Megan Hansen

Date of Award


Degree Type

Honors College Thesis

Academic Program

Chemistry BS


Chemistry and Biochemistry

First Advisor

Alan Shiller, Ph.D.

Advisor Department

Marine Science


This study examined the distribution of dissolved copper (Cu) in the western Mississippi Sound, as the element can be beneficial or harmful to organisms depending on its concentration and its chemical form. A mixing experiment eliminated flocculation as a control on Cu distributions during estuarine mixing in both dissolved and colloidal fractions. Field sampling of the western Mississippi Sound occurred during a low river discharge period, and distributions of Cu indicated conservative mixing between fresh ([Cu] ≈ 17 nM) and saline ([Cu] ≈ 2 nM) sources in mid-to-high salinities. Storm outfalls were sampled after rain events to evaluate the impact of road runoff, with inconclusive results. However, stable isotope ratios of water (18O/ 16O for oxygen and 2H/ 1H for hydrogen) in field samples showed a fresh source with an isotopic signature (δ18O = -2.2‰) unique from prior analyses of both the Mississippi River (δ18O = -6.6‰) and local rivers (δ18O = -3.9‰). This isotopic anomaly was not found to be significantly influenced by evaporation, indicating a freshwater source other than local rivers. Prior western Mississippi Sound work has shown groundwater with high Cu concentrations and a similar isotopic signature ([Cu] ≈ 20 nM; δ18O ≈ -2.6‰), and other work has found that submarine groundwater discharge (SGD) is a seasonally important source of water to the region. Using the observations collected here, this study proposes SGD as an unrecognized source to the western Mississippi Sound’s Cu mass balance.