African Lakes Research Articles

What affects fisheries in African lakes: Climate change or fishing effort? A case study from Lake Kariba

AbstractLake Kariba, created in 1958, experienced changes, notably the decline of the Limnothrissa miodon fishery, which have been attributed to climatic change. Air temperatures rose abruptly by 1.1°C between 1980 and 1981, but the temperature of the lake did not follow this pattern. Temperatures at 10 m depth increased by 8% between 1961 and 1971, remained stable until 1984, then declined and by 1992 the temperature was about 7% lower than in 1961. The causes of this are unclear but it followed the hot and dry El Niño droughts of 1982-83 and 1991-92. The lake warmed again by 2007-2011 with temperatures at 10 m being about 10% higher than in 1961, while at 40 m it was 16% higher indicating a faster warming rate in deeper waters. The thermocline fell from 15-20 m in 1968 and 1986 to 20-25 m in 2011 and the temperature gradient decreased by > 50%. The epilimnion became more homogenous, with no evidence of anoxia in the upper 20 m in 2007-08, and the normal monomictic thermal regime may change, thus affecting nutrient circulation and the seasonal abundance of plankton. Both zooplankton and phytoplankton communities have evolved since the lake was created, but these changes occurred before any evidence of warming. The fishery has been declining since 1996 but there is no evidence that climate change is responsible; the number of fishing vessels is presently about three times the recommended level and fishing effort is almost certainly the main cause of the problems. All African lakes support fisheries and it is essential to consider fishing, which changes fish species composition, demographics and abundance, characters that could also be affected by climate change.

Using the Multi-metric Index of Biotic Integrity methodological approach to determine the major river catchment that most pollutes a lake

Abstract We present the Multi-metric Index of Biotic Integrity methodological approach that allows for the ranking of major river catchments based on pollution status in the Kenyan portion of Lake Victoria, Africa. The study has a broader applicability to all of Lake Victoria, other African Great Lakes, and all lakes that have riverine discharge. The method presented utilizes water quality and environmental data, local knowledge, and pre-existing literature. The parameters considered were sampled from 2016 to 2018 during the dry season (July sampling) and the wet season (March sampling). Separation power of Mann-Whitney U test (p < 0.05) qualified 11 discriminant metrics for both macroinvertebrate and fish samples into the scoring system of 1, 3 and 5 in the formulation of final Multi-metric Index of Biotic Integrity methodological approach. Rivers in the northern section had lower Multi-metric Index of Biotic Integrity methodological approach scores, as compared to southern counterparts. The Multi-metric Index of Biotic Integrity methodological approach ranking herein was validated by community perceptions on pollution levels. River Nzoia catchment emerged as the most polluted, followed by River Yala, River Kuja, and Sondu-Miriu. Siltation, domestic washing, litter and refuse emerged as the main agents of pollution. Management authorities ought to reinforce a balanced utilization of the vital water resources to minimize future impacts, and promote catchment wide practices that ensure ecological health sustainability of the lake ecosystem.

African Great Lakes Region: Governance and Politics

This article aims to indicate the sources of problems in the field of governance and politics in the African Great Lakes Region. The countries of this region play an essential role in the global socio-political and economic system. Their development is hampered by numerous external and internal conflicts resulting from both the historical and contemporary problems of the countries. Colonialism had a major impact on the development of African countries. It manifested itself, among other things, in the spread of political domination. Adopting state management patterns from European culture and attempt to transplant them on African ground without understanding local cultural conditions contributed too much post-colonial fresh and modern conflict. Examples of this are failures to establish liberal democracy and its crises in the African Great Lakes Region.

Cholera: Still a Major Public Health Issue in Sub-Saharan Africa.

