From drones to Daphnia: Exploring eutrophication and climate change impacts on algal blooms at various scales

Abstract

Climactic variations and cultural eutrophication alter aquatic ecosystems by promoting harmful algal blooms (HABs) that destabilize aquatic food webs and degrade the quality and safety of aquacultured fish, recreational waterbodies, and drinking water sources. The goal of my dissertation work was to gain a holistic understanding of these complex events by studying HABs at multiple scales. At the food web level, many aquatic organisms will have to cope with toxic cyanobacteria and thermal stress. I tested the potential energetic trade-offs associated with local adaptations to toxic cyanobacteria in the keystone zooplankton grazer, Daphnia pulicaria, under multiple stressor conditions. Results from this lab study suggest local adaptations to toxic cyanobacteria and elevated temperatures are synergistic, leading to higher survivorship during summer HAB events. At the aquaculture production level, I tested whether unoccupied aerial systems (i.e., drones) were a viable tool for monitoring the abundance of potentially toxic cyanobacteria in small eutrophic systems. Four sensors were used to monitor 54 eutrophic ponds that varied in size and trophic state. Results indicate that while drones are well-equipped for estimating total phytoplankton abundance, commercial sensors are not equipped to reliably monitor cyanobacteria abundance. At the state level, a comprehensive two-year sampling of all drinking water utilities in Alabama was used to determine the prevalence of cyanobacteria, cyanotoxins, and off-flavor compounds in the state’s surface drinking water sources. Raw water samples show that drinking water sources were high in nutrients (i.e., nitrogen and phosphorus), but deficient. In cyanobacteria, cyanotoxins, and off-flavor compounds. These results suggest that cultural eutrophication does not necessarily lead to HABs, and therefore monitoring phytoplankton abundance is a better indicator of the trophic state of these systems than nutrients. Finally, to understand algal bloom intensification trends at the national level, a 30-year survey of 650 lakes located across 11 freshwater ecoregions was completed to determine if spatial patterns were associated with algal bloom intensification. Results indicate that 65% of lakes are not significantly increasing or decreasing in algal bloom intensity and algal bloom trends were closely related to eutrophication. These findings suggest researchers may be overestimating the widespread intensification of algal blooms.