Browsing by Author "Asrat, Asfawossen (Professor)"

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    Environmental Impact Analysis of Infrastructures Development and Lake Beseka Expansion on the Integrity of Fentale-Metehara Blister Caves in the Main Ethiopian Rift
    (Addis Ababa Universty, 2017-01) Belay, Dershaye; Asrat, Asfawossen (Professor)
    This study deals with the analysis of environmental impact of the Lake Beseka expansion and the infrastructures development on the Fentale-Metehara blisters and blister caves in the Main Ethiopian Rift. The Fentale-Metehara blisters and blister caves are unique and spectacular geological features found in such number and extent in this area only. The aerial extent of the blistered region is about 54 km². However, the area of the individual blisters and blister caves ranges from about 7m² to 24000m². Decadal landuse and land cover (LU/LC) change of the area analyzed using supervised classification system of Landsat images have been processed in ERDAS IMAGINE 2014 version. In addition, 161 blister caves and 478 blisters were mapped and documented in a geo-database schema using Google Earth accompanied by detailed field investigation. Susceptibility to destruction of these features has been analyzed based on the frequency ratio technique and non-hierarchical cluster analysis of natural (topographical factors, drainage systems, Lake Beseka expansion and lava flows) and human induced (urbanization, irrigation activities and infrastructure lines) triggering factors. For the susceptibility mapping of these blister fields 119 blisters and blister caves were selected and categorized as affected/threatened blister fields. Most of the blister fields fall on the high to very high susceptibility zones. These techniques revealed that the Lake, irrigation fields and the rapid expansion of the urban settlements led to a destruction of some of the blister fields during the past four decades. It was found out that further expansion of Lake Beseka, as well as the human induced factors including the infrastructure development could lead to further destruction of the remaining blister fields. The LULC analysis further corroborates this conclusion as it has been observed that the Lake Beseka, farmlands and settlements expanded at about 46.2 km², 46.6 km² and 3.3 km² area during the last four decades. In conclusion, proper and well-organized documentation of the blister fields in a geo-database schema and also the high quality susceptibility zonation map, which were produced in this study will help in the preservation efforts of these unique geoheritage resources
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    Metagenomic Analysis of Microorganisms in Hyper Saline Aquatic and Acidic Habitats of Danakil Depression of the Afar Region of Ethiopia and their Biotechnological Potential
    (Addis Ababa University, 2021-12-04) Tilahun, Lulit; Simachew, Addis (PhD); Asrat, Asfawossen (Professor); Wessel, Gary M. (PhD)
    The Danakil Depression is one of the hottest place on Earth and is considered as an exceptional place where different extreme environments are found. Five locations in the Danakil Depression were studied for the presence of extremophiles and their biotechnological potentials. The sample sites for this study are the Hyper-saline Acid Ponds [HsAP] (Dallol [DAL], Black Water [BLA], Gaet’ale [GAL]) as well as the Hyper-saline Aquatic Systems [HsAqS] (coastal parts of Lake Asale [LA, LADP5, LADP6], Mud’ara pond [MUP]). All the sites were located South to Mount Dallol at less than -100 m below sea level. In our investigation, we tested for the presence of DNAbased life in the studied sites using Whole Metagenome Shotgun (WMS) DNA sequencing approaches. Bioinformatic tools that adopt techniques of assembly free (Bowtie, MetaPhlAn2) and assembly (MetaSpades, DIAMOND and MEGAN 6-CE) were used to identify the microbial communities and predict the major nutrient metabolic networks. Accordingly, the HsAqS were found to be mainly dominated by archaea Operational Taxonomic Units (OTUs), while the HsAP were dominated by bacteria OTUs. More than 95% of the total OTUs of HsAqS was grouped under phylum Euryarchaea, while more than 90% of the OTUs of HsAP was classified in the phyla Proteobacteria, Actinobacteria and Firmicutus. Halonotius sp J07HN6 and unclassified Salinibacter ruber were the two abundant archaeal and bacterial OTUs in the HsAqS, respectively. On the other hand, unclassified strain of Paraburkholderia fungorum was profiled as the most abundant OTU for DAL and BLA, while unclassified Escherichia and unclassified Burkholderia were top two abundant OTUs for GAL. Insilico prediction of gene functions and metabolic pathways using SEED and KEGG indicated presence of carbon fixation, sulfate oxidation, assimilative nitrogen and sulfate reduction reactions in DAL and BLA samples. Carbon fixation was also predicted in the HsAqS while methanogenesis was exclusively predicted in GAL. Based on the investigation of the sources of the genes of interest, it is clear that syntrophic metabolism is the main strategy adapted to utilize the nutrients in the studied sampling sites. Moreover, the predicted genes from DAL’s and BLA’s nitrogen metabolism helped to discover new protein sequences of cysteine desulfurase and [4Fe-4S] ferredoxin with less than 80% similarity to the homologous reference protein sequence. Images of DAL extremophiles obtained from Transmission Electron Microscopy (TEM) showed high production of nano sized Extracellular Membrane Vesicles (EMV). Further investigation on resistance of DAL’s extremophiles to phenolic compounds under lysing conditions indirectly signified their bio-remediation capability. In general, this preliminary investigation indicates great biotechnological and bioremediation potentials of extremophiles of Danakil Depression.
