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Mekelle is the capital city of Tigray, located in Northern Ethiopia. Water samples collected from 18 springs, spatially covering the study area, were analyzed for their physical properties, and major cation and anion concentrations. Geologically, the study area is characterized by limestone, shale, limestone-shale-marl intercalation, and a dolerite rock unit. The fractured dolerite and fractured limestone are the main water-bearing geological formations. The objective of this research was to determine the groundwater type, from springwater chemistry, and evaluate its quality status for irrigation purposes. The total dissolved solids (TDS), chloride (Cl), and pH range from 330 to 1346 mg/l, 5.76 to 250.6 mg/l, and 7.01 to 8.13 respectively. A piper diagram showed the presence of three groundwater types in this area: calcium magnesium chloride, mixed type, and calcium magnesium bicarbonate hydrochemical facies. The dominant of the three, with about 70 %, was the calcium magnesium bicarbonate type. The sodium adsorption ratio (SAR) and sodium percentage (Na %) were calculated to determine the suitability of the water for irrigation. The SAR and Na % values ranged from 1.71 to 5.36 and 10.69 to 20.54, respectively. As per the international water quality permissible limit for irrigation, both values fall under suitable status. Therefore, based on the outputs of this research, all of the spring waters found in this thematic area can be directly used for irrigation without any prior treatment.&nbsp, The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Mekelle, the regional capital of Tigray, faces difficulties managing and monitoring the quality of its water resources. The identified geological formations in the area are fractured limestone, fractured limestone shale-marl intercalation, and fractured dolerites. The hydrogeological setting of the Mekelle area is strongly controlled by geology and associated tectonic and non-tectonic geological structures. In comparison to other locations of Tigray, Mekelle and its environs have a higher concentration of various governmental and nongovernmental industries. Agricultural and mining activities, landfill sites, fuel and gas stations, health centers, car wash stations, garment and textile factories, and mega industries, are among the identified possible sources of water resource contamination in the area. Most of the water wells are found either within or around the agricultural lands and industrial zones. Chemicals and wastewater discharged from those industries, as affluent, are the sources of anthropogenic water resources pollution. The impacts and extent of pollution sources are not thoroughly investigated in the area. In this context, water resource vulnerability mapping was performed using the DRASTIC method and hydrogeological settings evaluation to identify the most vulnerable areas to anthropogenic pollution. The potential sources of groundwater pollution in the area were inventoried and mapped. The final DRASTIC vulnerability map with indexes ranging from 54 to 140 is classified into four classes: low (54 –75.5), moderate (75.5 – 97), high (97 – 118.5), and very high (118.5 – 140) vulnerability indexes. A modified DRASTIC vulnerability method was developed, that includes lineament density and land use thematic layers. The modified DRASTIC vulnerability map with indexes ranging from 91 to 192 is also similarly classified into four classes: low (91 – 116), moderate (116 -141), high (141 – 166), and very high (166 – 192). Single parameter sensitivity analysis and map removal sensitivity analysis were performed. The results from single parameter analysis show the impact of the vadose zone, depth to the water table and aquifer media have higher effective weightings (mean effective weightings = 23.7%, 22.9%, and 16.9%, respectively). In addition, the map removal sensitivity analysis confirms high variation of the vulnerability index is expected from the removal of impact of the vadose zone (1.5 %) and depth to the water table (1.4 %), respectively. Nitrate, used to validate both models, indicates a positive, moderate correlation (with Pearson’s correlation coefficient, r, of 0.681 and 0.702) for the DRASTIC and modified DRASTIC indexes, respectively. A comparison of both maps shows that the significant pollution sites are located in areas with high to very high vulnerability. The results of this research will directly aid water resources protection, pollution studies, and monitoring tasks of the Mekelle area.

The Dallol geothermal area in the northern part of the Danakil Depression (up to 124–155 meter below sea level) is deemed one of the most extreme environments on Earth. The area is notable for being part of the Afar Depression, an incipient seafloor-spreading center located at the triple junction, between Nubian, Somali and Arabian plates, and for hosting environments at the very edge of natural physical-chemical extremities. The northern part of the Danakil Depression is dominated by the Assale salt plain (an accumulation of marine evaporite deposits) and hosts the Dallol volcano. Here, the interaction between the evaporitic deposit and the volcanisms have created the unique Dallol hot springs, which are highly acidic (pH ~ 0) and saline (saturation) with maximum temperatures ranging between 90 and 109 °C. Here we report for the first time evidence of life existing with these hot springs using a combination of morphological and molecular analyses. Ultra-small structures are shown to be entombed within mineral deposits, which are identified as members of the Order Nanohaloarchaea. The results from this study suggest the microorganisms can survive, and potential live, within this extreme environment, which has implications for understanding the limits of habitability on Earth and on (early) Mars., European Union’s Horizon 2020 research and innovation program under Grant Agreement No 654208

An amendment to this paper has been published and can be accessed via a link at the top of the paper.