Are wetlands really effective in reducing nitrate and other chemicals?

Yes.

Wetlands are extremely effective at reducing nitrate and other chemicals if properly designed and managed. The rates of some biological processes in wetlands are known and this area is the subject of ongoing research by the Wetlands Research Group at Iowa State University. Using this information, ratios of wetland area to cropland drained can be estimated based on a desired processing efficiency.

The major questions addressing the efficacy of wetlands for treatment of NPS pollutants relate to siting wetlands at the watershed level to maximize efficiency and providing the incentives and cost-shares required to effect implementation. In some midwestern streams baseflow consists primarily of water from field drainage tiles. These tiles by-pass riparian buffers carrying water rapidly from the uplands under the buffers and into the stream. In assessing the upper third of the Bear Creek Watershed over 100 tiles were found entering the creek. Of these 8 were large tiles that contributed over 80% of the tile flow to the creek. The present strategy is to construct large wetlands to intercept the largest of the large tiles to have an impact on reducing nutrient loading from the tiles.