Reducing MCPA herbicide pollution at catchment scale using an agri-environmental scheme
Date
2022-05-20
Journal Title
Journal ISSN
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Publisher
Elsevier
Abstract
In river catchments used as drinking water sources, high pesticide concentrations in abstracted waters require an expensive
treatment step prior to supply. The acid herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) is particularly
problematic as it is highly mobile in the soil-water environment following application. Here, an agri-environmental
scheme (AES) was introduced to a large-scale catchment (384 km2) to potentially reduce the burden of pesticides in
the water treatment process. The main measure offered was contractor application of glyphosate by weed wiping as
a substitute for boom spraying of MCPA, supported by educational and advisory activities. A combined innovation applied
in the assessment was, i) a full before-after-control-impact (BACI) framework over four peak application seasons
(April to October 2018 to 2021) where a neighbouring catchment (386 km2) did not have an AES and, ii) an enhanced
monitoring approach where river discharge and MCPA concentrations were measured synchronously in each catchment.
During peak application periods the sample resolution was every 7 h, and daily during quiescent winter periods.
This sampling approach enabled flow- and time-weighted concentrations to be established, and a detailed record of
export loads. These loads were up to 0.242 kg km−2 yr−1, and over an order of magnitude higher than previously reported
in the literature. Despite this, and accounting for inter-annual and seasonal variations in river discharges, the
AES catchment indicated a reduction in both flow- and time-weighted MCPA concentration of up to 21% and 24%, respectively,
compared to the control catchment. No pollution swapping was detected. Nevertheless, the percentage of
MCPA occurrences above a 0.1 μg L−1 threshold did not reduce and so the need for treatment was not fully resolved.
Although the work highlights the advantages of catchment management approaches for pollution reduction in source
water catchments, it also indicates that maximising participation will be essential for future AES.
Description
Publication history: Accepted - 16 May 2022; Published online - 20 May 2022.
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Article
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Keywords
MCPA, Drinking water, Before-after-control-impact, Herbicides, Agri-environmental scheme, Water quality monitoring
Citation
Cassidy, R., Jordan, P., Farrow, L., Floyd, S., McRoberts, C., Morton, P. and Doody, D. (2022) ‘Reducing MCPA herbicide pollution at catchment scale using an agri-environmental scheme’, Science of The Total Environment. Elsevier BV. doi:10.1016/j.scitotenv.2022.156080.