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Controls of MacRopore Network Characteristics on Preferential Solute Transport : Volume 11, Issue 8 (12/08/2014)

By Larsbo, M.

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Book Id: WPLBN0004012232
Format Type: PDF Article :
File Size: Pages 38
Reproduction Date: 2015

Title: Controls of MacRopore Network Characteristics on Preferential Solute Transport : Volume 11, Issue 8 (12/08/2014)  
Author: Larsbo, M.
Volume: Vol. 11, Issue 8
Language: English
Subject: Science, Hydrology, Earth
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Historic
Publication Date:
2014
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications

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Koestel, J., Jarvis, N., & Larsbo, M. (2014). Controls of MacRopore Network Characteristics on Preferential Solute Transport : Volume 11, Issue 8 (12/08/2014). Retrieved from http://hawaiilibrary.net/


Description
Description: Department of Soil and Environment, Swedish University of Agricultural Sciences (SLU), P.O. Box 7014, 750 07 Uppsala, Sweden. In this study we examined the relationships between macropore network characteristics, hydraulic properties and state variables and measures of preferential transport in undisturbed columns sampled from four agricultural topsoils of contrasting texture and structure. Macropore network characteristics were computed from 3-dimensional X-ray tomography images of the soil pore system. Non-reactive solute transport experiments were carried out at five steady-state water flow rates from 2 to 12 mm h−1. The degree of preferential transport was evaluated by the normalised 5% solute arrival time and the apparent dispersivity calculated from the resulting breakthrough curves. Near-saturated hydraulic conductivities were measured on the same samples using a tension disk infiltrometer placed on top of the columns. Results showed that many of the macropore network characteristics were inter-correlated. For example, large macroporosities were associated with larger specific macropore surface areas and better local connectivity of the macropore network. Generally, an increased flow rate resulted in earlier solute breakthrough and a shifting of the peak concentration towards smaller drained volumes. Columns with smaller macroporosities, poorer local connectivity of the macropore network and smaller near-saturated hydraulic conductivities exhibited a greater degree of preferential transport. This can be explained by the fact that, with only two exceptions, global (i.e. sample-scale) continuity of the macropore network was still preserved at low macroporosities. Thus, for any given flow rate pores of larger diameter were actively conducting solute in soils of smaller near-saturated hydraulic conductivity. With less time for equilibration between the macropores and the surrounding matrix the transport became more preferential. Conversely, the large specific macropore surface area and well-connected macropore networks associated with columns with large macroporosities limit the degree of preferential transport because they increase the diffusive flux between macropores and the soil matrix and they increase the near-saturated hydraulic conductivity. The normalised 5% arrival times were most strongly related with the estimated hydraulic state variables (e.g. with the degree of saturation in the macropores R2 = 0.589), since these combine into one measure the effects of irrigation rate and the near-saturated hydraulic conductivity function, which in turn implicitly depends on the volume, size distribution, global continuity, local connectivity and tortuosity of the macropore network.

Summary
Controls of macropore network characteristics on preferential solute transport

Excerpt
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