Atrazine Transport through a Soil–Epikarst System

• Published in: Journal of environmental quality 2018-09, Vol.47 (5), p.1205-1213
• Main Authors: Lerch, R. N., Groves, C. G., Polk, J. S., Miller, B. V., Shelley, J.
• Format: Article
• Language: English
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2017.12.0492

Row crop and livestock production contaminate soils and groundwater of the karst aquifers within south‐central Kentucky's Pennyroyal Plateau. Transport of atrazine from field application to the epikarstic drainage system beneath a field with active row‐crop farming was investigated. The Crumps Cave study site is a shallow autogenic drainage system with a recharge area of ∼1 ha that contains two epikarst drains (WF‐1 and WF‐2) which were monitored for atrazine, deethylatrazine (DEA), and deisopropylatrazine (DIA) concentrations from January 2011 to May 2012. Atrazine concentrations in both drains did not increase above winter background levels for nearly 2 mo after application when levels suddenly spiked and reached peak concentrations for the study during an event in May 2011. Atrazine, DEA, and DIA were detected in 100% of samples, and metabolites accounted for 54 to 94% of the monthly total loads, except in May 2011. Median dealkylated metabolite/atrazine ratios (DMAR) were ∼5:1 at both sites, and seasonal DMAR patterns corresponded with changes in soil temperature. These data support the hypothesis that a combination of sorption and degradation in the soil column above the epikarst controlled the transport of atrazine and its metabolites. This resulted in delayed atrazine transport after application and prolonged transport of atrazine and its weakly sorbed metabolites to the epikarst aquifer. Management practices that reduce herbicide inputs, such as diverse crop rotations, cover crops, and use of low‐rate and strong‐sorbing herbicides, would improve groundwater quality in areas of the Corn Belt with intensive row cropping on karst topography. Core Ideas Atrazine leaching to the epikarst was comparable with surface runoff losses. Sorption and degradation in soil controlled atrazine transport. After 10 mo, atrazine concentrations showed zero‐order kinetic declines.