Pcic Science Brief 5: Water-quality Impacts from Climate-induced Forest Die-off

University House 1, PO Box 1700, STN CSC, University of Victoria, Victoria, British Columbia, Canada, V8W 3R4 Phone: 250-721-6236 | Fax: 250-721-7217 | pacificclimate.org In a recent paper in Nature Climate Change, Mikkelson (2013) and colleagues find that municipal water supplies that draw from mountain pine beetle-infested source regions have higher concentrations of both organic carbon and potentially harmful disinfection byproducts1. There is an ongoing mountain pine beetle epidemic in the Rocky Mountains. There have been several contributing factors. The prevalence of warmer winters has allowed more beetles to survive each year. Wildfire suppression has caused there to be large expanses of mature pine trees that the beetles prefer. Persistent drought conditions have also weakened some trees, making them more susceptible to beetle infestation. Mountain pine beetle infestations can cause large-scale tree death. The beetles lay their eggs under the bark of the trees and introduce a blue stain fungus that blocks resin, water and nutrients from flowing in the tree. The beetle larvae also feed on the tree, further damaging it and preventing the flow of water and nutrients. Large-scale tree death can increase organic matter decay, change the flow of groundwater, increase erosion and increase the leaching of organic matter to surface water. When this organic material is mixed with chlorinated disinfection agents as part of the processing of water in municipal water supplies, the chemical reactions that result can form harmful disinfection byproducts. Mikkelson (2013) et al. examined water quality data from nine treatment plants in Colorado for total organic carbon concentrations and disinfection byproducts, including five haloacetic acids and total trihalomethane2 concentrations. Of the nine treatment plants considered in the study, five were processing water from watersheds impacted by mountain pine beetles. Four were processing water from control areas with mountain pine beetle infestation levels that were a quarter of the PCIC SCIENCE BRIEF 5: WATER-QUALITY IMPACTS FROM CLIMATE-INDUCED FOREST DIE-OFF