Global warming is reducing thermal stability and mitigating the effects of eutrophication in Lake Victoria (East Africa)

Abstract

The impacts of global warming have been reported from several deep lakes in the African Rift Valley and in each thermal gradients within the water column have increased thus strengthening already existing oxyclines, below which the water is permanently anoxic^1,2,3,4^. The temperature of Lake Victoria rose by 0.9°C between 1960 and 1990 raising fears that thermal stability would increase resulting in more extensive and severe anoxia in the deeper waters^5^. This is of concern because of the eutrophication of the lake, which began in the 1960s,^6,7^ and led to dense blooms of sometimes toxic cyanobacteria, increased deoxygenation of the bottom waters, and fish kills in some parts of the lake^8,9,10^. Here we show that thermal gradients in the water column have weakened over the last decade and that deoxygenation of deeper waters is less pronounced than expected. Since 1927 the temperature of the deeper waters has risen by 1.3°C compared to only 1.0°C in the surface layers, thereby decreasing thermal and density differentials in the water column. This contradicts the view that eutrophication would increase deoxygenation of the water column perhaps to the point where fish production could not be sustained^11^. Our results suggest that the impacts of global warming on tropical lakes are likely to highly variable and may not, in the short term at least, be uniformly detrimental.

Morphometry and trophic state modify the thermal response of lakes to meteorological forcing

“…This isolation may cause nutrient depletion in the epilimnion and anoxia in the hypolimnion while the strength of impact depends on the stability and duration of the stratification. As water column stability derives from vertical density increase, in most lakes global warming strengthens stratification and thermal stability, although opposite examples exist in some tropical lakes where in long-term more heat is trapped in bottom layers than in surface layers (Marshall et al, 2009).…”

Assessment of trophic state in Lake Malombe, Malawi, using Sentinel-2 Multi-Spectral Instrument imagery

“…For example, large-scale algal blooms can result in water quality deterioration, leading to a collapse of the lake shery. Gophen et al (1995) pointed out that the effects of eutrophication, which include changes in phytoplankton composition -shifting from diatoms to cyanobacteria along with an increase in algal biomass, may result in sh kills in shallow water bodies and more severe deoxygenation in deeper waters such as Lake Tanganyika and Lake Malawi (Marshall, et al, 2009). Several researchers have also reached a consensus that eutrophication in shallow water bodies represents a signi cant ecological problem and could detrimentally affect the ecosystem functioning and sh population dynamics and species composition, leading to a trophic cascade (Smith, during the rainy season could be linked to ecological changes in the lake.…”

Advances of High-Performance Triboelectric Nanogenerators for Blue Energy Harvesting

“…It is less investigated in the past for its complexity, which should be emphasized with further development of blue energy. (4) The interaction of devices with water motion is crucial for power-take-off (PTO) performance of the system, which should be theoretically investigated and optimized based on fluid-structure interaction dynamics.…”

“…Covering over 70% of the earth's surface, ocean plays a crucial role for lives on the planet and can be regarded as an enormous source of blue energy, whose exploitation is greatly beneficial for dealing with energy challenges for human beings [1][2][3]. With extreme climate conditions taking place more frequently nowadays, the world feels the urge to take immediate action to alleviate climate deterioration caused by global warming [4][5][6]. Carbon neutrality is thus put forward as a goal to reach balance between emitting and absorbing carbon in the atmosphere [7].…”