Regenerative Stormwater Conveyance (RSC) for reducing nutrients in urban stormwater runoff depends upon carbon quantity and quality
Citation:
Duan, S., P. Mayer, S. Kaushal, B. Wessel, AND T. Johnson. Regenerative Stormwater Conveyance (RSC) for reducing nutrients in urban stormwater runoff depends upon carbon quantity and quality. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 652:134-146, (2019). https://doi.org/10.1016/j.scitotenv.2018.10.197
Impact/Purpose:
Nutrient enrichment of water bodies continues to be a significant risk globally to human health and ecosystems. Regenerative Stormwater Conveyance (RSC) is a stream restoration approach considered a best management practice to control nutrients in urban ecosystems. However, little information is available to document the efficacy of this technique or whether nutrient credits under the Chesapeake Bay TMDL should be granted to entities utilizing this technique. This study examines RSCs effects on nutrients (P and N) and trace metals at two RSC sites in the Washington DC area, using combined field and lab measurements. Preliminary field measurements showed no consistent longitudinal change in any water quality parameter across sites. However, lab experiments showed consistent removal of N and P when sediment was amended with wood chips and leaf litter. Nutrient management effectiveness in RSCs may depend upon quantity and quality of organic matter added to the stream bed and from the adjacent riparian zone.
Description:
Regenerative stormwater conveyance (RSC), a relatively new stormwater management approach, is extensively implemented throughout the mid-Atlantic for nutrient control, but little is known of its pollutant reduction capabilities and controlling factors. This study examined effects of organic carbon (C) quantity and quality on stream water quality and nutrient retention at two RSCs near Annapolis, Maryland, by comparing longitudinal changes in water quality at paired restored and unrestored stream reaches, and conducting lab experiments simulating RSC processes. We hypothesized that organic carbon enrichment in RSCs causes decreases in dissolved oxygen and pH, therefore affecting retention of nitrogen (N) and release of phosphorus (P). Results showed that RSCs consistently had lower dissolved oxygen saturation (DO%) and pH relative to unrestored tributaries. Lab simulation experiments showed a decrease in DO% and pH and increase in dissolved organic carbon (DOC) release with increasing organic C quantity and quality. At one RSC, with high nitrate (NO3-) inputs, retention of N (16-37%) and release of DOC (18-54%) were observed with the highest retention during summer, and the rates of N retention and DOC release were larger than that of the adjacent unrestored tributary (N: 5-8%, DOC: <18%). Consistently lower N and higher DOC concentrations in groundwater than stream water supported the occurrence of N retention and DOC release across the water-sediment interface. At another RSC site with lower NO3- concentrations, N retention and DOC release were not apparent. Lab simulation experiments showed that NO3- retention varies with organic C quantity and quality depending on incubating temperature, and retention of total N did not increase with organic C due to release of other N species. Lab simulation experiments showed an increase in the release of soluble reactive P (SRP) with increasing organic C quantity and quality. However, field measurements did not show any evidence of SRP release at RSCs. The changes in SRP concentrations in streams seemed to be a function of iron levels and leaf litter inputs, but control factors for SRP warrant further investigation. This study suggests that RSCs as a restoration approach to nitrogen management may be effective for reducing nutrients depending upon C quantity and quality as well as water temperature and ambient nitrogen levels.
URLs/Downloads:
DOI: Regenerative Stormwater Conveyance (RSC) for reducing nutrients in urban stormwater runoff depends upon carbon quantity and quality