting from open-water conversion and the degraded tidal wetlands that are exhibiting a significant transition towards open water is the prerequisite for employing conservation and restoration efforts. Previous studies have focused on the former information while often neglecting the latter. This will hamper coastal managers to make comprehensive decisions. In this study, tidal wetlands along the mainland coast of China are taken as a case. Using a linear regression model, we first verify that the time series water percent maps can capture the changes in inundation of tidal wetlands at the local scale, and then employ this dataset and method to identify the portions within the current tidal wetlands (2020) that are exhibiting a significant transition toward open-water at the national scale. Furthermore, we optimize the spatial information of the lost tidal wetlands resulting from open-water conversion on the mainland coast of China from 1999 to 2019 based on a global intertidal change database. The results suggest that a total of 5.3 × 104 ha of tidal wetlands were converted into open-water on the mainland coast of China between 1999 and 2019, with over 57% of this occurring in Jiangsu Province and Shandong Province. Nearly 12% of China’s current tidal wetlands, equivalent to 10.1 × 104 ha, are undergoing a significant transition toward open water. The area proportion of these degraded wetlands in the provinces north of Shanghai is generally higher than that in the provinces south of Shanghai, except for Hainan Province. The four-quadrant model is utilized to provide conservation and restoration recommendations for different coastal segments based on the comprehensive spatial information on the open-water conversion of tidal wetlands. The datasets and methods used in this study provide novel insights for determining open-water conversion of tidal wetlands. Our findings have the potential to assist coastal managers in optimizing the spatial patterns of the national restoration projects along the mainland coast of China.

Keywords

• Tidal wetlands
• Open-water conversion
• Water percent maps
• Time series analysis
• Mainland coast
• China