Spatiotemporal patterns and drivers of phytoplankton primary productivity in China's lakes and reservoirs at a national scale

Phytoplankton primary productivity (PP) plays an important carbon (C) balance role in aquatic ecosystems. In China, although phytoplankton PP and affiliated environmental controlling factors have been widely studied in various lake systems, most relevant studies have only focused on individual lakes. As the absence of long-term and large-scale phytoplankton PP measurements, there still exists a large knowledge gap on the spatiotemporal patterns and drivers of phytoplankton PP in China's lakes and reservoirs at a national scale. This study evaluated the spatiotemporal dynamics of phytoplankton PP and the carbon sequestration capacity (CSC) of China's lakes and reservoirs nationwide by building a vertically generalized production model (VGPM) based on long-term in situ water quality monitoring data. Generally, the seasonal pattern of phytoplankton PP was higher in spring and summer and lower in autumn and winter. Annual phytoplankton CSC was estimated at 18.69 ± 10.7 Tg C yr−1, nearly half of which derives from lakes and reservoirs in China's continental basin and the Yangtze River basin. The relative contributions of 11 potential environmental variables to spatiotemporal changes in phytoplankton PP were quantified in China's nine prominent basins based on multivariate generalized linear model (GLM) regression analysis. Of these 11 potential driving factors, chlorophyll content, nitrogen (N) and phosphorus (P), and turbidity were determined to be the major drivers of phytoplankton PP. This study provides the first national scale estimate of phytoplankton PP in China's lakes and reservoirs, which will help us better understand aquatic-based ecosystem C budgets throughout the entire country.