QUANTIFYING THE WATER DYNAMICS OF PREFERNTIAL FLOW: II. VARIANT CLAYEY LOAM AT CORNELL SITE

Authors: KUNG, SAMUEL - UNIVERSITY OF WISCONSIN; STEENHUIS, TAMMO - CORNELL UNIVERSITY; GISH, TIMOTHY; KLADIVKO, ELAINE - PURDUE UNIVERSITY; GERING, LARRY - CORNELL UNIVERSITY; BUBENZER, GARY - UNIVERSITY OF WISCONSIN; HELLING, CHARLES

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Field experiments were conducted at Cornell and Purdue universities to better understand how agricultural chemicals move through soil. To make accurate assessments of chemical behavior tile-drained facilities were used at both locations. The major flow process being evaluated on a field-scale was preferential flow, a processes that can rapidly move both water and chemicals to groundwater. At both sites four soluble tracers were applied, each moves through soil as would nitrate. One tracer was applied prior to irrigation while one of the others tracers were applied at either+2, +4, and +6 hours into the irrigation event, respectively. The irrigation was a mild 3 cm irrigation event that was distributed over 10 hours. It was found that preferential flow was very significant at both sites and that the impact of the water flux distributions due to preferential flow were almost identical. The data strongly suggests that the water flow pathways at both sites gradually became hydraulically-active during a prolonged precipitation even though the soils of these two sites had completely different origins and textures. We hypothesized that the spectrum of the hydraulically-active pores, which constituted the preferential flow paths, was primarily dictated by the root growth and activities of soil-dwelling biota. It was possible that water flux distribution of preferential flow paths derived from a shallow soil could be used to predict contaminant transport in other sites with similar agricultural history.

Technical Abstract: Field experiments were conducted at the Cornell and Purdue Universities to quantify preferential water dyanmics. The tile drain facilities at both locations were used to monitor movement of conservative tracers, which were sequentially applied during a 3 mm hour intensity precipitation event with a ten hour duration. Bromide was sprayed on the soil surface prior to irrigation, while three different fluorobenzoic acids, i.e., PFBA, o-TFMBA, and 2,6 DFBA were applied at +2, +4, and +6 hours after irrigation began, respectively. Results showed that the bromide first appeared in tile drains about 4 hours after irrigation started while three benzoic acids, PFBA, o-TFBA, and 2,6 DFBA appeared in the tile drainage at 54, 42, and 12 minutes after their applications, respectively. The patterns associated with the tracer arrival times confirmed that: (1) water movement and contaminant transport would shift toward the larger end of the pore spectrum of the preferential flow paths as the soil profile became wetter during a precipitation event; and (2) water dynamics of preferential flow dictated deep leaching of newly applied agrichemicals. About 6% of total applied bromide was recovered from tile drainage at both sites. The similarity of the tracer breakthrough patterns from the two sites strongly suggested that the spectrum of soil structural pores in the top 1 m of the two sites, and how these pores gradually became hydraulically-active, were very similar even though the two sites had completely different origins and textures.