**5. Conclusions**

The monitoring and assessment for cross-boundary WPAs is essential to define the wetland dynamics as well as underpin knowledge-based conservation policies and funding decisions by bilateral governmen<sup>t</sup> and managers. In the study, combining a rule-based object-oriented classification method, landscape metrics, spatial analysis and a Mann–Kendall test, we identified dynamic changes in natural wetlands and their influencing factors in the Wusuli River Basin from 1990 to 2015. Our results showed that the natural wetlands, as a whole, experienced a loss and fragmentation process, particularly in the Chinese section. Agricultural encroachment was the primary contributor to natural wetland degradation. In addition, differences in population trends and wetland conservation policies

in the Chinese and Russian regions had differing effects on their natural wetland dynamics. The methods and results from this study can help our understanding of natural wetland changes and their driving forces in a cross-boundary study setting. These conclusions can be used as a guide for the bilateral governmen<sup>t</sup> policies to effectively protect and manage natural wetlands.

**Author Contributions:** C.L. conceived and designed the research, process the Landsat image data, and wrote the manuscript draft. C.R., Z.W., and B.Z. helped to conceive the research and reviewed the manuscript. W.M. and H.Y. conducted the fieldwork and analyzed the land cover data. Y.G. analyzed the climate change trend. M.L. contributed materials.

**Funding:** This study was jointly funded by the National Key Research and Development Project (No. 2016YFA0602301), the Key Deployment Project of Chinese Academy of Sciences (No. KZZD-EW-08-02), the National Natural Science Foundation of China (No. 41730643), the funding from Youth Innovation Promotion Association of Chinese Academy of Sciences (2017277, 2012178), and the Fujian Natural Science Foundation General Program (2017J01457).

**Acknowledgments:** We appreciate the satellite and geospatial data provide by the Northeast Branch of National Earth System Science Data Center of China, as well as thank Leonie Seabrook, PhD, from Liwen Bianji, Edanz Group China (www.liwenbianji.cn/ac), for editing the English text of a draft of this manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
