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Title: MODELING MANURE-BORNE BROMIDE AND FECAL COLIFORM TRANSPORT WITH RUNOFF AND INFILTRATION AT A HILLSLOPE

Author
item KOUZNETSOV, M - BEN GURION U., ISRAEL
item ROODSARI, REZA - U. OF MD, COLLEGE PARK
item Pachepsky, Yakov
item Shelton, Daniel
item Sadeghi, Ali
item SHIRMOHAMMADI, A - U. OF MD, COLLEGE PARK
item Starr, James

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2006
Publication Date: 9/10/2006
Citation: Kouznetsov, M.Y., Roodsari, R., Pachepsky, Y.A., Shelton, D.R., Sadeghi, A.M., Shirmohammadi, A., Starr, J.L. 2006. Modeling manure-borne bromide and fecal coliform transport with runoff and infiltration on a hillsope. Journal of Environmental Management. 84(2007):336-346.

Interpretive Summary: Hillslope vegetated buffers are recommended to prevent water pollution from agricultural runoff. There is no consensus in the literature on whether the efficiency of the vegetated buffer strips is the same with respect to nutrient and microbial transport. The difficulty in predicting the relative transport rates of manure-borne microorganisms vs. solutes is due, in large measure, to the lack of appropriate models. The objective of this work was to develop and test a mechanistic model of coupled surface and subsurface flow and transport of bacteria and a conservative tracer on hillslopes. We developed the model of interacting surface and subsurface water flow and surface and subsurface transport of microorganisms and a conservative tracer, i.e. dissolved chemical that does not interact with soil and vegetation. The model was tested with data on rainfall-induced fecal coliforms (FC) and bromide (Br) transport from manure applied at vegetated and bare 6-m long plots. The parameters of the FC and Br transport were found independently, and appeared to be similar. This indicates that, at least at short distances, the vegetated buffer strips may have similar efficiency in retention of mobile chemicals and microorganisms coming from the land applied manure. The model developed in this work is suitable to simulate surface and subsurface transport of agricultural contaminants on hillslopes and to evaluate efficiency of grass strip buffers, especially when lateral subsurface flow is important.

Technical Abstract: Hillslope vegetated buffers are recommended to prevent water pollution from agricultural runoff. However, models to predict the efficacy of different grass buffer designs are lacking. The objective of this work was to develop and test a mechanistic model of coupled surface and subsurface flow and transport of bacteria and a conservative tracer on hillslopes. The testing should indicate what level of complexity and observation density might be needed to capture essential processes in the model. We combined the three-dimensional FEMWATER model of saturated-unsaturated subsurface flow with the Saint-Venant model for runoff. The model was tested with data on rainfall-induced fecal coliforms (FC) and bromide (Br) transport from manure applied at vegetated and bare 6-m long plots. The calibration of water retention parameters was unnecessary. The same manure release parameters could be used both for simulations of Br and FC. Surface straining rates were similar for bromide and bacteria. Simulations of Br and FC concentrations were least successful for the funnels closest to the source. This could be related to the finger-like flow of the manure from the strip along the bare slopes, to the transport of Br and FC with manure colloids that became strained at the grass slope, and to the presence of micro-ponds at the grassed slope. The two-dimensional model abstraction of the actual 3D transport worked well for flux-averaged concentrations. The model developed in this work is suitable to simulate surface and subsurface transport of agricultural contaminants on hillslopes and to evaluate efficiency of grass strip buffers, especially when lateral subsurface flow is important.