Vegetated treatment systems reduce pesticides in surface waters
August 01, 2011
Constructed wetlands or ditches planted with dense vegetation can cut pesticide concentrations in downstream waters by more than 70%, suggesting that widespread implementation of these low-cost “vegetated treatment systems” could put a major dent in the pesticide pollution flowing from farmlands.
That’s according to a study appearing in the current issue of the Journal of Environmental Quality, led by Sebastian Stehle of University of Koblenz-Landau in Germany. Although building and directing water through these systems is already a popular best management practice (BMP) for retaining, accumulating, and degrading agricultural pesticides, scientists still know very little about how much pesticide is removed or which designs are most effective, say the researchers.
To find out, a team from the University of Koblenz-Landau and collaborators in France combed the scientific literature for all published papers on flow-through vegetated treatment systems, and recorded the pesticide concentrations reported by the studies before and after water passed through the systems. The team also extracted information on the physicochemical properties of specific pesticides, and the specifications of treatment systems, including their surface area, depth, plant density, and hydraulic retention time.
This information was then combined with findings from the four-year, European LIFE ArtWET project, which analyzed pesticide reduction in five vegetated treatment system prototypes installed in small agricultural streams in France and Germany.
The scientists’ meta-analysis of the combined data revealed that nearly half the pesticide concentrations in surface waters upstream of vegetated treatment systems exceeded acute toxicity threshold levels. After passing through these systems, however, pesticide levels in surface waters dropped by more than 70% on average. This included levels of highly toxic, modern insecticides—an especially important finding, the researchers say, considering that outbreaks of insect pests may increase with global warming, resulting potentially in even heavier use of insecticides. To remove pesticides most effectively, the study identified high plant density and long hydraulic retention times as especially important factors in system design.
The integration of findings from many analyses, or meta-analysis, promises to facilitate the optimization of existing vegetated treatment systems, the authors says, as well as promote the installation of these low-cost and easy-to-implement technologies in agricultural surface waters worldwide.
However, because these systems can’t reduce pesticide contamination in upstream stretches of streams, the researchers also caution that vegetated treatment systems should be located as close as possible to areas where pesticides are being applied, and implemented with other BMPs as part of a holistic, catchment-wide approach to environmental management.
Material summarized from:
Pesticide Risk Mitigation by Vegetated Treatment Systems: A Meta-Analysis
Sebastian Stehle, David Elsaesser, Caroline Gregoire, Gwenaël Imfeld, Engelbert Niehaus, Elodie Passeport, Sylvain Payraudeau, Ralf B. Schäfer, Julien Tournebize and Ralf Schulz
Journal of Environmental Quality