SOLUTE AND MOISTURE FLUX BENEATH CATTLE FEEDLOT PENS

Abstract

Seepage of manure beneath cattle feedlot pens can be responsible for groundwater contamination. In semiaridclimates, such as the Canadian Prairies, there can be deep unsaturated zones, thus slowing solute travel to the water table.The purpose of this study was to determine the depth and rate of manure seepage and soil moisture flux using profile analysistechniques. Manure seepage was represented by the solutes K + , Cl , NH4N, and NO3N. Solute concentrations from soilcores beneath three 30yearold feedlots near Saskatoon, Saskatchewan, were examined. Although nitrate and ammonia ionswere measured, the objectives were met using chloride and potassium as they are not affected by biological transformationand can be used to approximate nitrate and ammonia ions. The concentrations of K + , Cl , and NH4 + N were at least two ordersof magnitude greater in the top soil layer than their background solute levels found at depth beneath the feedlot. In soil cores,Cl decreased to background levels by 2.2 to 4.9 m depth and was at 50% relative concentration by 0.2 to 0.6 m depth, whereasK + background and 50% concentrations occurred at depths between 1/3 to 2/3 that of chloride. Moisture flux beneath thesepens is between 2 and 6 mm/yr, which although low, is not atypical for the prairies. Movement by diffusion accounts for 1 to2 mm per year. This study indicates that although most of the manure solutes are moving as bulk flow (matrix) and movementis thus very slow, there is sufficient bypass flow to contaminate shallow piezometers located up to 20 m outside of the pens.