The impacts of human activities on lake levels is discussed in later chapters. Wetlands Wetlands have an essential role to play in controlling water levels in the Great Lakes ecosystem. Wetlands are reservoirs that moderate the sometimes extreme water level changes in the lakes. In periods of high precipitation, wetlands store large quantities of water, gradually releasing it later. In periods of normal or low precipitation, wetlands are discharge areas, which maintain the water levels of water bodies in the Great Lakes Basin.
Wetlands are also important areas for groundwater recharge.
They trap water and allow it time to seep deep into the ground to replenish aquifers. Because wetlands are thickly vegetated, they act as a buffer zone for shorelines against the waves coming off the lakes. Fluctuating water levels are crucial to the vegetation of wetlands. Lower water levels provide the conditions for a number of species to emerge from buried seeds, while trees and shrubs can begin to move closer to the lakes. Higher water levels, on the other hand, open up a dense growth of cattails, trees, and shrubs.