Impact of Preferential Flow on the Transport of Adsorbing and Non‐Adsorbing Tracers

Abstract

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.

Water and Bromide Recovery in Wick and Pan Lysimeters under Conventional and Zero Tillage

“…These results are similar to those observed by Kung et al (2000), who applied Br with the water in a 7.5 h irrigation event at a rate of 7.5 mm h 21 . Kung et al (2000) first observed Br in the tile drainage within 2 h of when a Br pulse was injected into the irrigation stream, reaching a peak concentration near 300 mg L 21 and then decreasing lognormally after that initial concentration spike. Increasing Br concentration through 13 to 17 h (Figure 2a) in this study was probably a consequence of the greater amount, and longer duration, of Br application.…”

“…Although the Rhodamine WT peak concentration in the tile water occurred at the same time as the peak for the conservative tracers [nitrate (NO 3 ) and Br] in this study (Everts et al 1989), the Rhodamine WT concentration decreased to near background levels almost immediately with the cessation of irrigation, while the conservative tracer concentrations remained at a relatively elevated level. Kung et al (2000) demonstrated similar results using the same tracers on larger tiledrained plots (18 by 65 m) and included an evaluation of two irrigation intensities in no-tilled (NT) and conventionally tilled (CT) fields. Arrival time (to the tile outlet) was similar for both types of tracers, and they did not observe a difference between tillage practices.…”

“…Although Kung et al (2000) indicated that preferential flow paths were behaving similarly between NT and CT systems when their study soils were wet, other researchers have indicated that tillage practices have an impact on preferential flow (Bicki and Guo 1991;Trojan and Linden 1994). Trojan and Linden (1994) suggested that different mechanisms may be controlling preferential flow depending on the antecedent soil moisture content and rainfall distribution pattern (e.g., intensity and duration).…”

A novel explicit approach to model bromide and pesticide transport in connected soil structures

“…A parameterisation of the Freundlich isotherm based on values reported in the Footprint data base (www.eufootprint.org) did not reveal any meaningful result. Based on the finding of Zehe and Flühler (2001) at this site, who report an effective retardation coefficient of one at the end to the experiment and similar findings of Kung et al (2000) who found similar behaviour for bromide and the sorbing tracer rhodamin WT, we reduced the k f values and thus the retardation coefficient stepwise to one. With this, the proposed model approach could be attuned to reproduce the overall IPU mass that leached to the tile drain.…”

Criteria for selecting fluorescent dye tracers for soil hydrological applications using Uranine as an example

“…Field investigations and modeling of water and tracer movement are important in studying numerous hydrological problems, including water resource contamination (Gödeke et al, 2006;Sudicky and Illman, 2011;Zheng et al, 2011), flood mitigation (Baker, 1987;Gubareva and Gartsman, 2010;Wood et al, 1990), and landslide initiation due to excess pore pressure generation (Iverson, 2000;Wilson et al, 2012). Usually the influence of PFP on mass transfer is determined experimentally by measuring water or tracer outflow from soil columns, lysimeters or in natural catchments (Everts and Kanwar, 1989;Ghodrati and Jury, 1992;Kung et al, 2000;Mallants et al, 1996;Tsuboyama et al, 1994;Vanderborght et al, 2000). Experimental data collected this way simplifies often tortuous flow pathways to a quasi-1-D process.…”