African River Research Articles

U–Pb chronology and geochemistry of detrital monazites from major African rivers: Constraints on the timing and nature of the Pan-African Orogeny

The African continent consists of several cratons rimmed by orogenic belts, which were mainly formed by collisions of the cratons during the Gondwana supercontinent assembly. Understanding of the timing and nature of the Pan-African Orogeny is essential to decipher the development of the African continent and Gondwana supercontinent. We carried out U–Pb dating and geochemical analyses of approximately 500 detrital monazites from the Nile, Niger, Congo, Zambezi and Orange Rivers. The U–Pb dating defined age peaks at ∼600Ma for the Nile, ∼580Ma for the Niger, ∼630, ∼610 and ∼550Ma for the Congo, ∼500Ma for the Zambezi and 1200–1000Ma for the Orange. All but the Orange age peaks correspond to the period of the Pan-African Orogeny. In the Niger, Congo and Zambezi, the Pan-African age peaks are 20–40Myr younger than those defined by the detrital zircons from the same rivers. In the Nile, however, the detrital monazite and zircon age peaks are contemporaneous. The geochemical analyses revealed significant variations in Eu/Eu∗, Gd/Lu and Th/U ratios among the detrital monazites, which can be attributed to elemental partitioning with the co-existing feldspars, garnet, and zircon/rutile, respectively. Considering that typical abundances of these minerals vary among igneous and metamorphic rocks, these geochemical data can be potentially linked to the genesis of the detrital monazites. The geochemical systematics, together with the discrepancy between the detrital monazite and zircon ages, suggest that the Pan-African monazite age peaks essentially reflect the timing of syn- to post-collisional metamorphic events in the source terranes, whereas the detrital zircons provide a more representative record of magmatic events. The results imply that the Pan-African Orogeny was promoted by pre- to syn-collisional felsic magmatism during the early stages and, 20–40Myr later, it was dominated by syn- and/or post-collisional metamorphism.

Choosing small sets of policy-relevant scenarios by combining vulnerability and diversity approaches

Computer simulation models can generate large numbers of scenarios, far more than can be effectively utilized in most decision support applications. How can one best select a small number of scenarios to consider? One approach calls for choosing scenarios that illuminate vulnerabilities of proposed policies. Another calls for choosing scenarios that span a diverse range of futures. This paper joins these two approaches for the first time, proposing an optimization-based method for choosing a small number of relevant scenarios that combine both vulnerability and diversity. The paper applies the method to a real case involving climate resilient infrastructure for three African river basins (Volta, Orange and Zambezi). Introducing selection criteria in a stepwise manner helps examine how different criteria influence the choice of scenarios. The results suggest that combining vulnerability- and diversity-based criteria can provide a systematic and transparent method for scenario selection.

Hydrological–morphological processes in the mouth area of the Congo R. and the effect of submarine canyon on these processes

The general geographic, hydrographic, climatic, and hydrological characteristics of the Congo R. basin are considered. The major features of the riverine and marine factors that have their effect on the hydrological regime and morphology of the delta and estuary of the Congo R. are identified; the effect of a submarine canyon on the morphological features of the estuary is analyzed in detail; and changes in river delta structure in the XX century and currently are considered. The hydrological—morphological characteristics of the largest mouths of African rivers, the formation conditions of water and sediment runoff, and variations of their deltas are compared.

Mediterranean outflow pump: An alternative mechanism for the Lago-mare and the end of the Messinian Salinity Crisis

