Why can building an impoundment alter or destroy a wetland?

Building an impoundment can significantly alter or destroy a wetland by disrupting its natural hydroperiod—the specific timing, duration, and quantity of water that defines the system.1

Wetlands rely on precise environmental conditions, including geomorphology and water flow, to maintain their unique ecosystem functions. When an impoundment is constructed, it forces water to gather and remain in areas where it might not naturally accumulate, or it prevents water from following its typical drainage patterns. This shift in water levels can lead to several consequences:1

• Soil Chemistry Changes: Wetlands are characterized by waterlogged soils that limit oxygen availability. Altering the water depth can change the oxygen levels in the soil, potentially making the environment uninhabitable for the specialized vegetation and organisms adapted to those specific conditions.1
• Habitat Disruption: While some structures, like beaver dams, can create new habitats, human-made impoundments often lack the natural, dynamic flow of riparian systems. By blocking natural channels, they can prevent the periodic flooding necessary for floodplain wetlands to thrive, effectively destroying the ecological connectivity of the area.2