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Lake Naivasha, Kenya's second-largest freshwater body is a wetland of international ecological importance and currently subjected to unprecedented anthropogenic influence. The study aims to chronologically reconstruct the main human activities and background weathering reactions that govern metal mobilizations into the lake and their potentially adverse effects on its ecological status. We combine extensive geochemical analyses (major, trace elements, Zn-Pb isotope ratios) in a dated lake sediment record and catchment rocks with remote sensing techniques. Downcore geochemical variations reflect natural ecosystem destabilizations occurring as early as the first half of the 20th century. These coincide with changes towards less radiogenic Pb-isotope values which persist towards the top of the core ( 206 Pb/ 207 Pb = 1.243 at core base ∼1843, to 206 Pb/ 207 Pb = 1.225 at ∼1978). We interpret the land-clearance for agricultural purposes on the Aberdare Range and documented early aviation activities as possible vectors of this early Pb-isotope excursion. The overlapping Pb-isotope signatures between sediment sources and anthropogenic contributions challenges a straightforward deconvolution of the two. Our conservative model calculations suggest, nevertheless, that an addition of up to ∼1.8 % Pb-gasoline influx to the total Pb flux, peaking in the 1980s is able to explain the Pb distribution trend. Homogeneous Zn-isotope compositions in sediments deposited until ∼1970s (δ 66/64 Zn = 0.216-0.225 ‰) do not follow major hydro-climatic events or anthropogenic forcing but likely reflect lake-specific natural cycling. Subsequent higher variations to both heavier (up to δ 66/64 Zn = 0.242 ± 0.005 ‰) and lighter (down to δ 66/64 Zn = 0.184 ± 0.003 ‰) Zn-isotope values are contemporaneous with intensification of large-scale horticultural industry in the catchment. Together with supporting indicators, the lighter Zn-isotope compositions in youngest analysed sediments (21st century) are attributable to increased biological productivity (algal blooms) and ongoing lake eutrophication. Our study demonstrates the applicability of the heavy metal isotope tool to reconstruct human influences on lake environments with complex geological settings such as the East African Rift System., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Nairobi River sediments from locations adjacent to the Kawangware and Kiambio slums were analyzed via Fourier transform ion cyclotron resonance mass spectrometry with atmospheric pressure photoionization (APPI-FT-ICR-MS). The data from these ultrahigh resolution, untargeted measurements provided new insights into the impacts of local anthropogenic activity, which included likely benzo- and dibenzothiophene pollution with a suspected petrogenic origin, and prominent surfactant-like compositions. Other features in the data included highly abundant tetra-oxygenated compounds, and oxygenated nitrogen compounds with sphingolipid interpretations. Most notably, several hydrocarbon and oxygenated compound classes in the sediment data featured intensity patterns consistent with steroid molecular formulas, including those associated with sewage contamination investigatory work. In support of this interpretation, standards of cholesterol, β-sitosterol, stigmasterol, coprostanol, cholestanol, and 5α-sitostanol were analyzed via APPI, to explore steroid ionization behavior. Generally, these analytes produced radical molecular ions ([M] •+ ), and water-loss pseudo molecular ion species ([M-H 2 O] •+ and [M+H-H 2 O] + ), among various other less intense contributions. The absence of pseudo molecular protonated species ([M+H] + ) was notable for these compounds, because these are often assumed to form with APPI. The standard measurements demonstrated how steroids can create the observed intensity patterns in FT-ICR-MS data, and hence these patterns have the potential to indicate sewage contamination in the analysis of other complex environmental samples. The steroid interpretation for the Kawangware and Kiambio data was further verified by subjecting the steroid standard radical molecular ions to collision-induced dissociation and comparing the detected fragments to those for the corresponding isolated ions from a Kawangware sediment sample.

