Stormwater Nitrogen Management – Evaluating the Intersection Between Stormwater Management Practice (SMP) Design, Nitrogen Speciation, and Performance
Nonpoint sources of contaminants and nutrients have led to impairments of many water systems in the Delaware and Susquehanna watersheds. Stormwater management practices (SMPs) have been implemented to improvement both water quantity and water quality outcomes, and Green Stormwater Infrastructure (GSI), a stormwater management approach which is largely based on water retention and infiltration, is increasingly being employed. Unfortunately, GSI can increase the amount of nutrients, and particularly nitrogen, in the water that permeates the GSI media, and removal of nitrogen is best achieved through denitrification in a permanently saturated anaerobic subsurface internal water storage (IWS) zone. This research will use laboratory and field approaches to evaluate nitrogen dynamics in SMPs, specifically focusing on the role of the IWS zone design considerations and nitrogen speciation. Laboratory evaluations will be conducted using 2-D reactor systems, where the impact of SMP underdrain height will be evaluated. The approach will combine bench-scale intermittent flow through reactor experiments with modeling efforts. Furthermore, processing of inorganic nitrogen and organic nitrogen will be considered, and it is expected that inorganic nitrogen will be more rapidly denitrified, while organic nitrogen must first be broken down into smaller molecules prior to denitrification thus slowing the process. Advanced analytical chemistry approaches will improve system understanding, including high resolution mass spectrometry (HRMS) to better characterize organic nitrogen components, and isotope ratio analysis for N and O. Complementary field studies will include monitoring of nitrogen species at a field site. This research will enhance our fundamental knowledge of nitrogen dynamics in stormwater SMPs and will also improve the fields ability to design for nitrogen removal. Dissemination of design optimization to stakeholders is a project objective and several existing relationships will be leveraged to achieve this goal.