Investigation of Water Temperature Variations and Sensitivities in a Large Floodplain Lake System (Poyang Lake, China) Using a Hydrodynamic Model

Although changes in water temperature influence the rates of many ecosystem processes in lakes, knowledge of the water temperature regime for large floodplain lake systems subjected to multiple stressors has received little attention. The coupled models can serve to derive more knowledge on the water temperature impact on lake ecosystems. For this purpose, we used a physically-based hydrodynamic model coupled with a transport model to examine the spatial and temporal behavior and primary causal factors of water temperature within the floodplain of Poyang Lake that is representative of shallow and large lakes in China. Model performance is assessed through comparison with field observations and remote sensing data. The daily water temperature variations within Poyang Lake were reproduced reasonably well by the hydrodynamic model, with the root mean square errors of 1.5–1.9 ◦C. The modeling results indicate that the water temperature exhibits distinct spatial and temporal variability. The mean seasonal water temperatures vary substantially from 29.1 ◦C in summer to 7.7 ◦C in winter, with the highest value in August and the lowest value in January. Although the degree of spatial variability differed considerably between seasons, the water temperature generally decreases from the shallow floodplains to the main flow channels of the lake. As expected, the lake water temperature is primarily affected by the air temperature, solar radiation, wind speed and the inflow temperature, whereas other factors such as cloud cover, relative humidity, precipitation, evaporation and lake topography may play a complementary role in influencing temperature. The current work presents a first attempt to use a coupled model approach, which is therefore a useful tool to investigate the water temperature behavior and its major causal factors for a large floodplain lake system. It would have implications for improving the understanding of Poyang Lake water temperature and supporting planning and management of the lake, its water quality and ecosystem functioning.