Seasonal sediment phosphate release flux of shallow lakes impacted by dual environmental factors

It is a difficult task to predict the phosphate release flux from sediments in shallow lakes in different seasons due to the uncertainty of seasonal changes in phosphate release, especially considering the combined influence of water temperature and dynamic disturbance. Therefore, it is worth investigating the spatiotemporal changes of phosphate release from sediments under the combined impacts of hydrodynamic processes and water temperature.

To analyze the seasonal patterns of phosphate release in shallow lakes, a physical model of sediment release in Chaohu Lake was established, and the phosphate release rates of 12 original sediment columns were observed under the combined effects of three levels of hydrodynamic disturbance intensity and temperature.

The experimental results showed that under the three hydrodynamic conditions, when the temperature increases from 10 to 30 °C, the phosphate release rate decreases at first and then increases. Through linear fitting, it is found that when the disturbance increases from weak to strong (three levels: I disturbed → II disturbed → III disturbed), the temperature corresponding to the minimum phosphate release rate (V_min) of the sediment decreases (24.64 °C → 24.14 °C → 23.68 °C). The corresponding tables of sediment release rate under five water temperatures and three hydrodynamic disturbances were developed, and then, the seasonal release flux of phosphate could be estimated.

According to the estimates, the phosphate release was the largest in summer, with little difference in spring and autumn, and was the smallest in winter. Future warming will induce the greatest impact in spring. The results of this study are of great significance to the scientific diagnosis of the phosphate cycle in shallow lakes.