Congo River Research Articles

Enteromius thespesios (Teleostei: Cyprinidae): a new minnow species with a remarkable sexual dimorphism from the south‐eastern part of the Upper Congo River

A new minnow species, Enteromius thespesios, is described from the south-eastern part of the upper Congo River; that is, the Kalule Nord, the Luvilombo and the Chambeshi Rivers. Enteromius thespesios belongs to the group of the soft-rayed species of Enteromius from the Congo Basin; that is, those with a weakly ossified, flexible last unbranched dorsal-fin ray that lacks serrations along its posterior edge. Within this group, E. thespesios is most similar to E. humeralis, from which it is distinguished by a higher number of circumpeduncular scales and shorter anterior and posterior barbels. Enteromius thespesios is a rheophilic and territorial species. It exhibits a marked sexual dimorphism, with males having: a red band towards the distal edge of dorsal, caudal and, to a lesser degree, anal fin; nuptial tubercles; a longer snout; longer pectoral fins; a shorter anal fin. This study gives extensive consideration to sexual shape differences for a species of Enteromius and also briefly reviews the current knowledge of sexual dimorphism in the species of Enteromius from the Congo Basin. Some conservation issues related to the new species are also highlighted.

Sedimentary Organic Carbon Budget Across the Slope to the Basin in the Southwestern Ulleung (Tsushima) Basin of the East (Japan) Sea

AbstractWith the total sediment oxygen uptake rates measured using an in situ benthic chamber, vertical distributions of organic carbon, and sedimentation rates estimated by excess 210Pb across the slope to the basin sediment of the southwestern region of the Ulleung (Tsushima) Basin (UB), the partitioning of organic carbon fluxes in the sediment was estimated to understand the biogeochemical cycles of organic carbon in the high productivity marginal sea. The results of depth attenuation of total oxygen uptake (TOU) demonstrate that the organic carbon oxidation of the UB sediment was 2.5 times higher than that obtained from the empirical relationship of the global's depth attenuation of TOU. Similar to TOU, the high mass accumulation rates observed in the slope region were 9.5 times higher than the rate in the basin, indicating that the slope may act as the depocenter of organic carbon. The organic carbon budget with water depth gradient implies that a significant fraction of the organic carbon deposited into sediment is supplied by lateral transport down the slope. Definite increasing C/N ratio with water depth indicates that the refractory organic carbon seems to be successively transported later from shelf to slope. The total burial flux in the sediment of southwestern UB was estimated to be 0.46±0.04 Tg C/year, which is similar to the megadepocenter of the Congo River fan. Our results imply that the UB sediment may be an important biogeochemical reaction place not only for organic carbon but also materials linked to primary production.

Terrestrial contributions to Afrotropical aquatic food webs: The Congo River case.

Understanding the degree to which aquatic and terrestrial primary production fuel tropical aquatic food webs remains poorly understood, and quantifying the relative contributions of autochthonous and allochthonous inputs is methodologically challenging. Carbon and nitrogen stable isotope ratios (δ 13C, δ 15N) can provide valuable insights about contributions of terrestrial resources and trophic position, respectively, but this approach has caveats when applied in typical complex natural food webs.Here, we used a combination of C, N, and H (δ 2H) stable isotope measurements and Bayesian mixing models to estimate the contribution of terrestrial (allochthonous) and aquatic (autochthonous) inputs to fish and invertebrate communities in the Congo River (and some tributaries).Overall, our results show that we gained power to distinguish sources by using a multiple tracer approach and we were able to discriminate aquatic versus terrestrial sources (esp. including hydrogen isotopes). Fish δ 2H values were clearly correlated with their food preferences and revealed a high level of variation in the degree of allochthony in these tropical aquatic communities.At the community level, it is clear that terrestrial C3 plants are an important source fueling the Congo River food web. However, in order to better constrain source contribution in these complex environments will require more robust constraints on stable isotope values of algal and methane‐derived C sources.

