Graduate Abstract

Yixin Wei
Fall 2004

Characterization of Dissolved Organic Carbon in Lake Mead

by

Yixin Wei

MS Chemistry
UNLV
2001

BS, Chemistry
Peking University
1987

A Thesis submitted in partial fulfillment
of the requirement for the degree of

Environmental Studies (Environmental Chemistry Track)
Department of Environmental Studies
Greenspun College of Urban Affairs

Fall 2004

Thesis Adviser: Dr Spencer Steinberg
Professor of Chemistry
University of Nevada, Las Vegas

ABSTRACT

Aquatic human substances are complex organic polyelectrolyte derived from the dissolution of soil organic matter and plant litter or formed in situ from the decomposition of algal and microbial biomass. They make up a large fraction of the dissolved organic carbon in natural waters. Aquatic human substances exhibit an important role on the properties of natural water systems, since they cause aesthetic concerns such as color, taste, and odor; act as buffers for the acid-base effect of freshwaters; lead to the binding and transport of organic and inorganic contaminants; produce undesirable disinfection byproducts; provide sources and sinks for carbon; or mediate photochemical processes. The objective of this research is to chemically characterize humic substances in Lake Mead and determine if spectroscopic and chemical characterization will allow the differentiation of humic materials (1-5ppm) in Southern Nevada waters, isolating sufficient aquatic humic materials will be challenging. In this research, solid phase extraction and evaporative concentration techniques will be explored. Molecular weight distribution of the organic matter recovered will be determined by high preference size exclusion chromatography (HPSEC) and split flow thin cell fractionation (SPLITT) methods. Spectroscopic characterization will include synchronous fluorescence, UV-Vis, Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR). Also, pyrolysis gas chromatography mass spectrometry (Py-GC-MS) will be performed. All these analysis will provide information on the chemical composition and the origin of humic substances. In addition, correlation analysis will be investigated to determine the relations among various parameters from various samples in the Lake, such as site profiles, depth profiles, and seasonal variations, etc.