Pesticide transport through the vadose zone under sugarcane in the Wet Tropics, Australia
Author:
Karim RezaulORCID, Reading LucyORCID, Dawes Les, Dahan Ofer, Orr GlynisORCID
Abstract
Abstract. Photosystem II (PS II) pesticides, recognized as a threat
to ecological health, were targeted for reduction in sugarcane farming in
Great Barrier Reef (GBR) catchments. Alternative herbicides, the non-PS
II herbicides (including glyphosate, paraquat, 2,4-D, imazapic,
isoxaflutole, metolachlor, and S-metolachlor), continue to be used in these
catchments. However, the potential ecological fate, transport, and off-site
environmental effects of non-PS II herbicides, with respect to their usage
scheme, local rainfall patterns, and infiltration dynamics, have not been
investigated previously. A vadose zone monitoring system, instrumented
beneath sugarcane land in a GBR catchment, was applied for real-time
tracing of pesticide migration across the unsaturated zone, past the root
zone during 2017–2019. The regularly applied pesticides (fluroxypyr and
isoxaflutole) exhibited substantial migration through the unsaturated zone.
Within 1 month of application of fluroxypyr, it leached to 2.87 m depth
in the vadose zone, with declining concentrations with depth. Isoxaflutole,
which was applied yearly, was found only once, in November 2018, at 3.28 m depth in the soil profile. Other pesticides (imazapic, metolachlor,
glyphosate, and haloxyfop) applied during the same period were not detected
in the vadose zone. However, imidacloprid, which was not applied at the
site during the monitored period, was detected across the entire vadose
zone, revealing substantial resistance to degradation. The results show no
evidence of any regularly applied pesticides in the site bores at the end of
the study, indicating their ultimate degradation within the vadose zone
before reaching the groundwater.
Publisher
Copernicus GmbH
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