T338 Rock Transforming to Soil—The Weathering Engine Intersects with the Carbon Cycle

Wednesday, 25 October 2017
1:30 PM - 5:30 PM
Skagit 3

LIGAND EXCHANGE PROCESSES IN ALPINE TUNDRA SOIL - IMPLICATIONS FOR SOIL ACIDIFICATION AND ALUMINUM TRANSPORT

Paper number: T338-13
Program: Technical Sessions
Time: 4:30 PM – 4:45 PM

Authors

Abstract

The transport of naturally occurring F- in alpine tundra soil is complex due to simultaneous multi-component processes involving ligand exchange between various soil components and aqueous Al3+ complexes. Ligand exchange processes, involving the release of OH-, F-, and low molecular weight organic acids (LMWOA) into soil solution, are of particular interest, since they can modify both the rate of soil acidification and Al3+ toxicity.

To examine ligand exchange processes in alpine tundra soil, a series of batch equilibration and column leaching studies were conducted using either 25 mg L-1 F- or 25 and 100 mg L-1 oxalate solutions. The solution pH of each treatment was adjusted to the corresponding soil pH for the O/A1, A2, and Bw soil horizons. Soil suspension pH was observed to significantly increase for all oxalate and F- treatments, resulting in pH increases ranging between 0.4 and 1.1 pH units. Both oxalate concentration levels resulted in an increase in F- concentration in suspension, with the largest F- release being observed for the 100 mg L-1 oxalate treatment in the O/A1 horizon. Soil columns eluted with 100 mg L-1 oxalate, showed continual F- leaching, with the highest F- leachate concentration being observed within the first 10 P.V., and the largest quantity of F- being released by the O/A1 horizon. Accelerated Al leaching was observed for soil columns eluted with 25 mg L-1 F-. Aluminum transport corresponded to F- column breakthrough, with Al leaching increasing in the order A2> Bw> O/A1. Sequential soil horizon leaching with D.I. H2O→ 25 mg L-1 F-→ D.I. H2O→ 100 mg L-1 oxalate demonstrated that adsorbed F- could be displaced by oxalate from soil surfaces, with F- displacement decreasing in the order O/A1>A2>Bw.

Soil pore water ionic composition within the initial wetting front, with respect to oxalate concentration, appears to be critical in determining the quantity of OH-, F- and total aluminum in solution. Results from this study suggest that ligand exchange between F-, oxalate and OH- on soil surfaces, and the subsequent release of Al3+ into the soil pore water, may be responsible for the formation of aluminum hydroxyl-sulfate solid phases and possible phase transitions between jurbanite (AlOHSO4), basaluminite (Al4(SO4)(OH)10), and alunite (KAl3(SO4)2(OH)6) in this soil.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-299221

© Copyright 2017 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.