The overarching goal of this research project is to determine how altered dissolved oxygen (DO) concentrations in the bottom waters of lakes and reservoirs affect zooplankton behavior, abundances, and species composition, and how these changes may have consequences for water quality and food webs. Zooplankton play a critical role in freshwater ecosystems; they feed on phytoplankton, the base of the food web, and are in turn consumed by fish. Consequently, changes in zooplankton populations have the potential to drastically alter water quality and food webs. Zooplankton in freshwater ecosystems around the world exhibit diel vertical migration, in which they migrate to the bottom waters of a lake or reservoir during the day to escape visual predation by fish and damaging ultraviolet (UV) radiation. At night, many zooplankton migrate to the water's surface to feed on phytoplankton when the risk of predation and UV exposure is lower. However, human activities are resulting in decreased DO concentrations in the bottom waters of waterbodies globally. As a result of decreased DO, zooplankton may remain in the surface waters during the day and no longer vertically migrate, resulting in decreased abundance and changes in the species composition. This research will be conducted in partnership with a local water utility, and all data and results will be shared with managers to inform their water quality decisions. The project will involve training of at least two undergraduate researchers in freshwater science laboratory and field methods in an interdisciplinary setting. In addition, results from this research will provide the basis for creating interactive and hands-on educational activities for school children at a nature center.
This project will integrate a unique whole-ecosystem manipulation of bottom water (hypolimnetic) DO concentrations, a cross-ecosystem survey of reservoirs on a hypolimnetic DO gradient, high-frequency sonar to observe the diel vertical distribution of zooplankton, and experimental analyses of zooplankton functional traits to examine how changes in DO concentrations alter zooplankton species composition, abundance, and behavior. Biweekly summer field surveys will be conducted across five reservoirs that exhibit a range of hypolimnetic DO concentrations. One of the reservoirs has a hypolimnetic oxygenation system that will be experimentally turned on and off (thereby controlling DO concentrations at the whole-ecosystem scale) to directly assess the effects of DO on zooplankton populations. Multiple diel sampling campaigns will also be conducted that use sonar acoustic technology to observe the vertical distribution of zooplankton in the water column. Taken together, these integrated research approaches will mechanistically determine the effects of changing DO concentrations on zooplankton communities and resulting implications for water quality in lakes and reservoirs.
