Publication Date

2014

Document Type

Honors Thesis

Department

Chemistry

Keywords

Watersheds-Massachusetts, Mercury, Soils-Mercury content, Introduced organisms., Water-Organic compound content, Watershed, Invasive species, Dissolved organic carbon, Soils

Abstract

Exotic Asian and European earthworm invasion in forest soils has been shown to disrupt carbon and nitrogen cycling, leading to the release of dissolved constituents from organic soil horizons. Organic decomposition likely releases anthropogenic mercury that has accumulated from atmospheric deposition since the Industrial Revolution. Similarly, climate warming is expected to accelerate soil decomposition rates via increased forest soil temperatures. Climate warming may induce increased organic decomposition rates, releasing mercury to surface water and posing public health risks. To evaluate these hypotheses, a series of microcosm experiments (earthworm and temperature) were conducted using O horizon soil collected from hemlock and deciduous stands in the Avery Brook Watershed, West Whately, MA. In the earthworm microcosms, worms were added and the soils watered weekly for seven weeks. Worms caused a dramatic increase in DOC and UV254 levels in leachate from the hemlock soils and mercury concentrations (63 ng/L) were double those from the non-worm hemlock controls. Worms appear to change the relationship between dissolved organic carbon (DOC) and UV254 such that with worms present, the values of UV254 are higher, suggesting that the worms produce leachate with higher aromaticity and this is more efficient in leaching Hg from soil organic material. Temperature microcosms of hemlock and deciduous soils were held at 4, 13, and 22ºC and treated the same as the worm microcosms. As hypothesized, DOC and Hg concentrations increased the most in microcosms at 22ºC. Hemlock soils continued to release both DOC and mercury over time, while deciduous soils appeared to reach equilibrium in the last four weeks. Decomposition rates comparing the earthworm and temperature microcosms indicate that temperature changes alter soil decomposition reactions more profoundly than an invasive earthworm. This implies that temperature changes from climate warming may be more important to soil chemistry changes than an invasive earthworm.

Language

English

Comments

100 pages : illustrations (some color). Honors Project-Smith College, 2014. Includes bibliographical references (pages 93-100)

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