Impact of bark beetle infestation on water quality and hydrology in the Rocky Mountain West, The
Contributor(s)Sharp, Jonathan O.
McCray, John E.
Figueroa, Linda A.
Maxwell, Reed M.
Voelker, Bettina M.
Stednick, John D.
Keywordsland cover changes
Bark beetles -- Rocky Mountains
Mountain pine beetle
Watersheds -- Environmental aspects -- Rocky Mountains
Forest biogeochemistry -- Rocky Mountains
Water quality -- Rocky Mountains
Hydrology -- Rocky Mountains
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Includes illustrations (some color), color maps.
Bibliography: pages 81-92.
The recent large-scale bark beetle infestations have altered the forested landscape covering much of the Rocky Mountain West. With canopy loss and changes in water and nutrient uptake, watershed hydrology and terrestrial biogeochemical cycling have been significantly altered. This dissertation contributes to our scientific understanding of these intertwined processes by addressing predicted hydrologic changes complimented by analysis of laboratory and field-scale water quality parameters. A synthesis of current literature studies regarding bark beetle infestations and their impact on hydrology and the intertwined biogeochemistry reveals tree-scale changes to soil-water chemistry (N, P, DOC and base cation concentrations and composition) are being observed in association with beetle outbreaks which ultimately could lead to larger-scale responses; however, the different temporal and spatial patterns of bark beetle infestations due to different beetle and tree species lead to inconsistent infestation impacts. Climatic variations and large-scale watershed responses provide a further challenge for predictions due to spatial heterogeneities within a single watershed; conflicting reports from different regions suggest that hydrologic and water quality impacts of the beetle on watersheds cannot be generalized. A three-dimensional numerical modeling study used to address the hydrologic and land energy changes anticipated throughout the various stages of bark beetle mortality demonstrates that infested watersheds will experience a decrease in evapotranspiration, an increase in snow accumulation accompanied by earlier and faster snowmelt and associated increases in runoff volume and timing. Impacts are similar to those projected under climate change, yet with a systematically higher snowpack. These results have implications for water resource management due to higher tendencies for flooding in the spring and drought in the summer. Laboratory column studies and field soil-water samples that were used to determine how changes in total organic carbon concentrations and composition will influence metal mobility under beetle-impacted trees indicate that a large needle pulse after bark beetle-induced tree death and subsequent decomposition will enhance soil-water concentrations of Cu, Zn and Al. The addition of large amounts of Zn from the pine needle leachate could create higher soil-water concentrations along with additional sorption of zinc to the soil matrix. This large input of Zn to soils could initiate prolonged impacts even after the needles are leached as the sorbed Zn is released. Field collected soil-water samples consistently had concentrations above EPA aquatic life criteria levels for Al and Zn but not for Cu, which would exacerbate existing water quality issues in Colorado where streams often exceed ecotoxicity levels for Al, Cu and Zn. The enhanced mobilization of the three metals from pine needle leachate could also create ecological toxicity issues for plants as well as inhibit regrowth beneath the dead canopies. Analysis of temporal field water-quality data sets containing total organic carbon and disinfection byproduct concentrations at water treatment facilities in healthy and bark beetle-impacted watersheds demonstrate higher total organic carbon (TOC) concentrations along with significantly more DBPs at water-treatment facilities using mountain pine beetle (MPB)-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 MPB watersheds related to the degree of infestation. Disproportionate DBP increases and seasonal decoupling of peak DBP and TOC concentrations further suggests that TOC composition is being altered in these systems.
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