Lakes Of Africa Research Articles

Niche expansion in a resilient endemic species following introduction of a novel top predator

Summary Introduced species can have profound direct ecological impacts on native species, yet their potential indirect effects remain relatively unexplored. For instance, introduced predators may directly affect some native species via predation, which may in turn have indirect consequences for other species that are released from competition. We explore this possibility in East Africa's Lake Victoria basin, where the introduction of the predatory Nile perch, Lates niloticus, in the 1950s and 60s contributed to the overall or local extinction of hundreds of native fish by the 1980s. We ask whether this dramatic change in assemblage composition has led to competitive release and niche expansion in Rastrineobola argentea, a resilient native cyprinid that has thrived in this highly perturbed ecosystem. To address this question, we compare the trophic ecology of R. argentea before (1966) and after (2011) the introduction of the Nile perch in Lake Victoria; and across eight satellite lakes that differ in their history of Nile perch invasion. Using this combination of spatial and temporal comparisons, we test for increases in dietary niche breadth (niche expansion) and changes in the level of individual specialisation of R. argentea in invaded versus uninvaded contexts. In our historical comparison, we find good evidence for dietary niche expansion and an increase in interindividual diet variation in R. argentea over time. Across lakes, however, strong bottom‐up effects (i.e. variation in prey availability) appear to obscure any potential top‐down effects of the Nile perch introduction on the trophic ecology of R. argentea. Overall, we find substantial temporal and spatial variation in the diet and niche breadth of R. argentea, but the underlying drivers remain uncertain, given the complexity of both anthropogenic and natural ecological changes in Lake Victoria over the past century. Understanding both the direct and indirect impacts of introduced species is challenging, but important for successful long‐term management of human‐altered ecosystems.

Recurrence Plots from Altimetry Data of Some Lakes in Africa

Recurrence Plots from Altimetry Data of Some Lakes in Africa

Riparian ecosystem resilience and livelihood strategies under test: lessons from Lake Chilwa in Malawi and other lakes in Africa

This paper reviews the importance of African lakes and their management challenges. African inland lakes contribute significantly to food security, livelihoods and national economies through direct exploitation of fisheries, water resources for irrigation and hydropower generation. Because of these key contributions, the ecosystem services provided are under significant stress mainly owing to high demand by increasing populations, negative anthropogenic impacts on lake catchments and high levels of poverty which result in unsustainable use. Climate variability exacerbates the stress on these ecosystems. Current research findings show that the lakes cannot sustain further development activities on the scale seen over the past few decades. Millions of people are at risk of losing livelihoods through impacts on livestock and wildlife. The review further shows that the problems facing these lakes are beyond the purview of current management practices. A much better understanding of the interactions and feedbacks between different components of the lake socio-ecological systems is needed to address the complex challenges of managing these ecosystem services. This review suggests that the three small wetlands of Chad, Chilwa and Naivasha provide an opportunity for testing novel ideas that integrate sustainability of natural resource management with livelihoods in order to inform policy on how future land use and climatic variability will affect both food security and the ecosystem services associated with it.

Recurrence Plots from Altimetry Data of Some Lakes in Africa

The paper shows recurrence plots obtained from time series of the level variations of four lakes in Africa (Nasser, Tana, Chad and Kainji). The data, coming from remote sensing, are provided by the United States Department of Agriculture. The recurrence plots allow a good visual comparison of the behaviours of local drainage basins.

Coupled human and natural system dynamics as key to the sustainability of Lake Victoria’s ecosystem services