Cholera continues to be a public health issue in sub-Saharan Africa, specifically the African Great Lakes region. Cases of cholera and deaths from cholera are increasing yearly. Studies have identified lakes and war/conflict as the risk factors for cholera in the African Great Lakes region. Other studies suggest that surveillance, handwashing, sanitation, oral cholera vaccine, education, and access to care are effective preventive measures against cholera in sub-Saharan Africa. But sub-Saharan Africa is not meeting the 2030 Sustainable Development Goal of ensuring availability and sustainable management of water and sanitation for all. This commentary calls for research and implementation of interventions, specifically tailored for the culturally, ethnically, and linguistically diverse populations in sub-Saharan Africa, also taking into account the historical context of each population.

Spatio-Temporal Variation of Atmospheric Nutrient Deposition in Different Land Uses/Covers around Lake Kivu

Atmospheric deposition of nutrients, particularly nitrogen and phosphorus has the capacity to significantly affect the productivity and biogeochemistry of aquatic ecosystems. The objective of this study was to assess the impact of land use/cover types on the atmospheric deposition of nutrients around Lake Kivu. Dry and wet atmospheric deposition samples were collected from four different land use/cover types (forest, wetland, agricultural and urbanized area) at four stations (Goma, Lwiro, Bukavu and Iko) around the Lake Kivu basin. The highest annual loading of dry total phosphorus (TP) was recorded at a station located in an urban area at Goma (4.4 ± 3.9 μmol/m2/yr) and the highest dry deposition of total nitrogen (TN) was recorded at Iko (84.5 ± 41.2 μmol/m2/yr). High wet TP and TN were at Bukavu (0.7 ± 1.1 μmol/m2/yr) and Iko (21.7 ± 34.7 μmol/m2/yr) respectively. High dry TP loads were recorded in the forest area of Goma and the highest dry TN at Lwiro. High wet TP loads were record in agriculture at Goma and high values of wet TN in agriculture at Iko. Phosphorus and nitrogen deposition rates around Lake Kivu were similar to those reported for other African lakes. The highest rate of TP was recorded mainly in the forest area for dry deposition while high TN was recorded in all types of land use/cover in the basin. This study found out that forest traps high concentration of nutrient than other land uses/covers.

Genetic Engineering of Banana Against Bacterial Diseases

Banana (<i>Musa</i> spp) is among the top ten most important food crops worldwide in terms of production and consumption. However, banana production is threatened by several bacterial diseases, including Banana Xanthomonas wilt (BXW) caused by <i>Xanthomonas campestris </i>pathovar (pv)<i>. musacearum</i>, Moko disease caused by <i>Ralstonia solanacearum,</i> and Blood disease caused by <i>Ralstonia syzygii </i>sub-species (subsp)<i>. Celebesensis. </i>Banana Xanthomonas wilt (BXW), caused by <i>Xanthomonas campestris pv. musacearum</i> (Xcm) is the most economically important bacterial disease affecting banana production, particularly in the African Great Lakes region. Banana breeding through conventional approach is key to overcoming yield losses to bacterial phytopathogens. However, conventional breeding of bananas is limited by low male and female fertility and the lack of diversity and important traits in the gene pool. At present, only <i>Musa</i> <i>balbisiana</i> (banana progenitor species) is resistant to BXW, but breeders do not prefer it for breeding because it harbors banana streak virus (BSV) sequences in its B genome, which get activated during abiotic stress, such as drought, leading Banana Streak Disease (BSD). Thus, genetic engineering serves as a viable alternative and complement to conventional breeding for banana improvement. This review highlights the strategies, challenges, status, and prospects of genetic engineering of bananas against bacterial diseases.

Seventh Pandemic Vibrio cholerae O1 Sublineages, Central African Republic.

Four cholera outbreaks were reported in the Central African Republic during 1997–2016. We show that the outbreak isolates were Vibrio cholerae O1 serotype Inaba from 3 seventh pandemic El Tor sublineages originating from West Africa (sublineages T7 and T9) or the African Great Lakes Region (T10).

