Vegetation enhances nitrogen removal in stormwater control measures in coastal South Carolina

Stormwater Control Measures (SCM) are used to mitigate stormwater impacts on downstream receiving waters. SCMs tend to be highly effective at removing particle-associated nutrients, such as phosphorus, but they are often much less effective at removing dissolved nitrogen. In excess amounts, inorganic nitrogen can lead to coastal eutrophication, harmful algal blooms, and coastal hypoxia (i.e. “dead zones”). In this research, we aimed to provide an estimate of nitrogen removal rates (i.e., by denitrification) and net N2 fluxes across the sediment-water interface for a series of stormwater detention ponds with varying amounts of vegetation. Rates of removal were significantly higher (p<0.001) in the vegetated stormwater detention ponds (2.73 – 42.98 µmol N m-2 h-1) compared to those without vegetation (0.6 – 3.5 µmol N m-2 h-1). Additionally, average net N2 fluxes were positive for vegetated ponds (2.03 – 22.23 µmol N m-2 h-1) but generally negative for unvegetated ponds (-20.96 – 1.68 µmol N m-2 h-1). These results indicate that sediments of conventional (unvegetated) stormwater ponds are significant sources of nitrogen. However, when ponds are intentionally or passively allowed to grow emergent vegetation (especially vegetated littoral shelves), they switch roles and become net sinks due to a substantial increase in rates of denitrification, demonstrating stormwater ponds have the potential to alleviate some of the negative effects of urbanization and improve overall water quality with encouraged use of vegetation.

Presentation Preference: Oral

Primary Presenter: Darcy Perin, University of South Carolina (dperin@email.sc.edu)

Authors:

Darcy Perin, University of South Carolina, School of the Earth, Ocean and Environment  (dperin@email.sc.edu)

Annie Bourbonnais, University of South Carolina, School of the Earth, Ocean and Environment  (abourbonnais@seoe.sc.edu)

Erik Smtih, University of South Carolina, Baruch Marine Field Laboratory  (erik@baruch.sc.edu)