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Issue 6, 2014
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Changes in metal mobility associated with bark beetle-induced tree mortality

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Abstract

Recent large-scale beetle infestations have caused extensive mortality to conifer forests resulting in alterations to dissolved organic carbon (DOC) cycling, which in turn can impact metal mobility through complexation. This study analyzed soil-water samples beneath impacted trees in concert with laboratory flow-through soil column experiments to explore possible impacts of the bark beetle infestation on metal release and transport. The columns mimicked field conditions by introducing pine needle leachate and artificial rainwater through duplicate homogenized soil columns and measuring effluent metal (focusing on Al, Cu, and Zn) and DOC concentrations. All three metals were consistently found in higher concentrations in the effluent of columns receiving pine needle leachate. In both the field and laboratory, aluminum mobility was largely correlated with the hydrophobic fraction of the DOC, while copper had the largest correlation with total DOC concentrations. Geochemical speciation modeling supported the presence of DOC–metal complexes in column experiments. Copper soil water concentrations in field samples supported laboratory column results, as they were almost twice as high under grey phase trees than under red phase trees further signifying the importance of needle drop. Pine needle leachate contained high concentrations of Zn (0.1 mg l−1), which led to high effluent zinc concentrations and sorption of zinc to the soil matrix representing a future potential source for release. In support, field soil-water samples underneath beetle-impacted trees where the needles had recently fallen contained approximately 50% more zinc as samples from under beetle-impacted trees that still held their needles. The high concentrations of carbon in the pine needle leachate also led to increased sorption in the soil matrix creating the potential for subsequent carbon release. While unclear if manifested in adjacent surface waters, these results demonstrate an increased potential for Zn, Cu, and Al mobility, along with increased deposition of metals and carbon beneath beetle-impacted trees.

Graphical abstract: Changes in metal mobility associated with bark beetle-induced tree mortality

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Supplementary files

Article information


Submitted
22 Nov 2013
Accepted
12 Mar 2014
First published
12 Mar 2014

Environ. Sci.: Processes Impacts, 2014,16, 1318-1327
Article type
Paper
Author version available

Changes in metal mobility associated with bark beetle-induced tree mortality

K. M. Mikkelson, L. A. Bearup, A. K. Navarre-Sitchler, J. E. McCray and J. O. Sharp, Environ. Sci.: Processes Impacts, 2014, 16, 1318
DOI: 10.1039/C3EM00632H

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