Lakes, despite their often tranquil appearance, are dynamic bodies of water that experience various forms of currents. These movements are fundamental to the ecological processes within lake environments. Understanding these currents helps to explain how lakes function and support diverse aquatic life.
What Drives Currents in Lakes?
Several forces contribute to currents in lakes, influencing water movement. Wind is a primary driver, creating stress on the water surface that pushes water in the direction of the wind. This initiates surface currents and, in larger lakes, influences deeper circulation patterns.
Temperature stratification, where water forms distinct layers based on temperature and density, also plays a role. Warmer, less dense water floats on top of cooler, denser water, resisting mixing. However, density differences can also drive currents, particularly during seasonal changes when the lake undergoes mixing, known as turnover.
Inflow from rivers and streams entering a lake, and outflow from outlets, create hydraulic currents as water moves through the basin, contributing to the lake’s overall circulation. The Earth’s rotation, through the Coriolis effect, can subtly deflect currents in larger lakes, leading to predictable circulation patterns like gyres.
Different Forms of Lake Currents
Lakes exhibit various types of currents, each with distinct characteristics. Surface currents are predominantly driven by wind and affect the uppermost layer of the lake, and are the most common type found in lakes.
Beneath the surface, deep currents and internal waves are driven by density differences or the oscillation of stratified layers. Internal waves move water along the boundaries between layers of different densities, such as the thermocline, and can move water both vertically and horizontally. A seiche is a standing wave that resembles water sloshing back and forth in a bathtub. Seiches are caused by strong winds or rapid changes in atmospheric pressure pushing water to one side of the lake.
Wind can also lead to upwelling and downwelling. Upwelling occurs when wind pushes surface water away from a shore, drawing colder, nutrient-rich water up from deeper areas. Conversely, downwelling happens when wind piles surface water against a shore, pushing it downwards. Near shorelines, currents like rip currents, longshore currents, channel currents, and structural currents can form due to interactions between waves, wind, and the lake’s bottom topography or man-made structures.
The Impact of Lake Currents
Lake currents influence the lake ecosystem and can affect human activities. They are important for distributing dissolved oxygen throughout the water column, which is important for aquatic organisms, especially in deeper waters where oxygen can become depleted. This mixing helps prevent the formation of “dead zones” where oxygen levels are too low to support most life.
Currents also play a role in nutrient transport, moving nutrients that support the food web, from algae to fish. This movement helps to circulate nutrients that might otherwise settle on the lakebed, making them available for organisms throughout the water column. Currents contribute to sediment transport, moving and depositing particles across the lakebed, which can reshape the lake’s bottom over time.
Regarding water quality, currents can help disperse pollutants, diluting their concentration and spreading them throughout the lake, though this also means they can spread contaminants more widely. Currents also regulate temperature by distributing heat throughout the lake, influencing the thermal structure and mixing of water layers. For recreation and safety, currents can impact boating, swimming, and fishing conditions, with certain types of currents, like rip currents, posing hazards to swimmers.