Abstract The final stage of the Messinian salinity crisis (MSC) was characterized by brackish-water “Lago-mare” conditions in the intermediate and marginal basins of the Mediterranean Sea. The presence of Paratethyan (former Black Sea) fauna in these deposits has fueled long-lasting controversies over the connectivity between the Mediterranean and Paratethys and contemporary sea-level drops in both basins. Here, we use the results of sub-precessional climate simulations to calculate the freshwater budget of the Mediterranean and Paratethys in the Messinian. We show that, during the MSC, the freshwater budget of Paratethys was positive, while the Mediterranean was negative. Using these numerical constraints, we propose a Mediterranean outflow pump as an alternative scenario for the two most dramatic hydrological changes in the MSC: (1) the Halite–Lago-mare transition and (2) the Pliocene reestablishment of marine conditions. Following the maximum MSC lowstand during halite formation, progressive Mediterranean sea-level rise resulting from African river runoff and overspill from both the Atlantic and Paratethys eventually reached the level of the Paratethys sill. A density contrast at this gateway caused dense Mediterranean waters to flow into the Paratethys, driving a compensatory return flow. This “pump” mechanism significantly enhanced Paratethyan inflow to the Mediterranean, creating suitable conditions for the Lago-mare fauna to migrate and thrive. When the Mediterranean sea level finally reached the height of the Gibraltar sill, Mediterranean outflow restarted there and enhanced exchange with the Atlantic Ocean. During this reorganization of the circulation, brackish and hypersaline waters were pumped out of the Mediterranean, and open-marine conditions were reestablished without major flooding of the basin at the Miocene-Pliocene boundary.

Assessment of water quality based on diatom indices in a small temperate river system, Kowie River, South Africa

This study aimed to assess the impact of land use patterns on water quality and benthic diatom community structure and to test the applicability of diatom indices developed in other regions of the world to a small temperate southern African river system. Sampling was conducted at eight study sites along the length of the river on four separate occasions. Multivariate data analyses were performed on the diatom community dataset to specify the main gradients of floristic variation and to detect and visualize similarities in diatom samples in relation to land-use patterns within the catchment. One hundred and twelve (112) diatom species belonging to 36 genera were recorded during the study. Canonical correspondence analysis (CCA) demonstrated that variations in the benthic diatom community structure were best explained by ammonium, nitrate, conductivity, pH, temperature, resistivity and water flow. OMNIDIA was used for calculation of selected diatom water quality indices. A number of the indices, e.g., the trophic diatom index (TDI), eutrophication/pollution index and biological index of water quality (BIWQ), either under- or over-estimated the water quality of the system. With few exceptions, there were no significant correlations (p> 0.05) between the diatom indices’ values and the nutrient variables. The absence of any significant correlations between the diatom indices’ values and selected physico-chemical variables suggests that indices developed in other regions of the world may not be suitable for temperate southern African rivers. Keywords : biomonitoring, diatom indices, diatom community, Kowie River, nitrogen, multivariate analysis, point-source pollution, water quality

Dietary niche constriction when invaders meet natives: evidence from freshwater decapods.

Invasive species are a key driver of global environmental change, with frequently strong negative consequences for native biodiversity and ecosystem processes. Understanding competitive interactions between invaders and functionally similar native species provides an important benchmark for predicting the consequences of invasion. However, even though having a broad dietary niche is widely considered a key factor determining invasion success, little is known about the effects of competition with functionally similar native competitors on the dietary niche breadths of invasive species. We used a combination of field experiments and field surveys to examine the impacts of competition with a functionally similar native crab species on the population densities, growth rates and diet of the globally widespread invasive red swamp crayfish in an African river ecosystem. The presence of native crabs triggered significant dietary niche constriction within the invasive crayfish population. Further, growth rates of both species were reduced significantly, and by a similar extent, in the presence of one another. In spite of this, crayfish maintained positive growth rates in the presence of crabs, whereas crabs lost mass in the presence of crayfish. Consequently, over the 3-year duration of the study, crab abundance declined at those sites invaded by the crayfish, becoming locally extinct at one. The invasive crayfish had a dramatic effect on ecosystem structure and functioning, halving benthic invertebrate densities and increasing decomposition rates fourfold compared to the crabs. This indicates that replacement of native crabs by invasive crayfish likely alters the structure and functioning of African river ecosystems significantly. This study provides a novel example of the constriction of the dietary niche of a successful invasive population in the presence of competition from a functionally similar native species. This finding highlights the importance of considering both environmental and ecological contexts in order to predict and manage the impacts of invasive species on ecosystems.

