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Nitrification and denitrification in seagrass communities in Chwaka bay, Zanzibar
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Science.
1996 (English)Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesisAlternative title
Nitrifikation och denitrifikation i sjögräsområden i Chwaka bay, Zanzibar (Swedish)
Abstract [en]

As a response to the environmental degradation of many coastal areas in east Africa research have been initiated aiming towards the understanding of the coastal ecosystems and the interactions between them. The sediment of three seagrass communities were investigated with regard to nitrification, denitrification, pore water nutrient content, organic content and physical character. The aim was to estimate the magnitude and importance of nitrification and denitrification and correlate those to any difference in organic load. Total organic carbon and total nitrogen decreased while C:N ratio increased with distance from the mangroves indicating a larger organic load closer to the mangroves. There was however no significant difference between the sites regarding ammonium and nitrate + nitrite concentrations in the porewater; nor regarding denitrification. Recalculated to ambient nitrate concentrations denitrification was less than 157 nmol N m-2h-1. No trend could be seen for nitrification either. Nitrification ranged from 0-12.0 µmol N m-2h-1, but the method used may underestimate the rates. Denitrification, and especially nitrification rates, varied considerably within each site indicating an extremely patchy environment. Considering that nutrient regeneration rates in tropical environments are usually high, nitrification and denitrification seemed to be minor pathways in the nitrogen cycle irrespective of organic load. The study also suggests that nitrification and denitrification may be of less importance in Chwaka bay compared to other areas studied.

Abstract [sv]

Som svar på den försämrade miljön i flera kustområden i Östafrika har forskning påbörjats inriktad på förståelsen av kustliga ekosystem samt samspelet dem emellan. Sedimentet i tre sjögräsområden undersöktes med avseende på nitrifikation, denitrifikation, näringshalt i porvattnet, organisk halt samt fysikalisk karaktär. Syftet var att uppskatta storleken och betydelsen av nitrifikation och denitrifikation samt att korrelera dessa med organisk belastning. Totala halten organiskt kol och totala halten kväve minskade medan C:N kvoten ökade med avståndet till mangroven vilket tyder på en större organisk belastning närmare mangroven. Det var däremot ingen signifikant skillnad mellan områdena beträffande ammonium- eller nitrat + nitrit koncentrationen i porvattnet; inte heller beträffande denitrifikation. Omräknad till föreliggande nitratkoncentrationer var denitrifikationen mindre än 157 nmol N m-2h-1. Nitrifikationen varierade från 0-12.0 µmol N m-2h-1, men den använda metoden kan ha underskattat hastigheterna. Någon trend i nitrifikationen syntes inte heller. Denitrifikationen och speciellt nitrifikationen varierade avsevärt inom varje område vilket tyder på en extremt omväxlande miljö. Med tanke på att regenerationen av näringsämnen ofta är hög i tropiska miljöer så verkade nitrifikationen och denitrifikationen vara mindre betydelsefulla delar i kvävecykeln oavsett organisk belastning. Denna studie tyder också på att nitrifikation och denitrifikation är mindre betydelsefulla i Chwaka bay än i andra studerade områden.

Place, publisher, year, edition, pages
1996. , p. 19
National Category
Oceanography, Hydrology and Water Resources
Identifiers
URN: urn:nbn:se:uu:diva-393143OAI: oai:DiVA.org:uu-393143DiVA, id: diva2:1351661
Educational program
Mathematics and Natural Sciences Programme
Available from: 2019-09-16 Created: 2019-09-16 Last updated: 2019-09-16Bibliographically approved

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