Quantifying MCPA load pathways at catchment scale using high temporal resolution data
Date
2022-05-24
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Publisher
Elsevier
Abstract
Detection of the agricultural acid herbicide MCPA (2-methyl-4-chlorophenoxyacetic acid) in drinking water
source catchments is of growing concern, with economic and environmental implications for water utilities and
wider ecosystem services. MCPA is poorly adsorbed to soil and highly mobile in water, but hydrological pathway
processes are relatively unknown at the catchment scale and limited by coarse resolution data. This understanding
is required to target mitigation measures and to provide a framework to monitor their effectiveness. To
address this knowledge gap, this study reports findings from river discharge and synchronous MCPA concentration
datasets (continuous 7 hour and with additional hourly sampling during storm events) collected over a 7
month herbicide spraying season. The study was undertaken in a surface (source) water catchment (384 km2โof
which 154 km2 is agricultural land use) in the cross-border area of Ireland. Combined into loads, and using two
pathway separation techniques, the MCPA data were apportioned into event and baseload components and the
former was further separated to quantify a quickflow (QF) and other event pathways. Based on the 7 hourly
dataset, 85.2 kg (0.22 kg km๔ 2 by catchment area, or 0.55 kg km๔ 2 by agricultural area) of MCPA was exported
from the catchment in 7 months. Of this load, 87.7 % was transported via event flow pathways with 72.0 %
transported via surface dominated (QF) pathways. Approximately 12 % of the MCPA load was transported via
deep baseflows, indicating a persistence in this delayed pathway, and this was the primary pathway condition
monitored in a weekly regulatory sampling programme. However, overall, the data indicated a dominant acute,
storm dependent process of incidental MCPA loss during the spraying season. Reducing use and/or implementing
extensive surface pathway disconnection measures are the mitigation options with greatest potential, the success
of which can only be assessed using high temporal resolution monitoring techniques.
Description
Publication history: Accepted - 21 May 2022; Published online - 24 May 2022.
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Article
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Keywords
Pesticides, MCPA, Catchments, Pathways, Export loads
Citation
Atcheson, K., Mellander, P.-E., Cassidy, R., Cook, S., Floyd, S., McRoberts, C., Morton, P.A. and Jordan, P. (2022) โQuantifying MCPA load pathways at catchment scale using high temporal resolution dataโ, Water Research. Elsevier BV. doi:10.1016/j.watres.2022.118654.