UC Merced

Globally, terrestrial aquatic interfaces, like deltas, face a large number of ecosystem stressors. Monitoring and characterizing mechanisms of change in these areas is relevant to supporting human populations while maintaining ecological integrity. This requires high spatial and temporal resolution satellite-based observations, which have only recently become available to observe rapid changes in these dynamic systems. Sentinel-2, launched in 2016, provides a 5-day temporal resolution and 10 m spatial resolution which allows for detecting fine-scale changes in both water quality and aquatic vegetation. This dissertation is motivated by two primary interacting themes: 1) using remote sensing to study water quality, vegetation composition and phenology across aquatic ecosystems, and 2) providing knowledge and insight to support ecosystem management and informed decision making. Using the high spatial and temporal resolution capabilities of Sentinel-2, this dissertation addresses three main research objectives that correspond to three manuscripts (Chapters 1 – 3). The study site for all works is the California Sacramento San Joaquin Delta. Chapter 1 evaluates the impacts of an emergency drought barrier on turbidity and endangered fish habitat suitability. This manuscript is already published in the Journal of American Water Resource Association. The results demonstrate how high spatial, high temporal resolution satellite data enhances field observations by providing additional spatial context. Chapter 2 provides a framework for mapping aquatic vegetation, specifically distinguishing between two types of invasive floating aquatic vegetation at the genus level – water primrose and water hyacinth. Classification accuracy assessments and comparisons to maps derived from higher resolution airborne imaging spectroscopy data demonstrate that Sentinel-2 can be used to fill in inter-annual gaps in aquatic vegetation maps from summer to fall. Chapter 3 builds off Chapter 2 and reveals the phenology of water primrose may be a key component of its recent invasion success. Water primrose patches show examples of niche breadth, priority effects, and environmental plasticity relative to water hyacinth and emergent vegetation. Our findings highlight the need for spatially resolved phenology metrics. Overall, this dissertation provides insights into water quality and aquatic vegetation invasion ecology and provides improved methods for ecosystem managers to continue to investigate ecosystem stressors.