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Woody Debris: Denitrification Hotspots and N2O Production in Fluvial Systems
Hyman, J., A. Gold, K. Addy, P. Mayer, K. Forshay, AND P. Groffman. Woody Debris: Denitrification Hotspots and N2O Production in Fluvial Systems. In Proceedings, AWRA 2012 Summer Specialty Conference - Riparian Ecosystem IV: Advancing Science, Economics, and Policy, June 27 - 29, 2012. American Water Resources Association, Middleburg, VA, 1-8, (2012).
Conference proceedings for the American Water Resources Association's Riparian Ecosystem meeting on June 27-29, 2012 in Denver, CO.
The maintenance and restoration of forested riparian cover is important for watershed nitrogen (N) cycling. Forested riparian zones provide woody debris to streams that may stimulate in-stream denitrification and control nitrous oxide (N2O) production. We examined the effects of woody debris on denitrification rates at stream sites with and without forested riparian zones to test the hypothesis that fresh input of natural woody debris would support higher denitrification rates than other common stream substrates because of the difference in labile carbon to fuel denitrification. Three different standardized substrates (fresh wood blocks, extant streambed wood and artificial stones) that were expected to vary in their carbon lability were incubated for 9 weeks in two streams, a high nitrate agricultural stream in Pennsylvania and a low nitrate forested stream in Rhode Island. The substrates and their biofilms were collected and subjected to lab mesocosm assays amended with 15N-labeled nitrate stream water to determine denitrification rates and N2:N2O ratios. Wood substrates from the forested site had significantly higher denitrification rates than all other substrate treatments. Artificial stones without biofilm and controls with stream water alone had negligible denitrification likely due to the lack of labile carbon available for denitrification. In the mesocosm incubation, N2 accounted for 99.9% of total denitrification, suggesting that across a range of fluvial conditions denitrification was complete and not a contributor to greenhouse gas production. Conservation and restoration practices that support woody debris in streams should be encouraged for denitrification and do not appear to generate high risks of in-stream N2O generation.