Estimating discharges for poorly gauged river basin using ensemble learning regression with satellite altimetry data and a hydrologic model

The Congo River is one of the least studied basins although it is the world’s second largest in size (~3.7 million km 2 ) and discharge ( Q ) (~40,600 m 3 s −1 ). Using remote sensing data and a hydrologic model, previous studies have successfully estimated Q of the Congo River at Brazzaville-Kinshasa stations with an accuracy of 10–40%. However, those studies depended on only a hydrologic model or estimated Q using remotely sensed data with a single rating curve. Recently, Kim et al. (2019) has also successfully applied the ensemble learning regression method, which is one of the machine learning techniques, to estimate Q (termed as ELQ) by linearly combining several rating curves over different locations. The study has estimated Q at the Brazzaville station with relative root-mean-square error (RRMSEs) of 7.17/5.53% for training/validation datasets whose temporal resolutions are 35-day for the period from 2002 to 2010. However, ELQ still requires in-situ Q data in order to train base learners and obtain their weights. In this study, we present a study estimating daily Q by applying ELQ with satellite altimetry data and the hydrologic-hydraulic Hillslope River Routing (HRR) model for the Congo River. We parameterized our model with the HRR-derived Q ( Q ^ HRR ) in training/validation datasets without the aid of in-situ Q . ELQ-derived Q ( Q ^ ELQ ) has not been calibrated or scaled with in-situ Q data in training/validation datasets. However, the HRR model has been calibrated to mean monthly historical gauge measurements (1903–1990). Q ^ HRR showed RRMSEs of 15.72/18.00% for training/validation datasets compared with daily in-situ Q data at the Kinshasa station spanning from November 2002 to September 2010. We used the Basic Ensemble Method ( f BEM ), which employs the uniformly distributed weights in ELQ process, that can provide improved estimates of Q . Q ^ ELQ using f BEM showed RRMSE of 11.32/9.05% on average for training/validation datasets. Moreover, we introduced the method generating more accurate ELQ using the ensemble mean of f BEM ( f BEM ‾ ) which yielded RRMSEs of 7–10%. This study demonstrates that ELQ can provide more accurate daily Q using satellite altimetry data and a hydrologic model for poorly gauged river basins.

Carbon and silica megasink in deep-sea sediments of the Congo terminal lobes

Carbon and silicon cycles at the Earth surface are linked to long-term variations of atmospheric CO2 and oceanic primary production. In these cycles, the river-sea interface is considered a biogeochemical hotspot, and deltas presently receive and preserve a major fraction of riverine particles in shallow water sediments. In contrast, periods of glacial maximum lowstand were characterized by massive exports of sediments to the deep-sea via submarine canyons and accumulation in deep-sea fans. Here, we calculate present-day mass balances for organic carbon (OC) and amorphous silica (aSi) in the terminal lobe complex of the Congo River deep-sea fan as an analogue for glacial periods. We show that this lobe complex constitutes a megasink with the current accumulation of 18 and 35% of the OC and aSi river input, respectively. This increases the estimates of organic carbon burial by 19% in the South Atlantic Ocean in a zone representing less than 0.01% of the basin. These megasinks might have played a role in carbon trapping in oceanic sediments during glacial times.

Mapping the availability of bushmeat for consumption in Central African cities

The trade of bushmeat from rural areas to supply burgeoning cities is a major conservation and livelihood concern. Using a whole-city sampling strategy we mapped the distribution and numbers of meat outlets in the Kinshasa–Brazzaville metropolitan area, two neighboring capital cities in Central Africa. We show that both cities differ in the number and density of meat outlets, with more in Brazzaville per area sampled and inhabitants. The number of meat outlets is related to human population densities and primarily concentrated along the banks of the Congo River, in the more affluent areas of the cities. Across the two cities, roughly 22% of all sampled markets (50% in Brazzaville and 19% in Kinshasa) and 24% of all visited restaurants (24% in each city) were selling bushmeat during our survey. Despite the relatively low number of establishments offering bushmeat for sale, extrapolated to the entire area and population of both cities, we expect the overall amount of wild animal meat consumed per annum to be significantly high. We suggest that the supply of such numbers of wild animal meat will strongly impact the animal populations sourcing these cities. Our data also indicate that the number of domestic meat outlets may be adequate to supply urban dwellers with sufficient animal protein.

