Rift Valley Lakes Research Articles

Assessing the Impact of Existing and Future Water Demand on Economic and Environmental Aspects (Case Study from Rift Valley Lake Basin: Meki-Ziway Sub Basin), Ethiopia

In the development of water resource projects there is an increase and extensive use of water resources, which causes exploitation of the existing systems and ecosystem of the natural environment. The Water Evaluation and Planning (WEAP) model is used to assess water demand by considering the existing development situation and future water resources development with scenarios analysis in the study area (Ziway Meki Sub Basin, Ethiopia). Three different development scenarios were developed to simulate water use at demand sites. In the simulations, the catchment was divided into 5 main sub-catchments where the supply and demand nodes were spatially located. The competing water sectors were irrigation development, domestic users, soda ash industry and environmental flow requirements. Hydro Meteorological data, net evaporation from Lake Reservoir, and monthly water demand from user sectors were the basic inputs to the model. The results of the reference scenario were validated using observed flows. Accordingly, the simulation result revealed that the total average annual inflow volume into the study area is declining significantly for reference scenarios and water availability is limited in the months of January (17 Mm3) and December (171 Mm3) while in the other months the availability is efficient and all users have 100% coverage. Except Langano irrigation site that have between 33.33% to 86.5% coverage in average during the month of Feb to May (2.57 Mm3) and April in Bulbula 95.2% coverage, others get full coverage. The minimum reliability observed mostly in the ongoing and likely future development scenarios at Bulbula irrigation demand sites which have 92.11% and 66.67% reliability in Langano irrigation demand sites throughout all development scenarios. On the other hand, in Sher-Ethiopia expansion, 51.75% reliability is observed in ongoing and likely future development scenarios and in demand site of Katar irrigation diversion and Meki irrigation from dam 51.75% is observed in likely future development scenarios.

Modeling for Inter-Basin Groundwater Transfer Identification: The Case of Upper Rift Valley Lakes and Awash River Basins of Ethiopia

Groundwater movement beneath watershed divide is one component of the hydrological cycle that is typically ignored due to difficulty in analysis. Numerical ground-water models, like TAGSAC, have been used extensively for predicting aquifer responses to external stresses. In this paper TAGSAC code was developed to identify the inter-basin groundwater transfer (IBGWT) between upper Awash River basin (UARB) and upper rift valley lakes basin (URVLB) of Ethiopia. For the identification three steady state groundwater models (for UARB, URVLB and for the two combined basins) were first created and calibrated for the 926 inventoried wells. The first two models are conceptualized by considering the watershed divide between the two basins as no-flow. The third model avoids the surface water divide which justifies IBGWT. The calibration of these three models was made by changing the recharge and hydrogeologic parameters of the basins. The goodness of fit indicators (GoFIs) obtained was better for the combined model than the model that describes the URVLB. Furthermore, the hydraulic head distribution obtained from the combined model clearly indicates that there is a groundwater flow that doesn’t respect the surface water divide. The most obvious effect of IBGWT observed in these two basins is that it diminishes surface water discharge from URVLB, and enhances discharge in the UARB. Moreover, the result of this study indicates potential for internal and cross contamination of the two adjacent groundwater.

Characterization of Water Level Variability of the Main Ethiopian Rift Valley Lakes

In this paper, the water level fluctuations of eight Ethiopian Rift Valley lakes were analyzed for their hydrological stability in terms of water level dynamics and their controlling factors. Long-term water balances and morphological nature of the lakes were used as bases for the analyses. Pettit’s homogeneity test and Mann–Kendall trend analysis were applied to test temporal variations of the lake levels. It is found that the hydrological stability of most of the Ethiopian Rift Valley lakes is sensitive to climate variability. In terms of monotonic trends, Lake Ziway, Hawassa, Abaya and Beseka experienced significant increasing trend, while Ziway, Langano and Chamo do not. In addition, homogeneity test revealed that Lake Hawassa and Abaya showed significant upward shift around 1991/1992, which was likely caused by climate anomalies such as the El Niño / Southern Oscillation (ENSO) phenomena. Lake Abiyata is depicted by its significant decreasing monotonic trend and downward regime shift around 1984/1985, which is likely related to the extended water abstraction for industrial consumption.

