Quantitative literacy (QL), the ability to understand and accurately use numbers for problem-solving, is an important skill across many areas of undergraduate study. In particular, prior research shows it has a strong, positive correlation with a student’s success in science courses. As such, the relationship between students’ incoming QL and course performance was examined in the context of online, general education astronomy science courses. One of the courses in this study was outfitted with intelligent tutoring, a tool that provides students in the online environment with immediate, specific feedback as they answer questions and complete course material, which may allow students with varying degrees of QL to benefit more from the course. Students' QL levels were measured pre- and post-completion of this course, in addition to a second online astronomy course with adaptive feedback limited to a select few lessons, to better assess the effects of this technology on both QL and course performance. No significant change in students’ QL levels pre- to post-course was found, consistent across courses with and without intelligent tutoring. Linear multiple regression indicated, however, that a student’s incoming level of QL was the most statistically significant predictor of course performance, specifically final grades, across both course types (with and without imbedded intelligent tutoring). This study motivates future discussion around the purpose of introductory astronomy courses more broadly, and what degree of emphasis should be placed on enhancing students’ QL skillset.

This dissertation is presented in two sections. First, I explore two methods of using stable isotope analysis to trace environmental and biogeochemical processes. Second, I present two related studies investigating student understanding of the biogeochemical concepts that underlie part one. Fe and Hg are each biogeochemically important elements in their own way. Fe is a critical nutrient for phytoplankton, while Hg is detrimental to nearly all forms of life. Fe is often a limiting factor in marine phytoplankton growth. The largest source, by mass, of Fe to the open ocean is windblown mineral dust, but other more soluble sources are more bioavailable. To look for evidence of these non-soil dust sources of Fe to the open ocean, I measured the isotopic composition of aerosol samples collected on Bermuda. I found clear evidence in the fine size fraction of a non-soil dust Fe source, which I conclude is most likely from biomass burning. Widespread adoption of compact fluorescent lamps (CFL) has increased their importance as a source of environmental Hg. Isotope analysis would be a useful tool in quantifying this impact if the isotopic composition of Hg from CFL were known. My measurements show that CFL-Hg is isotopically fractionated, in a unique pattern, during normal operation. This fractionation is large and has a distinctive, mass-independent signature, such that CFL Hg can be uniquely identified from other sources. Misconceptions research in geology has been a very active area of research, but student thinking regarding the related field of biogeochemistry has not yet been studied in detail. From interviews with 40 undergraduates, I identified over 150 specific misconceptions. I also designed a multiple-choice survey (concept inventory) to measure understanding of these same biogeochemistry concepts. I present statistical evidence, based on the Rasch model, for the reliability and validity of this instrument. This instrument will allow teachers and researchers to easily quantify learning outcomes in biogeochemistry and will complement existing concept inventories in geology, chemistry, and biology.