Field experiments were conducted by using a tile drain monitoring facility to determine the impact of preferential flow on the transport of adsorbing and non‐adsorbing tracers. Simulated rainfall with 7.5 mm h−1 intensity and 7.5 h duration was applied to a 18‐ by 65‐m no‐till plot. After 72 min of irrigation, a pulse of Br− and rhodamine WT (water tracer) was applied through irrigation, and 4 h later, a second pulse of Cl− and rhodamine WT was applied. The breakthrough curves (BTC) of these tracers were measured by sampling the tile. The same experiments were repeated in an adjacent conventional‐till plot, except the rainfall intensity was reduced to 5 mm h−1 The results showed that both the non‐adsorbing and the adsorbing tracers applied in the same pulse arrived at the tile line at the same time and their BTC peaked at the same time. This suggested that water dynamics of preferential flow paths dominated the initial phase of the contaminant transport, regardless of the retardation properties of contaminants. The tracers from the second pulse were detected at only 13 min after application. Among the four tracer pulses in two plots, the BTC from the second pulse in the no‐till plot had the longest period in which the non‐adsorbing and adsorbing tracers had identical patterns. This indicated that the wetter the soil profile, the longer the water dynamics of preferential flow paths dominate the contaminant transport. The BTC from the second pulse applied to the two plots had identical arrival and peak times.

Field experiments were conducted on tile‐drained plots at the South East Purdue Agricultural Center in Butlerville, Indiana, to quantify contaminant transport via preferential flow paths in a silt loam soil. Breakthrough patterns of three fluorobenzoic acids (pentafluorobenzoic acid [PFBA], o‐trifluoromethylbenzoic acid [o‐TFMBA], and 2,6‐difluorobenzoic acid [2,6‐DFBA]) in a preliminary study indicated that they were transported as conservatively as is bromide (Br−). These four tracers were then sequentially applied, in an adjacent plot, during simulated precipitation (3 mm h−1 intensity, 10‐h duration). Bromide was sprayed shortly before irrigation started, while PFBA, o‐TFMBA, and 2,6‐DFBA were applied at 2, 4, and 6 h thereafter, respectively. Tile flow began increasing at around 3 h, and Br− appeared in tile drain flow ≈4 h after irrigation started, yet benzoic acids, PFBA, o‐TFMBA, and 2,6‐DFBA, were detected in the tile drainage at 102 min, 42 min, and 18 min after their applications, respectively. Tracer mass recovery from tile drainage was Br− (7.04%), PFBA (13.9%), o‐TFMBA, (18.7%), and 2,6‐DFBA (19.7%) of applied mass. The faster arrival time and greater recovery of sequentially applied tracers confirmed that water movement and contaminant transport shifts toward increasingly larger pores of the preferential flow paths as soil becomes wet during a precipitation event. The breakthrough patterns of these tracers can be used to quantify the water flux distributions of preferential paths. Because ≈90% of the chemical leached from this precipitation event occurred during the first day, it was critical to intensively monitor contaminant transport during the first 24 h after a rainfall. A soil sampling protocol based on collecting soil cores at random locations once every several days is unsuitable for determining the deep leaching under field conditions.

Sediment and nutrient retention was studied in a seasonally flooded lakeside wetland as a natural mechanism for preventing water quality deterioration. Both wetland and upland soils in the watershed had comparable concentrations of inorganic P on a per‐volume basis, while NH4+‐N and organic forms of N and P were much higher in the wetland soils. Nitrate concentrations expressed in a per‐volume basis were lower in the wetland soils than in the upland soils.The distribution of sediment and nutrients in the wetland was correlated with distance from a small stream flowing through the wetland. Deposition patterns were affected by recent stream channel migrations.The accumulation of nutrients and sediment delivered from the upland to wetland soils was estimated in two ways: (i) by calculating the volume of alluvium deposited in low natural levees adjacent to the stream; and (ii) by estimating nutrient and ash enrichment of histic surface soils farther away from the stream. Although the levees constituted only about 20% of the wetland surface area, they accounted for 81% of the sediment, 84% of the N, and 67% of the P retained by the wetland.The depth of Cs‐137 in the soil was used to estimate net sedimentation rates. Average annual accumulations over the wetland as a whole were: 2.0 kg sediment m−2 yr−1, 2.6 g P m−2 yr−1, and 12.8 N g m−2 yr−1. Since these values exceed those published for average annual storage by wetland plants, soil mechanisms are more important than vegetative uptake for long‐term nutrient and sediment retention in the White Clay Lake wetland.

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Solute concentration and soluble dye studies inferring that preferential flow accelerates field-scale contaminant transport are common but flux measurements quantifying its impact are essentially nonexistent. A tile-drain facility was used to determine the influence of matrix and preferential flow processes on the flux of mobile tracers subjected to different irrigation regimes (4.4 and 0.89 mm h(-1)) in a silt loam soil. After tile outflow reached steady state either bromide (Br; 280 kg ha(-1)) or pentafluorobenzoic acid (PFBA; 121 kg ha(-1)) was applied through the irrigation system inside a shed (3.5 x 24 m). Bromide fluxes were monitored at an irrigation rate of 4.4 mm h(-1) while PFBA fluxes were monitored at an irrigation rate of 0.89 mm h(-1). At 4.4 mm h(-1) nearly one-third of the surface-applied Br was recovered in the tile line after only 124 mm of irrigation and was poorly fit by the one-dimensional convective-dispersive equation (CDE). On the other hand, the one-dimensional CDE fit the main PFBA breakthrough pattern almost perfectly, suggesting the PFBA transport was dominated by matrix flow. Furthermore, after 225 mm of water had been applied, less than 2% of the applied PFBA had been leached through the soil compared with more than 59% of the applied Br. This study demonstrates that the methodology of applying a narrow strip of chemical to a tile drain facility is appropriate for quantifying chemical fluxes at the small-field scale and also suggests that there may be a critical input flux whereby preferential flow is initiated.