Abstract:

Lake water quality monitoring is the foundation for the effective implementation of comprehensive management of lake water environment as well as water pollution prevention and control. Moreover, the dynamic monitoring of water quality can provide an important basis for the assessment of the risk of algal bloom in lakes and the ecological safety construction in the lake area. Dongting Lake is the second largest freshwater lake in China, the acceleration industrialization and urbanization had caused the lake water pollution to be more and more serious in recent years. Many studies were focused on the traditional water quality monitoring method that rely on chemical analysis after water sample collection, but paid less attention to the remote sensing technique due to the shortages of aerospace imagery. In this paper, the GF-1 image during the period 2014-2016 were collected based on the high resolution earth observation system Hunan Data and Application Center, and the inversion of water quality parameters of Dongting Lake was carried out including chlorophyll-a concentration, suspended matter concentration and transparency. The water boundary of Dongting Lake was extracted by the normalized water index (NDWI), and water quality parameters were quantitatively retrieved by the remote sensing model. The results show that the chlorophyll-a was mainly concentrated in the Anle Lake, Daxiao West Lake and the western part of East Dongting Lake, where the flow speed is slow, the chlorophyll-a content in other parts of Dongting Lake is relatively low due to water disturbance. The transparency of water quality is relatively high in the tributaries, then decreases from south to north and reaches the peak in the Yangtze River Estuary. There is a negative correlation of spatial distribution between transparency and suspended matter concentration as a whole, which is consistent with the routine monitoring rule. The water quality of the East Dongting Lake is much worse than that of the southern Dongting Lake and the West Dongting Lake. The water pollution of East Dongting Lake is at the highest level of the whole lake, which is closely related to human activities, causing a large amount of pollutants, agriculture and forestry chemical fertilizer being discharged into the East Dongting Lake. The GF-1 PMS imagery can accurately reflect the spatial variation of chlorophyll a concentration, suspended solids concentration and transparency index, and this study is expected to provide an important reference for the study of theory, method and application of inland lake water quality monitoring based on high-resolution remote sensing images.

Key words: Dongting Lake region, chlorophyll-a concentration, suspended solids concentration, transparency