2008 BES Annual Meeting Presentation and Poster Abstracts
Characterization of Nitrogen Dynamics in Urban Restored Streams: An Evaluation of Wetlands and Engineered Floodplain Features
Co-Authors: M.D.Harrison¹ and P. M. Groffman
Abstract: Characterization of N-dynamics in remnant and engineered features is important for assessing their effectiveness for reducing nitrogen loads within urban restored stream ecosystems. This study combines hydrology, geomorphology, and biogeochemistry to examine the impacts of urban stream restoration on nitrogen dynamics in streams in Baltimore, Maryland.. We focused on a section of Minebank Run, a small urban stream in Baltimore County, MD, draining approximately 2.06 mi2. Restored in 1998 and 2002 to re-establish stability of the stream channel, the restoration straightened a fairly sinuous channel leaving behind relict wetland features. The main objective of this study was to identify areas within the study reached where transformation of N-processing are optimal for nitrogen removal and retention. The most effective mechanism of nitrate attenuation in riparian areas being microbial denitrification. In this study we focus on in-stream processes and measured denitrification potential (DEA), net nitrification, organic matter content and moisture content, in pool, riffle and organic debris dam s in six sites (two degraded, two restored, two forested ) streams in the Baltimore Metropolitan area. Results show pools tended to have higher denitrification rate than riffles; forested sites showed significantly higher nitrification rates than all other sites for each feature. As expected, organic debris dams located in forested sites had significantly higher DEA compared to degraded and restored sites. The significant difference in denitrification potential between forested reference and urban streams suggests that incorporation of organic debris structures within restored sites could potentially increase microbial denitrification rates. Based on this preliminary work, we selected riparian areas (relict wetlands) within the study reach for future investigation of N-dynamics and the affects of flow on denitrificantion potential. Given the importance of nitrogen removal in urban watersheds, the high denitrification potential, and the tight cycling of N often found in wetlands suggests that if a portion of the stream flow can be routed through these areas (e.g. engineered or relict wetlands), these sites could function as important sinks for NO3- in urban restored streams.