Diagenetic pathways linked to labile Mg-clays in lacustrine carbonate reservoirs: a model for the origin of secondary porosity in the Cretaceous pre-salt Barra Velha Formation, offshore Brazil

Abstract The lacustrine carbonate reservoirs of the South Atlantic host significant accumulations of chemically reactive and Al-free Mg-silicate minerals (e.g. stevensite, kerolite and talc). Petrographic data from units such as the Cretaceous Barra Velha Formation in the Santos Basin suggest that Mg-silicate minerals strongly influenced, and perhaps created, much of the observed secondary porosity. The diagenetic interactions between reactive Mg-silicate minerals and carbonate sediments are, however, poorly known. Here we develop a conceptual model for the origin of secondary porosity in the Barra Velha Formation guided by considerations of the chemistry that triggers Mg-silicate crystallization, as well as the geochemical and mineralogical factors that act as prerequisites for rapid Mg-silicate dissolution during early and late diagenesis. We conclude that sub-littoral zones of volcanically influenced rift lakes would have acted as the locus for widespread Mg-silicate accumulation and preservation. Organic-rich profundal sediments, however, would be especially prone to Mg-silicate dissolution and secondary porosity development. Here, organic matter diagenesis (especially methanogenesis) plays a major role in modifying the dissolved inorganic carbon budget and the pH of sediment porewaters, which preferentially destabilizes and then dissolves Mg-silicates. Together, the sedimentological, stratigraphic and geochemical predictions of the model explain many enigmatic features of the Barra Velha Formation, providing a novel framework for understanding how Mg-silicate–carbonate interactions might generate secondary porosity more broadly in other lacustrine carbonate reservoirs across the South Atlantic.

Determination of the status of stakeholder participation in the management of the Lake Malawi basin through application of Integrated Lake Basin Management

Lake Malawi is the southernmost of the Great Rift Valley Lakes of Africa and boasts the world's greatest freshwater fish biodiversity. Along with its basin, the lake provides many benefits to the country of Malawi. Settlements, agriculture and fishing are some of the major uses of the lake basin, making community involvement a necessary component of its management. With the use of key informant interviews, questionnaire survey, document review and site observations, this study demonstrates the applicability of the Integrated Lake Basin Management framework in the Lake Malawi Basin in regard to stakeholder participation. The main objective was to assess the participation of stakeholders, especially local communities, in the management of the lake basin. The framework applied in this study is discussed. The study findings indicate strong to very strong stakeholder participation, with notably high levels of awareness and women's involvement. Enhancing the understanding of the complex nature of lake basin issues, especially those related to the linkages between the water body and the basin, is a topic requiring further attention.

Understanding the relative impacts of natural processes and human activities on the hydrology of the Central Rift Valley lakes, East Africa

Significant changes have been observed in the hydrology of Central Rift Valley (CRV) lakes in Ethiopia, East Africa as a result of both natural processes and human activities during the past three decades. This study applied an integrated approach (remote sensing, hydrologic modelling, and statistical analysis) to understand the relative effects of natural processes and human activities over a sparsely gauged CRV basin. Lake storage estimates were calculated from a hydrologic model constructed without inputs from human impacts such as water abstraction and compared with satellite-based (observed) lake storage measurements to characterize the magnitude of human-induced impacts. A non-parametric Mann–Kendall test was used to detect the presence of climatic trends (e.g. a decreasing or increasing trends in precipitation), while the Standard Precipitation Index (SPI) analysis was used to assess the long-term, inter-annual climate variability within the basin. Results indicate human activities (e.g. abstraction) significantly contributed to the changes in the hydrology of the lakes, while no statistically significant climatic trend was seen in the basin, however inter-annual natural climate variability, extreme dryness, and prolonged drought has negatively affected the lakes. The relative contributions of natural and human-induced impacts on the lakes were quantified and evaluated by comparing hydrographs of the CRV lakes. Lake Abiyata has lost ~6.5 m in total lake height between 1985 and 2006, 70% (~4.5 m) of the loss has been attributed to human-induced causes, whereas the remaining 30% is related to natural climate variability. The relative impact analysis utilized in this study could potentially be used to better plan and create effective water-management practices in the basin and demonstrates the utility of this integrated methodology for similar studies assessing the relative natural and human-induced impacts on lakes in data sparse areas. Copyright © 2015 John Wiley & Sons, Ltd.

