Freshwater wetlands can, in some circumstances, renovate added secondarily treated wastewater, thus providing an alternative to land or water disposal or expensive physical‐chemical treatment processes. This review summarizes North American studies in the contexts of ecosystem function and water quality changes, for both natural and artificial wetland ecosystems. All components of an ecosystem are involved in the alteration of the dissolved nutrient status and sediment content of the water. The results of recent studies are interpreted in terms of the principles of hydrology and nutrient cycling in wetlands. Initial uptake and alteration mechanisms involve sorption and microbial processes, such as denitrification. Peat soils provide a maximum condition for this rapid uptake. Detritus supports microbial populations and active periphyton, which coupled with other algae, represent a second temporary sink. The vascular plant community also represents nutrient storage which may be exploited by herbivores or detritivores. Decomposition subsequently releases some of the nutrients to recycle, while the remainder is stored as peat. The buffer performance of these ecosystems is interpreted in light of prevailing economic, political, and regulatory considerations.