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Title:   Author  item
                                            McCarty, Gregoryitem
                                            HAPEMAN, C.J. - Collaboratoritem
                                            RICE, C.P. - Collaboratoritem
                                            HIVELY, DEAN W. - Us Geological Survey (USGS)item
                                            Sadeghi, Aliitem
                                            Lang, Meganitem
                                            WHITALL, D.R. - National Oceanic & Atmospheric Administration (NOAA)item
                                            BIALEK, K.K. - Collaboratoritem
                                            DOWNEY, P. - Collaborator
  Submitted to: Meeting Abstract
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 3/1/2014
                                    Publication  Date: 4/1/2014
                                    Citation: Mccarty, G.W., Hapeman, C., Rice, C., Hively, D., Sadeghi, A.M., Lang, M.W., Whitall, D., Bialek, K., Downey, P. 2014. Use of a metolachlor metabolite (MESA) to assess agricultural nitrate-n fate and transport in choptank river watershed, Maryland USA [abstract]. 2014 Annual European Geological Union Meeting,  April 27 -  May 2, 2014, Vienna, Austria.Interpretive Summary:
                                Technical Abstract: A majority of streams in the Chesapeake Bay watershed have been rated as poor or very poor based on biological assessments.  The Choptank River estuary, a Bay tributary on the eastern shore, is an example, where crop production in upland areas of the watershed contribute significant loads of nutrients to streams.  We used a novel approach based on the relationship between the concentration of nitrate-N and the stable, water-soluble herbicide degradation product MESA {2-[2-ethyl-N-(1-methoxypropan-2-yl) -6-methylanilino]-2-oxoethanesulfonic acid} to distinguish between dilution and denitrification effects on the stream concentration of nitrate-N in agricultural subwatersheds.  The ratio of mean nitrate-N concentration/(mean MESA concentration * 1000) for 15 subwatersheds was examined as a function of percent cropland on hydric soil.  The observed inverse relationship (R2 = 0.65, p < 0.001) accounts for not only dilution and denitrification of nitrate-N, but also the stream sampling bias of the croplands caused by extensive drainage ditch networks.  MESA was also used to track nitrate-N fate within the estuary of the Choptank River.  The relationship between nitrate-N and MESA concentrations in samples collected over three years was linear (0.95 = R2 = 0.99) for all eight sampling dates except one where R2 = 0.90.  This very strong correlation indicates that nitrate-N was conserved in much of the Choptank River estuary, that dilution alone is responsible for the changes in nitrate-N and MESA concentrations, and more importantly nitrate-N loads are not reduced in the estuary prior to entering the Chesapeake Bay.


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