LINKING VEGETATION-DERIVED CARBON TO DISINFECTION BYPRODUCTS IN LITTER, AND STREAMWATER IN BARK BEETLE-INFESTED FORESTS

Forests in the Rocky Mountain Region have undergone dramatic changes during the past decade due to a severe mountain pine bark beetle infestation. Bark beetles have killed mature lodgepole pine (Pinus contorta) trees across Colorado, and this widespread disturbance is projected to alter forest structure and species composition for the coming century. Headwater streams that drain the affected forests provide water to population centers along Colorado’s Front Range and changes in water quality resulting from forest disturbance have implications for millions of people. Dissolved organic matter (DOM) exported from headwater forests may interact with common disinfecting agents used in water treatment to form certain disinfection by-products (DBPs) that pose threats to human health. The chemical characteristics and amount of DOM originating from subalpine forests are influenced by tree species-level differences in DOM production; such variability has implications for DBP formation and may be relevant given projected tree species changes following bark beetle infestations. Our objectives were to quantify the types and concentrations of DBPs released by the dominant tree species and to track those compounds in soil and streamwater in bark beetle affected forests at the US Forest Service, Fraser Experimental Forest. We found species differences in the DBP type and concentration formed when foliage leachate was reacted with chorine. The DBP chloroform was found in leachate from all tree species, but formation of another DBP, dichloroacetonitrile, was restricted to certain species. Nuclear magnetic resonance spectroscopy indicates that aliphatic and aromatic molecular structures account for the primary organic matter differences among tree species. On-going characterization of molecular compositional differences using Fourier transform ion cyclotron resonance mass spectrometry will help elucidate species-level differences in the DBP production. Our preliminary findings suggest that changes in forest species composition in headwater forests can alter the quantity and type of DBP’s formed during drinking water treatment.