Characterizing seasonal and long-term dynamics of a lacustrine wetland in Xinjiang, China, using dense time-series remote sensing imagery

Abstract

ABSTRACT Wetland degradation and ecological restoration has become a topic of key research interest, particularly in the context of climate change and excessive water resource utilization. The Aiximan wetland, a major lacustrine wetland in Xinjiang, China, has shrunk in area by approximately 80% over the last 30 years. An ecological water transfer project (EWTP) was implemented in 2017 in an attempt to reverse this shrinking. The project involves seasonal flooding through three canals during the growing season of the wetland. In this paper, we explore the history of the Aiximan wetland over the last 30 years using a dense time series of remote sensing images to analyse the spatio-temporal changes of the wetland. We focus on intermittent flood inundation and wetland vegetation growth before and after the EWTP initiation, as well as the role of agricultural expansion in the decline of the wetland. The results indicate the following: (1) The annual maximum of open water area, which had fallen to 25.91 km2 by 2016, increased to 47.54 km2 in 2019 due to the water transfers. However, although the area of wetland vegetation also increased following the water transfers, it did not regain the maximum extent it had in 2013. (2) The percentage of the total wetland area with vegetation cover steadily declined from 54.2% in 1990 to 13.4% in 2019, and 72.84% of the loss of wetland was due to conversion to farmland. (3) The loss of wetland vegetation over the last 20 years corresponds to a period when the wetland water area fell below a threshold of 30 km2, and the wetland vegetation accounted for less than 60% of the wetland area. (4) The Aiximan wetland has recently shown signs of recovery due to the EWTP. However, the remote sensing time series suggests that wetland vegetation restoration will require the wetland water area to exceed 30 km2. Adjusting the timing of intermittent flood inundation to encourage vegetation growth may also be important for sustainable restoration of the Aiximan wetland ecology.