East Africa's Lake Victoria provides resources and services to millions of people on the lake's shores and abroad. In particular, the lake's fisheries are an important source of protein, employment, and international economic connections for the whole region. Nonetheless, stock dynamics are poorly understood and currently unpredictable. Furthermore, fishery dynamics are intricately connected to other supporting services of the lake as well as to lakeshore societies and economies. Much research has been carried out piecemeal on different aspects of Lake Victoria's system; e.g., societies, biodiversity, fisheries, and eutrophication. However, to disentangle drivers and dynamics of change in this complex system, we need to put these pieces together and analyze the system as a whole. We did so by first building a qualitative model of the lake's social-ecological system. We then investigated the model system through a qualitative loop analysis, and finally examined effects of changes on the system state and structure. The model and its contextual analysis allowed us to investigate system-wide chain reactions resulting from disturbances. Importantly, we built a tool that can be used to analyze the cascading effects of management options and establish the requirements for their success. We found that high connectedness of the system at the exploitation level, through fisheries having multiple target stocks, can increase the stocks' vulnerability to exploitation but reduce society's vulnerability to variability in individual stocks. We describe how there are multiple pathways to any change in the system, which makes it difficult to identify the root cause of changes but also broadens the management toolkit. Also, we illustrate how nutrient enrichment is not a self-regulating process, and that explicit management is necessary to halt or reverse eutrophication. This model is simple and usable to assess system-wide effects of management policies, and can serve as a paving stone for future quantitative analyses of system dynamics at local scales.

Shell middens and other anthropogenic soils as global stratigraphic signatures of the Anthropocene

Abstract Evidence for aquatic foraging, fishing, and scavenging by hominins dates back at least two million years, but aquatic resource use intensified with the appearance of Homo sapiens . The development of new fishing and seafaring technologies contributed to population growth and the spread of humans around the world. By the late Pleistocene and early Holocene, fishing peoples lived along coastlines, rivers, and lakes in Africa, Eurasia, Australia, and the Americas, creating shell midden soils marked by accumulations of mollusk shells, animal bones, artifacts, and other cultural debris. After global sea level rise slowed ∼8000 years ago, a proliferation of shell middens formed an increasingly prominent stratigraphic signature for identifying and defining an Anthropocene Epoch. The formation of these distinctive cultural soils, often marked by unique soil chemistry and biotic communities, is essentially contemporaneous with the development of agricultural economies and the widespread soil and landscape changes associated with them. Defined by these global and highly visible anthropogenic soil signatures, I propose that the Anthropocene began about 10,000 years ago and should replace or be merged with the Holocene.

A hierarchical Bayesian approach to the classification of C3 and C4 grass pollen based on SPIRAL δ13C data

Differentiating C3 and C4 grass pollen in the paleorecord is difficult because of their morphological similarity. Using a spooling wire microcombustion device interfaced with an isotope ratio mass spectrometer, Single Pollen Isotope Ratio AnaLysis (SPIRAL) enables classification of grass pollen as C3 or C4 based upon δ13C values. To address several limitations of this novel technique, we expanded an existing SPIRAL training dataset of pollen δ13C data from 8 to 31 grass species. For field validation, we analyzed δ13C of individual grains of grass pollen from the surface sediments of 15 lakes in Africa and Australia, added these results to a prior dataset of 10 lakes from North America, and compared C4-pollen abundance in surface sediments with C4-grass abundance on the surrounding landscape. We also developed and tested a hierarchical Bayesian model to estimate the relative abundance of C3- and C4-grass pollen in unknown samples, including an estimation of the likelihood that either pollen type is present in a sample. The mean (±SD) δ13C values for the C3 and C4 grasses in the training dataset were −29.6±9.5‰ and −13.8±9.5‰, respectively. Across a range of % C4 in samples of known composition, the average bias of the Bayesian model was <3% for C4 in samples of at least 50 grains, indicating that the model accurately predicted the relative abundance of C4 grass pollen. The hierarchical framework of the model resulted in less bias than a previous threshold-based C3/C4 classification method, especially near the high or low extremes of C4 abundance. In addition, the percent of C4 grass pollen in surface-sediment samples estimated using the model was strongly related to the abundance of C4 grasses on the landscape (n=24, p<0.001, r2=0.65). These results improve δ13C-based quantitative reconstructions of grass community composition in the paleorecord and demonstrate the utility of the Bayesian framework to aid the interpretation of stable isotope data.