Mapping of land use/ land cover (LULC) dynamics has gained significant attention in the past decades. This is due to the role played by LULC change in assessing climate, various ecosystem functions, natural resource activities and livelihoods in general. In Gedaref landscape of Eastern Sudan, there is limited or no knowledge of LULC structure and size, degree of change, transition, intensity and future outlook. Therefore, the aims of the current study were to (1) evaluate LULC changes in the Gedaref state, Sudan for the past thirty years (1988-2018) using Landsat imageries and the random forest classifier, (2) determine the underlying dynamics that caused the changes in the landscape structure using intensity analysis, and (3) predict future LULC outlook for the years 2028 and 2048 using cellular automata-artificial neural network (CA-ANN). The results exhibited drastic LULC dynamics driven mainly by cropland and settlement expansions, which increased by 13.92% and 319.61%, respectively, between 1988 and 2018. In contrast, forest and grassland declined by 56.47% and 56.23%, respectively. Moreover, the study shows that the gains in cropland coverage in Gedaref state over the studied period were at the expense of grassland and forest acreage, whereas the gains in settlements partially targeted cropland. Future LULC predictions showed a slight increase in cropland area from 89.59% to 90.43% and a considerable decrease in forest area (0.47% to 0.41%) between 2018 and 2048. Our findings provide reliable information on LULC patterns in Gedaref region that could be used for designing land use and environmental conservation frameworks for monitoring crop produce and grassland condition. In addition, the result could help in managing other natural resources and mitigating landscape fragmentation and degradation., Competing Interests: The authors declare that no conflict of interest exist., (Copyright: © 2023 Osman et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Climate change threatens African countries' economic development and affects agriculture and food security. Ethiopia is especially vulnerable to the negative effects of climate change because its economy is dependent on climate-sensitive livelihoods that have limited potential for adaptation. Emerging evidence indicates that climate-smart agriculture (CSA) can help smallholder farmers adapt to climate change and increase agricultural productivity, thereby enhancing household income and food security. In the study area, different CSA practices have been adopted to mitigate the negative effects of climate change and improve agricultural productivity, income, and food security. Therefore, this study examines the impact of CSA practices on household income and food security in southern Ethiopia. A total of 385 households were selected using multistage sampling. Primary and secondary data were used, and propensity score matching with different types of matching algorithms, such as nearest neighbor, kernel, and radius matching, was employed to quantify the conditional impacts of CSA intervention on farm income and food security. In comparison with non adopters farmers that have adopted CSA practices had a higher food consumption score between 6.27 and 8.15, which was statistically significant at the 1% level. Overall, 34.55% of interviewed households had acceptable food consumption scores, 44.68% had borderline, and 20.77% had poor food consumption scores. Furthermore, households that adopted CSA practices had a 20.30% higher average annual farm income per hectare than non-adopters. The study suggests that effective extension services, accurate climate information, and sound policy support are required to promote and scale up CSA measures in the study area to improve farmers' adaptive capacity, farm income, and food security., Competing Interests: Conflict of interestAll authors declare that they have no conflict of interest., (© The Author(s) 2023.)

Climate change has the greatest negative impact on low-income countries, which burdens agricultural systems. Climate change and extreme weather events have caused Ethiopia's agricultural production to decline and exacerbated food insecurity over the last few decades. This study investigates whether farmers' awareness and perceptions of climate change play a role in climate change adaptation using climate-smart agricultural practices. To collect data, 385 households in Southern Ethiopia were sampled using a multistage sampling. A Heckman probit two-stage selection model was applied to investigate the factors influencing farmers' perceptions to climate change and adaptation measures through adoption of climate-smart agriculture practices, complemented with key informant interviews and focused group discussions. The results indicated that most farmers (81.80%) perceived that the local climate is changing, with 71.9% reporting increased temperature and 53.15% reporting decreasing rainfall distribution. Therefore, farmers attempted to apply some adaptation practices, including soil and water conservation with biological measures, improved crop varieties, agroforestry, improved breeds, cut and carry system, controlled grazing, and residue incorporation. The empirical results revealed that farmers adaptation to climate change through adoptions of CSA practices was significantly influenced by education, family size, gender, landholding size, farming experience, access to climate information, training received, social membership, livestock ownership, farm income and extension services. The study found that farmers' perceptions of climate change and variability were significantly influenced by their age, level of education, farming experience, and access to climate information, hence, the need to focus on enhancing the accuracy of weather information, strengthening extension services, and considering a gender-sensitive adaptation approach toward improving farmers' knowledge and aspirations. Agricultural policies should support the efforts of farmers to increase the reliance on climate risk and alleviate farmers' difficulties in adopting climate-smart agriculture practices., Competing Interests: The authors declare no conflict of interest., (© 2022 The Author(s).)

