S.C. Sea Grant Consortium

Sustainable Coastal Development and Economy Research Projects

Evaluating Nitrogen Removal Strategies to Improve Stormwater Management Practices in Coastal South Carolina

Principal Investigator: Annie Bourbonnais, University of South Carolina
Co-Principal Investigator: Erik Smith, University of South Carolina

Nitrogen is the macronutrient limiting primary productivity in coastal waters, such that excess nitrogen can result in coastal eutrophication, harmful algal blooms and dissolved oxygen impairment, both in coastal South Carolina and globally. Nitrogen is also increasingly recognized as the nutrient limiting algal production in freshwater ecosystems, specifically including stormwater ponds. Although ponds are generally effective at retaining and removing most of the phosphorus and other particulate and particle-associated pollutants prior to discharge to receiving waters, they are often much less effective at removing nitrogen and other dissolved pollutants.

Improving nitrogen removal performance in ponds and other SCMs is thus essential for effective water quality management associated with coastal development. In practice, this will depend on the ability to maximize biogeochemical nitrogen removal through improved pond design and retrofits to existing ponds. However, specific mechanisms responsible for net nitrogen removal and the factors that affect their variability within and among various SCMs remains poorly resolved. A comprehensive assessment of nitrogen transformation rates in various types of SCMs represents a critical information need in the application of SCM design recommendations and management practices for promoting effective nitrogen retention for water quality protection in coastal South Carolina.

On Borrowed Time: Age as a Predictor of Phosphorus Mobility in Coastal Stormwater Ponds and Implications for Management

Principal Investigator: Debabrata Sahoo, Clemson University

The overall objective of this study is to assess the influence of age of the residential stormwater pond on internal sediment Phosphorus (P) dynamics. The study will evaluate if internal benthic sediment acts as a source or sink for the water column P. Over time, sediment P sorption capacity decreases due to increased P loading and decreased sediment loading from the watershed, thus reducing the ability of P storage and could gradually become a net source.

The specific objectives of the project are to assess the spatial (e.g., inlet, middle, outlet of the pond) behavior of the benthic sediment in adsorbing or desorbing water column P within the pond; and, evaluate the temporal (e.g., summer and winter) behavior of the benthic sediment in adsorbing or desorbing water column P. The results will assist stormwater managers, extension specialists and agents, residents, state and local decision-makers, and resource managers in making well-informed decisions regarding sediment, associated P, cyanobacteria management and health of downstream receiving water bodies.

Guiding Successful Applications of Floating Treatment Wetlands in Brackish Coastal Ponds

Principal Investigator: Bill Strosnider, University of South Carolina
Co-Principal Investigators: Sarah White and Amy Scaroni, Clemson University; Matthew Kimball, University of South Carolina

The overall goal of this research project is to guide the development of floating treatment wetlands as viable treatment technologies for brackish systems.

The project team will 1) screen plant species to determine which will survive in floating treatment wetlands deployed in oligohaline to mesohaline (0.5 – 18 ppt) waters and 2) quantify the relative contribution of select plant and volunteer species to habitat provision and nutrient removal in these systems. The project team will develop guidance to enable successful floating treatment wetland installations using three scales of experimental complexity: greenhouse, mesocosm, and field.

Greenhouse trials will reveal plant species suitability and nutrient removal capacity. Mesocosm trials will further evaluate plant species suitability while adding habitat provision quantification for above- and below-mat fauna as well as plant colonization. Full-scale field trials guided by greenhouse and mesocosm findings, and coupled with an extension workshop, will illuminate plant community dynamics, nutrient removal capacity, and above- and below-mat habitat provisioning.