Aquatic Ecology Sub-Project

Alan Wilson, Jim Stoeckel, and Michael Chislock

Plankton—suspended, microscopic plants (i.e., phytoplankton) and animals (i.e., zooplankton) found in aquatic  ecosystems—are one facet of the interdisciplinary Tallapoosa Watershed Project (TWP) that is helping to lay the foundation for future management plans to protect water quality in the Tallapoosa watershed and beyond.  Urbanization and development continue to threaten water quality in many reservoir systems throughout the southeastern United States, and therefore, the ability to successfully manage plankton communities carries broad implications in a region historically impacted by water shortages.  

Phytoplankton comprise the base of aquatic food webs, using resources such as sunlight and nutrients to proliferate while also providing food for zooplankton.  As zooplankton are a key food source for small fish (and in turn, small fish are consumed by top fish predators), phytoplankton abundance indirectly regulates populations of many economically important sport fish.  However, some types of phytoplankton, primarily blue-green algae (i.e., cyanobacteria), can form dense blooms and degrade water quality by releasing intracellular compounds that are harmful to fishes, livestock, and in some cases, humans.  Moreover, when heavy blooms of phytoplankton die due to environmental changes, the decaying phytoplankton settle to the bottom of a lake where they are decomposed by bacteria and fungi.  Intense respiration by microbes decreases oxygen concentrations in the water which can make huge sections of a water body uninhabitable for fish, resulting in fish kills.

Therefore, controlling phytoplankton blooms as a means to improving water quality is a major impetus for the TWP project.  For example, maintaining a healthy abundance of innocuous phytoplankton species is a common goal for water quality managers. Since zooplankton eat phytoplankton, management strategies aimed at controlling zooplankton abundance and species diversity could be an important alternative for controlling phytoplankton blooms in lieu of other approaches such as using herbicides.  Because phytoplankton have such a profound impact on water quality, TWP scientists are focusing on these organisms in an attempt to establish the current water quality status of two sites in the Tallapoosa watershed, the mouth of Saugahatchee Creek and Yates Lake.

As part of the current study, the team takes frequent samples at two sites—one on Saugahatchee Creek and another in a bay in Yates Lake just upstream from where the creek enters.  Water samples are analyzed for important inorganic nutrients, such as phosphorus and nitrogen, which can influence phytoplankton abundance.  Phytoplankton and zooplankton samples are also collected to determine changes in plankton abundances and species diversity over time. 

Using information gleaned from the monitoring efforts, the research team conducts realistic, replicated, field, mesocosm experiments using a unique system of plastic cans maintained within a floating PVC pipe frame at both study sites.  The mesocosms are filled with water from each site, half of which are then treated with either high levels of phosphorus and/or zooplankton.  The containers are sampled after filling and again one week later.  The goals of these studies are to see how increases in nutrient loading effects phytoplankton production, whether zooplankton grazing can reduce the effects of nutrient loading, and whether these effects differ between sites.   To date, two experiments have been conducted, one in the winter and another in the spring.  Results from these experiments have shown that phosphorus availability or zooplankton can affect phytoplankton abundance, but that their effects vary over time and space.  More field experiments are planned during the upcoming summer and fall seasons.  These experiments will inform the team regarding how seasonal environmental changes mediate the effects of excess nutrients and zooplankton on phytoplankton dynamics in Saugahatchee Creek and Yates Lake.  Data produced from these monitoring and experimental efforts will be made available to the general public through peer-reviewed publications and will help improve water monitoring and protection guidelines for the Tallapoosa watershed and, ultimately, for the many other watersheds in the Southeast.  And, of equal importance, it will show residents of the Tallapoosa watershed what’s really happening in their own backyards and why they should care about plankton and water quality issues.