Chironomid assemblage structure and morphological response to pollution in an effluent-impacted river, Eastern Cape, South Africa

Achieving sustainable freshwater resource management and conserving biodiversity require accurate and reliable pollution impact assessment. Biomonitoring is an integrative and holistic approach to assessing impact of pollution using biological indicators. In this study, we use the assemblage structure of the freshwater macroinvertebrate family Chironomidae to assess the impact of pollution in a South African river: the Swartkops River. Based on morphological deformities in the mentum of selected genera, we developed a new index, the extended toxic score index (ETSI), to assess the extent of deviation of ecological conditions at the impacted sites from that at the control site. Four sites i.e. Sites 1–4 characterised by different degrees of pollution were selected for chironomids and physico-chemical sampling over a period of three years (August 2009–September 2012). The ETSI was developed by taking into account the severity of deformities, and genera tolerances to pollution. The index was based on the deformities in the mentum of the five most dominant genera: Chironomus, Polypedilum, Tanytarsus, Dicrotendipes and Cricotopus. The values of nutrients, electrical conductivity and turbidity were elevated, and dissolved oxygen depleted at Sites 2, 3 and 4 compared with Site 1. Metal concentrations in the water column were relatively low (<0.3mg/l). Site 1, i.e. the control site, supported more chironomid species (30 species). Site 2, situated upstream of the Kelvin Jones wastewater effluent discharge point, but influenced by diffuse pollution sources, had more species (22 species) than Sites 3 (10 species) and 4 (18 species). The species assemblage structure clustered largely by sites than by seasons, with the assemblage at Site 1 distinct to those at Sites 2, 3 and 4. The newly developed ETSI was sensitive to pollution, distinguishing between the ecological conditions at the sampling sites. The index placed Site 2 in Category D, indicative of poor ecological condition and Sites 3 and 4 in Category E, indicative of very poor conditions. We found the ETSI to be an appropriate and useful deformity-based tool for biomonitoring, and it can easily be modified and used in other river systems, both locally and internationally.

Nutrients, trace metals and B-vitamin composition of the Moulouya River: A major North African river discharging into the Mediterranean Sea

We analyzed dissolved nutrient, trace metal and vitamin (B-vitamins and methionine) concentrations in the lower course of the Moulouya River (MR, Morocco) and its estuary. The flow of this African river has changed drastically (a reduction of almost 50%) in the last 50 years due to the regulation of the river flow through dams and alterations of the course constructed to satisfy population necessities and growing agricultural requirements. Consequently, it has produced a remarkable increase in nitrate concentrations (up to 270 μM) and alteration of N:P ratios within the river, as well as a reduction of overall P and Si efflux to nearby coastal waters. Despite the historical mining activities in the upper MR, concentrations of Pb, Zn and other metals in sediments and waters do not display significant contamination as compared with other Mediterranean rivers, mainly due to the retention by dams of upstream metal contamination. Mean concentrations of dissolved B-vitamins in the river showed lower levels (13–55% lower) than those in coastal waters and hence the river does not represent an important B-vitamin source.

Evolutionary history of the river frog genus Amietia (Anura: Pyxicephalidae) reveals extensive diversification in Central African highlands

The African river frog genus Amietia is found near rivers and other lentic water sources throughout central, eastern, and southern Africa. Because the genus includes multiple morphologically conservative species, taxonomic studies of river frogs have been relatively limited. We sampled 79 individuals of Amietia from multiple localities in and near the Albertine Rift (AR) of Burundi, Democratic Republic of the Congo, and Uganda. We utilized single-gene (16S) and concatenated (12S, 16S, cyt b and RAG1) gene-tree analyses and coalescent species-tree analyses to construct phylogenetic trees. Two divergence dating approaches were used in BEAST, including secondary calibration points with 12S, 16S, cyt b and RAG1, and a molecular clock with the 12S, 16S, and cyt b genes. All analyses recovered Amietia as monophyletic with strong support, and revealed several well-supported cryptic lineages, which is consistent with other recent phylogeography studies of AR amphibians. Dating estimates were similar, and Amietia diversification is coincident with global cooling and aridification events in the Miocene and Pliocene, respectively. Our results suggest additional taxonomic work is needed to describe multiple new species of AR Amietia, some of which have limited geographic distributions that are likely to be of conservation concern.

