Denitrification in the Hyporheic Zone during Base Flow
Citation:
Mayer, P. AND S. Kaushal. Denitrification in the Hyporheic Zone during Base Flow. Chesapeake Bay Urban Stormwater Work Group, Annapolis, Maryland, February 12, 2019.
Impact/Purpose:
This presentation is for a meeting at the Chesapeake Bay Program Office in Annapolis, MD on Feb 12 as part of the process by the Chesapeake Bay Urban Stormwater Work Group to begin revising the 2013 multi-agency authored report “Recommendations of the Expert Panel to Define Removal Rates for Individual Stream Restoration Projects”. The charge of the panel during this meeting is to craft a revision to protocol #2, “Credit for Instream and Riparian Nutrient Processing within the Hyporheic Zone during Base Flow” so that State and Municipal Agencies can apply for stream restoration permits and receive nutrient credits under the Chesapeake Bay TMDL. The group will meet several times during the year to draft a final version of the protocols.
Description:
Excess nitrogen (N) and phosphorus (P) from human activities have contributed to degradation of coastal waters globally. A growing body of work suggests that hydrologically restoring streams and rivers in agricultural and urban watersheds has potential to increase N and P retention, but rates and mechanisms have not yet been analyzed and compared across studies. We present nearly two decades of collective research assessing the effects of stream restoration on nutrient uptake in the Chesapeake Bay area. We also conducted a review of 79 studies on nutrient retention within hydrologically reconnected streams and rivers in other areas. We developed a typology characterizing different forms of stream and river restoration, and analyzed nutrient retention across this typology. The studies we reviewed used a variety of methods to analyze nutrient cycling. Nitrate uptake metrics were significantly related to watershed surface area, impervious surface cover, and average reach width. More research is necessary to characterize nutrient uptake during periods of high flow, and more long-term studies are needed to understand changes in nutrient dynamics as projects evolve over time. Overall, the analysis suggests that the size of the stream restoration (surface area), hydrologic connectivity, and hydrologic residence time are key drivers influencing nutrient retention at broader watershed scales and along the urban watershed continuum; suggesting an approach for improving the efficacy of stream restoration.