Do constructed wetlands in grass strips reduce water contamination from drained fields?

Area of Science:

• Environmental Science
• Agricultural Engineering
• Water Quality Management

Background:

• Agricultural runoff pollutes rivers with nitrates and pesticides.
• Constructed wetlands in regulatory grass strips are a potential mitigation strategy.
• Evaluating their efficiency for nutrient and pesticide removal is crucial.

Purpose of the Study:

• To assess the nitrate and pesticide removal efficiency of small constructed wetlands.
• To determine the influence of wetland type and season on removal rates.
• To identify factors affecting pesticide removal and inform management strategies.

Main Methods:

• Installation and monitoring of two small constructed wetlands in agricultural buffer zones.
• Measurement of nitrate and pesticide concentrations in influent and effluent water.
• Calculation of mass budgets and removal efficiencies for various pesticide molecules.
• Analysis of pesticide properties (Koc, DT50) in relation to removal performance.

Main Results:

• Nitrate removal efficiencies were consistently low (5.4–10.9%) and unaffected by season or wetland type.
• Pesticide mass budgets varied widely (-618.5% to 100%), with negative values indicating runoff and remobilization.
• High removal efficiencies were observed for pesticides with high Koc and low DT50 values (indicating sorption and degradation).
• Wetlands were less effective for pesticides with low Koc or high DT50 values.

Conclusions:

• Small constructed wetlands offer limited nitrate removal but show variable pesticide removal.
• Pesticide removal is strongly dependent on molecular properties like sorption (Koc) and degradation rate (DT50).
• Reducing the use of less effectively removed pesticides is essential.
• Widespread implementation could reduce agricultural water pollution, but long-term performance requires further study.