The Zambian Macrophyte Trophic Ranking scheme, ZMTR: A new biomonitoring protocol to assess the trophic status of tropical southern African rivers

The Zambian Macrophyte Trophic Ranking system (ZMTR) is a new bioassessment scheme to indicate the trophic status of tropical southern African river systems. It was developed using a dataset of 218 samples of macrophytes and water chemistry, collected during 2009–2012, from river sites located in five world freshwater ecoregions primarily represented in Zambia. A typology based on these ecoregions, and three stream order categories, was used to determine soluble reactive phosphate (SRP) reference conditions. Zambian Trophic Ranking Scores (ZTRSsp) were calculated for 156 species, using direct allocation from SRP data for 80 species, in samples for which sufficient available SRP data existed. An indirect quantitative procedure, based upon occurrence of species in six sample-groups, of differing mean SRP status, produced by TWINSPAN classification, allocated provisional ZTRSsp values for the remaining 76 species. Additional data for nitrate, pH, alkalinity and conductivity were used to help assess the trophic preferences of macrophyte species showing differing ZTRSsp values. ZMTRsample values were calculated as the mean ZTRSsp score of species present per sample. ZMTR indicated trophic status reasonably accurately for 83.1% of Zambian samples, and for all samples within a test dataset from Botswanan rivers. Examples of application of the methodology, and its potential for hindcasting river trophic status are provided. The scheme currently underestimates highly-enriched conditions, and, to a lesser extent, overestimates the trophic status of some very low-nutrient rivers, but at this pilot stage of development it generally predicts the trophic status of tropical southern African river systems quite well.

An In Vitro and In Vivo Assessment of Endocrine Disruptive Activity in a Major South African River

Endocrine-disrupting contaminant (EDC) loads in rivers, and the associated risk to wildlife, may be linked to different anthropogenic stressors occupying river catchments. The aims of this study were to evaluate seasonal and spatial variation in steroid estrogen loads, and (anti)estrogenic and (anti)androgenic activity in a river catchment (upper Olifants River, South Africa), subject to a diversity of anthropogenic impacts. In addition, Mozambique tilapia, Oreochromis mossambicus, was applied as African-endemic sentinel and source of in vivo biomarkers. In particular, the expression of selected genes linked with reproductive, thyroid and adrenal signalling were determined in juveniles exposed to organic compounds extracted from surface water. Estradiol and ethinylestradiol were detected at all locations, yet the highest concentrations were observed during summer at a waste water treatment plant (WWTP)-impacted site (30.8 and 10.83 ng.l−1, respectively). Moreover, in vitro estrogenic and androgenic activity was detected solely at the aforementioned locality. Anti-androgenic activity was more widespread, and detected at four of the localities sampled, with the highest potency at WWTP-impacted sites. The expression of the aromatase coding gene, cyp19a1b, was significantly downregulated in O. mossambicus representing a site dominated by agricultural land use. Moreover, the thyroid-linked type 2 deiodinase (dio2) was upregulated in fish representing three of the five localities, although with no clear link to a specific land use area. The present study suggests that different land cover areas contribute differentially to endocrine disruptive activity, and that a combinational approach (in vitro and in vivo biomarkers) is required to screen for EDC risk.

Spatiotemporal Variation and the Role of Wildlife in Seasonal Water Quality Declines in the Chobe River, Botswana

Sustainable management of dryland river systems is often complicated by extreme variability of precipitation in time and space, especially across large catchment areas. Understanding regional water quality changes in southern African dryland rivers and wetland systems is especially important because of their high subsistence value and provision of ecosystem services essential to both public and animal health. We quantified seasonal variation of Escherichia coli (E. coli) and Total Suspended Solids (TSS) in the Chobe River using spatiotemporal and geostatistical modeling of water quality time series data collected along a transect spanning a mosaic of protected, urban, and developing urban land use. We found significant relationships in the dry season between E. coli concentrations and protected land use (p = 0.0009), floodplain habitat (p = 0.016), and fecal counts from elephant (p = 0.017) and other wildlife (p = 0.001). Dry season fecal loading by both elephant (p = 0.029) and other wildlife (p = 0.006) was also an important predictor of early wet season E. coli concentrations. Locations of high E. coli concentrations likewise showed close spatial agreement with estimates of wildlife biomass derived from aerial survey data. In contrast to the dry season, wet season bacterial water quality patterns were associated only with TSS (p<0.0001), suggesting storm water and sediment runoff significantly influence E. coli loads. Our data suggest that wildlife populations, and elephants in particular, can significantly modify river water quality patterns. Loss of habitat and limitation of wildlife access to perennial rivers and floodplains in water-restricted regions may increase the impact of species on surface water resources. Our findings have important implications to land use planning in southern Africa’s dryland river ecosystems.

