Nitrification is a prokaryote-mediated oxygen consumptive process of the oxidation of ammonia to nitrite/nitrate that traditionally has been only viewed as a nutrient transformation process. Renewed concern about hypoxia in the shallow hypolimnion of the Central Basin of Lake Erie provides impetus for examining whether nitrification has a significant impact on oxygen dynamics. To evaluate the contribution of nitrification to oxygen demand, water column and sediment samples were collected during the summers of 2008-2010 in Lake Erie and the oxygen consumption due to nitrification and the abundance and distribution of potential bacterial (AOB) and archaeal (AOA) that oxidize ammonia to nitrite was characterized in water column and sediment samples by qPCR of a portion of the ammonia monooxygenase (amoA) gene. Environmental variables and nitrification rates were examined for correlations to understand factors that may control nitrification rates and/or the distribution of nitrifiers. The nitrification rate in the epilimnion and hypolimnion was 3.1 ± 3.2 micromole N/L/day and 3.7 ± 2.9 (mean ± 1 SD) micromole oxygen/L/day respectively. Nitrification accounted for 28.2 ± 23.1% of the total oxygen consumption in the epilimnion and 32.6 ± 22.2% in the hypolimnion. Oxygen consumption by nitrification in sediment slurries and intact sediment cores was 7.1 ± 5.8 micromole oxygen/gram/day and 682 ± 61.1 micromole oxygen/square m/day respectively. Nitrification accounted for 27.0 ± 19.2% of the total oxygen consumption in sediment slurries and 30.4 ± 10.7% in intact sediment cores. AOA and AOB were present in all samples, with a distribution that was variable over time and space. Highlighting the potential importance of archaeal nitrifiers, the AOA/AOB ratio in the epilimnion, hypolimnion, and sediments was 1.02, 1.08, and 5.25. The nitrification rate or nitrifier numbers did not strongly correlate with environmental factors such as oxygen, nitrate or ammonium. In the water column, respiration and the percentage of oxygen used due to nitrification were negatively correlated. While nitrification is unlikely to be the dominant oxygen consumptive process, the rates observed in Lake Erie were sufficient to theoretically deplete a large portion of the hypolimnetic oxygen pool during the stratified period.
|Advisor:||Bade, Darren L.|
|School:||Kent State University|
|School Location:||United States -- Ohio|
|Source:||DAI-B 75/08(E), Dissertation Abstracts International|
|Keywords:||Archaea, Bacteria, Hypoxia, Lake erie, Nitrification, Oxygen consumption|
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