Primary productivity of phytoplankton and its influencing factors in cold and arid regions: A case study of Wuliangsuhai Lake, China

Abstract

This study measured the primary productivity (PPeu) of phytoplankton in Wuliangsuhai Lake from April 2014 to January 2019 based on the monitoring and on-site exploration of 20 sampling points in the entire lake using a vertically generalized production model (VGPM). The relationship between the spatiotemporal variation in PPeu and environmental factors was also analyzed. Our findings indicated that the temporal heterogeneity of PPeu was strong, and the average annual PPeu of the four seasons was significantly different (P < 0.05, F = 54.74), exhibiting the following descending order: summer (1279.89 ± 111.04 mg C∙m−2∙d−1) > spring (782.42 ± 59.34 mg C∙m−2∙d−1) > autumn (465.03 ± 49.30 mg C∙m−2∙d−1) > winter (96.34 ± 10.36 mg C∙m−2∙d−1). Even in winter with harsh environmental conditions, PPeu under the ice sheet can reach 8 % of that in summer. The spatial heterogeneity was weak, and only the average annual PPeu in spring exhibited a significant spatial difference (P < 0.05, F = 5.18): north > central > south. However, there were no significant differences in other seasons. Redundancy analysis (RDA) and multiple linear regression (MLR) results showed that in addition to directly participating in the calculation of the environmental factors of PPeu, PPeu in spring was mainly affected by total nitrogen (TN), total phosphorus (TP), and dissolved oxygen (DO). PPeu in summer was mainly affected by dissolved inorganic phosphorus (DIP), dissolved oxygen (DO), salinity (S), electrical conductivity (EC), and water temperature (WT). PPeu in autumn was mainly affected by pH, electrical conductivity (EC), suspended solids (SS), and water temperature (WT). PPeu in winter was mainly affected by water temperature (WT) and ice thickness (IT). The mechanisms through which environmental factors affect primary productivity are complex and dynamic. Therefore, long-term monitoring and research of PPeu in Wuliangsuhai Lake are necessary to explore the adaptation strategies of phytoplankton in ice and ice-free periods and understand the operation of natural life support systems under the alternation of ice generation and extinction. In turn, this would facilitate the development of strategies to maintain phytoplankton biodiversity and prevent algal blooms.