Seasonal stratification characteristics of Nuozhadu Reservoir and influence of temperature changes

Abstract

[Objective] Thermal stratification is an important characteristic of lake and reservoir water ecosystems, affecting mixing, convection, nutrient cycling of water bodies, and the vertical distribution of dissolved oxygen(DO). Therefore, understanding the stratification patterns and their key influencing factors is essential. [Methods] Based on the high-frequency profile data collected over one year from Nuozhadu Reservoir, the temporal variations of temperature profiles, thermal stratification parameters, and thermal stability were analyzed on a daily scale. The driving factors of thermal stratification during different stratification periods were explored, and the impact of climate warming on thermal stratification and the water ecological environment was examined. [Results] The water column of Nuozhadu Reservoir showed clear stratification, with significant seasonal variations in the vertical distribution of water temperature and DO. The temperature difference between the surface and the bottom layers ranged from 2.8 to 12.3 ℃, with a minimum DO concentration of 0.59 mg/L occurring in the oxycline. The maximum thermocline thickness reached 14.85 m, while the relative water column stability(RWCS) peaked at 359.9 during the same period. [Conclusion] The daily variations in thermal stratification parameters reveal the formation, stabilization, and weakening phases of thermal stratification. Surface water temperature is identified as the main factor affecting thermal stratification. Additionally, climate warming may lead to more stable thermal stratification, extending the duration of stratification, changing DO concentration profiles and distributions, and causing other environmental issues. The findings provide scientific evidence for understanding the seasonal stratification and water chemistry characteristics of Nuozhadu Reservoir and the impacts of climate warming. The result are significant for reservoir water quality management and ecological environment protection.

Keywords

Nuozhadu Reservoir / thermal stratification / thermal stability / dissolved oxygen / climate change