Systematic change in global patterns of streamflow following volcanic eruptions.

Following large explosive volcanic eruptions precipitation decreases over much of the globe1–6, particularly in climatologically wet regions4,5. Stratospheric volcanic aerosols reflect sunlight, which reduces evaporation, whilst surface cooling stabilises the atmosphere and reduces its water-holding capacity7. Circulation changes modulate this global precipitation reduction on regional scales1,8–10. Despite the importance of rivers to people, it has been unclear whether volcanism causes detectable changes in streamflow given large natural variability. Here we analyse observational records of streamflow volume for fifty large rivers from around the world which cover between two and 6 major volcanic eruptions in the 20th and late 19th century. We find statistically significant reductions in flow following eruptions for the Amazon, Congo, Nile, Orange, Ob, Yenisey and Kolyma amongst others. When data from neighbouring rivers are combined - based on the areas where climate models simulate either an increase or a decrease in precipitation following eruptions – a significant (p<0.1) decrease in streamflow following eruptions is detected in northern South American, central African and high-latitude Asian rivers, and on average across wet tropical and subtropical regions. We also detect a significant increase in southern South American and SW North American rivers. This suggests that future volcanic eruptions could substantially affect global water availability.

A pan-African medium-range ensemble flood forecast system

Abstract. The African Flood Forecasting System (AFFS) is a probabilistic flood forecast system for medium- to large-scale African river basins, with lead times of up to 15 days. The key components are the hydrological model LISFLOOD, the African GIS database, the meteorological ensemble predictions by the ECMWF (European Centre for Medium-Ranged Weather Forecasts) and critical hydrological thresholds. In this paper, the predictive capability is investigated in a hindcast mode, by reproducing hydrological predictions for the year 2003 when important floods were observed. Results were verified by ground measurements of 36 sub-catchments as well as by reports of various flood archives. Results showed that AFFS detected around 70 % of the reported flood events correctly. In particular, the system showed good performance in predicting riverine flood events of long duration (&gt; 1 week) and large affected areas (&gt; 10 000 km2) well in advance, whereas AFFS showed limitations for small-scale and short duration flood events. The case study for the flood event in March 2003 in the Sabi Basin (Zimbabwe) illustrated the good performance of AFFS in forecasting timing and severity of the floods, gave an example of the clear and concise output products, and showed that the system is capable of producing flood warnings even in ungauged river basins. Hence, from a technical perspective, AFFS shows a large potential as an operational pan-African flood forecasting system, although issues related to the practical implication will still need to be investigated.

Globally significant greenhouse-gas emissions from African inland waters

Carbon dioxide emissions to the atmosphere from inland waters—streams, rivers, lakes and reservoirs—are nearly equivalent to ocean and land sinks globally. Inland waters can be an important source of methane and nitrous oxide emissions as well, but emissions are poorly quantified, especially in Africa. Here we report dissolved carbon dioxide, methane and nitrous oxide concentrations from 12 rivers in sub-Saharan Africa, including seasonally resolved sampling at 39 sites, acquired between 2006 and 2014. Fluxes were calculated from published gas transfer velocities, and upscaled to the area of all sub-Saharan African rivers using available spatial data sets. Carbon dioxide-equivalent emissions from river channels alone were about 0.4 Pg carbon per year, equivalent to two-thirds of the overall net carbon land sink previously reported for Africa. Including emissions from wetlands of the Congo river increases the total carbon dioxide-equivalent greenhouse-gas emissions to about 0.9 Pg carbon per year, equivalent to about one quarter of the global ocean and terrestrial combined carbon sink. Riverine carbon dioxide and methane emissions increase with wetland extent and upland biomass. We therefore suggest that future changes in wetland and upland cover could strongly affect greenhouse-gas emissions from African inland waters. Inland waters are important sources of greenhouse gases. Measurements over eight years suggest that African inland waters are a substantial source of greenhouse gases, equivalent to a quarter of the global land and ocean carbon sink.