English

Lake Hawassa is one of the eight Major Ethiopian Rift Valley Lakes and the smallest among them which is situated in southern regional state; it is a closed basin system and receives water from only perennial Tikurwuha River and runoff from the catchment areas. It is an important source of water for surrounding rural communities for various uses like domestic, irrigation, livestock watering, fishing and recreation. Quality of the lake water is vital for the surrounding rural and urban communities for proper and safe use of the lake. The present study was designed to determine the water quality status of the lake for multiple designated water uses by employing the water quality index. To assess the status water samples were collected in monthly intervals for a period of three months from December to February (dry period), 2011/12. From all water quality parameters analyzed turbidity, Mn, Na+, K+, F-, PO43-, total coliform and fecal coliform were higher than the recommended limits of national and international standards for designated water uses. Based on the water quality index calculation the lake water is categorized under marginal category which reveals the water is frequently threatened and impaired and as well departs from natural condition. Accordingly the lake water is under fair category for irrigation and aquatic life; however, it needs great care on selection of crops and soil condition. The lake is under higher risk by deleterious anthropogenic activities on watershed and it needs mitigation measures to prevent it from further deterioration.   Key words: Water quality index, Lake Hawassa, water quality status, designated water use

Soils, slopes and source rocks: Application of a soil chemistry model to nutrient delivery to rift lakes

The topographic evolution of rift basins may be critical to the deposition of lacustrine source rocks such as the organic-rich Lower Cretaceous shales of the South Atlantic margin. Soils have been proposed as a key link between topography and source rock deposition by providing nutrients for the algae growth in rift lakes. Decreasing topographic relief from active rift to late rift has several effects on soils: soils become thicker and finer, erosion of dead surface and soil organic matter decreases, and the fractionation of precipitation between runoff and infiltration may favor increased infiltration.This hypothesis is tested by application of CENTURY, a complex box model that simulates transfer of nutrients within soil pools. The model is first applied to a rainforest soil, with several parameters individually varied. Infiltration experiments show that the concentrations of C, N and P in groundwater decrease rapidly as infiltration decreases, whether due to increased slope or to decreased precipitation. Increased erosion of surface plant litter and topsoil results in substantially decreased nutrient concentrations in groundwater. Increased sand content in soil causes an increase in nutrient concentration.We integrate these variables in analyzing topographic swathes from the Rio Grande Rift, comparing the southern part of the rift, where topography is relatively old and reduced, to the northern rift. C and P concentrations in groundwater increase as slope gradient decreases, resulting in substantially larger C and P concentrations in groundwater in the southern rift than the northern rift. Nitrogen concentrations in groundwater depends on whether infiltration varies as a function of slope gradient; in experiments where the fraction of infiltrated precipitation decreased with increasing slope, N concentrations was also substantially higher in the southern rift; but in experiments where that fraction was held constant, N concentrations was lower in the southern rift. These simulations demonstrate that evolving topography during rift development can significantly influence nutrient concentrations in groundwater and, if these nutrients flow into rift lakes and stimulate organic productivity, account for the deposition of rich oil-prone source rocks in late rift stages.

Serological and Molecular Study of Newcastle Disease Virus in Village Chickens in Selected Rift-Valley Areas, Ethiopia

