What is the most significant reason for turnover in a surface water reservoir?

The most significant reason for turnover in a surface water reservoir is related to changes in surface water temperature and density. Turnover occurs when water at different temperatures and densities mixes, usually driven by seasonal temperature variations. In warmer months, the surface water becomes heated and less dense, leading to stratification where layers of water remain separate. As autumn approaches and surface temperatures cool, the water becomes denser and can sink, causing turnover. This process is crucial for distributing nutrients, oxygen, and other essential elements within the reservoir, helping to maintain a healthy aquatic ecosystem.

While increased evaporation rates can impact water levels and quality, they do not fundamentally drive the mixing process related to turnover. Similarly, pollution runoff affects water quality but does not directly influence turnover dynamics. While seasonal weather changes can initiate temperature shifts, it is the specific change in temperature and corresponding density shifts that are the most critical factors leading to turnover in a reservoir.