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Predicting the Contribution of Atmospheric Deposition to the Seasonal Nitrogen Loads in the East Fork Little Miami River Watershed, Ohio

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Watershed ManWatershed Management to Meet Water Quality Standards and TMDLS (Total Maximum Daily Load) Proceedings of the 10-14 March 2007, San Antonio, Texas  701P0207.(doi:10.13031/2013.22447)
Authors:   Diana P Mitsova-Boneva, Xinhao Wang
Keywords:   Keywords: dry deposition, wet deposition, CASTNet, NADP/NTN, inorganic nitrogen, ordinary kriging, semivariogram, land cover, retention and export coefficients

The purpose of this study is to estimate the contribution from atmospheric deposition to the seasonal loads of wet and dry deposited nitrogen species in the streams of East Fork Little Miami River (EFLMR) watershed, OH. The study expands on a previous investigation which estimated with BASINS-HSPF the daily loads of inorganic nitrogen in surface runoff for the same watershed. The study is based on the measurements collected from January 1993 to December 1995 at eleven CASTNet (USEPA, 1995) and eleven NADP/NTN (National Atmospheric Deposition Program/ National Trends Network, 2000) monitoring sites. Since there are no CASTNet and NADP/NTN monitoring stations within the watershed, wet and dry deposition fluxes and their spatial variability are estimated by ordinary kriging methods based on significant Gaussian and spherical semivariogram models. Nitrogen export and retention coefficients based on land cover and hydrologic soil group are considered to estimate the actual contribution of atmospheric deposition to the total nitrogen delivery rates to the watershed. CASTNet dry deposition and NADP/NTN wet deposition estimates are grouped by land cover classification and season. The goodness of fit of the semivariogram models, the wet to dry seasonal deposition ratios, and assessment of each land cover class as a contributing factor are also discussed. The study found that both the deposition of inorganic nitrogen and its export to the surface water of the watershed are seasonally dependent and, therefore, seasonal variability should be considered when total maximum daily loads (TDMLs) are designed and implemented.

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