East Africa is a global biodiversity hotspot and exhibits distinct longitudinal diversity gradients from west to east in freshwater fishes and forest mammals. The assembly of this exceptional biodiversity and the drivers behind diversity gradients remain poorly understood, with diversification often studied at local scales and less attention paid to biotic exchange between Afrotropical regions. Here, we reconstruct a river system that existed for several millennia along the now semiarid Kenya Rift Valley during the humid early Holocene and show how this river system influenced postglacial dispersal of fishes and mammals due to its dual role as a dispersal corridor and barrier. Using geomorphological, geochronological, isotopic, and fossil analyses and a synthesis of radiocarbon dates, we find that the overflow of Kenyan rift lakes between 12 and 8 ka before present formed a bidirectional river system consisting of a "Northern River" connected to the Nile Basin and a "Southern River," a closed basin. The drainage divide between these rivers represented the only viable terrestrial dispersal corridor across the rift. The degree and duration of past hydrological connectivity between adjacent river basins determined spatial diversity gradients for East African fishes. Our reconstruction explains the isolated distribution of Nilotic fish species in modern Kenyan rift lakes, Guineo-Congolian mammal species in forests east of the Kenya Rift, and recent incipient vertebrate speciation and local endemism in this region. Climate-driven rearrangements of drainage networks unrelated to tectonic activity contributed significantly to the assembly of species diversity and modern faunas in the East African biodiversity hotspot.

The contribution of oxic methane production to greenhouse gas emissions from lakes is globally relevant, yet uncertainties remain about the levels up to which methanogenesis can counterbalance methanotrophy by leading to CH 4 oversaturation in productive surface waters. Here, we explored the biogeochemical and microbial community variation patterns in a meromictic soda lake, in the East African Rift Valley (Kenya), showing an extraordinarily high concentration of methane in oxic waters (up to 156 µmol L -1 ). Vertical profiles of dissolved gases and their isotopic signature indicated a biogenic origin of CH 4 . A bloom of Oxyphotobacteria co-occurred with abundant hydrogenotrophic and acetoclastic methanogens, mostly found within suspended aggregates promoting the interactions between Bacteria, Cyanobacteria, and Archaea. Moreover, aggregate sedimentation appeared critical in connecting the lake compartments through biomass and organic matter transfer. Our findings provide insights into understanding how hydrogeochemical features of a meromictic soda lake, the origin of carbon sources, and the microbial community profiles, could promote methane oversaturation and production up to exceptionally high rates.

Groundwater is used extensively in the Central Kenya Rift for domestic and agricultural demands. In these active rift settings groundwater can exhibit high fluoride levels. In order to address water security and reduce human exposure to high fluoride in drinking water, knowledge of the source and geochemical processes of enrichment are required. A study was therefore carried out within the Naivasha catchment (Kenya) to understand the genesis, enrichment and seasonal variations of fluoride in the groundwater. Rocks, rain, surface and groundwater sources were sampled for hydrogeochemical and isotopic investigations, the data was statistically and geospatially analyzed. Water sources have variable fluoride concentrations between 0.02-75 mg/L. 73% exceed the health limit (1.5mg/L) in both dry and wet seasons. F(-) concentrations in rivers are lower (0.2-9.2mg/L) than groundwater (0.09 to 43.6 mg/L) while saline lake waters have the highest concentrations (0.27-75 mg/L). The higher values are confined to elevations below 2000 masl. Oxygen (δ(18)O) and hydrogen (δD) isotopic values range from -6.2 to +5.8‰ and -31.3 to +33.3‰, respectively, they are also highly variable in the rift floor where they attain maximum values. Fluoride base levels in the precursor vitreous volcanic rocks are higher (between 3750-6000 ppm) in minerals such as cordierite and muscovite while secondary minerals like illite and kaolinite have lower remnant fluoride (<1000 ppm). Thus, geochemical F(-) enrichment in regional groundwater is mainly due to a) rock alteration, i.e. through long residence times and natural discharge and/or enhanced leakages of deep seated geothermal water reservoirs, b) secondary concentration fortification of natural reservoirs through evaporation, through reduced recharge and/or enhanced abstraction and c) through additional enrichment of fluoride after volcanic emissions. The findings are useful to help improve water management in Naivasha as well as similar active rift setting environments., (Copyright © 2015 Elsevier B.V. All rights reserved.)