SS2.02 Biogeochemical Process at the Sediment-Water Interfaces
Date: Tuesday, June 11, 2002
Time: 10:15:00 AM
Location: Carson B
 
VoytekMA, USGS, Reston, USA, mavoytek@usgs.gov
Harvey, J, W, USGS, Reston, USA, jwharvey@usgs.gov
Kirshtein, J, D, USGS, Reston, USA, jkirshte@usgs.gov
 
Vertical distribution of the genetic diversity and relative abundance of denitrifying bacteria in stream bed sediments
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Denitrification is a key process in controlling nitrogen loads because it has the capability of permanently removing fixed nitrogen. In order to understand the controls on sedimentary denitrification, the vertical distribution and potential activity of denitrifiers were evaluated on sediment cores collected from two streams in an agricultural watershed, where nitrogen loads are elevated. Denitrifiers were detected by PCR and the community structure was evaluated by T-RFLP analysis of the nitrite reductase gene nirS, the enzyme which catalyzes the first committed step in the denitrification pathway. A comparative analysis of nirS profiles down core and between sites demonstrated a relationship between abundance and genetic diversity of nirS and geochemical and physical properties of the streambed environment. Denitrifiers tended to be more abundant, diverse and active in surface sediments (upper 3cm) and in sediments with a low C/N. Fine grain sediments or sediments with high C/N exhibited poorly developed and less active denitrifying communities. This study revealed the influence of environmental gradients on denitrifier abundance and diversity and may explain differences in denitrification rates under different environmental conditions.