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Measuring Instantaneous Solute Flux and Loading with Time Domain Reflectometry
Author(s) -
Hart G. L.,
Lowery B.
Publication year - 1998
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1998.03615995006200010004x
Subject(s) - reflectometry , tracer , hydraulic conductivity , flux (metallurgy) , soil water , steady state (chemistry) , soil science , water flow , transient (computer programming) , time domain , flow (mathematics) , geology , hydrology (agriculture) , environmental science , chemistry , mechanics , geotechnical engineering , physics , organic chemistry , computer science , nuclear physics , computer vision , operating system
Time domain reflectometry (TDR) can be used to measure water content and conservative tracer concentration in soils. An important contribution of TDR for assessing or monitoring water‐soluble contaminant loading in real time under transient flow may be possible because of the ability to acquire rapid, multiplexed measurements of variables necessary for calculating loading — the water flux and resident contaminant concentration. An empirically derived equation relating resident soil Br − concentration ( C Br , mg L −1 ) to apparent soil bulk electrical conductivity (σ a , dS m −1 ) and soil water content (θ, m 3 m −3 ) was established for Sparta sand (mesic, uncoated Typic Quartzipsamment). This equation has the form C Br = ασ a γ θ δ , where α, γ, and δ are empirical constants. Using TDR, we conducted real‐time monitoring of a Br − tracer transported through a repacked Sparta sand soil column at four depths. Under steady‐state and transient‐flow experiemntal conditions and assuming a unit gradient and uniform vertical flow, instantaneous water flux at each monitored depth was estimated from TDR‐acquired θ data and soil hydraulic conductivity. For steady‐state conditions, recovery of Br − ranged from 72% at 15 cm to 133% at 45 cm, while water recovery averaged 92% for all depths. Under transient conditions, Br − recovery ranged from 65% at 15 cm to 121% at 60 cm. Percentages of Br − recovery were congruent across depths between steady‐ and transient‐flow experiments, leading us to conjecture that nonhomogeneous flow patterns and pockets of immobile water had developed within the column.