Graduation Year

2015

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Geology

Major Professor

Bogdan P. Onac, Ph.D.

Committee Member

Jonathan G. Wynn, Ph.D.

Committee Member

Philip van Beynen, Ph.D.

Keywords

Bat, Bat Guano, Carbon, Cave, Nitrogen, Stable Isotopes

Abstract

Because nitrogen isotopes are fractionated along the soil-plant-insect-bat-guano pathway, it may be possible to reconstruct environmental and climatic changes reflected in the nitrogen isotopic composition of guano. A 1.5-m core of bat guano from Zidită Cave (western Romania) provides a record of climatic and anthropogenic influence on the regional nitrogen cycle and paleoenvironmental controls on nitrogen transforming processes. Increasing and decreasing trends of nitrogen isotopic composition (δ15N values) correspond well with changes in the influence of farming practices, deforestation, and forest expansion. These influences likely had a significant effect on the openness of the nitrogen cycle, resulting in changes in δ15N values of soil, plants, and ultimately guano. While δ15N values have gradually decreased since AD 1700, decadal trends towards more positive values at AD 1840 and 1920 coincide with increases in tree pollen (forest recovery). Additionally, the accumulation of relatively15N-depleted guano coincides with periods of increased fire frequency, deforestation, and crop/herbaceous pollen (agricultural practices).

δ13C record of bulk guano indicates that carbon isotopic variation results from changes in water availability. Comparison of δ13C to δ15N indicates that there is a significant correlation between nitrogen and carbon isotopic composition of guano. When water availability was high (low δ13C values), δ15N values of bulk guano trend towards higher values. Although this connection to climate is the opposite of the findings from previous work correlating δ15N values of plant foliage and precipitation amount, the relationship between nitrogen isotopic values and water availability still appears to have merit. Based on these findings, δ15N of guano appears to be a signal for changes in N cycling of the Mada region that occurs, primarily in response to the precipitation received, further modified by intense changes in anthropogenic activity.

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