R/EH-7

Strategic focus area:

Description:

Objectives: The proposed study will (1) quantify the potential for stream restoration to reduce nitrogen loads from rapidly urbanizing coastal watersheds (kg N removed per restoration), and (2) identify which stream restoration features (e.g. armored pools and riffle sequences, oxbow ponds and riparian wetlands) are best at removing nitrogen. Methodology: Rates of N removal will be measured in a range of reference, degraded and restored streams (small reaches so that individual restoration features can be isolated) using 15N-nitrate tracer additions to whole streams and riparian zones. In situ denitrification rates will be integrated with annual estimates of hydrologic flux through streams and sediments of the riparian zone (and within the context of habitat and geomorphic characterization) to obtain annual estimates of N removal across restoration sites and stream features compared with forest reference and urban degraded streams and identify key factors controlling nitrogen retention. Rationale: Despite the overflow $400 million invested in stream restoration in the Chesapeake Bay watershed since 1990, there are few data on the effects of N removal. Our preliminary data at 1 site show that certain restoration features support high rates of in situ denitrification leading to substantial reductions in concentrations of nitrate in riparian ground water and stream water in restored reaches. The proposed project would assess the potential of other different urban stream restorations to produce similar nitrogen removal benefits to coastal watersheds. Results will be integrated with a large restoration database containing information on the types, numbers, costs, and river miles of restoration projects to: (1) estimate how much N can be removed by stream restoration projects, (2) what are the most economic restoration strategies for N removal, and (3) how many urban streams would need to be restored to substantially reduce N loads to Chesapeake Bay and its tributaries from rapidly urbanizing watersheds.