Deoxygenation of the deep water of Lake Victoria, East Africa

Abstract

The annual cycle of the vertical distribution of oxygen concentrations at a deep water station on Lake Victoria in 1990–1991 was compared with data collected in 1960–1961. Oxygen concentrations in the mixed layer are higher now, with nearly continuous oxygen supersaturation in surface waters. Oxygen concentrations in hypolimnetic waters are lower now for a longer period, with values <1 mg liter−1 occurring in water as shallow as 40 m compared with a shallowest occurrence of >50 m in 1961. The changes in oxygenation are consistent with measurements of higher algal biomass and productivity. The causes for the eutrophication of Lake Victoria are as yet undetermined, although higher nutrient loading, altered climate, and food‐web changes are all potentially involved. The persistent and areally extensive deoxygenation of the hypolimnion must negatively affect the formerly productive and species‐rich demersal fish community.

The invasion of an introduced predator, Nile perch (Lates niloticus, L.) in Lake Victoria (East Africa): chronology and causes

“…Other causes for the decline of the haplochromines were local over-exploitation (Witte and Goudswaard 1985;Acere 1988;Harrisson et al 1989;Bundy and Pitcher 1995;Kudhongania and Chitamwebwa 1995) and eutrophication, leading to oxygen deficiencies (Hecky 1993;Hecky et al 1994;Verschuren et al 2002; but see Witte et al 2005) and to increased turbidity (Seehausen et al 1997). …”

Developmental stages until hatching of the Lake Victoria cichlid Haplochromis piceatus (Teleostei: Cichlidae)

“…In Lake Victoria, several environmental changes have taken places during the last few decades that may affect cichlid embryos. Two important changes are as follows: i) the decrease in dissolved oxygen levels (Hecky et al, 1994;Wanink et al, 2001) and ii) an increase of heavy metal concentrations in the lake (Kishe and Machiwa, 2003). Both can interfere with the development of fish embryos (Yediler and Jacobs, 1995;Weis and Weis, 1995a,b;Latif et al, 2001).…”

Diez años de monitoreo limnológico de un lago natural modificado en los trópicos: el lago Cote, Costa Rica.

“…Although the effect of global climate change is controversial, for example see Nedebele-Murisa, Frank and Miles (2012) and Marshall (2012) on the changes in lake Kariba. Other tropical lakes, albeit larger in size, have shown clear effects that can be attributed to global warming (Hecky et al, 1994;Plisnier, 2000;verburg et al, 2003). According to the empirical equation of Lewis (1987), the bottom and surface temperatures of the lake are expected to be 21.9°C and 26.4°C, respectively; these values are within the observed range of temperatures of Lake Cote, but in recent years surface and bottom temperature reached higher values than expected.…”

“…An analysis for the region has revealed a warming trend in the past decades (Aguilar et al, 2005) and Lake Cote could reveal some signs of these effects. According to the literature it would be possible to observe changes such as an increase in the intensity of the stratification, or a shallower thermocline, and a resulting decrease in productivity (Hambright, Gophen, & Serruya, 1994;Hecky et al, 1994;Plisnier, 2000;verburg, Hecky, & Kling, 2003).…”