Yu, QZ; Mickler, RA; Liu, YJ; Sun, LG; Zhou, L; Zhang, BH; Deng, HG; Liang, LL (2020). Remote Sensing of Potamogeton crispus L. in Dongping Lake in the North China Plain Based on Vegetation Phenology. JOURNAL OF THE INDIAN SOCIETY OF REMOTE SENSING, 48(4), 563-573.

Curly-leaf pondweed (Potamogeton crispus L.) is a perennial, submerged plant native to Eurasia, Africa, and Australia that tolerates fresh or slightly brackish water. The pondweed has been found widely in many lakes in northern China. The Dongping Lake is a typical shallow macrophytic lake in north China, and it is an important junction at the East Route Project of China's South-to-North Water Diversion Project (ERP-CSNWDP). In mid-summer, the pondweed die-offs result in a critical loss of dissolved oxygen and decaying plants can result in Dongping Lake eutrophication, blocked waterway, and fish kills. In order to maintain the environment security of the ERP-CSNWDP, there is an urgent need to understand the spatial and temporal changes of pondweed's rapid range expansion in Dongping Lake. We employed moderate-resolution imaging spectroradiometer, normalized difference vegetation index data, and field investigations to extract its phenological characteristic. Landsat images from pondweed blooming and decay phases were acquired for eight representative growth stage years during the period of 1985-2017 to extract pondweed distribution. Through the validation, there was an accuracy of more than 89% for pondweed extraction in 2017. Then, we used a dimidiate pixel model to calculate its fractional green vegetation coverage (FVC). The results illustrated that its range expanded continuously during the 32-year study period. Its habitat changed from the scattered near shore distribution in 1985 to the contiguous coverage of large areas of the lake surface in 2017. The range expansion of pondweed was grouped into three stages. From 1985 to 1996, it had a slow growth stage with a maximum species range of 10.34 km(2) in Dongping Lake. During the period of 1996-2001, there was an explosive growth stage during which it become the dominant species in the Lake. From 2001 to 2017, the range continued to increase to 49.07 km(2), which comprised 40% of the surface area of the Lake. By spearman rank correlation analysis, we found that there was a significant correlation between pondweed area and the lake eutrophication level (R = 0.79, P < 0.05). The FVC spatial pattern after 2001 exhibited a gradual horizontal decrease from the southeast to the northwest of Dongping Lake. This study illustrates the application of vegetation phenology to assess the spatial and temporal pattern of pondweed. The opening of the ERP-CSNWDP is diverting a fraction of the total flow of the Yangtze River to Northern China via the Dongping Lake and presents an ongoing environmental security risk which will require future pondweed invasive species control and mitigation strategies utilizing ground and satellite-based spectrum observations.