Description of a new small-sized Synodontis species (Siluriformes: Mochokidae) that is important for local subsistence fisheries in the middle Lufira (upper Congo River, DR Congo).

Synodontis denticulatus sp. nov. is an endemic from the middle Lufira Basin and its associated tributaries and lakes. The species shows close morphological resemblance to Synodontis greshoffi and Synodontis unicolor, which are widespread Congo Basin and Bangweulu-Mweru endemic species, respectively. However, it differs from both S. greshoffi and S. unicolor by its non-villous skin (v. villous skin), strong and numerous serrations on the posterior margin of the dorsal spine (v. weak and fewer serrations), weak and few serrations on the posterior margin of the pectoral spine (v. strong and numerous serrations), relatively short maxillary barbels (v. long) and its small maximum standard length (89.1 mm LS v. 148.0 and 190.7 mm LS respectively). A DNA barcoding study (coI, mtDNA) revealed that S. denticulatus forms a distinct genetic clade with a genetic distance of 2.18% with S. greshoffi and 0.84% with S. unicolor. Synodontis denticulatus is caught regularly and abundantly as a by-catch in the gillnet fisheries in the middle Lufira lakes. Owing to its small overall size and large bony head, the species has usually no real commercial value but is an important food fish for the fishermen's families.

The Guide schématique de la ligne [1957]. Tracing the infrastructure landscape along the Matadi-Kinshasa railway line (DR Congo) through a living archive

Introduction In his book The River Congo, an 1895 travelogue of his journey to the lower reaches of the Congo River, the British scientist Harry Hamilton Johnston, used an array of tactile adjectives to describe the landscape of the Bas-Congo region, largely unknown to his audience of the late nineteenth century. In one particularly colorful passage, leaving all scientific objectivity behind, Johnston discusses the “boldly shaped hills,” the “velvety woods,” the “tiny streams” and the “soundi...

Spatial Dynamical Complexity of Precipitation and Temperature Extremes over Africa and South America

This study investigates the linear and nonlinear dynamics of precipitation and temperature extremes. Monthly daily temperature range (DTR) and maximum 5-day precipitation (RX5) data for sixty three years were obtained from the archives of the Expert Team on Climate Change Detection and Indices (ETCCDI). Spatial maps were constructed for the descriptive statistics (mean, standard deviation, skewness, trend and variance) of both DTR and RX5, as well as nonlinear analysis (entropy, Hurst exponent, determinism and laminarity) for Africa and South America. The research focuses on identifying the unique signature of climate extremes using linear and nonlinear approaches. The deserts of Africa and South America were found to exhibit lower complexity (determinism greater than 0.7) and higher persistence in RX5 values compared to the rest of the continent. The high complexity observed on the African continent were attributed to dynamic atmospheric circulation patterns in the region. The dynamics of equatorial West Africa and Congo River basin were found to be less complex (determinism greater than 0.3) than the rest of the continent when DTR values were analyzed. Using determinism and laminarity (greater than 0.5), the complexity of the Brazilian highlands were observed to be the highest in both DTR and RX5 analysis. Quantitative analysis of climate extremes using nonlinear approaches have been found to be detailed and useful.

