ARS | Publication request: Metolachor-ESA as a marker for nitrate flux in a first-order stream and riparian zones

Submitted to: Soil and Water Conservation Society
Publication Type: Abstract Only
Publication Acceptance Date: July 17, 2011
Publication Date: N/A

Technical Abstract: There appears to be a connection with nitrate cycling in subsurface systems of the soil and metolachlor ethane sulfonic acid (MESA) which is a major environmental metabolite of metolachlor. This linkage has the potential to better define agricultural inputs of nitrate versus non-agricultural sources at stream and even watersheds levels. Metolachlor, as a major-use corn and soybean herbicide, is almost exclusively linked to agriculture and MESA concentrations, the major environmental metabolite of metolachlor, are often measured in ground and surface waters at more than ten times its parent. Certain properties about MESA support its high mobility in aqueous phases in soil. MESA is extremely water soluble, has very low binding affinity, and once formed in soil system is very stable to further breakdown. Data will be presented on measurements of MESA and nitrate in groundwater taken from lysimeters positioned in a riparian wetland system. Some of these wells had fast upwelling rates and some were very slow. Relative differences in concentrations of nitrate and MESA were observed over the depth of these wells which suggests different processing may be affecting these observations. This information will be assessed in terms of known properties of these different chemicals and implication to larger scale cycling processes involving nitrate and MESA.