Joining Water Quantity and Water Quality: Assessing Altered River Thermal Regimes with Satellite Remote Sensing

Abstract

Open-surface inland waterbodies (i.e., rivers, streams, lakes, and reservoirs) are a key source of freshwater for ecosystems and society. Increasing pressures from the intensifying effects of climate change and anthropogenic environmental alterations are impacting both the quantity (e.g., extent, elevation, volume, discharge) and quality (e.g., physical, chemical, or biological conditions) of Earth's freshwater systems. Assessments of inland waterbodies are commonly made using automated sensors for in-situ measurements, which are both logistically and cost prohibitive for large spatiotemporal scales. Alternatively, satellite-based methods can offer a solution for making large-scale holistic assessments of inland waterbodies and determining the effects of anthropogenic changes. Despite increasing access to global satellite data and advanced data processing capabilities, there are still knowledge gaps about inland waterbody processes. Water quantity and quality are inherently connected but are often studied separately in remote sensing. For example, dams are a well-known source of anthropogenic change within rivers because they interrupt natural flows and alter water quality. To date, the study of dams' impacts on river systems has primarily focused on local scales (i.e., single dams, single basins), thus limiting our ability to make broad-scale assessments and ascertain what drives dam-induced river changes. The goal of this dissertation is to explore the connections between water quantity and quality to improve our understanding of inland water dynamics with satellite remote sensing. This dissertation (1) explores how water quantity and water quality connections are addressed in the field of satellite remote sensing; (2) identifies the broad scale impacts of dams on river surface temperatures; and (3) examines the primary drivers of dam-induced river temperature changes. Chapter 2 provides a bibliometric analysis of satellite-based inland waterbody studies (1991 to 2021) and reveals that few studies integrate water quantity and water quality in the field of satellite remote sensing. Chapter 3 uses satellite-based methods to quantify river surface temperature differences up- and downstream of large dams in the United States (2013 to 2024). This study demonstrates that a majority (71%) of observed river profiles experience altered downstream river temperatures. Chapter 4 uses machine learning to examine the potential drivers of dam-induced river temperature changes. This study highlights the complex role that dams play in riverine thermal regimes and illustrates that dam characteristics have the largest role during the spring. This body of work reviews the use of satellite-based methods to assess water quantity and quality amongst increasing pressures of anthropogenic change and elucidates the role dams play on riverine thermal regimes at a national scale.