Greater Water Surface Variability Revealed by New Congo River Field Data: Implications for Satellite Altimetry Measurements of Large Rivers

AbstractLarge river hydrodynamics studies inform global and regional issues pertaining to biogeochemical cycling, ecology, water availability, and flood risk. Such studies rely increasingly on satellite measurements, but these are limited by resolution, coverage, and uncertainty and their inability to directly measure bathymetry or discharge. We obtain new in situ data covering 650 km of the Congo's main stem, including elusive bathymetry and discharge measurements that complement space‐borne data sets. Our key findings relate to our water surface elevation measurements, which show that spatial coverage of existing satellite altimetry for deriving river water surface profiles may be adequate through the globally important Cuvette Centrale but is not at its outlet where our field data reveal significant spatial variability in water surface slope. The findings have implications for altimetry‐based hydrodynamics studies of other large rivers, such as those that involve estimating discharge or modeling multichannel river hydraulics.

Fishes in the lower Congo River. An extreme case of species divergence and convergent evolution

Fishes in the lower Congo River. An extreme case of species divergence and convergent evolution

Agricultural innovation and environmental change on the floodplains of the Congo River

Climate‐driven environmental changes bring new risks but also opportunities to populations living along the world's major rivers. Based on ethnoecological fieldwork, in this paper we examine how people living in the cuvette centrale of the Congo basin have adopted flood‐recession agriculture on islands in the Congo River, taking advantage of a secular shift since the 1980s in the hydrological regime of the Congo River. Analyses of the hydrological data reveal that this shift decreased flood risk and significantly extended the growing season on the islands, long enough to enable cultivation of fast‐maturing varieties of manioc and other crops. Flood‐recession farming on islands in the river is today not only an important source of food, but also a source of income for women, who are primarily responsible for seasonal cultivation of fields during the low‐water season. Hydrological changes alone are insufficient to explain the adoption of the new agricultural practice; adoption also arose as a result of dynamic interactions among river fishing, trading, and broader socio‐economic forces. Climate‐change models project an increased frequency of extreme floods. Our results suggest that this change may limit island cultivation in the future. More generally, our findings point to the importance of looking beyond single‐factor, solely environmental explanations in studies of climate‐change adaptation.

The near-complete mitogenome of the critically endangered Pseudocleopatra dartevellei (Caenogastropoda: Paludomidae) from the Congo River assembled from historical museum material

Here, we present the first near-complete mitogenome of a member of the freshwater gastropod family Paludomidae, Pseudocleopatra dartevellei. This Congo River species is of particular importance because the sister to the Lake Tanganyika radiation is supposed to be a paludomid riverine species. We used ancient DNA (aDNA) techniques including single-stranded DNA library preparation in order to assemble the mitogenome from historical museum material collected in 1937. The mitogenome was 15,368 bp long and showed typical characteristics as identified in other freshwater gastropods. The present phylogeny shows a closer relationship between Pseudocleoptra dartevellei and another non-Tanganyikan species, Cleopatra johnstoni.

AFRICAN VOICES FROM THE CONGO COAST: LANGUAGES AND THE POLITICS OF IDENTIFICATION IN THE SLAVE SHIPJOVEM MARIA (1850)

AbstractBetween 1845 and 1850, the Congo coast became the most important source of slaves for the coffee growing areas in the Brazilian Empire. This essay develops a new methodology to understand the making of the ‘nations’ of 290 Africans found on the slave shipJovem Maria, which boarded slaves in the Congo river and was captured by the Brazilian Navy near Rio de Janeiro in 1850. A close reading of such ‘nations’ reveals a complex overlapping between languages and forms of identification that alters the historian's use of concepts such as ‘ethnolinguistic group’ and ‘Bantu-basedlingua franca’ in the Atlantic world. Building on recent developments in Central African linguistics, the article develops a social history of African languages in the Atlantic that foregrounds how recaptives negotiated commonalities and boundaries in the diaspora by drawing on a political vocabulary indigenous to their nineteenth-century homes in Central Africa.

