Analysis of Influencing Factors on Phytoplankton Primary Productivity Across Ice-Free and Ice-Covered Seasons Through Remote Sensing and Optical Parameter Correction

The primary productivity of phytoplankton (PPeu) is critical to the carbon cycle in aquatic ecosystems. However, in complex lakes covered by ice, the estimation of PPeu using remote sensing techniques is constrained. To address this limitation, this study developed an estimation model for ice-covered PPeu by incorporating optical parameters such as the ice surface refractive index and the extinction coefficient of the ice layer into the vertical generalized production model (VGPM). This approach overcomes the challenges associated with remote sensing-based estimation of PPeu during ice-covered periods. The results indicate that the annual carbon sequestration of the WLSHL is 1.72 × 104 t C, with an average annual PPeu of 316.96 mg C·m−2·d−1. In addition to the indicators that are directly involved in the estimation of PPeu, the environmental factors that affect PPeu include water temperature (WT), ice thickness (IT), snow, water depth (D), total dissolved solids (TDSs), salinity (S), ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), and oxidation–reduction potential (ORP). The PPeu in the ice period is found to be only 17% lower than that in the ice-free period. However, the PPeu during the ice period is considerably higher than that during the ice + snow period. The findings indicate that the impact of freezing on PPeu during the winter is relatively limited, whereas the influence of snowfall is more pronounced. In order to mitigate the elevated PPeu and the occurrence of algal blooms during the summer, the intensity of underwater radiation can be regulated on a periodic basis. To optimize the function of the carbon sink in winter lakes, the PPeu can be enhanced through initiatives such as water replenishment prior to freezing and snow removal following freezing.