A spatiotemporal assessment of urbanization and water quality in the subtropics

Abstract

Urban populations and urban lands are expanding globally, which is predicted to continue in the coming decades. Through mechanisms like the heat island effect and diminished infiltration, urbanization confers a variety of negative impacts to water quality. These impacts are well cataloged in streams, while urban lakes lack the same concerted attention. In this dissertation I leverage paleoenvironmental techniques and a diverse suite of proxies (e.g., nutrients, metals, photosynthetic pigments, and cyanotoxins) from lakes in Polk County, FL, USA and Coba, Quintana Roo, MEX to better understand the biogeochemical signatures of urban lakes. In Chapter 1, surface sediments from multiple urban lakes reveal toxic concentrations of heavy metals in nearly every system as well as a strong correlation between impervious surface cover and N-fixing cyanobacteria markers. In Chapter 2, paleoenvironmental reconstructions from two unconnected urban systems independently implicate canal construction as the primary driver of synchronous pollutant enrichment and eventually cyanobacteria dominance in both lakes. In Chapter 3, a paleoenvironmental record reveals significant differences in periods of ancient Maya-era agricultural activity, urban development, urban quiescence and recovery. Here, I also found that maximum cyanobacteria and cyanotoxin concentrations coincided with local Maya-era population maximums at the site. Collectively, this dissertation highlights the outsized role of the built environment on urban water quality as well as demonstrate the effectiveness of sediment studies and multi-proxy datasets in identifying and addressing water quality problems.