Landscape Control on the Spatial and Temporal Variability of Chromophoric Dissolved Organic Matter and Dissolved Organic Carbon in Large African Rivers

The characteristics of colored dissolved organic mat- ter (CDOM) as well as the concentrations and stable isotope composition (d 13 C) of dissolved organic car- bon (DOC) were characterized in several large rivers of Africa including the Congo, Niger, Zambezi, and Ogoouebasins. We compared the spatial and tem- poral patterns of dissolved organic matter (DOM) quantity and quality along with various environ- mental gradients, including hydrology, river size, catchment vegetation, and connectivity to land. The optical proxies used include the absorption coeffi- cient at 350 nm, the specific ultra-violet absorbance, and the spectral slope ratio (SR = 275-295-nm slope divided by 350-400-nm slope). Our results show that land cover plays a primary role in controlling both DOC concentration and optical properties of DOM in tropical freshwaters. A higher cover of dense forest in the catchment leads to a higher quantity of highly aromatic DOM in the river network, whereas an increasing savannah cover results in lower DOC concentrations and less absorptive DOM. In addition to land cover, the watershed morphology (expressed by the average slope) exerts a strong control on DOC and CDOM in tropical rivers. Our results also show that the percentage of C3 and C4 vegetation cover is not an accurate predictor for DOM and CDOM quality in rivers due to the importance of the spatial distribution of land cover within the drainage net- work. The comparison of our results with previously published CDOM data in temperate and high-lati- tude rivers highlights that DOM in tropical freshwa- ters is generally more aromatic, and shows a higher capacity for absorbing sunlight irradiance.

Spatial patterns in CO2 evasion from the global river network

AbstractCO2 evasion from rivers (FCO2) is an important component of the global carbon budget. Here we present the first global maps of CO2 partial pressures (pCO2) in rivers of stream orders 3 and higher and the resulting FCO2 at 0.5° resolution constructed with a statistical model. A geographic information system based approach is used to derive a pCO2 prediction function trained on data from 1182 sampling locations. While data from Asia and Africa are scarce and the training data set is dominated by sampling locations from the Americas, Europe, and Australia, the sampling locations cover the full spectrum from high to low latitudes. The predictors of pCO2 are net primary production, population density, and slope gradient within the river catchment as well as mean air temperature at the sampling location (r2 = 0.47). The predicted pCO2 map was then combined with spatially explicit estimates of stream surface area Ariver and gas exchange velocity k calculated from published empirical equations and data sets to derive the FCO2 map. Using Monte Carlo simulations, we assessed the uncertainties of our estimates. At the global scale, we estimate an average river pCO2 of 2400 (2019–2826) µatm and a FCO2 of 650 (483–846) Tg C yr−1 (5th and 95th percentiles of confidence interval). Our global CO2 evasion is substantially lower than the recent estimate of 1800 Tg C yr−1 although the training set of pCO2 is very similar in both studies, mainly due to lower tropical pCO2 estimates in the present study. Our maps reveal strong latitudinal gradients in pCO2, Ariver, and FCO2. The zone between 10°N and 10°S contributes about half of the global CO2 evasion. Collection of pCO2 data in this zone, in particular, for African and Southeast Asian rivers is a high priority to reduce uncertainty on FCO2.