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    Origin of High Groundwater Salinity in the Omo Delta and its Surroundings (Southwestern Ethiopia) Hydrochemistry and Isotope Approaches
    (Addis Ababa University, 2020-09-23) Tadesse, Abebayehu; Kebede, Seifu (PhD); Asrat, Asfawossen (Professor)
    The groundwater of the Omo Delta is characterized by the presence of fresh and saline groundwater side by side and the success of having fresh water is well below 50%. Therefore, most wells are abandoned due to elevated salt content. However, research on the origin of groundwater salinity and salinization processes, detail hydrochemical and isotopic composition of the Delta groundwater are lacking. The main objective of this work is to characterize the source of salinity and mechanism(s) of salinization in the Omo Delta (Southern Ethiopia) groundwater giving special emphasis on characterizing various morphological units and depositional environments recognized in the area and their implication on groundwater salinity. To achieve the objectives converging pieces of evidences from the conventional hydrogeological investigation, litho-hydrostratigraphic relationships, water chemistry, and isotope hydrology were used to elucidate the cause of groundwater salinity. The geochemical dataset and isotope were analyzed using different but complementary, approaches that allowed for insights into the process of salinization of groundwater in the study area. The correlation matrices of major anions, cations, and physical parameters of water indicate that elements chloride, sodium, fluoride, sulphate, and bicarbonates contributed from mineralization processes. The dominant effects of rainfall, rock weathering, and evaporation play a major role in the geochemical evolution of groundwater. Rock weathering was the main mechanism controlling the chemical compositions of the Hammer basement groundwater whereas; evaporation–crystallization is in the Delta aquifer groundwater system. The saturation index of anhydrite, aragonite, calcite, dolomite, gypsum, and halite shows that the groundwater in the study area was below the saturation with anhydrite, gypsum, and halite, indicating that these minerals are anticipated to dissolve. Moreover, groundwater samples were saturated to over-saturated with aragonite, calcite, and dolomite, implying that the three major carbonate minerals may have affected the chemical composition of groundwater in the study area. The variation of the hydraulic parameters at different locations and layers have been resulted from aquifer materials formed under different depositional environment. These deposits represent different aggradations and degradation phases that were usually accompanied by lake level changes. Groundwater movement and recharge are highly dependent on geomorphic features and depositional environments. Groundwater that is close to surface water sources ii (River and Wadies) is fresh relative to other farther away from it, in the alluvial fan geomorphic feature, the fan apex is characterized by fresh groundwater compared to fan toe, which is more saline. The thickness of clay layers significantly affects the salinity of groundwater as it acts as the adsorption media and filtering membrane for groundwater in the Delta. The isotopic composition of most groundwater samples from sediment plot slightly far from the Global meteoric water line (GMWL) compared to the waters from the Hammer basement indicating that evaporative fractionation before recharge the sediments. The increase in groundwater salinity due to evaporation has resulted in a simultaneous isotopic enrichment. Both hydrochemical and isotope techniques indicate the dominance of local recharge and flow systems. The radon-222 concentration in groundwater samples showed a very wide range from 58.7 to 982.5Bq/m3 compared to the River and Lake Water samples that are range from 18.65 to 105.2Bq/m3 and 10.49 to 10.85Bq/m3 respectively. The highest concentration was found in the samples that were collected from wells close to the Omo River. From converging evidence of geology, hydrogeology, hydrochemistry, and stable isotopes of water, three processes are responsible for the salinization of groundwaters in Omo Delta: salinity originated from water-rock interaction, evaporation at or near the surface, and clay membrane filtration. The results of this study will also be useful to the development of a sound management plan for water resources and the direction of further research in the study area.
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    Petrogenetic Evolution of the Melka Wakena Pyroclastic Deposits: Implications for the Depositional History of the Intercalated Volcano-Sedimentary Rocks
    (Addis Ababa Universty, 2017-05) Resom, Angesom; Asrat, Asfawossen (Professor)
    The study area is located east of the Assasa town in the Arsi zone on the shoulder of the rift-plateau escarpment and close to the Gadeb archaeological sites. The main objective of the study was therefore to determine the petrogenetic evolution of the pyroclastic rocks using standard field (mapping and description), geochronological (stratigraphic logging, correlation and Ar-Ar dating of some selected samples), petrographic (thin section analysis) and geochemical (major and trace element geochemistry) methods, and constraining the depositional history of the intercalated volcano-clastic sediments in the area. A total of 26 samples were analyzed in this study: 9 for petrography, 13 for geochemistry and 4 for Ar-Ar dating. The pyroclastic rocks have been formed 1.617 to 0.696 Ma ago in a topographically complex area resulting in non-continuous and erratically distributed layers. They are generally of rhyolitic (the ignimbrite, ash fall and pumiceous ash units) and dacitic (the ash flow unit) composition. The geochemical characteristics and modeling suggest that the rhyolites were formed by fractional crystallization of basaltic magmas involving crustal input, while the dacites were formed by Assimilation Fractional crystallization followed by post depositional leaching of the mobile elements. The Melaka Wakena archaeological site was a geomorphologically active area during the Early to Middle Pleistocene where overbank sedimentary sequences (conglomerates and sands) formed by a big meandering river, dotted with possible temporary ponds and ox-bow lakes (depositing clays), have been covered by episodic volcanic eruptions and the products thereof. A dense network of channels and streams have been subsequently down cutting through the older volcanic and sedimentary sequences before the deposition of the younger volcanic and reworked volcaniclastic rocks. This episodic eruption of pyroclastic rocks on actively depositing and eroding sedimentary sequences containing cultural sequences allow constraining the age of the archaeological remains in the area as well as their depositional history. Key words: Melka Wakena, Petrogenetic evolution, Stratigraphy, Geochronology, Fractional Crystallization, Crustal contamination