The Uncertain Influence of the African Great Lakes and the Indian Ocean Dipole on Local-scale East Africa Short Rains

The Uncertain Influence of the African Great Lakes and the Indian Ocean Dipole on Local-scale East Africa Short Rains

Carbon Fixation Trends in Eleven of the World’s Largest Lakes: 2003–2018

Large freshwater lakes provide immense value to the surrounding populations, yet there is limited understanding of how these lakes will respond to climate change and other factors. This study uses satellite remote sensing to estimate annual, lake-wide primary production in 11 of the world’s largest lakes from 2003–2018. These lakes include the five Laurentian Great Lakes, the three African Great Lakes, Lake Baikal, and Great Bear and Great Slave Lakes. Mean annual production in these lakes ranged from under 200 mgC/m2/day to over 1100 mgC/m2/day, and the lakes were placed into one of three distinct groups (oligotrophic, mesotrophic, or eutrophic) based on their level of production. The analysis revealed only three lakes with significant production trends over the study period, with increases in Great Bear Lake (24% increase over the study period) and Great Slave Lake (27%) and a decline in Lake Tanganyika (−16%). These changes appear to be related to climate change, including increasing temperatures and solar radiation and decreasing wind speeds. This study is the first to use consistent methodology to study primary production in the world’s largest lakes, allowing for these novel between-lake comparisons and assessment of inter-annual trends.

Evolutionary divergence of novel open reading frames in cichlids speciation

Novel open reading frames (nORFs) with coding potential may arise from noncoding DNA. Not much is known about their emergence, functional role, fixation in a population or contribution to adaptive radiation. Cichlids fishes exhibit extensive phenotypic diversification and speciation. Encounters with new environments alone are not sufficient to explain this striking diversity of cichlid radiation because other taxa coexistent with the Cichlidae demonstrate lower species richness. Wagner et al. analyzed cichlid diversification in 46 African lakes and reported that both extrinsic environmental factors and intrinsic lineage-specific traits related to sexual selection have strongly influenced the cichlid radiation, which indicates the existence of unknown molecular mechanisms responsible for rapid phenotypic diversification, such as emergence of novel open reading frames (nORFs). In this study, we integrated transcriptomic and proteomic signatures from two tissues of two cichlids species, identified nORFs and performed evolutionary analysis on these nORF regions. Our results suggest that the time scale of speciation of the two species and evolutionary divergence of these nORF genomic regions are similar and indicate a potential role for these nORFs in speciation of the cichlid fishes.

Gene expression dynamics during rapid organismal diversification in African cichlid fishes.

Changes in gene expression play a fundamental role in phenotypic evolution. Transcriptome evolutionary dynamics have so far mainly been compared among distantly related species and remain largely unexplored during rapid organismal diversification, in which gene regulatory changes have been suggested as particularly effective drivers of phenotypic divergence. Here, we studied gene expression evolution in a model system of adaptive radiation, the cichlid fishes of African Lake Tanganyika. By comparing gene expression profiles of six different organs in 74 cichlid species representing all subclades of this radiation, we demonstrate that the rate of gene expression evolution varies among organs, transcriptome parts, and the subclades of the radiation, indicating different strengths of selection. We found that the non-coding part of the transcriptome evolved more rapidly than the coding part, and that the gonadal transcriptomes evolved more rapidly than the somatic ones, with the exception of liver. We further show that the rate of gene-expression change was not constant over the course of the radiation but accelerated at its later phase. Finally, we show that – at the per-gene level – the evolution of expression patterns is dominated by stabilizing selection.

BMAA, Neurodegeneration, and Neuroprotection.

