Ecological Indicators (Oct 2022)
Dynamic monitoring of phycocyanin concentration in Chaohu Lake of China using Sentinel-3 images and its indication of cyanobacterial blooms
Abstract
Phycocyanin (PC) is an indicator pigment of cyanobacteria in water. Monitoring the dynamic variation of PC concentration in lakes by satellite remote sensing is of great significance for the effective prevention and control of cyanobacterial blooms (CBs). Few studies have quantitatively monitored the long-term PC concentration variation in water and explored the relationship between PC concentration and CBs based on the advantages of the high temporal and spectral resolution of Sentinel-3 OLCI images. In this study, a retrieval model of PC concentration suitable for Sentinel-3 OLCI images was constructed and applied to the Sentinel-3 image dataset from May 2016 to November 2021 to analyze the spatiotemporal PC concentration variations in Chaohu Lake of China. The factors influencing PC concentration and its indicative significance for CBs outbreak were also explored. The results show that the PC concentration retrieval model based on the gradient boosting regression algorithm has the best performance (R2 = 0.86, root mean square error = 45.44 ug/L, and mean absolute percentage error = 26.27 %), which has great application potential in the retrieval of other water quality parameters. In summer and autumn, the PC concentration in western Chaohu Lake was higher than that in other lake parts, which was mainly related to the higher nutrient concentration and prevailing wind direction in this part. During 2016–2021, the average PC concentration in Chaohu Lake in 2019 was the highest, and that in 2017 was the lowest, mainly affected by air temperature and precipitation. The variation of PC concentration in Chaohu Lake has a high temporal consistency with the proportion of CBs area, and the PC concentration of 303.9 μg/L is a necessary condition for CBs outbreak. This study revealed that Sentinel-3 OLCI images could provide a useful data source for high-frequency dynamic monitoring of PC concentrations in lakes and reservoirs, and the quantitative monitoring of PC concentrations in water has relevant indicative significance for early warning of CBs in inland water.