Sources and sinks of methane in Lake Kivu

Africa's Lake Kivu, which borders Rwanda and the Republic of the Congo, contains huge amounts of methane (an estimated 60 cubic kilometers) and carbon dioxide (an estimated 300 cubic kilometers). Although the methane could provide a source of energy if it could be tapped, the high concentrations of gases pose a risk of dangerous gas eruptions, threatening the local population. Furthermore, it has been reported that concentrations of methane have risen by as much as 15% in the past 30 years. Scientists need to learn more about the sources and sinks of methane in Lake Kivu to better assess the risk of catastrophic outgassing and sustainability of methane harvesting.

Determination of Heavy Metal Content in Water, Sediment and Microalgae from Lake Victoria, East Africa

Lake Victoria, which is the largest fresh water lake in Africa, represents a unique ecosystem that has the largest fresh water fishery in the continent. However, increased anthropogenic activities has increased the potential pollution of the lake especially the heavy metal pollutants which may be toxic to humans and aquatic fauna. There is need therefore for continuous monitoring of pollution levels in the lake. Samples of water, soil sediments and algae were collected in dry, long and short rainy periods of 2008 and analyzed for heavy metal by Atomic Absorption Spectrophotometry. The highest concentration of trace metals were found in sediment samples with Zn having the highest mean concentration values in both Winam (1.019 ppm) and Mwanza gulf (0.889 ppm). The mean concentration of Pb was higher in water samples from Winam gulf (0.823 ppm), while Hg in microalgae samples from Winam gulf had a mean concentration of 0.000148 ppm. The highest concentration of Zn (1.589 ppm) was determined in the sediment samples from Kirumba bay of the Mwanza gulf and the lowest was in sediments from Kishimba bay (0.327 ppm). Levels of trace metals in microalgae were not significant in different sites of the Mwanza Gulf. Like in the Mwanza gulf, levels of Zn was high in sediments from all the sites sampled in Winam Gulf, the highest recorded at Kisat. Pb levels were highest in the water samples from Hippo point, whereas concentration levels of Cd, Cr and Hg were lowest in all the four sites sampled. The maximum biomass of micro- algae occurred at Kisat during the short rain season (November-December) followed by Kamito in the same season.

Persistent Phytoplankton Bloom in Lake St. Lucia (iSimangaliso Wetland Park, South Africa) Caused by a Cyanobacterium Closely Associated with the Genus Cyanothece (Synechococcaceae, Chroococcales)

Lake St. Lucia, iSimangaliso Wetland Park, South Africa, is the largest estuarine lake in Africa. Extensive use and manipulation of the rivers flowing into it have reduced freshwater inflow, and the lake has also been subject to a drought of 10 years. For much of this time, the estuary has been closed to the Indian Ocean, and salinities have progressively risen throughout the system, impacting the biotic components of the ecosystem, reducing zooplankton and macrobenthic biomass and diversity in particular. In June 2009, a bloom of a red/orange planktonic microorganism was noted throughout the upper reaches of Lake St. Lucia. The bloom persisted for at least 18 months, making it the longest such bloom on record. The causative organism was characterized by light and electron microscopy and by 16S rRNA sequencing and was shown to be a large, unicellular cyanobacterium most strongly associated with the genus Cyanothece. The extent and persistence of the bloom appears to be unique to Lake St. Lucia, and it is suggested that the organism's resistance to high temperatures, to intense insolation, and to hypersalinity as well as the absence of grazing pressure by salinity-sensitive zooplankton all contributed to its persistence as a bloom organism until a freshwater influx, due to exceptionally heavy summer rains in 2011, reduced the salinity for a sufficient length of time to produce a crash in the cyanobacterium population as a complex, low-salinity biota redeveloped.

Correction to “Distributions and temperature dependence of branched glycerol dialkyl glycerol tetraethers in recent lacustrine sediments from China and Nepal”

[1] In the paper “Distributions and temperature dependence of branched glycerol dialkyl glycerol tetraethers in recent lacustrine sediments from China and Nepal” by Q. Sun et al. (Journal of Geophysical Research, 116, G01008, doi:10.1029/2010JG001365, 2011), several errors have become apparent after publication, and they are corrected below. The authors apologize for any inconvenience this has caused. [2] 1. Figure 3 had an incorrectly labeled x axis. The correct Figure 3 is given here. [3] 2. On page 5, in the section “3.1. Distribution Pattern of GDGTs,” the reference of “[Weijers et al., 2007b]” was incorrectly cited and should be cited as “[Weijers et al., 2006a].” [4] 3. In the Figure 9 caption, “lakes in Africa, South America, and North America” was incorrectly cited and should be cited as “lakes in Europe, the Americas, and Africa.”

