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Sediment denitrification and nitrification is enhanced by the presence of macrophytes in a restored agricultural stream, Black Earth Creek, WI USA
Citation:
FORSHAY, K. J. AND S. I. Dodson. Sediment denitrification and nitrification is enhanced by the presence of macrophytes in a restored agricultural stream, Black Earth Creek, WI USA. Presented at EPA Regional Wetlands & Watershed Conference, Kansas City, MI, April 07 - 11, 2008.
Impact/Purpose:
Present information at the EPA Regional Wetlands & Watershed Conference
Description:
Restoration of habitats that support microbial processing can enhance nitrate removal in agricultural streams. Macrophytes are common both in-stream and in the wetted fringe of agricultural stream systems, but are often removed in restoration to increase stream velocity or stabilize banks. However, these macrophytes and the associated sediment may improve nitrate removal through denitrification as well as facilitate conversion of ammonium to less toxic nitrate through nitrification. We measured rates of denitrification and nitrification in the dominant substrate types, macrophyte beds and bare sediment, in a restored agricultural stream, Black Earth Creek, WI in 2004 and 2005. Denitrification potential was evaluated for limiting nutrients (carbon and / or nitrate) along with ambient nitrification rates. Our results show that sediments with submerged and emergent macrophytes (e.g. Potomageton spp. and Phalaris arudinacea.) have greater denitrification rates than bare sediments in the channel without macrophytes (p < 0.05). Sediments with macrophytes were not carbon limited, while substrates without macrophytes were carbon and nitrate co-limited. Nitrification was greatest in the emergent macrophyte beds of the wetted fringe. Our results demonstrate that substrate associated with macrophytes have greater nitrogen processing rates than bare sediments, which suggests that maintenance of macrophytes in agricultural streams is critical in stream restoration if nitrogen removal is a goal.