Understanding climatic and terrestrial drivers of lake phytoplankton blooms using high resolution satellite imagery
- The global expansion of harmful algal blooms (HABs) over the past half-century poses a serious threat to human health and ecosystem services in lake systems. HABs dominated by toxic cyanobacteria reduce shoreline recreational opportunities, damage vital fisheries and other aquaculture, and elevate the risk of dangerous toxins in drinking water supplies. While it is well known that phosphorus loading is the main driver of algal blooms in lakes, the apparent proliferation of HABs has prompted deeper examination of the factors contributing to HAB formation and occurrence. Past studies have been limited by the paucity of long-term in situ data in individual lakes, and few have leveraged new opportunities made possible by continental-scale lake surveys to understand drivers of algal blooms in large numbers of lake systems. The studies in this dissertation leverage advances in satellite remote sensing and cloud-based parallel computing over the past decade to study the long-term drivers of lake phytoplankton blooms at regional and global scales. I examine whether different monitoring approaches lead to ambiguity over basic questions of HAB occurrence, spatial extent, and timing, motivating the need for consistent long-term data for understanding HABs. I then describe a novel methodological approach for evaluating satellite remote sensing algorithms that is used to identify an algorithm to detect phytoplankton blooms in Lake Erie, one of the Laurentian Great Lakes. This algorithm is used to hindcast historical algal blooms in Lake Erie since 1984, and the historical record is then used to explore long-term drivers of phytoplankton blooms. The algorithm is also applied to dozens of lakes across six continents in order to characterize long-term trends in historical phytoplankton bloom intensity globally and to examine both climatic and terrestrial drivers at the global scale. In the final component of the dissertation, I explore the hypothesized mechanisms by which climate change is expected to impact harmful algal blooms, doing so by leveraging over twelve hundred summertime lake observations from across the continental U.S. Overall, the findings suggest that management efforts should consider the impacts of global climate change as well as the long-term effects of cumulative nutrient loading in designing mitigation strategies. The research as a whole highlights how knowledge of HABs is being expanded beyond local understanding in a few well-studied systems to a more global understanding based on many systems, and informs strategies to protect water quality within a changing climate.
|Type of resource
|electronic resource; remote; computer; online resource
|1 online resource.
|Ho, Jeffrey Chi-Fung
|Michalak, Anna M
|Michalak, Anna M
|Degree committee member
|Stanford University, Civil & Environmental Engineering Department.
|Statement of responsibility
|Jeffrey Chi-Fung Ho.
|Submitted to the Civil & Environmental Engineering Department.
|Thesis Ph.D. Stanford University 2018.
- © 2018 by Jeffrey Chi Fung Ho
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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