Assessing the vulnerability of Africa's freshwater fishes to climate change: A continent-wide trait-based analysis

Climate change is a key driver of biodiversity loss across the globe, and freshwater fishes are predicted to be among the most vulnerable taxa. African freshwater ecosystems are home to one of the most unique and diverse ichthyo-faunas on the planet, and freshwater fish species provide essential livelihoods for millions of people living in riparian communities across the continent. Although nearly one sixth of African freshwater fishes have been designated as endangered or vulnerable to extinction by the IUCN Red List assessment, the effects of climate change on these species have not been explored on a continent-wide scale. In this study, we present the first trait-based climate change vulnerability assessment (CCVA) comprising the majority (85%) of Africa's currently described freshwater fishes. We assembled data relating to three dimensions of vulnerability including sensitivity, adaptive capacity, and exposure. In addition, we developed an index of ‘conservation value’ based on traditional conservation metrics including extinction risk, endemism, and provision of ecosystem services. We found that almost 40% of African freshwater fishes are vulnerable to climate change, mostly owing to the many species with highly specialized habitat and life-history requirements, and because of the numerous anthropogenic stressors they face. High proportions of species within the Nothobranchiidae and Cichlidae families were found to be vulnerable. Regions with high frequencies of vulnerable species included the African rift valley lakes, the Congo River drainage, and the coastal rivers of West Africa. Several important data deficiencies were identified relating to species' population sizes, genetic variability, and life history traits, and constitute priority research areas for the future. In addition, we highlighted some cases where traditional conservation approaches overlook species and regions that are predicted to be threatened by climate change.

Genetic variation of the most abundant forest‐dwelling rodents in Central Africa (Praomys jacksoni complex): Evidence for Pleistocene refugia in both montane and lowland forests

AbstractAimWe investigate the Plio‐Pleistocene evolutionary history of one of the most abundant rodents in Afrotropical forests. Specifically, we ask how their diversification was influenced by climate change, topography and major rivers.LocationTropical Africa: Lower Guinea (including Cameroon volcanic line; CVL), Congolia, Albertine Rift (AR), Kenyan highlands (KH).TaxonMurine rodents of the Praomys jacksoni complex.MethodsWe used 849 genotyped individuals to describe the overall diversity and spatial genetic structure across a majority of their known distribution area. The combination of one mitochondrial and three nuclear markers was used to infer dated phylogenies using Bayesian and maximum likelihood approaches. Genetic structure was further assessed by multispecies coalescent species delimitation. Current and past distributions of particular taxa were predicted using environmental niche modelling.ResultsThe complex is composed of five major genetic clades (proposed species). Two of them are restricted to specific habitat types (either montane forests of AR or wetlands in lowland forests along the Congo River), three others have wide geographic distributions and lower levels of ecological specialization. The earliest divergence is dated to the Plio‐Pleistocene boundary and is in accordance with the separation of AR forests and Guineo‐Congolian forests. Further diversification of the complex is associated with Pleistocene climate changes. Relatively stable refugia of suitable climatic conditions were identified in lowland Congolia (for two species currently distributed only in lowland forests) as well as in montane forests of CVL, AR, KH (playing the role of reservoirs of diversity). Large rivers, especially the Congo River, are important barriers to gene flow for most taxa, but probably were not the primary cause of differentiation.Main conclusionsThe evolutionary history of the complex was primarily affected by Pleistocene climate changes and diversification in forest refugia. There is little support for ecological parapatric speciation or the riverine barrier hypothesis.

Description of two new Geissleria species (Bacillariophyta) from Central and West tropical Africa

During a recently started-up project in the Biosphere Reserve at Yangambi, DR Congo, an unknown Geissleria taxon was observed in a small tributary of the Congo River. This taxon is here described as new to science based on detailed light and scanning electron microscopy observations. Geissleria lubiluensis sp. nov. can be distinguished by the slightly tri-undulate valve margins and the very distinct annulus located at a distance of 3 striae from the apex. The comparison of this taxon with various other Geissleria taxa with resembling valve outline or with resembling annulus structure, led to the description of another new species: Geissleria fogedii sp. nov. reported by Foged from Ghana as Navicula paludosa. This taxon resembles very well Geissleria lubiluensis but differs in the distinct annulus located closer to the apex mostly at the distance of one stria, the broader valves and the denser striation.

