Reducing MCPA herbicide pollution at catchment scale using an agri-environmental scheme

Area of Science:

• Environmental Science
• Agricultural Science
• Water Resource Management

Background:

• High pesticide concentrations in drinking water sources necessitate costly treatment.
• The herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) is highly mobile and problematic in water catchments.
• Agri-environmental schemes (AES) are implemented to mitigate pesticide pollution in water sources.

Purpose of the Study:

• To assess the effectiveness of an agri-environmental scheme (AES) in reducing pesticide (MCPA) concentrations in a drinking water source catchment.
• To evaluate the impact of substituting boom spraying of MCPA with contractor-applied glyphosate via weed wiping.
• To determine if the AES reduced the need for advanced water treatment processes.

Main Methods:

• A Before-After-Control-Impact (BACI) framework was employed over four peak application seasons (2018-2021).
• A neighboring catchment without an AES served as a control.
• Enhanced monitoring involved synchronous measurement of river discharge and MCPA concentrations (high-resolution sampling).

Main Results:

• The AES catchment showed reductions in flow-weighted (up to 21%) and time-weighted (up to 24%) MCPA concentrations compared to the control.
• MCPA export loads were substantial (up to 0.242 kg km⁻² yr⁻¹), exceeding previous literature values.
• No evidence of pollution swapping was detected.

Conclusions:

• The agri-environmental scheme demonstrated a positive impact on reducing MCPA concentrations in source waters.
• Despite reductions, MCPA occurrences above the 0.1 μg L⁻¹ threshold persisted, indicating the continued need for water treatment.
• Maximizing participation in AES is crucial for effectively resolving water treatment needs in source water catchments.