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RISS 인기검색어
- 검색키워드
- 저자 : Sharpe-Aparicio, Elizabeth Deirdre (검색결과 1 건)
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Nitrogen cycling in sediments with the seagrass Halodule wrightii in a south Texas estuary
Sharpe-Aparicio, Elizabeth Deirdre Texas A&M University 2000 해외박사(DDOD)
The productivity of estuaries depends on the availability of nutrients, particularly nitrogen [N]. Decomposition of organic matter and the subsequent release of mineral nutrients, is largely a function of benthic bacterial. To better understand benthic N cycling in Baffin Bay, we studied populations of N-transforming bacteria and rates of nitrification, denitrification, and N<sub>2</sub> fixation in sediments from sites with and without the seagrass <italic> Halodule wrightii</italic> Aschers. Total bacteria and N-transforming bacteria were enumerated using direct counts and most probable number methods. Ammonium [NH<sub>4</sub><super>+</super>] disappearance was used to measure nitrification rates, denitrification was measured using the acetylene block technique, and the acetylene reduction assay (AR) was used to measure N<sub>2</sub> fixation in sediment slurries. Total counts of bacteria in the water column ranged from 1.6 × 10<super>7</super>–1.0 × 10<super>8</super> cells mL<super>−1 </super> and rose in the summer. This trend was not observed in the sediments where total numbers ranged from 9.7 × 10<super>8</super>–3.0 × 10<super>10</super> g<super>−1</super>. Ammonifiers ranged from 1.3 × 10<super>4</super>–3.6 × 10<super>10</super> cells g<super> −1</super>, NH<sub>4</sub><super>+</super> oxidizers from 5.7 × 10<super>1</super>–4.3 × 10<super>5</super> cells g<super>−1 </super>, NO<sub>2</sub><super>−</super>-oxidizers from not detectable to 2.9 × 10<super>5</super> cells g<super>−1</super>, denitrifiers from 1.3 × 10<super>1</super>–2.81 × 10<super>6</super> cells g<super>−1</super>, and N<sub>2</sub> fixers ranged from not detectable to 1.5 × 10<super>4</super> cells g<super>−1</super>. Numbers of all N-transforming bacteria peaked during the summer except the nitrifiers, which decreased during this period. Nitrifying bacteria were active in NH<sub>4</sub><super>+</super>-amended sediment slurries in which concentrations of NH<sub>4</sub><super>+</super> decreased at an average rate of 1.6 mg g<super>−1</super> d<super>−1 </super>. Denitrification rates ranged from 0.01 to 1.83 nmol N<sub>2</sub>O g<super>−1</super>d<super>−1</super> in unamended sediments except Alazon Bay, which showed rates of 12 nmol g<super>−1</super> in March 1999. Seasonal variation was only observed in Alazon Bay. Denitrification increased significantly after amendment of sediment slurries with glucose and nitrate. Acetylene reduction rates in unamended vegetated and nonvegetated sediments were very low (0–4 nmol ethylene g<super>−1</super> d<super>−1</super>) and no seasonal variation was observed. Substantial increases were observed after glucose addition. Results indicated that bacteria mediating the major N transformations were abundant year round. Nitrification was active in sediments of Baffin Bay. Denitrification was NO<sub>3</sub><super>−</super> and C limited at all sites and all seasons except in the spring of 1999 in Alazon Bay. Nitrogen fixation was C limited in sediments.
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