Wetland nutrient removal: a review of the evidence

Data from 57 wetlands from around the world have been collated to investigate whether wetlands affect the nutrient loading of waters draining through them: the majority of wetlands reduced nutrient loading and there was little difference in the proportion of wetlands that reduced N to those that reduced P loading. However, some wetlands increased nutrient loadings by increasing the loading of soluble N and P species thus potentially driving aquatic eutrophication. Studies conducted over a period of a year or more, or that involved frequent sampling during high flow events, were more likely to indicate that the wetland increased nutrient loadings. Swamps and marshes differed from riparian zones in their nutrient function characteristics by being slightly more effective at nutrient reduction than riparian zones, The attributes that enable wetlands to be effective in reducing N and P loadings need consideration when constructing or managing wetlands to reduce nutrient loadings. Their wise use will be an important strategy for meeting the Water Framework Directive requirements for many water bodies.