In this volume, studies springing from a BMAA symposium held in Salt Lake City, Utah, in April 2019 are presented. Although most studies of neurotoxicity consider the effects of BMAA as an isolated molecule, it is now known that environmental exposures can be to a combination of BMAA-related molecules, including enantiomers, isomers, other co-occurring cyanotoxins, and BMAA carbamates. Within the body, BMAA may exist in equilibrium with α- and β-carbamates formed in the presence of bicarbonate. BMAA and its isomers 2,4-DAB and AEG, accumulate over decades in biocrusts and persist at depths in soil profiles of the Gulf deserts. In Florida, releases of cyanobacterially ladened water from Lake Okeechobee can extend into coastal environments where diatoms and possibly dinoflagellates also produce BMAA and isomers in addition to brevetoxins. Along the African Lake Chad, neurotoxic risks from consumption of dried cyanobacterial cakes may, however, be outweighed by their amino acid addition to otherwise protein-deficient diets. Discrepancies in the detection and quantification of BMAA from different laboratories likely originate in the use of different analytical methods. C-18 columns, used to study derivatized BMAA, can efficiently separate BMAA from its isomers in validated methods, while validation is not possible for HILIC columns in the study of underivatized BMAA, since they do not adequately separate BMAA from its isomer BAMA. The presence of BMAA dimers, metal adducts, and carbamates may result in underestimation of BMAA by mass spectrometry. BMAA research led to the identification of the dietary amino acid L-serine as a neuroprotective molecule. In animal and clinical trials, L-serine appears to slow neurodegeneration, although the modes of action are still under study. Based on zebra fish sensitivity to platinum-based chemotherapeutic agents, investigators have found that L-serine reduces reactive oxygen species (ROS) but does not protect auditory hybridoma cells from cisplatin. Another possible mode of action of L-serine, induction of autophagic-lysosomal enzymes, is also being explored. The hypothesis that cyanobacterial exposures in general, and chronic exposures to BMAA in particular, may prove to be risk factors for neurodegenerative illnesses has not been without critics. Emerging from the symposium, a multi-authored response to one such critical paper appears in this collection of articles. Instead of waiting until there is a conclusive proof of risk, the adoption of the "precautionary default principle," proposed by Ingvar Brandt and his colleagues in Sweden, is suggested. Avoidance of exposures to cyanobacterial blooms and other sources of BMAA is suggested, until further research indicates such precautions to be unnecessary.

Seasonal variability and sources of in situ brGDGT production in a permanently stratified African crater lake

Abstract. Lake sediments are important archives of continental climate history, and their lipid biomarker content can be exploited to reconstruct paleoenvironmental conditions. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial membrane lipids widely used in paleoclimate studies to reconstruct past temperature. However, major gaps still exist in our understanding of the environmental controls on in situ (i.e. aquatic) production in lake systems. In Lake Chala, a permanently stratified tropical crater lake in East Africa, we determined the concentrations and fractional abundances of individual brGDGTs along depth profiles of suspended particulate matter collected monthly from September 2013 to January 2015 and in settling particles collected monthly at 35 m water depth from August 2010 to January 2015 and compared these brGDGT distributions with those in surficial lake bottom sediments and catchment soils. We find that brGDGTs are primarily produced within the water column and that their concentrations and distributions vary greatly with depth and over time. Comparison with concentration–depth profiles of the monthly distribution and abundance of bacterial taxa, based on 16S rRNA gene amplicon sequencing and quantification, indicates that Acidobacteria are likely not the main producers of brGDGTs in Lake Chala. Shallowing of the oxic–anoxic boundary during seasonal episodes of strong water column stratification promoted production of specific brGDGTs in the anoxic zone. BrGDGT distributions in the water column do not consistently relate with temperature, pH, or dissolved-oxygen concentration but do respond to transitions between episodes of strong stratification and deep (but partial) lake mixing, as does the aquatic bacterial community. Hence, the general link between brGDGT distributions and temperature in brGDGT-based paleothermometry is more likely driven by a change in bacterial community composition than by membrane adaptation of specific members of the bacterial community to changing environmental conditions. Although temperature is not the principal driver of distributional changes in aquatic brGDGTs in this system, at least not during the 17-month study period, abundance-weighted and time-integrated averages of brGDGT fractional abundance in the 53-month time series of settling particles reveal systematic variability over longer timescales that indirectly relates to temperature. Thus, although we do not as yet fully understand the drivers of modern-day brGDGT fluxes and distributions in Lake Chala, our data do support the application of brGDGT paleothermometry to time-integrated archives such as sediments. Highlights. BrGDGTs in the tropical African lake Chala are produced in situ. Acidobacteria are not the dominant source of aquatic brGDGTs. Stratification and mixing drive aquatic brGDGT production and their signature.

