Changes to Subsurface Metal Mobility in a Bark Beetle-Infested Forest
Presented on Monday, May 5, 2014
Kristin M. Mikkelson1, Lindsay Bearup2, Alexis Navarre-Sitchler, Ph.D.3, John E. McCray, PhD1 and Jonathan Sharp3, (1)Civil and Environmental Engineering, Colorado School of Mines, Golden, CO, (2)CEE, Colorado School of Mines, Golden, CO, (3)CSM, Golden, CO
Recent large-scale mortality in conifer forests due to beetle infestations has led to changes in terrestrial biogeochemical carbon cycling through the cessation of rhizodeposition and associated large needle drop. As subsurface carbon cycling is altered, aqueous metal transport can also change through complexation with dissolved organic carbon (DOC) that increases its mobility. This study compared DOC and metal concentrations in field soil-water samples beneath beetle-killed trees, along with using laboratory column experiments to determine if subsurface aqueous metal concentrations and loading will increase after beetle infestation. The columns mimicked field conditions by leaching pine needle tea and artificial rainwater through duplicate homogenized soil columns and measuring effluent metal (specifically Al, Cu, and Zn) and DOC concentrations. All three metals were found in higher concentrations in the effluent of columns receiving pine needle leachate. Correlations between DOC and specific metals were observed in both the field and the lab, supporting the hypothesis of DOC-enhanced metal mobility beneath beetle-killed trees after needle drop. Pine needle leachate also contained high concentrations of zinc, which corresponded to high effluent concentrations in the columns along with sorption to the soil matrix. Field concentrations of zinc beneath trees that had already lost their needles were twice as high as samples from under trees that still held their needles, corroborating the observations seen in the column studies. While unclear if manifested in adjacent surface waters, these results demonstrate an increased potential for Zn, Cu, and Al mobility in the subsurface in association with beetle-impacted trees.
Kristin M. Mikkelson
Civil and Environmental Engineering, Colorado School of Mines, Golden, CO
Kristin Mikkelson is a Ph.D. candidate graduating May 2014 in the Hydrological Sciences and Engineering program at the Colorado School of Mines. Her research focuses on investigating the hydrological and biogeochemical changes after a bark beetle infestation. Her recent research has been published in Nature Climate Change and has been featured internationally. Research interests include the interrelationships between water and nutrient cycles with possible implications for contaminant transport. Current research investigates this concept in the context of the land cover change from the Mountain Pine Beetle epidemic in the Rocky Mountain West.
Lindsay Bearup
CEE, Colorado School of Mines, Golden, CO
Research interests include the interrelationships between water and nutrient cycles with possible implications for contaminant transport. Current research invesitgates this concept in the context of the land cover change from the Mountain Pine Beetle epidemic in the Rocky Mountian West. Previous work approached the question from a geochemical perspective to understand groundwater residence times for which metal desorption kinetics are important.
Alexis Navarre-Sitchler, Ph.D.
CSM, Golden, CO
Navarre Sitchler is a professor of aqueous geochemistry in the Department of Geology and Geological Engineering at Colorado School of Mines.
John E. McCray, PhD
Civil and Environmental Engineering, Colorado School of Mines, Golden, CO
John McCray is the Head of the Civil and Environmental Engineering Department, and the former Founding Director of the Hydrologic Science and Engineering Graduate Program at Colorado School of Mines. He has served as Associate Editor on many hydrologic journals, including Groundwater, Water Resources Research, Journal of Contaminant Hydrology, Vadose Zone Journal, and JAWRA. His current research interests include carbon geosequestration, groundwater remediation, urban hydrology, and wastewater reclamation using the vadose zone and other natural systems.
Jonathan Sharp
CSM, Golden, CO
Environmental concerns are a predominant theme for the 21st century as society realizes the importance of sustainability and resource conservation for our long-term health and prosperity. As an environmental engineer trained in combining molecular and microbiological tools with geochemistry, my research focuses on the applications and implications of biological processes that relate to water quality and reuse. I have applied my cross-disciplinary perspective towards investigating the bacterial degradation of emerging drinking water and biosolids-associated organics and towards understanding bacterially-mediated redox transformations of both metals and radionuclides.