Late Pleistocene Fish Remains from the Rurubu River, Tanzania

ABSTRACTA collection of fish bones was recovered from upper Pleistocene (Gamblian) deposits near the confluence of the Kagera and Rurubu rivers in Tanzania, west of Lake Victoria. The Rurubu/Kagera bones include two families: the Clariidae (Clarias gariepinus, Clarias sp.) and Cichlidae (tribes Oreochromini, Haplochromini; Oreochromis sp.). Geological, paleontological, and molecular data presented here provide new insights into Pleistocene eastern African biogeography and into the evolution and past affiliations of the Rurubu/Kagera and Lake Victoria fish taxa. The data indicate that the Rurubu/Kagera taxa were descended from Miocene-aged populations in the Congo and/or Nile rivers. Data also suggest that the Rurubu/Kagera haplochromines may have been part of a shared Kagera River/Lake Victoria basin haplochromine clade, whose later members radiated into hundreds of species in Lake Victoria over the past approximately 15,000 years.

Recurrent Cholera Outbreaks, Democratic Republic of the Congo, 2008-2017.

In 2017, the exacerbation of an ongoing countrywide cholera outbreak in the Democratic Republic of the Congo resulted in >53,000 reported cases and 1,145 deaths. To guide control measures, we analyzed the characteristics of cholera epidemiology in DRC on the basis of surveillance and cholera treatment center data for 2008–2017. The 2017 nationwide outbreak resulted from 3 distinct mechanisms: considerable increases in the number of cases in cholera-endemic areas, so-called hot spots, around the Great Lakes in eastern DRC; recurrent outbreaks progressing downstream along the Congo River; and spread along Congo River branches to areas that had been cholera-free for more than a decade. Case-fatality rates were higher in nonendemic areas and in the early phases of the outbreaks, possibly reflecting low levels of immunity and less appropriate prevention and treatment. Targeted use of oral cholera vaccine, soon after initial cases are diagnosed, could contribute to lower case-fatality rates.

A Physically Based Empirical Localization Method for Assimilating Synthetic SWOT Observations of a Continental-Scale River: A Case Study in the Congo Basin

Water resource management has faced challenges in recent decades due to limited in situ observations and the limitations of hydrodynamic modeling. Data assimilation techniques have been proposed to improve hydrodynamic model outputs of local rivers (river length ≤ 1500 km) using synthetic observations of the future Surface Water and Ocean Topography (SWOT) satellite mission to overcome limited in situ observations and the limitations of hydrodynamic modeling. However, large-scale data assimilation schemes require computationally efficient filtering techniques, such as the Local Ensemble Transformation Kalman Filter (LETKF). Expansion of the assimilation domain to maximize observations is limited by error covariance caused by limited ensemble size in complex river networks, such as the Congo River. Therefore, we tested the LETKF algorithm in a continental-scale river (river length > 1500 km) using a physically based empirical localization method to maximize the observations available while filtering error covariance areas. Physically based empirical local patches were derived separately for each river pixel, considering spatial auto-correlations. An observing system simulation experiment (OSSE) was performed using empirical localization parameters to evaluate the potential of our method for estimating discharge. We found our method could improve discharge estimates considerably without affected from error covariance while fully using the available observations. We compared this experiment using empirical localization parameters with conventional fixed-shape local patches of different sizes. The empirical local patch OSSE showed the lowest normalized root mean square error of discharge for the entire Congo basin. Extending the conventional local patch without considering spatial auto-correlation results in very large errors in LETKF assimilation due to error covariance between small tributaries. The empirical local patch method has the potential to overcome the limitations of conventional local patches for continental-scale rivers using SWOT observations.