Variations in pesticide leaching related to land use, pesticide properties, and unsaturated zone thickness

Journal of Environmental Quality
By: , and 



Pesticide leaching through variably thick soils beneath agricultural fields in Morgan Creek, Maryland was simulated for water years 1995 to 2004 using LEACHM (Leaching Estimation and Chemistry Model). Fifteen individual models were constructed to simulate five depths and three crop rotations with associated pesticide applications. Unsaturated zone thickness averaged 4.7 m but reached a maximum of 18.7 m. Average annual recharge to ground water decreased from 15.9 to 11.1 cm as the unsaturated zone increased in thickness from 1 to 10 m. These point estimates of recharge are at the lower end of previously published values, which used methods that integrate over larger areas capturing focused recharge in the numerous detention ponds in the watershed. The total amount of applied and leached masses for five parent pesticide compounds and seven metabolites were estimated for the 32-km2 Morgan Creek watershed by associating each hectare to the closest one-dimensional model analog of model depth and crop rotation scenario as determined from land-use surveys. LEACHM parameters were set such that branched, serial, first-order decay of pesticides and metabolites was realistically simulated. Leaching is predicted to be greatest for shallow soils and for persistent compounds with low sorptivity. Based on simulation results, percent parent compounds leached within the watershed can be described by a regression model of the form e−depth (a ln t½−b ln KOC) where t 1/2 is the degradation half-life in aerobic soils, K OC is the organic carbon normalized sorption coefficient, and a and b are fitted coefficients (R 2 = 0.86, p value = 7 × 10−9).

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Variations in pesticide leaching related to land use, pesticide properties, and unsaturated zone thickness
Series title Journal of Environmental Quality
DOI 10.2134/jeq2007.0245
Volume 37
Issue 3
Year Published 2008
Language English
Publisher ACSESS
Contributing office(s) Washington Water Science Center
Description 13 p.
First page 1145
Last page 1157
Online Only (Y/N) N
Additional Online Files (Y/N) N
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