Lake turnover

Lake turnover is the seasonal mixing of a lake’s water when temperature-driven density differences between layers weaken, allowing wind to circulate water through the lake.

Thermal stratification: The layering of water by temperature and density, which restricts vertical mixing. Turnover occurs when seasonal cooling or warming weakens these distinct layers.
Dissolved oxygen: Molecular oxygen dissolved in water and available to aquatic organisms. Turnover can carry oxygen-rich surface water into deeper layers.
Dimictic lake: A lake that typically mixes twice yearly, in spring and autumn. Its two annual mixing periods are the classic pattern of seasonal turnover.
Climate change in lakes: The physical, chemical, and ecological changes in lakes caused by a changing climate. Warming and altered ice cover can shift turnover timing and frequency.
Water density: Mass per unit volume; freshwater reaches its greatest density near 4°C. Temperature-dependent density differences create the layers that turnover disrupts.
Nutrient cycling: The movement and transformation of nutrients through organisms and the environment. Mixing transports nutrients between lake sediments, deep water, and surface waters.
Monomictic lake: A lake that mixes completely once each year. Its single annual mixing event contrasts with the twice-yearly pattern.
Lake ice phenology: The seasonal timing of lake ice formation, persistence, and breakup. Earlier ice breakup can change spring mixing and the onset of stratification.
Wind-driven circulation: The movement of water produced when wind transfers momentum to a lake’s surface. Wind supplies much of the force that mixes a lake once layering weakens.
Lake eutrophication: The enrichment of a lake with nutrients, often leading to excessive algal growth and oxygen depletion. Turnover can redistribute nutrients that support blooms or compounds released from deep water.

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