In-stream nitrogen processing in urban degraded and restored streams in Baltimore, MD

Recent studies have shown that in-stream processing of nitrogen by headwater streams may prove to be an important sink for anthropogenic nitrogen. Little is currently known though about the effects of restoration practices on whole stream rates of nitrogen removal. The purpose of this study was to quantify nitrate retention and removal rates in urban restored and unrestored streams using the nutrient spiraling metrics of uptake length, uptake rate, and uptake velocity. Nutrient injections of KNO₃ and a conservative tracer (Br-), were conducted in four streams located in Baltimore County, MD: two of which were recently restored, Minebank Run and Spring Branch, and two unrestored, Glyndon and a tributary of Dead Run. Isotope additions, using ¹⁵N-KNO₃ were also conducted at the restored Minebank Run. We hypothesized that uptake length would be shorter and uptake rates would be higher in restored streams than unrestored implying greater retention and removal of nitrate in restored streams. Preliminary results of uptake length and uptake rate for Minebank Run, were 770m and 1.01 μg N m^-2 s^-1 , and for Spring Branch, 238m and 1.55 μg N m^-2 s^-1, respectively. Information on nitrogen removal rates in these streams will be useful to engineers, planners, and management agencies and may provide incentive for future restoration projects by helping to identify effective restoration approaches. Results also may lead to further research into how restoration engineering can be changed to facilitate higher nitrogen removal rates in urbanizing watersheds and increase ecosystem functions relevant to improving coastal water quality.