Newcastle Disease (ND) is a serious and commonly fatal viral poultry disease, which is widely distributed throughout the world. In most developing countries including Ethiopia, ND is the most important disease causing huge economic losses. A cross sectional study was conducted in February 2014 in village chickens at three selected districts in and around rift valley lakes of Ethiopia to determine the prevalence of Newcastle disease virus (NDV) by serological and molecular methods. A total of 155 sera and 155 swab samples were collected from village chickens in Bishoftu, Tikur wuha and Ziway districts. The sera samples were analyzed by Competitive-ELISA. ND viruses were isolated from the tracheal swab specimens, through inoculation in embryonated chicken eggs and were characterized genetically by using molecular methods. Real-time RT-PCR targeting a conserved region of the M gene was employed to amplify all APMV1. M-gene positive samples were further analyzed by Real-time RT-PCR targeting F-gene to specifically amplify the virulent strains. The overall sero prevalence of ND was 11.6% with no statistically significant differences between the study districts at 95% confidence level. Thirteen isolates were positive for APMV1 out of which 38.4% (5/13) were virulent NDV strains. This study provides important information on serological and virological profile of NDV and highlights the importance of continuous surveillances to better understand the epidemiology of the disease.

Strong isolation by distance revealed among Cyperus papyrus populations in the Rift Valley lakes, Lake Victoria, and isolated wetlands of Kenya

Many aquatic plant populations occur in isolated habitats surrounded by land masses which can act as barriers to gene flow, unless other mechanisms exist to facilitate connectivity. This isolation together with life history processes influences greatly genetic diversity and structure among populations of aquatic species. We assessed clonal diversity, genetic variation, and genetic structure of Cyperus papyrus that occur in large geographical scale in freshwater wetlands of Kenya using eight nuclear microsatellite markers. A total of 60 alleles were found across 14 populations. The genetic diversity measures varied widely among populations, with both Lakes Naivasha and Victoria displaying higher allelic and gene diversity than isolated wetlands. C. papyrus maintained relatively high levels of clonal diversity and gene diversity at species level (PP=79%, AT=25, HE=0.41, HO=0.40) comparable to other clonal aquatic plants. Whereas, two monoclonal wetlands suggested recent founder effects, we attributed variation in clonal diversity to different levels of sexual reproduction and perennation among populations. AMOVA revealed overall high genetic differentiation among populations (FST=0.250, p=0.001) which varied from very low (FST=0.014) within lakes to very high (FST=0.565) among Lake Victoria–Rift Valley lakes and isolated wetlands. Lack of genetic differentiation among populations within Lakes Victoria and Naivasha implicated hydrochorous dispersal. A Mantel test showed significant isolation-by-distance among populations whereas a PCoA and Bayesian analysis of individuals grouped populations according to drainage basins. We hypothesized that connectivity among distant isolated locations could be by migratory waterfowl or large herbivores (through both endozoochory and epizoochory) and historical inter-basin connection.

Applying a BP Neural Network Approach to the Evolution Stage Classification of China Rift Lakes

Applying a BP Neural Network Approach to the Evolution Stage Classification of China Rift Lakes

Zooplankton abundance, species composition and ecology of tropical high-mountain crater lake Wonchi, Ethiopia

The highlands of Ethiopia represent some of the remnants of undisturbed aquatic ecosystems; they are however highly threatened by significant socio–economic developments and associated anthropogenic impacts. Lake Wonchi is one of the few remaining fairly pristine high–mountain crater lakes in the central highlands and has never been investigated in detail. We present a first study on zooplankton taxa composition, abundance and biomass conducted over more than one year including the underlying environmental drivers. The lake is basic (pH 7.9-8.9), dilute (specific conductivity 185-245 µS cm -1 ) and oligotrophic with mean trophic status index of 36. The zooplankton community composition showed low species richness comprising a total of fourteen taxa with six cladocerans, one copepod and seven rotifers. Simpson´s index of diversity with values between 0.6 and 0.8 pointed towards a homogenous taxa occurrence within the single sample units. The overall mean (±SD) standing biomass of zooplankton was 62.02±25.76 mg dry mass m -3 ,which is low compared to other highland and rift valley lakes in Ethiopia. Cyclopoid copepods, in particular Thermocyclops ethiopiensis were the most abundant group and contributed 50% to the total zooplankton abundance followed by cladocerans (38%) and rotifers (12%). Non-metric multi-dimensional scaling resulted in a 3-dimensional model, which revealed similar community composition on successive sampling dates except in December/January and May. Temperature, alkalinity, conductivity and nitrate-N had significant influence on this seasonal pattern. A weak, but significant positive correlation (r=0.482, N=20, P=0.037) between Chlorophyll a and zooplankton biomass mirrors a bottom-up effect of phytoplankton biomass on zooplankton dynamics. The zooplankton of Lake Wonchi displayed some degree of segregation along the epi– and metalimnion during this study, but diel vertical migration was not observed. The results show that fish predation is not the key factor in structuring the vertical distribution of zooplankton in Lake Wonchi.

