Suction Cup Sampler Bias in Leaching Characterization of an Undisturbed Field Soil

Abstract

An accurate assessment of leaching losses in the vadose zone requires measurement of both solute and water flux to compute flux concentrations (CF). Leachate collected at a depth of 1.2 m in 32 passive capillary samplers (PCAPS), which sample soil‐pore water continuously at tensions of 0–50 cm H2O was compared to that collected in 32 suction cup samplers operated under a falling head vacuum of 530‐cm H2O over a 2‐year period. There was evidence that PCAPS collected CF and suction cup samplers collected resident concentrations (CR) as shown by the earlier breakthrough of a bromide tracer in the PCAPS as compared to the suction cup samplers. CR was up to 100% lower than CF during the rising branch of Br tracer breakthrough and up to 78% greater during the declining branch of breakthrough. Br content and water flux into PCAPS were correlated with correlation coefficients changing from positive to negative values with the advancement of the tracer breakthrough peak through the profile indicating the declining importance of preferential flow on Br transport. CR and CF differed significantly (P < 0.05) for 35% of the sampling events for NO3, but seasonal means were mostly insignificantly different for this regularly applied and therefore more uniformly distributed anion. The early breakthrough of Rhodamine WT and Brilliant Blue FCF, which was applied with the Br, was very low with 0.15% and 0.08% of the initial concentration C0, respectively, with CR differing from CF by up to −100%. For all tracers, mass leached using CR is therefore prone to bias for short‐term (<0.6 pore volumes) monitoring.

Impact of redox and transport processes in a riparian wetland on stream water quality in the Fichtelgebirge region, southern Germany

“…Instead, it is more likely that the piezometer samples are composed mainly of the mobile soil water fraction, whereas the continuous vacuum of the suction cups captures more of the immobile fraction (Litaor, 1988;Brandi-Dohr et al, 1996;Landon et al, 1999). Correspondingly, temporal patterns are less discernible in soil suction cups than in piezometer samples.…”

Combining Hydrometric and Hydrochemical Data Sets for Investigating Runoff Generation Processes: Tautologies, Inconsistencies and Possible Explanations

“…Figure 1). In fact, systematic differences of solute concentration have been found between the two compartments (Brandi-Dohrn et al 1996;Grossmann and Udluft 1991). In soil physics, the microscale heterogeneity of the vadose zone is accounted for by differentiating between a mobile and an immobile soil water compartment (Gerke and van Genuchten 1993).…”

An experimental and numerical study on flow and transport in a field soil using zero‐tension lysimeters and suction plates

“…Zero‐tension (or pan) samplers collect gravitational water and require that the soil above the samplers be saturated during collection, whereas passive capillary (wick) samplers use fiberglass wicks to apply a small capillary suction that varies as a function of water flow (e.g. Rimmer et al 1995; Brandi‐Dohrn et al 1996). Vacuum solution samplers, like suction cups or suction plates (Litaor, 1988), collect an approximation of the flux concentration when operated in a continuous mode.…”