Arthrospira fusiformis (Voronichin) Komarek et Lund (Cyanoprokaryota) A new species for Europe

The first algological research on salty puddles in two localities, Slatina and Pecena Slatina near the river Tamis, north-east Serbia, was carried out in 2003 and contin- ued in 2006. These habitats are distinguished by a great amount of salt and increased pH value of water. The cyanobacterial species Arthrospira fusiformis (Cyanoprokaryota, Oscillatoriales), up to now mainly known from tropical regions in Africa and Asia, was found in the phytoplankton of both mentioned localities. The first occurrence of this par- ticular species, which is typical of salty alkaline lakes in Africa, is remarkable in Serbia and is described.

Microalgal biomass in the St Lucia Estuary during the 2004 to 2007 drought period

Phytoplankton and microphytobenthic biomass were investigated over a 4 yr period in the drought-stricken St Lucia Estuary, KwaZulu-Natal, South Africa. This is the largest estuarine lake in Africa and part of the iSimangaliso Wetlands Park, South Africa's first World Heritage Site and a Ramsar Wetland of International Importance. The present study aimed at identifying the factors con- trolling the extreme variability in its ecological functioning. Water-column chlorophyll a (chl a) con- centrations averaged (±SD) 32.3 ± 53.4 mg m -3 , with the highest value reaching 413 mg m -3 . Within the sediment, average (±SD) chl a concentration was 201 ± 377 mg m -2 , with a maximum of 2576 mg m -2 . Both are among the highest values so far reported in the literature for any estuarine ecosystem and by far the highest values reported for any South African estuary. Areal phytoplankton biomass was highest in the Mouth and Narrows region, declining in the South and North lakes, while micro- phytobenthos showed the reverse trend. Ordinations and cluster analysis revealed that phytoplankton biomass differed between the southern and northern halves of the system, while differences in micro- phytobenthic biomass were found between the Narrows and the rest of the system. Dissolved inor- ganic nitrogen to phosphorus ratios were greater and lower than the Redfield optimum (16) 60% and 27% of the time, respectively, indicating that microalgal production may be limited by availability of either P or N for part of the year, with a peak in growth during summer. Water level and mouth state are key factors controlling microalgal biomass within the estuary. During the closed phase, the shal- low waters and vast surface area of the lakes region led to the development of hypersaline conditions and temperatures occasionally approaching 50°C. The negative effects of such extreme conditions on grazers, as well as negative correlations between grazer densities and microalgal biomass, have been documented in previous work on the system. This would suggest that the interaction between the physical environment and grazers may be important in regulating microalgal biomass in the estuary.

Effect of hypersaline and low lake conditions on ecological functioning of St Lucia estuarine system, South Africa: An overview 2002–2008

Lake St Lucia, the largest estuarine lake in Africa has been subjected to hypersaline conditions and low lake levels over the past eight years following the closure of its mouth due to drought in the region. This paper documents the physical changes through which the lake has passed and summarises the main findings of research undertaken on the three major biotic components that have been subjected to these conditions. A review of the anthropogenic impacts which have affected the system is provided. These indicate that in combination with drought conditions greater pressure is placed on the system that was the case in the historical past. Available data indicate that the current situation is not only impacting on the lake and its fauna but also on the adjacent nearshore marine environment, It is considered that the Meta area is potentially also under threat. Medium to long term relief possibilities that are under consideration are discussed in relation to the restructuring of something resembling the historically combined uMfolozi–St Lucia ecosystem that existed in the past. It is concluded that in the short term only two options are available to potentially provide relief for the system, the first is to breach the connection between the mouth and the sea. The second is to re-establish some form of more permanent connection, between uMfolozi and St Lucia.

Earth science: A lakeful of trouble

Africa's Lake Kivu contains vast quantities of gas, which makes it both dangerous and valuable. Anjali Nayar asks whether it is possible to tap the gas without causing a disaster.

