| This study uses batch experiments to determine the evolution of pine needle leachate chemistry in a mountain pine beetle (MPB) infested watershed to better understand the impact of mountain pine beetles (MPBs) on soil porewater and groundwater geochemistry. Green, red and gray pine needles are stripped directly from lodgepole pine tree branches and undergo four subsequent leaching increments. Needle leachates are analyzed for total organic carbon, metals, UV absorbance, fluorescence, and organic acids. These data show that precipitation pulse has more influence on concentration than needle water contact time. With increased precipitation pulse, concentrations, UV absorbance and fluorescence decrease. The chemistry of gray leachates is the most variable, likely due to a larger variability in the age of the needles compared to red and green needles. Metals release in appreciable amounts only in the first increment and TOC may have a relatively long lasting impact on soil porewater concentrations. pH tends to decrease slightly with infestation stage. In general, red and gray leachates have higher concentrations of organic acids than green leachates in an 8 hour experiment. Delayed citric and succinic acid release, and resulting high red leachate organic acid release over a 16 hour experiment, may be attributed to a time component in water needle contact time, rather than water pulse. UV absorbance and fluorescence data observe that green leachates have the highest overall aromaticity, and a tryptophan-like component or epicuticular waxes may also be present in the green leachate. Red and grey leachates have high concentrations of humic-like and fulvic-like (high molecular weight) organic acids. If these leachates are representative of the pine needle contribution to soil porewater composition from a MPB infested watershed, then pine tree death from MPB will lead to changes in soil pore waters, including increased potential of metal mobility related to increased dissolved organic carbon flux. |
