Fluxes of agricultural nitrogen and metolachlor metabolites are highly correlated in a first order stream in Maryland, USA

Authors: Rice, Clifford; HIVELY, W. DEAN - Us Geological Survey (USGS); McCarty, Gregory; Hapeman, Cathleen

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2020
Publication Date: 1/8/2020
Citation: Rice, C., Hively, W.D., McCarty, G.W., Hapeman, C.J. 2020. Fluxes of agricultural nitrogen and metolachlor metabolites are highly correlated in a first order stream in Maryland, USA. Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2020.136590.
DOI: https://doi.org/10.1016/j.scitotenv.2020.136590

Interpretive Summary: Nitrate is a major problem in rivers and outfalls fed by water transiting major agricultural production areas of the US. For cropping systems, many best management practices have been implemented to abate these sources. So far, however, there are major difficulties in modeling the impact of the pollution abatement practices. One difficulty is distinguishing agricultural sources from point source and urban pollution. Agricultural tools to model nitrate need to be easily measured and track the transport of nitrate effectively. An abundant herbicide metabolite, metolachlor ethane sulfonic acid (MESA), was found to match nitrate movement into a stream near a metolachlor-treated field with high consistency over three years. In high cropping areas of the US, MESA is abundantly present in groundwater and stream water at concentrations typically exceeding all other herbicide-related compounds in these waters. It is proposed that MESA can be used as a tool to model nitrate transport that will be intrinsically linked to agricultural cropping practices. This information will be useful to scientists.

Technical Abstract: Nitrate pollution near heavy cropping areas of the US is a serious problem in the US. Cropping practices intended to reduce releases to impacted areas are being implemented by many states without adequate tools to model the effectiveness of these abatement tools. An abundant herbicide metabolite, metolachlor ethane sulfonic acid (MESA), was found to match nitrate movement into a small first-order stream near a metolachlor-treated field with high consistency, regression coefficient of 0.93 over three years. In high cropping areas of the US, MESA is abundantly present in groundwater and stream water at concentrations typically exceeding all other herbicide-related compounds in these waters. It is proposed that MESA can be used as a tool to model nitrate transport that will be intrinsically linked to agricultural cropping practices.