Democratization and War in Political Science

This article explores what political science literature has to say about the promises and perils of expanding democratic governance. International relations literature and comparative politics literature both deal with the claim that stable democracies do not fight each other. However, these two strands of literature only to a minor extent exchange research findings on the causes of war. International relations scholars are well aware of the fact that the early stages of democratization in particular may trigger conflict, and they explain that they are referring to the size of a country's power and the distribution of capabilities among the major powers, among other factors. In contrast, comparativists focus on the opening of domestic political space. In a transitional state, open political space fosters elite competition, which cannot be regulated by weak political institutions and therefore may cause civil war. They are less aware of the fact that these internal dynamics may even enhance the risk of political violence beyond territorial borders. Both of these approaches must be used to focus on the consequences of democratization on a regional scale. In ‘bad neighbourhoods’, including the Balkans, the Caucasus, the Middle East and the Great Lakes in Africa, democratization can trigger conflict beyond state frontiers by altering the incentives and opportunities of political actors.

Marine Incursion: The Freshwater Herring of Lake Tanganyika Are the Product of a Marine Invasion into West Africa

The spectacular marine-like diversity of the endemic fauna of Lake Tanganyika, the oldest of the African Great Lakes, led early researchers to suggest that the lake must have once been connected to the ocean. Recent geophysical reconstructions clearly indicate that Lake Tanganyika formed by rifting in the African subcontinent and was never directly linked to the sea. Although the Lake has a high proportion of specialized endemics, the absence of close relatives outside Tanganyika has complicated phylogeographic reconstructions of the timing of lake colonization and intralacustrine diversification. The freshwater herring of Lake Tanganyika are members of a large group of pellonuline herring found in western and southern Africa, offering one of the best opportunities to trace the evolutionary history of members of Tanganyika's biota. Molecular phylogenetic reconstructions indicate that herring colonized West Africa 25–50MYA, at the end of a major marine incursion in the region. Pellonuline herring subsequently experienced an evolutionary radiation in West Africa, spreading across the continent and reaching East Africa's Lake Tanganyika during its early formation. While Lake Tanganyika has never been directly connected with the sea, the endemic freshwater herring of the lake are the descendents of an ancient marine incursion, a scenario which may also explain the origin of other Tanganyikan endemics.

The Aid ‘Darlings’ and ‘Orphans’ of the Great Lakes Region in Africa

This paper looks at the developmental consequences of aid flows on the Great Lakes region in Africa. Our main hypothesis is that political considerations and donor coordination problems still play an important role in directing aid and is much less dependent on objective criteria such as the need for aid or good governance. The region of the Great Lakes in Africa is a good illustration of the ‘darlings’ versus ‘orphans’ policy of official development assistance (ODA). Departing somewhat from the dominant pessimist stance on the effectiveness of aid in sub-Sahara Africa we will try to show that overall, the costs of exclusion of certain countries from aid are detrimental for human development. In order to avoid this inclusion/exclusion pattern of aid, a regional donor approach should overarch the dominant country by country donor policy.

Africa's lakes: atlas of our changing environment

Africa's lakes: atlas of our changing environment

African lake management initiatives: The global connection

AbstractThere is a global dimension to lake management in Africa and elsewhere that will require a concerted action not only from individual riparian states, but also from regional, continental and global communities. The current global lake threats arise from climate change, regional land degradation and semivolatile contaminants, and share the common feature that the atmosphere is the vector that spreads their impacts over large areas and to many lakes. The Great Lakes of Africa (Malawi, Victoria and Tanganyika) are particularly sensitive to these problems because of their enormous surface areas, slow water flushing rates, and the importance of direct rainfall in their water budgets. Their response times might be slow to yield a detectable change and, unfortunately, their recovery times might also be slow. It is possible for atmospheric effects to act antagonistically to the impacts of catchment change, but antagonistic effects could become synergistic in the future. Improved understanding of the physical dynamics of these lakes, and development of models linking their physical and biogeochemical behaviour to regional, mesoscale climate models, will be necessary to guide lake managers.