English

This study describes hydrological fluctuations of Lake Abaya-Chamo via direct local measurements in relation to time-integrated climate anomalies. Reconstruction of an index involved compositing lake level and flow discharge station records in the period 1983-2009. Satellite and model interpolated rainfall, latent heat flux and run-off anomalies follow the hydrological records when summed over and lagged by one year. Correlation of ECMWF climate fields reveals that east Pacific and subtropical Atlantic surface temperature are influential on continuous flow discharge, while the Indian Ocean dipole has influence in September to November season. A predictive algorithm accounts for 44% of inter-annual fluctuations in the period 1983-2009. Rapid increases in lake level coincide with maturing El Niño and Indian Ocean dipole, bringing floods for example in October 1997. Early season dry spells prevail when the equatorial trough remains over Tanzania, and dry northerly winds accelerate evaporation such as in March 2000.   Key words: Ethiopia rift lakes, hydrological fluctuations.

Sediment load of the main rivers of Lake Baikal in a changing environment (east Siberia, Russia)

The results of the analysis of discharge and sediment flow changes of the main rivers flowing into Lake Baikal are presented. Long-term observation record of sediment flow is divided into two periods differing in average values and scale fluctuations of annual average values. During the first period, the dynamics of sediment flow of rivers was determined by hydro-climatic factors, i.e. fluctuations of sediment flow, in general, are synchronous to fluctuations of water flow. During the second period (from the mid-1970s) there is a downward trend of sediment flow change (decrease by 49%–82%) against the background of increased discharge of rivers. This trend is caused by both anthropogenic influence, and natural processes connected to global and regional changes of climatic characteristics. In general, natural processes of sediment flow changes in the different areas of Baikal basin are altered by anthropogenic factors to a greater or lesser extent. The present article can be used as analytical material for further research and forecast of sediment flow changes in the Baikal basin as well as in other rift-valley lakes of the world.

The early Upper Palaeolithic of the Tunka rift valley, Lake Baikal region, Siberia

This paper presents recent results of geological and archaeological research at Late Pleistocene sites in the Tunka rift valley (Lake Baikal region, southern Siberia), including new radiocarbon dating of the Palaeolithic layers at Bol'shoi Zangisan, Slavin Yar and Tuyana. The sites range in age from ∼26 to 45 ka 14C BP and represent the earliest evidence of human habitation in the area. Numerous faunal remains have also been identified in the archaeological horizons from which palaeoenvironmental conditions can be reconstructed. These data also provide important new information about the age, context, and development of an early microlithic industry in the Tunka-Pribaikal'e region during the late Karginskii interstadial, attributed to Marine Isotope Stage 3 (MIS3). Although further research is needed to verify the reconstructed site age models, archaeological evidence recovered at Tuyana and Bol'shoi Zangisan represent among the oldest known occurrences of microcore-microblade technology in North Asia.

Phylogeny and age of chromidotilapiine cichlids (Teleostei: Cichlidae)

Chromidotilapiine cichlid fishes (Teleostei: Cichlidae) of West and Central Africa represent the most species rich ancient African cichlid lineage. In contrast to the mega-diverse haplotilapiine cichlids from the African rift valley and crater lakes, very little is known about their phylogenetic history. Based on mitochondrial and nuclear DNA sequences and a representative taxon sampling, we present a first molecular phylogenetic hypothesis and propose age estimates for their origin and diversification. Our data support the monophyly and an Oligocene/Eocene origin of chromidotilapiines. Within chromidotilapiines, two large, reciprocally monophyletic clades are present and the enigmatic genus Teleogramma could be phylogenetically placed for the first time. The two distantly distributed species Limbochromis robertsi and Chromidotilapia schoutedeni were identified as sister group to the Congolian species complexes of Nanochromis and Congochromis. This unexpected phylogenetic link between a region in West Africa and the Congo basin suggests an ancient hydrogeographic corridor spanning almost half of the African continent. The nearly complete taxon sampling, good knowledge on species distribution patterns and well resolved phylogenies allow the presumption that paleogeographic patterns rather than ecological factors shaped the ancient divergence within chromidotilapiines, which predates the origin of the mega-diverse austrotilapiine lineage, comprising the majority of African cichlid species.

