08 Feb 2024
 | 08 Feb 2024
Status: this preprint is open for discussion.

Evaluating adsorption isotherm models for determining the partitioning of ammonium between soil and soil-pore water in environmental soil samples

Matthew Gordon Davis, Kevin Yan, and Jennifer Grace Murphy

Abstract. Ammonium in soil pore water is thought to participate in bidirectional exchange with the atmosphere; however, common soil nutrient analysis methods determine the bulk quantity of ammonium associated with the soil particles, rather than determining the aqueous ammonium concentration. Previous works have applied the Langmuir and Freundlich isotherm equations to ammonium-enriched soils to estimate partitioning, but this may not be representative of conditions in natural, unmanaged soils. In this work, environmental soil samples were collected from greenspaces in Toronto and used to evaluate several commonly used adsorption isotherm equations, including the Langmuir, Freundlich, Temkin and Toth equations, to determine their applicability in lightly managed and non-fertilized soils. We then compare ammonia emission potentials (a quantity predicting the propensity of ammonia to volatilize from a liquid reservoir) calculated using a conventional nutrient analysis method to that modelled using the Temkin and Langmuir equations, and demonstrate that conventional approaches may overestimate emission potentials from soils by a factor of 5 – 12.

Matthew Gordon Davis, Kevin Yan, and Jennifer Grace Murphy

Status: open (until 21 Mar 2024)

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  • RC1: 'Comment on egusphere-2024-126', Anonymous Referee #1, 23 Feb 2024 reply
Matthew Gordon Davis, Kevin Yan, and Jennifer Grace Murphy
Matthew Gordon Davis, Kevin Yan, and Jennifer Grace Murphy


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Short summary
Ammonia applied as fertilizer can volatilize into the atmosphere, this can threaten vulnerable ecosystems and human health. We investigated the partitioning of ammonia between an immobile adsorbed phase and mobile aqueous phase using several adsorption models. Using the Temkin model we determined that previous approaches to this issue may over-estimate the quantity available for exchange by a factor of 5 – 12, suggesting that ammonia emissions from soil may be overestimated.