Preferential Flow and Transport of Nitrate and Bromide in Clay pan Soil

Abstract

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 NO3−1 fertilizer in the unsaturated zone through a claypan soil using 15N‐NO3−1 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 15N‐NO3−1 concentrations in ground water indicate that substantial quantities of fertilizer‐derived NO3−1 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.

Identification of Lateral Macropore Flow in a Forested Riparian Wetland through Numerical Simulation of a Subsurface Tracer Experiment

“…Bromide was used previously in several tracer experiment studies in wetlands (e.g. Parsons et al 2004;Kelly and Pomes 1998). Sodium bromide was weighed and dissolved to near saturation before the amendment commenced.…”

Estimation of soil cracking and the effect on surface runoff in a Texas Blackland Prairie watershed

“…In the Blackland Prairie of Texas, it is estimated to approach 100 million dollars a year (Allen and Maier, 1993). In agriculture, soil shrinkage cracking allows rapid transport of water, nutrients and pesticides to the subsoil where they are both inaccessible to shallow rooting plants and can pollute the local groundwater system (Kissel et al, 1974;Harris et al, 1994;Bronswijk et al, 1995;Kelly and Pomes, 1998). In addition, seasonal cracking of the soil matrix results in poor estimates of runoff and infiltration due to the changing soil storage conditions (Smettem et al, 1991;Stolte et al, 1997;Ruan and Illangasekare, 1998).…”

Experiment evidence on the temperature dependence of desiccation cracking behavior of clayey soils

“…In the case of earth dam, the presence of crack may also turn into piping leaks, leading to dam failures as for the Stockton and Wister dams (Sherard, 1973). In the agricultural field, as desiccation cracks control the rate and velocity at which water, solutes and micro-organisms are transported in the soil, they can significantly affect the crops growth and production (Bronswijk et al, 1995;Kelly and Pomes, 1998).…”