Competitive transport processes of chloride, sodium, potassium, and ammonium in fen peat

Abstract

There is sparse information on reactive solute transport in peat; yet, with increasing development of peatland dominated landscapes, purposeful and accidental contaminant releases will occur, so it is important to assess their mobility. Previous experiments with peat have only evaluated single-component solutions, such that no information exists on solute transport of potentially competitively adsorbing ions to the peat matrix. Additionally, recent studies suggest chloride (Cl) might not be conservative in peat, as assumed by many past peat solute transport studies. Based on measured and modelled adsorption isotherms, this study illustrates concentration dependent adsorption of Cl to peat occurred in equilibrium adsorption batch (EAB) experiments, which could be described with a Sips isotherm. However, Cl adsorption was insignificant for low concentrations (<500 mg L) as used in breakthrough curve experiments (BTC). We found that competitive adsorption of Na, K, and NH transport could be observed in EAB and BTC, depending on the dissolved ion species present. Na followed a Langmuir isotherm, K a linear isotherm within the tested concentration range (~10 - 1500 mg L), while the results for NH are inconclusive due to potential microbial degradation. Only Na showed clear evidence of competitive behaviour, with an order of magnitude decrease in maximum adsorption capacity in the presence of NH (0.22 to 0.02 mol kg), which was confirmed by the BTC data where the Na retardation coefficient differed between the experiments with different cations. Thus, solute mobility in peatlands is affected by competitive adsorption.

Short Term Effects of Salinization on Compound Release from Drained and Restored Coastal Wetlands

“…The volumetric water content of the immobile region for all soil cores was 0.17 ± 0.07 cm 3 cm −3 ; this water fraction did not participate in the convective transport of chloride. The fractions of immobile water found in this study were lower than those found for pristine peat or less decomposed peat soils [18,33], but comparable to those of highly degraded peat soils and peat sand mixtures [13,28]. The amount of immobile water content is related to peat type, the stage of peat degradation, and boundary conditions [32,33].…”

“…In this study, the Peclet number of the mobile water region ranged from 2.8 to 4.5, indicating that advection processes dominated in the leaching tests [30]. The optimized β values of all soil cores ranged between 0.5 and 1 (Table 2), which can be taken as an indication that the investigated peat soils constituted a dual-porosity medium containing active and dead-end pores [31][32][33], where the active pores or mobile water region dominated the pore space of the four soil cores. The volumetric water content of the immobile region for all soil cores was 0.17 ± 0.07 cm 3 cm −3 ; this water fraction did not participate in the convective transport of chloride.…”

Effect of anisotropy on solute transport in degraded fen peat soils

“…Tracer techniques provide useful tools to explore water flow and solute transport processes in soils (Leibundgut, Maloszewski, & Kulls, ).Various forms of tracers such as isotope 18 O (Ronkanen & Kløve, ), salt (Baird & Gaffney, ; Hoag & Price, ; Liu et al, ; McCarter, Weber, & Price, ), fluorescence (Ramirez, Baird, & Coulthard, ) and dyes (Liu & Lennartz, ; Liu et al, ; Mooney, Holden, Ward, & Collins, ) have been applied onto peat in the field or laboratory. All tracer experiments verify that preferential flow is a common phenomenon in peat soils.…”

“…The determination of solute transport properties and the identification of preferential flow also depend on the properties of applied tracers. Chloride as well as tritium tracers were retarded in less degraded peat soils (Liu et al, ; McCarter et al, ). The adsorption of chloride onto peat was found to be related to its concentration (e.g.…”

“…The adsorption of chloride onto peat was found to be related to its concentration (e.g. >500 mg l −1 , McCarter et al, ) and the soil organic matter content (Sheppard, Long, Sanipelli, & Sohlenius, ). Although there are several studies on solute transport in peat soils (Hoag & Price, ; Liu et al, ; McCarter et al, ; Rezanezhad, Price, & Craig, ), to our knowledge, there is no discussion on the effect of soil anisotropy on solute transport and strength of preferential flow in degraded fen peat soils in the existing literature.…”