Histories of authority in the African Great Lakes: trajectories and transactions

AbstractThis article reflects on how scholars have engaged with the past and with notions of authority in the African Great Lakes. A dominant ‘presentist’ perspective on the region mobilizes historical knowledge in an uncritical fashion, reducing authority to a set of historical clichés and building on a familiar focus on crises and the state. Bridging history and political science, we propose two concepts to analyse histories of political authority to unsettle presentist biases: trajectories and transactions. To illustrate the contribution these alternative lenses make, we present two historical vignettes. First, we revisit the 1973 coup in Rwanda as an ambiguous trajectory of authority-making and unmaking. Then, we consider languages of praise and petitioning in Burundi in the 1960s, to show how authority is lived, manifested and challenged through local transactional relations.

Path dependence and critical junctures: three decades of interstate conflict in the African great lakes region

ABSTRACT As opposed to the three decades following independence, interstate wars have become frequent in the African great lakes region since 1990. This article analyses the unravelling of these wars and looks at their causes and consequences. The conceptual framework to analyse the clear but convoluted line linking these conflicts is that of path dependence and critical junctures. Each stage is defined in these terms. The article shows that path dependence is the main explanatory factor, but that critical junctures have played out at crucial moments, including when the initial stage was set in Uganda. It concludes that a very longue durée path dependence can be found in Rwanda, where most threads of the conflicts converge. However, it also finds that extreme state weakness in Zaire/DR Congo has been and still is a major contributory factor to the cross-border violence. The article finally argues that the conceptual framework is not only useful as an analytical tool, but may also assist efforts in conflict prevention and management.

Methane paradox in tropical lakes? Sedimentary fluxes rather than pelagic production in oxic conditions sustain methanotrophy and emissions to the atmosphere

Abstract. Despite growing evidence that methane (CH4) formation could also occur in well-oxygenated surface fresh waters, its significance at the ecosystem scale is uncertain. Empirical models based on data gathered at high latitude predict that the contribution of oxic CH4 increases with lake size and should represent the majority of CH4 emissions in large lakes. However, such predictive models could not directly apply to tropical lakes, which differ from their temperate counterparts in some fundamental characteristics, such as year-round elevated water temperature. We conducted stable-isotope tracer experiments, which revealed that oxic CH4 production is closely related to phytoplankton metabolism and is a common feature in five contrasting African lakes. Nevertheless, methanotrophic activity in surface waters and CH4 emissions to the atmosphere were predominantly fuelled by CH4 generated in sediments and physically transported to the surface. Indeed, CH4 bubble dissolution flux and diffusive benthic CH4 flux were several orders of magnitude higher than CH4 production in surface waters. Microbial CH4 consumption dramatically decreased with increasing sunlight intensity, suggesting that the freshwater “CH4 paradox” might be also partly explained by photo-inhibition of CH4 oxidizers in the illuminated zone. Sunlight appeared as an overlooked but important factor determining the CH4 dynamics in surface waters, directly affecting its production by photoautotrophs and consumption by methanotrophs.

Reflections on the Predictability of Evolution: Toward a Conceptual Framework.

SummaryEvolution is generally considered to be unpredictable because genetic variations are known to occur randomly. However, remarkable patterns of repeated convergent evolution are observed, for instance, loss of pigments by organisms living in caves. Analogous phenotypes appear in similar environments, sometimes in response to similar constraints. Alongside randomness, a certain evolutionary determinism also exists, for instance, the selection of particular phenotypes subjected to particular environmental constraints in the “evolutionary funnel.” We pursue the idea that eco-evolutionary specialization is in some way determinist. The conceptual framework of phenotypic changes entailing specialization presented in this essay explains how evolution can be predicted. We also discuss how the predictability of evolution could be tested using the case of metabolic specialization through gene losses. We also put forward that microorganisms could be key models to test and possibly make headway evolutionary predictions and knowledge about evolution.