Environmental occurrence and biota concentration of phthalate esters in Epe and Lagos Lagoons, Nigeria

The high global occurrence of phthalates in different environmental matrixes has resulted in the detection of their metabolites in human urine, blood, and breast milk, indicating a widespread human exposure. In addition, the notorious endocrine disrupting effects of phthalates have shown that they mimic or antagonize the action of endogenous hormones, consequently producing adverse effects on reproduction, growth and development. Herein, we have studied the occurrence of phthalate esters (PEs) in water, sediment and biota of two lagoons (Epe and Lagos) in Nigeria. Two fish species (Tilapia guineensis, and Chrysichthys nigrodigitatus) and a crustacean (the African river prawn - Macrobrachium vollenhovenii) were analyzed for PEs levels using a HPLC method and the derived values were used for calculating bioconcentration factor (BCF), biota-sediment accumulation factor (BSAF) and phthalate pollution index (PPI) in the biota and environment. We observed that the growth and health condition of the fish species were normal with a k-factor of >1. Sediment PE levels were compared with water, at both lagoons showing concentration pattern that is characterized as DEHP = DEP > DBP. We observed that DBP was the predominant compound in T. guineensis, C. nigrodigitatus and African prawn, at both lagoons, showing organ-specific differences in bioconcentration (BCF and BSAF) patterns in the fish species. While there were no observed consistency in the pattern of PE concentration in fish organs, elevated DBP levels in different fish organs may be related to fish habitat and degradation level of phthalates. Low concentration of DEHP, compared with DBP and DEP, was measured in fish organs and whole prawn body. The BSAF values for DEHP were lowest, and highest for DBP for all species at both lagoons, and DEHP easily accumulated more in the sediment (sediment PPI = 0.28 and 0.16 for Epe and Lagos lagoon, respectively). Overall, our findings suggest a broader environmental and human health implication of the high PE levels in these lagoons since they represent significant sources of aquatic food resources for the neighboring communities.

Carbon stable isotopes suggest that hippopotamus‐vectored nutrients subsidize aquatic consumers in an East African river

The common hippopotamus, Hippopotamus amphibius, transports millions of tons of organic matter annually from its terrestrial feeding grounds into aquatic habitats. We evaluated whether carbon stable isotopes (δ13C) can be used as tracers for determining whether H. amphibius‐vectored allochthonous material is utilized by aquatic consumers. Two approaches were employed to make this determination: (1) lab‐based feeding trials where omnivorous river fish were fed a H. amphibius dung diet and (2) field sampling of fish and aquatic insects in pools with and without H. amphibius. Lab trials revealed that fish fed exclusively H. amphibius dung exhibited significantly more positive δ13C values than fish not fed dung. Fish and aquatic insects sampled in a river pool used for decades by H. amphibius also exhibited more positive δ13C values at the end of the dry season than fish and insects sampled from an upstream H. amphibius‐free reference pool. Fish sampled in these same pools at the end of the wet season (high flow) showed no significant differences in δ13C values, suggesting that higher flows reduced retention and use of H. amphibius subsidies. These data provide preliminary evidence that δ13C values may be useful, in certain contexts, for quantifying the importance H. amphibius organic matter.

Environmental drivers of aquatic macrophyte communities in southern tropical African rivers: Zambia as a case study

The first-ever extensive macrophyte survey of Zambian rivers and associated floodplain waterbodies, conducted during 2006–2012, collected 271 samples from 228 sites, mainly located in five freshwater ecoregions of the world primarily represented in Zambia. The results supported the hypothesis that variation in macrophyte community structure (measured as species composition and diversity) in southern tropical African river systems, using Zambia as a case study area, is driven primarily by geographical variation in water physico-chemical conditions. In total, 335 macrophyte taxa were recorded, and a chronological cumulative species records curve for the dataset showed no sign of asymptoting: clearly many additional macrophyte species remain to be found in Zambian rivers. Emergent macrophytes were predominant (236 taxa), together with 26 floating and 73 submerged taxa. Several species were rare in a regional or international context, including two IUCN Red Data List species: Aponogeton rehmanii and Nymphaea divaricata. Ordination and classification analysis of the data found little evidence for temporal change in vegetation, at repeatedly-sampled sites, but strong evidence for the existence of seven groups of samples from geographically-varied study sites. These supported differing sets of vegetation (with eight species assemblages present in the sample-groups) and showed substantial inter-group differences in both macrophyte alpha-diversity, and geographically-varying physico-chemical parameters. The evidence suggested that the main environmental drivers of macrophyte community composition and diversity were altitude, stream order, shade, pH, alkalinity, NO3-N, and underwater light availability, while PO4-P showed slightly lower, but still significant variation between sample-groups.