Water-quality impacts from climate-induced forest die-off

Increased ecosystem susceptibility to pests and other stressors has been attributed to climate change(1), resulting in unprecedented tree mortality from insect infestations(2). In turn, large-scale tree die-off alters physical and biogeochemical processes, such as organic matter decay and hydrologic flow paths, that could enhance leaching of natural organic matter to soil and surface waters and increase potential formation of harmful drinking water disinfection by-products(3,4) (DBPs). Whereas previous studies have investigated water-quantity alterations due to climate-induced, forest die-off(5,6), impacts on water quality are unclear. Here, water-quality data sets from water-treatment facilities in Colorado were analysed to determine whether the municipal water supply has been perturbed by tree mortality. Results demonstrate higher total organic carbon concentrations along with significantly more DBPs at water-treatment facilities using mountain-pine-beetle-infested source waters when contrasted with those using water from control watersheds. In addition to this differentiation between watersheds, DBP concentrations demonstrated an increase within mountain pine beetle watersheds related to the degree of infestation. Disproportionate DBP increases and seasonal decoupling of peak DBP and total organic carbon concentrations further suggest that the total organic carbon composition is being altered in these systems.