The danger lurking in an African lake

The danger lurking in an African lake

Microbial co-occurrence networks of gut microbiota reveal community conservation and diet-associated shifts in cichlid fishes

BackgroundThe extent to which deterministic rather than stochastic processes guide gut bacteria co-existence and ultimately their assembling into a community remains largely unknown. Co-occurrence networks of bacterial associations offer a powerful approach to begin exploring gut microbial community structure, maintenance and dynamics, beyond compositional aspects alone. Here we used an iconic model system, the cichlid fishes, with their multiple lake assemblages and extraordinary ecological diversity, to investigate a) patterns of microbial associations that were robust to major phylogeographical variables, and b) changes in microbial network structure along dietary shifts. We tackled these objectives using the large gut microbiota sequencing dataset available (nine lakes from Africa and America), building geographical and diet-specific networks and performing comparative network analyses.ResultsMajor findings indicated that lake and continental microbial networks were highly resembling in global topology and node taxonomic composition, despite the heterogeneity of the samples. A small fraction of the observed co-occurrences among operational taxonomic units (OTUs) was conserved across all lake assemblages. These were all positive associations and involved OTUs within the genera Cetobacterium and Turicibacter and several OTUs belonging to the families of Peptostreptococcaceae and Clostridiaceae (order Clostridiales). Mapping of diet contribution on the African Lake Tanganyika network (therefore excluding the geographic variable) revealed a clear community change from carnivores (C) to omnivores (O) to herbivores (H). Node abundances and effect size for pairwise comparisons between diets supported a strong contrasting pattern between C and H. Moreover, diet-associated nodes in H formed complex modules of positive interactions among taxonomically diverse bacteria (mostly Verrucomicrobia and Proteobacteria).ConclusionsConservation of microbial network topologies and specific bacterial associations across distinct lake assemblages point to a major host-associated effect and potential deterministic processes shaping the cichlid gut microbiota. While the origin and biological relevance of these common associations remain unclear, their persistence suggests an important functional role in the cichlid gut. Among the very diverse cichlids of L. Tanganyika, diet nonetheless represents a major driver of microbial community changes. By intersecting results from predictive network inferences and experimental trials, future studies will be directed to explore the strength of these associations, predict the outcome of community alterations driven by diet and ultimately help understanding the role of gut microbiota in cichlid trophic diversification.

Revisiting growth and decline of late Quaternary mega-lakes across the south-central Tibetan Plateau

Lake basins record critical interactions between the hydrosphere, cryosphere and atmosphere. Their sediments and shoreline landforms archive timing, duration, and intensity of past climatic variability and environmental impacts over a variety of timescales. Thousands of lake systems spread across the internally drained Tibetan Plateau today, of which many are only the salty remains of much more expansive paleolakes in the past. This study presents new shoreline ages integrated with quantitative digital topographic analysis and regional geomorphic evidence to reconstruct the sizes and extents of late Quaternary rift lake systems for the south-central Tibetan Plateau. This study presents optically stimulated luminescence (OSL) and the first K-feldspar post-infrared infrared (pIRIR) stimulated luminescence ages for Zabuye Caka and Dawa Tso and tests if these lakes were once part of a singular Pleistocene mega-lake established across four N–S rift systems. Our new results show that two large but separate paleolake systems developed in the latest Pleistocene-earliest Holocene and no lake larger than ∼6460 km2 has existed since at least 41 ka in the Lunggar region. Early Holocene paleolakes expanded up to 7× modern (+220–335 km3) with two to four-fold asymmetric lake expansion in the west compared to the east. Findings corroborate earlier investigations, implying that dramatic runoff increase and/or evapotranspiration reduction prompted rapid earliest Holocene lake expansion. Precipitation variability, in combination with permafrost degradation, temperature and wind strength, governed paleolake moisture balance. Open-system lake behavior and evolving drainage configurations across complex topography explain delayed onsets of lake regression and punctuated lake decline. This suggests abrupt Holocene climate shifts are not necessarily required for punctuated lake decline. Lastly, unique geomorphological and paleoclimatic similarities between Tibetan and East African rift lakes highlight the potential for some Tibetan paleolakes to function as natural climate amplifiers over both short and geologic timescales.