The distribution of temperature, oxygen and nutrients in Lake Bukoni, Uganda

Autor: Clement Nyakoojo, Stephen M. Byarujali
Rok vydání: 2009
Předmět:
Zdroj: African Journal of Ecology. 47:658-663
ISSN: 1365-2028
0141-6707
DOI: 10.1111/j.1365-2028.2009.01036.x
Popis: Temperature, oxygen and nutrients were determined in the permanently stratified Lake Bukoni from July 2004 to December 2005. Meromixis has resulted from the nature of the surrounding hilly topography and the almost vertical crater walls that exclude the effects of light winds. These circumstances and the tropical temperature regime ensure permanent stratification in the offshore part of the lake. From about 20 m to the bottom, the water was out of circulation and devoid of oxygen. Water samples from such depths had a strong smell of hydrogen sulphide gas. The inshore site, with greater turbulence and littoral area, had a uniformly oxygenated water column compared with the offshore site. According to information from members of the community around the lake, ‘fish kills’ have taken place but on irregular occasions. The nutrients (N, P and Si) were well distributed in the inshore site. In the offshore site, the concentrations were generally lower in the uppermost 20 m but more than double near the mud surface. Soluble reactive phosphorous was the least abundant nutrient while soluble reactive silicon was the most abundant nutrient. The high Si : P ratios have led to the dominance of species like Synedra ulna Ehr. Resume De juillet 2004 a decembre 2005, la temperature, l’oxygene et les nutriments ont ete determines dans le lac Bukoni, dont la stratification est permanente. La meromicticite resulte de la nature de la topographie montagneuse environnante et des murs presque verticaux du cratere qui excluent tout effet des vents legers. Ces conditions, ainsi que le regime de temperature tropicale, garantissent la stratification permanente de la partie du lac eloignee des berges. Entre 20 metres environ et le fond, l’eau ne circule pas et est depourvue d’oxygene. Les echantillons d’eau qui proviennent de ces profondeurs ont une forte odeur d’hydrogene sulfure. En comparaison, le site cotier, plus agite avec sa partie littorale, presentait une colonne d’eau uniformement oxygenee. Selon les membres de la communaute qui vit autour du lac, des hecatombes de poissons ont deja eu lieu mais de facon irreguliere. Les nutriments (N, P, et Si) etaient bien distribues sur le site cotier. Au large, les concentrations etaient generalement plus faibles dans les 20 metres superieurs, mais plus que doubles pres de la surface de la vase. Le phosphore reactif soluble (PRS) etait le nutriment le moins abondant alors que la silice reactive soluble (SiRS) etait le plus abondant. Les rapports Si/P eleves ont entraine la dominance d’especes telles que Synedra ulna Ehr.
Databáze: OpenAIRE
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