Phytoplankton Dynamics

Nitrogen is the most important nutrient driving algal growth in Jordan Lake, but Phosphorous is not off the hook.

Key Questions

• What nutrients are driving algal growth in Jordan Lake?
• How are algae in Jordan lake adapted to growing in different light conditions?

Findings

• Nitrogen is the main nutrient driving algae growth.
• Phosphorous can also drive algal growth.
• To control algal growth, inputs of nitrogen into the lake need to be reduced by more than 30%.
• Reductions of phosphorous of about the same amount are also likely needed.
• But reduction of Phosphorous alone will not control algal growth.
• Long term nutrient management should target both Nitrogen and Phosphorous inputs. Best management strategies will target both nutrients.
• Algae in Jordan Lake are better able to grow in low light conditions than previously thought.
• The current water quality models do not account for this shade adaptation, so there is a need to take this into account to properly model Jordan Lake.

Hans Paerl | UNC-Chapel Hill

Hans W. Paerl is Kenan Professor of Marine and Environmental Sciences, at the UNC-Chapel Hill Institute of Marine Sciences, Morehead City. His research includes; microbially-mediated nutrient cycling and primary production dynamics of aquatic ecosystems, environmental controls of harmful algal blooms, and assessing the causes and consequences of man-made and climatic (storms, floods) nutrient enrichment and hydrologic alterations of inland, estuarine and coastal waters. He has published over 300 peer reviewed articles and book chapters on these subjects. His studies have identified the importance and ecological impacts of atmospheric nitrogen deposition as a new nitrogen source supporting estuarine and coastal eutrophication. He is involved in the development and application of microbial and biogeochemical indicators of aquatic ecosystem condition and change in response to human and climatic perturbations. He heads up the Neuse River Estuary Modeling and Monitoring Program, ModMon and ferry-based water quality monitoring program, FerryMon, which employs environmental sensors and a various microbial indicators to assess near real-time ecological condition of the Pamlico Sound System, the USAs second largest estuarine complex.

Nathan Hall | UNC-Chapel Hill

My research seeks to understand the top down and bottom up drivers of phytoplankton biomass and community composition in lakes, rivers, and estuaries. I am particularly interested in how natural ecosystem characteristics such as residence time, grazer communities, and vertical mixing regimes interact with nutrient and light availability to affect bloom dynamics, phytoplankton community composition, and water quality conditions. Recent studies have underscored the critical role of interactions between hydrological forcing and nutrient loading in determining phytoplankton biomass and community structure, including toxic harmful algal bloom species.