Unintended consequences of urban stream restoration

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. However, certain restoration techniques and circumstances may yield unintended, undesired consequences including low dissolved oxygen levels, metal and phosphorus mobilization, loss of biota, loss of riparian trees, and increased sediment loads from banks. I discuss the causes of undesired outcomes after stream restoration and suggest alternative approaches to avoid unintended consequences. This discussion is to facilitate and stimulate discussion by the Chesapeake Bay Program technical panel as to how to best revise the 2013 report “Recommendations of the Expert Panel to Define Removal Rates for Individual Stream Restoration Projects” to estimate N removal rates for the purpose of crediting stream restoration projects under the Chesapeake Bay TMDL.

Impact/Purpose

This presentation is for a meeting at the Chesapeake Bay Program Office in Annapolis, MD on 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 draft a final version of the protocols in 2020.

Citation

Mayer, P. Unintended consequences of urban stream restoration. Chesapeake Bay Urban Stormwater Work Group, Annapolis, MD, December 02, 2019.