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Instream Large Wood: Dentrification Hotspots With Low N2O Production
Citation:
Lazar, J., A. Gold, K. Addy, P. Mayer, Ken Forshay, AND P. Groffman. Instream Large Wood: Dentrification Hotspots With Low N2O Production. JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION. American Water Resources Association, Middleburg, VA, 50(3):615-625, (2014).
Impact/Purpose:
Coarse woody debris (CWB) is an important component of stream ecosystems because CWB provides organic carbon and a substrate for microbial growth including denitrying bacteria which can process and remove nutrients from the stream water column. This paper shows that there is a significant effect of both natural and artificial forms of CWB on denitrification and N2O production in both streams. Adding CWB to aquatic ecosystems may enhance removal of excess anthropogenic nitrogen.
Description:
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 nitrous oxide (N2O) production. We examined the effects of woody and mineral substrates on N removal and denitrification at streams with and without forested riparian zones to determine if fresh inputs of woody debris support higher denitrification than other common stream substrates due to the difference in labile carbon (C). Three different substrates (fresh wood blocks, extant streambed wood and artificial stones) expected to vary in their C lability were incubated in two streams, a high N agricultural stream in Pennsylvania and a low N forested stream in Rhode Island and subjected to mesocosm conditions with 15N-nitrate. Denitrification rates did not significantly differ between extant wood and in-stream wood block substrates. Wood substrates at the forested site had significantly higher denitrification than all other substrates. Nitrate-N removal rates were markedly higher on woody substrates compared to artificial stones. Nitrate-N removal rates were significantly correlated to biofilm biomass. N2 accounted for 99.9% of total denitrification. Restoration practices that generate woody debris in streams should be encouraged for N removal and do not appear to generate high risks of in-stream N2O generation.