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Theses and Dissertations

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Browsing Theses and Dissertations by Subject "beetle"

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    Response of streamflow and stream chemistry to pine beetle induced tree mortality across northern Colorado
    (Colorado State University. Libraries, 2015) Menger, Ashley Lynn, author; Stednick, John D., advisor; Fassnacht, Steven R., committee member; Ronayne, Michael C., committee member
    The lodgepole pine (Pinus contorta) forests of western North America recently endured the most severe insect-induced mortality in recorded history. The hydrological and biogeochemical impacts of mountain pine beetle (Dendroctonous ponderosae) (MPB) induced die-off are uncertain even with recent conceptual and physical research. The purpose of this study is to provide insight into changes in annual water yield, streamflow generation mechanisms and stream water nutrient concentrations due to the recent MPB epidemic. To evaluate the possible impact, watersheds with varying amounts of MPB induced tree mortality in the north-central Colorado Rocky Mountains are examined. It was hypothesized that the canopy loss associated with the MPB epidemic has led to significant changes in annual water yield, streamflow generation mechanisms and stream water total nitrogen, nitrate, and total organic carbon (TOC) concentrations. Data stationarity analysis using the Mann-Kendall test showed no significant trend in annual water yield from 1991-2013 with increasing beetle-killed area. Annual mean isotopic signature (¹⁸O and ²H) analysis of rain, snow, soil water and stream water showed snow (44%) to be the largest contributor to annual streamflow followed by soil water (38%) and rain (14%). No correlation was found between any mean annual source water and percent beetle-killed area. Isotopic analysis of peak streamflow showed soil water (43%) and snow (42%) to be the largest contributors to peak flow. Snow's streamflow contribution was negatively correlated (p = 0.02) to percent beetle-killed indicating that snow as a source for streamflow decreased as a watershed had a higher proportion of MPB-killed trees. No correlation was found between rain or soil water as source waters to peak streamflow and percent beetle-killed. Stream water total nitrogen, nitrate and TOC concentrations and fluxes were not significantly changed by the MPB epidemic. There was no correlation between stream water total nitrogen, nitrate or TOC concentrations or flux and percentage of beetle-killed area. Even though Colorado's forests have been significantly impacted by MPB induced tree mortality, this study suggests that percentage of beetle-killed watershed area has had little impact on annual water yield and stream water nutrient levels. Source water contribution to streamflow is impacted as a result of MPB induced tree mortality as the fraction of peak streamflow from snow decreased with increasing percentage of beetle-killed area.