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*Dr. Wayne S. Gardner*, from The University of Texas Marine Science Institute, will be giving a seminar on Wednesday August 30, as a part of the NOAA/ University of Michigan Great Lakes Seminar Series.

Please find details of his talk listed below.

Title: Dissimilatory nitrate reduction to ammonium (DNRA), a mechanism for retaining bioavailable nitrogen in coastal ecosystems

Speaker: *Dr. Wayne S. Gardner*, University of Texas Marine Science Institute

Date: Wednesday August 30

Time: 1030 AM

Location: NOAA/ GLERL
2205 Commonwealth Blvd., Ann Arbor, MI, 48105
Denitrification and DNRA are dissimilatory heterotrophic nitrate reduction processes, which occur at the sediment-water interface in coastal or other aquatic environments. Denitrification converts nitrate-N into the relatively inert N_2, whereas DNRA converts it to NH_4 ^+ , an N form that can be re-assimilated by plants and bacteria. Denitrification has been measured in a variety of freshwater and marine systems but DNRA has not been considered as often, in part because measurement is cumbersome. Nitrogen transformations, relative to oxygen consumption rates, were examined in a variety of shallow coastal marine and lake systems. Concentration changes of nutrients and gases between inflow and outflow waters were measured as site water was passed continuously over intact cores before and after addition of ^15 N-labeled nitrate to inflow water. DNRA is an important process in some Texas coastal systems and its importance increases with salinity. DNRA is also a significant mechanism for retaining nitrogen in Florida Bay. DNRA rates related to sediment oxygen consumption rates in that region, regardless of season (August 2004 vs. January 2005), whereas denitrification rates were low in summer. DNRA thus provides an explanation for the high NH_4 ^+ :NO_3 ^- and high NH_4 ^+ :PO_4 ^3- ratios, often observed in Florida Bay. It may be an important mechanism affecting N and O_2 dynamics in marine “low-oxygen dead zones,” as occur in the northern Gulf of Mexico and other regions, but is less important in comparable freshwater systems such as Lake Erie.


If you have any questions or concerns, please email me at kanika.suri@noaa.gov; or call 734-741-2147.

For more information about the seminar series, please visit our website at http://www.glerl.noaa.gov/news/seminars/



Kanika Suri
Web Designer Associate

NOAA Great Lakes Environmental Research Laboratory
2205 Commonwealth Blvd.,
Ann Arbor, MI

Tel: (734) 741-2147
Fax: (734) 741-2055


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