Spencer Tassone, PhD Candidate at the University of Virginia will present a seminar on his dissertation research.
ABSTRACT: Increasing climatic variability has amplified the frequency of pulsed disturbance events including extremes in temperature. These heatwaves are discrete periods of anomalously high temperature and have gained growing attention due to their disproportionate destructive impacts on aquatic ecosystems relative to longer-term increases in mean water temperature. While positive water temperature trends have been documented in many inland waterways, heatwaves have not been analyzed. In this dissertation, I quantified trends in heatwaves for rivers, estuaries, and coastal sediments. I also tested seagrass resilience (i.e., recovery rate) to a heatwave-like disturbance event. Riverine heatwaves increased in frequency throughout the United States and varied based on atmospheric temperature, discharge, stream order, and position relative to a reservoir. There were no significant trends in estuarine heatwaves although estuarine heatwaves co-occurred with deleterious water quality conditions such as extreme low dissolved oxygen and acidic pH events. Coastal sediment heatwaves increased in frequency and co-occurred with water column heatwaves. Lastly, recovery was faster in seagrass meadow interiors relative to meadow edges likely due to greater hydrodynamic stress at the meadow edge. Seagrass recovered linearly at both locations and was facilitated by lateral clonal growth from the disturbance edges and seedling recruitment from within the meadow. This dissertation provides the first assessment of heatwaves in rivers, estuaries, and coastal sediments and the largest-scale experimental analysis of seagrass recovery.