Insights from using in-situ ultraviolet-visible spectroscopy to assess nitrogen treatment and subsurface dynamics in a regenerative stormwater conveyance (RSC) system

Adrienne R Cizek; Jeffrey P Johnson; François Birgand; William F Hunt; Richard A McLaughlin

doi:10.1016/j.jenvman.2019.109656

Insights from using in-situ ultraviolet-visible spectroscopy to assess nitrogen treatment and subsurface dynamics in a regenerative stormwater conveyance (RSC) system

J Environ Manage. 2019 Dec 15:252:109656. doi: 10.1016/j.jenvman.2019.109656. Epub 2019 Oct 12.

Authors

Adrienne R Cizek¹, Jeffrey P Johnson², François Birgand³, William F Hunt⁴, Richard A McLaughlin⁵

Affiliations

¹ Stormwater Solutions Engineering, Milwaukee, WI, 53204, USA. Electronic address: adrienne.cizek@gmail.com.
² Department of Biological and Agricultural Engineering, Campus Box 7625, North Carolina State University, Raleigh, NC, 27695, USA. Electronic address: jeffrey_johnson@ncsu.edu.
³ Department of Biological and Agricultural Engineering, Campus Box 7625, North Carolina State University, Raleigh, NC, 27695, USA. Electronic address: birgand@ncsu.edu.
⁴ Department of Biological and Agricultural Engineering, Campus Box 7625, North Carolina State University, Raleigh, NC, 27695, USA. Electronic address: wfhunt@ncsu.edu.
⁵ Department of Crop and Soil Sciences, Campus Box 7620, North Carolina State University, Raleigh, NC, 27695, USA. Electronic address: rich_mclaughlin@ncsu.edu.

PMID: 31614259
DOI: 10.1016/j.jenvman.2019.109656

Abstract

Regenerative stormwater conveyance (RSC) is a recently developed stormwater control measure that marries the concepts of bioretention and stream restoration. RSC mitigates stormwater runoff by converting surface flow to subsurface seepage using a series of pools and riffles built over a sand media bed. Subsurface seepage flows through media and exits the RSC beneath the outlet weir. Previous studies on RSC pollutant mitigation have focused on surface flow discharges from the RSC. To date, no known research has been conducted on the potential pollutant contributions of RSC seepage, despite the fact that this water also enters receiving waters. This research used Multi-Point Sampling coupled with in-situ ultraviolet-visual spectroscopy to measure nitrogen in seepage during simulated storm events (n = 9) at a field-scale RSC in Raleigh, North Carolina. Calibrations between light absorbance and concentrations were acceptable (Nash-Sutcliffe coefficient > 0.65) for nitrate and total ammoniacal nitrogen (TAN) and very good (Nash-Sutcliffe coefficient > 0.90) for total Kjehdahl nitrogen (TKN). Early storm simulations revealed some initial nutrient flushing from the substrate, which subsided by the third simulation. Overall, subsurface seepage nitrate, TAN, and TKN concentrations were lower by 29%, 57%, and 4% relative to storm inflow concentrations, respectively. Computed subsurface nitrogen concentrations demonstrated temporal variability, highlighting dynamic transport and biogeochemical transformations in saturated and unsaturated conditions. Nitrogen concentrations were lower in seepage than in surface flow; however, due to the high volume of runoff converted to seepage, nitrogen loads discharged in seepage can be larger than those of surface flow. Further research is needed to examine subsurface pollutant reductions under varying hydrologic and seasonal conditions.

Keywords: Nitrogen; Regenerative stormwater conveyance; Seepage; Stormwater; UV spectroscopy; Ultraviolet–visual spectroscopy.

MeSH terms

Nitrogen*
North Carolina
Rain
Rivers
Spectrophotometry, Ultraviolet
Water Movements
Water Pollutants, Chemical*

Substances

Water Pollutants, Chemical
Nitrogen