Measurement and simulation of subsurface tracer migration to tile drains in low permeability, macroporous soil

Abstract

Multiyear monitoring and simulation of a conservative tracer was used in this study to investigate preferential flow and macropore-matrix interactions in low permeability, macroporous soil. 2,6-Difluorobenzoic acid (DFBA) tracer was applied to a 20 3 20 m drip irrigated test plot situated over two tile drains. Tracer movement over the 2009 and 2010 field seasons was monitored using tile drain effluent, suction lysimeters, monitoring wells, and soil cores. Despite similar volumes of water application to the plot in each season, 10 times more water and 14 times more DFBA were captured by the drains in 2010 due to wetter regional hydrologic conditions. The importance of preferential flow along macropores was shown by rapid DFBA breakthrough to the tile (<47 h), and DFBA detections in sand units below the tile drains. Preferential flow resulted in less than 8% of the DFBA mass being captured by the tiles over both years. With much of the DFBA mass (75%) retained in the upper 0.25 m of the soil at the end of 2009, numerical simulations were used to quantify the migration of this in situ tracer during the subsequent 2010 field season. Dual permeability and dual porosity models produced similar matches to measured tile drain flows and concentrations, but solute leaching was captured more effectively by the dual permeability formulation. The simulations highlighted limitations in current descriptions for small-scale mass transfer between matrix and macropore domains, which do not consider time-dependent transfer coefficients or nonuniform distributions of solute mass within soil matrix blocks.

Impacts of Subsurface Tile Drainage on Age—Concentration Dynamics of Inorganic Nitrogen in Soil

“…In recent decades, a number of studies (Arora et al, ; Beven & Germann, ; Bishop et al, ; Cuthbert et al, ; Ford et al, ; Kohne et al, ; Nimmo, ; Simunek & van Genuchten, ) have demonstrated that water flow and nutrient transport in the unsaturated zone is greatly influenced by preferential flow paths. Consistent with these previous findings, the inclusion of macropore flow into Dhara significantly increases its ability to predict subsurface nitrogen losses.…”

Understanding Preferential Flow in the Vadose Zone: Recent Advances and Future Prospects

“…For these reasons, DP models are now sometimes used as management and decision‐making tools, for example in pesticide risk assessment (Jarvis et al, 2012; Jarvis and Larsbo, 2012). Two‐ and three‐dimensional versions of DP models have also been developed that have been used to explore the impacts of pore‐scale processes on soil hydrology and water quality in both drained and undrained soils at hillslope and field scales (e.g., Gärdenäs et al, 2006; Warsta et al, 2013; Gerke et al, 2013; Bishop et al, 2015; Dusek and Vogel, 2016). One disadvantage of DP models is that the properties of the macropore system are only implicitly reflected in model parameters that cannot easily be directly measured.…”

Picturing and modeling catchments by representative hillslopes

“…Coenders-Gerrits et al (2013) used the same model structure to examine the role of interception and slope in the subsurface runoff generation. Bishop et al (2015), Wienhöfer and Zehe (2014) and Klaus and Zehe (2011) used physically based models to investigate the influence of vertical and lateral preferential flow networks on subsurface water flow and solute transport, including the issue of equifinality and its reduction. These and other studies (e.g., Ebel et al, 2008;Scudeler et al, 2016) show that physically based models can be set up using a mix of expert knowledge and observed parameters and may be tested against a variety of observations beyond streamflow -such as soil moisture observations, groundwater tables or tracer breakthrough curves.…”