Date of Award

Spring 2014

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Earth, Atmospheric, and Planetary Sciences

First Advisor

Darryl Granger

Committee Member 1

Timothy Filley

Committee Member 2

Yuch-Ning Shieh

Abstract

10 Bemet , or cosmogenic beryllium, has a long half-life of 1.4 million years and quick adsorption on soil particles, which may make it ideal for dating soil erosion in historical context. However, there are questions on about the fundamental assumptions of the retentivity of 10 Bemet . This manuscript explores these assumptions and the context of nutrient cycling in a natural forest setting.

To see if 10 Bemet was being cycled through the trees, and at what rate, we looked at the[10 Bemet ] in the soil, 4 species of trees, and their leaves. The isotopic ratio 10 Be/9 Be in all four tree species was comparable to the soil on which they grow, ranging from 6-8 x 10 -9 . However, there was one exception with hickory (Carya spp. ) which strongly bioaccumulate beryllium with an average of 0.38 ppm dry weight in the wood. Abscised hickory leaves have a higher [Be] of 2.0 ppm, over 10 times higher than in the soil.

Using standard allometric equations relating tree biomass to trunk diameter, and assuming that belowground biomass has the same [Be] as aboveground, we calculate that hickory trees at our site contain approximately 1% of the total 10 Bemet under their canopy and that ~10% of this Be is cycled annually by leaf abscission. It is not clear at this point what fraction of litterfall Be is recycled into the plant, returned to the soil, or carried to groundwater as organic chelates.

Hickory trees occupy an average of ~10% of the oak-hickory forest area. Assuming that trees are randomly distributed, that litterfall Be is returned to the soil, and maintaining a constant 10 Bemet budget over time for simplicity, then more than half of all 10 Be met in the forest soil will have passed through a hickory tree over the past 10 ky. Fully 90% of all 10 Bemet will pass through a hickory tree over a period of ~25 ky. It is clear that hickory trees can transport a sizable fraction of the total 10 Bemet in their nutrient cycle, and that they may be responsible for landscape-scale Be mobility.

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