Sudden flamingo deaths in Kenyan Rift Valley lakes

The East African Rift Valley Lakes Bogoria and Nakuru sometimes host around 75% of the world population of lesser flamingos Phoeniconaias minor. In this area, mysterious flamingo die‐offs have occupied researchers for four decades. Recently, cyanobacterial toxins came into the fore as a possible explanation for mass mortalities because the main food source of lesser flamingos is the cyanobacterium Arthrospira fusiformis. We took weekly samples from July 2008 to November 2009 from Lakes Nakuru and Bogoria and analyzed them by high performance liquid chromatography for microcystins. Monthly, samples were cross‐checked using protein phosphatase inhibition assays with lower detection limits and additionally screened for polar toxins. During our study period, three flamingo die‐offs occurred at L. Bogoria and we were able to analyze tissues of 20 carcasses collected at the shoreline. No cyanotoxins were detected either in plankton samples or in flamingo tissues. Accordingly, other reasons such as food composition or bird diseases played a key role in the observed flamingo die‐offs.

Concentrations and human health risk assessment of organochlorine pesticides in edible fish species from a Rift Valley lake—Lake Ziway, Ethiopia

Fish consumption is known to have several health benefits for humans. However, the accumulation of organic pollutants, like organochlorine pesticides (OCPs) could pose health hazards. Thus, OCPs in edible fish species (Oreochromis niloticus, Tilapia zillii, Carassius spp., and Clarias gariepinus) from Lake Ziway, an Ethiopian Rift Valley Lake were investigated to assess the potential human health hazards of these contaminants. Dichlorodiphenyltrichloroethanes (DDTs), hexachlorocyclohexanes (HCHs), chlordanes, and heptachlors were observed with ΣOCPs concentration ranging from 1.41 to 63.8ngg−1 ww. DDTs were the predominant contaminants (0.9 to 61.9ngg−1 ww), followed by HCHs. The predominance of DDTs may be attributed to their current use in vector control and contamination from past usage. The estimated daily intakes (EDIs) of OCPs from all fish species were much lower than the acceptable daily intakes (ADIs), indicating that consumption of fish is at little risk to human health at present. However, the cancer risk estimates in the area of concern and the hazard ratios (HRs) of HCHs, DDTs, and heptachlors exceeded the threshold value of one, indicating daily exposure to these compounds is a potential concern. This may result in a lifetime cancer risk greater than of 1 in 106.

Surveillance of avian influenza virus in poultry and wild birds in Ethiopian Rift Valley Lakes

Surveillance of avian influenza virus in poultry and wild birds in Ethiopian Rift Valley Lakes

Irrigation Water Management in Small Scale Irrigation Schemes: the Case of the Ethiopian Rift Valley Lake Basin

Appraisals of irrigation water management scenarios are crucial in project performance monitoring. A comprehensive irrigation water management study has been conducted on four small scale irrigation schemes in the Ethiopian rift valley lake basin. It is observed that from 147 irrigators 68% faced irrigation water supply unreliability, 79.1% encountered unfair distribution of water and 66 % underwent through timeliness problem in water distribution occasionally. All the investigated schemes witnessed a weak (50 % of all scheme users noted poor) organization of irrigation scheme administration. The Water Users Associations (WUAs) lack clear laws/by-laws and strategies to lead small or major canal operations and maintenances. Without a strong WUA it is impossible to think of filling farmer’s skill gap, to have a working maintenance strategy, fair distribution of irrigation water, reliable irrigation water supply and timely delivery of irrigation water. DOI: http://dx.doi.org/10.5755/j01.erem.67.1.6240