Assessing algal blooms in Taihu Lake using hourly data: Seasonal characteristics and the relationship with...

Large-scale algal blooms attack Taihu Lake frequently in recent years. In this study, the hourly coverage area of algal blooms in Taihu Lake is detected using Geostationary Ocean Color Imager (GOCI) images and its relationship with environmental factors is analyzed based on the measurements including fluorescent dissolved organic matter(fDOM), water temperature (Tw), hourly air temperature (Ta), hourly maximum air temperature (Tm) and wind speed (V). Other remote sensing products are also employed, including photosynthetically active radiation (PAR). The data in this study covers a period from March 2020 to March 2021 with a temporal resolution of one hour. Tw, Ta, and Tm exhibit a positive relationship with the coverage area of algal blooms in spring, autumn, and winter, and a negative relationship in summer. In winter, the coverage area of algal blooms is more sensitive to water temperature (r = 0.85). A method was proposed to investigate the coverage area of algal blooms in Taihu Lake based on environmental factors. The maximum likelihood estimation method was adopted in this proposed method, and the results were determined using BIC methods. The coefficients of determination (R²) for the regression model are 0.75, 0.74, 0.57, 0.83 in spring, summer, autumn and winter, respectively. The algal blooms happen in a fDOM ranging from 12 to 20 QSU, with highest Tw of 33 °C (37 °C for Ta and Tm) and the highest wind speed of 9 m/s. The wind speed is negatively correlated with the coverage area of algal blooms, while the PAR is positively correlated. When water temperature is below 26.86 °C, an increase in temperature promotes the growth of algal blooms(r = 0.71). However, the growth of the algal bloom becomes inhibited when water temperature exceeds 26.86 °C (r = -0.33) or the fDOM concentration exceeds 15.97 QSU.