A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters
Includes bibliographical references Nitrification is the oxidation of ammonium to nitrate through a two step biological process. Nitrification in the euphotic zone has, in the past, been considered negligible even though quantifying this process correctly is important when linking carbon export to n...
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Department of Oceanography
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ftunivcapetownir:oai:open.uct.ac.za:11427/16794 2024-09-15T18:37:03+00:00 A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters Philibert, Marie Catherine Raïssa Waldron, Howard Clark, Darren 2015 application/pdf http://hdl.handle.net/11427/16794 eng eng Department of Oceanography Faculty of Science University of Cape Town http://hdl.handle.net/11427/16794 Oceanography Doctoral Thesis Doctoral PhD 2015 ftunivcapetownir 2024-06-25T03:57:49Z Includes bibliographical references Nitrification is the oxidation of ammonium to nitrate through a two step biological process. Nitrification in the euphotic zone has, in the past, been considered negligible even though quantifying this process correctly is important when linking carbon export to nitrate uptake by phytoplankton. However, studies of both nitrogen uptake and nitrification rates in surface waters are rare. This thesis presents such data for the Southern Ocean and St-Helena Bay, located in the Southern Benguela upwelling system. Using 15N tracers, Nitrogen uptake and regeneration rates were measured in the Southern Ocean (during a winter cruise in July 2012 and a summer cruise in February-March 2013) and St-Helena Bay (during three studies in November 2011, March 2012 and March 2013). In St-Helena Bay, the upwelling (bloom) cycle was one of the main drivers of the nitrogen cycle. As the bloom cycle started, nitrate uptake rates (5:47 ± 670:48nmol∙L⁻¹∙h⁻¹) and nitrite regeneration (4:36 - 1:28 ± 22:83 - 1:63nmol∙L⁻¹∙h⁻¹) were high but the contribution of nitrification to the nitrate demand was low. Nitrite regeneration at this time could have been driven by phytoplankton excretion. In contrast, at the end of the bloom cycle, nitrate uptake rates were low and was exceeded by nitrate regeneration rates (25:34 - 6:16 ± 82:74 - 34:41nmol∙L⁻¹∙h⁻¹). Nitrite regeneration decreased and was most likely due to ammonium oxidation at this stage of the upwelling cycle. Nitrification in the Southern Ocean was more variable than in St-Helena Bay. It was only detected at five stations out of fifteen and the accuracy of the high nitrite oxidation rates (37:21 - 9:13 ± 217 - 88nmol∙L⁻¹∙h⁻¹) observed can only be assessed with repeat measurements. Nitrate uptake rates ranged from 0.07 to 57:00nmol∙L⁻¹∙h⁻¹ while ammonium uptake rates ranged from 0.81 - 160:94nmol∙L⁻¹∙h⁻¹. The nitrogen uptake rates were similar for both seasons. Using multivariate statistical approach, it was found that during winter, in the Southern ... Doctoral or Postdoctoral Thesis Southern Ocean University of Cape Town: OpenUCT |
institution |
Open Polar |
collection |
University of Cape Town: OpenUCT |
op_collection_id |
ftunivcapetownir |
language |
English |
topic |
Oceanography |
spellingShingle |
Oceanography Philibert, Marie Catherine Raïssa A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
topic_facet |
Oceanography |
description |
Includes bibliographical references Nitrification is the oxidation of ammonium to nitrate through a two step biological process. Nitrification in the euphotic zone has, in the past, been considered negligible even though quantifying this process correctly is important when linking carbon export to nitrate uptake by phytoplankton. However, studies of both nitrogen uptake and nitrification rates in surface waters are rare. This thesis presents such data for the Southern Ocean and St-Helena Bay, located in the Southern Benguela upwelling system. Using 15N tracers, Nitrogen uptake and regeneration rates were measured in the Southern Ocean (during a winter cruise in July 2012 and a summer cruise in February-March 2013) and St-Helena Bay (during three studies in November 2011, March 2012 and March 2013). In St-Helena Bay, the upwelling (bloom) cycle was one of the main drivers of the nitrogen cycle. As the bloom cycle started, nitrate uptake rates (5:47 ± 670:48nmol∙L⁻¹∙h⁻¹) and nitrite regeneration (4:36 - 1:28 ± 22:83 - 1:63nmol∙L⁻¹∙h⁻¹) were high but the contribution of nitrification to the nitrate demand was low. Nitrite regeneration at this time could have been driven by phytoplankton excretion. In contrast, at the end of the bloom cycle, nitrate uptake rates were low and was exceeded by nitrate regeneration rates (25:34 - 6:16 ± 82:74 - 34:41nmol∙L⁻¹∙h⁻¹). Nitrite regeneration decreased and was most likely due to ammonium oxidation at this stage of the upwelling cycle. Nitrification in the Southern Ocean was more variable than in St-Helena Bay. It was only detected at five stations out of fifteen and the accuracy of the high nitrite oxidation rates (37:21 - 9:13 ± 217 - 88nmol∙L⁻¹∙h⁻¹) observed can only be assessed with repeat measurements. Nitrate uptake rates ranged from 0.07 to 57:00nmol∙L⁻¹∙h⁻¹ while ammonium uptake rates ranged from 0.81 - 160:94nmol∙L⁻¹∙h⁻¹. The nitrogen uptake rates were similar for both seasons. Using multivariate statistical approach, it was found that during winter, in the Southern ... |
author2 |
Waldron, Howard Clark, Darren |
format |
Doctoral or Postdoctoral Thesis |
author |
Philibert, Marie Catherine Raïssa |
author_facet |
Philibert, Marie Catherine Raïssa |
author_sort |
Philibert, Marie Catherine Raïssa |
title |
A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
title_short |
A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
title_full |
A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
title_fullStr |
A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
title_full_unstemmed |
A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
title_sort |
comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
publisher |
Department of Oceanography |
publishDate |
2015 |
url |
http://hdl.handle.net/11427/16794 |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_relation |
http://hdl.handle.net/11427/16794 |
_version_ |
1810481374552915968 |