n field than beneath the corn field (Paterson & Schnoor, 1993, p. 991).
The reputed impact of a "riparian forest buffer" for the removal of nitrogen and phosphorus from a Virginia agricultural field, draining through the "forest" to an adjacent stream, is highly suspect (Snyder et al., 1998).
Zinc, lead, and iron in urban runoff--in addition to suspended solids removed by simple straining or filtration--have been adsorbed onto grassed urban roadway medians and "grassy swales" placed near roadways for that purpose for many years (Barret et al., 1998).
Organic Contaminants Removed. Uptake by rows of poplar trees of the herbicide, atracine, has been thoroughly investigated by researchers at the University of Iowa (Nair et al., 1993). They also reported work by others on removal of nitrobenzene and trichloroethylene (TCE) (Nair et al., 1993, p. 843). In addition to the metabolic uptake of these organics, the Iowa researchers learned through their own work and that of others that the trees are able first to change the initial, encountered chemical structure of the organic poisons to less toxic forms--essentially "detoxifying" themselves (Nair et al., 1993, p. 844).
Probably the best known P-R application by environmental engineers has been the use (since 1970) of a hardy noxious weed, the water hyacinth, placed in man-made greenhouses or "raceways" to treat already-treated municipal wastewater with a tertiary, polishing step prior to discharge of effluent to receiving streams (Karpiscak et al., 1994, p. 217). The major constituent of concern is general waste organic matter still in the dissolved state, measured as "biochemical oxygen demand" (BOD5) remaining in the water after 5 days. Removals at the Tucson facility averaged 62 to 74% for BOD5 (compared to influent levels of 15-30 mg/L)(Karpiscak et al., 1994, pp. 224-225), and 88 to 93% for nitrate-nitrogen (Karpiscak et al., 1994, p. 225).
Chang and Corapcioglu (1998) ...