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Preferential Flow and Transport of Nitrate and Bromide in Clay pan Soil
Author(s) -
Kelly Brian P.,
Pomes Michael L.
Publication year - 1998
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.1998.tb02820.x
Subject(s) - groundwater recharge , soil water , hydraulic conductivity , topsoil , environmental science , vadose zone , subsurface flow , hydrology (agriculture) , water flow , groundwater , fertilizer , geology , lysimeter , soil science , aquifer , chemistry , geotechnical engineering , organic chemistry
The in situ measurement of water flow and chemical transport through clay pan soils is crucial to understanding potential water contamination from agricultural sources. It is important due to the large areal extent of these soils in agricultural regions of the midwestern United States and because of preferential flow paths caused by desiccation cracks, worms burrowing, and root development. A study plot at the Missouri Management Systems Evaluation Area near Centralia, Missouri, was instrumented to determine the rate of preferential flow of water and transport of NO 3 −1 fertilizer in the unsaturated zone through a claypan soil using 15 N‐NO 3 −1 and Br‐1 tracers. The areal distribution of preferential flow paths was between 2 and 20% in the topsoil. Gravity lysimeter flow caused by preferential flow through the claypan was as much as 150 times greater than the estimated average rate of vertical recharge. As much as 2.4% of the volume of the soil below the clay pan may be occupied by preferential flow paths. The 15 N‐NO 3 −1 concentrations in ground water indicate that substantial quantities of fertilizer‐derived NO 3 −1 were transported to ground water through the claypan during the first recharge event following fertilizer application even though that event occurred six months after application. Hydraulic conductivity, measured at three scales, ranged from 6.2 × 10 −8 to 7.5 × 10 −3 cm/s. The observed increase of calculated hydraulic conductivity with each increase in scale was attributed to the inclusion of more and larger preferential flow paths within the volume over which the measurement was made, indicating hydraulic conductivity measured at one scale may not describe flow and transport at another scale.