Structural controls on fluid pathways in an active rift system : a case study of the Aluto volcanic complex

Hutchison was funded by NERC studentship NE/J5000045/1.In volcanically and seismically active rift systems, preexisting faults may control the rise and eruption of magma, and direct the flow of hydrothermal fluids and gas in the subsurface. Using high-resolution airborne imagery, field observations, and CO2 degassing data on Aluto, a typical young silicic volcano in the Main Ethiopian Rift, we explore how preexisting tectonic and volcanic structures control fluid pathways and spatial patterns of volcanism, hydrothermal alteration and degassing. A new light detection and ranging (lidar) digital elevation model and evidence from deep geothermal wells show that the Aluto volcanic complex is dissected by rift-related extensional faults with throws of 50-100 m. Mapping of volcanic vent distributions reveals a structural control by either rift-aligned faults or an elliptical caldera ring fracture. Soil-gas CO2 degassing surveys show elevated fluxes (>>100 g m-2 d-1) along major faults and volcanic structures, but significant variations in CO2 flux along the fault zones reflect differences in near-surface permeability caused by changes in topography and surface lithology. The CO2 emission from an active geothermal area adjacent to the major fault scarp of Aluto amounted to similar to 60 t d-1; we estimate the total CO2 emission from Aluto to be 250-500 t d-1. Preexisting volcanic and tectonic structures have played a key role in the development of the Aluto volcanic complex and continue to facilitate the expulsion of gases and geothermal fluids. This case study emphasizes the importance of structural mapping on active rift volcanoes to understand the geothermal field as well as potential volcanic hazards.Publisher PDFPeer reviewe

The usefulness of school-based syndromic surveillance for detecting malaria epidemics: experiences from a pilot project in Ethiopia.

BACKGROUND: Syndromic surveillance is a supplementary approach to routine surveillance, using pre-diagnostic and non-clinical surrogate data to identify possible infectious disease outbreaks. To date, syndromic surveillance has primarily been used in high-income countries for diseases such as influenza--however, the approach may also be relevant to resource-poor settings. This study investigated the potential for monitoring school absenteeism and febrile illness, as part of a school-based surveillance system to identify localised malaria epidemics in Ethiopia. METHODS: Repeated cross-sectional school- and community-based surveys were conducted in six epidemic-prone districts in southern Ethiopia during the 2012 minor malaria transmission season to characterise prospective surrogate and syndromic indicators of malaria burden. Changes in these indicators over the transmission season were compared to standard indicators of malaria (clinical and confirmed cases) at proximal health facilities. Subsequently, two pilot surveillance systems were implemented, each at ten sites throughout the peak transmission season. Indicators piloted were school attendance recorded by teachers, or child-reported recent absenteeism from school and reported febrile illness. RESULTS: Lack of seasonal increase in malaria burden limited the ability to evaluate sensitivity of the piloted syndromic surveillance systems compared to existing surveillance at health facilities. Weekly absenteeism was easily calculated by school staff using existing attendance registers, while syndromic indicators were more challenging to collect weekly from schoolchildren. In this setting, enrolment of school-aged children was found to be low, at 54%. Non-enrolment was associated with low household wealth, lack of parental education, household size, and distance from school. CONCLUSIONS: School absenteeism is a plausible simple indicator of unusual health events within a community, such as malaria epidemics, but the sensitivity of an absenteeism-based surveillance system to detect epidemics could not be rigorously evaluated in this study. Further piloting during a demonstrated increase in malaria transmission within a community is recommended

Improvement of Grassland Through Community Participation in the Middle AwashValley of Ethiopia

The natural resources of the grassland in the middle Awash valley of Ethiopia are subjected to competing claims: development to generate revenue for the state, conservation of wildlife and wilderness areas, as well as use for local production. The combination of climatic conditions causing drought and the over use of the natural resource can be cited as the primary cause of grassland deterioration in the area. Since the problems of the grasslands are complex and multi-dimensional, they are not amenable to quick and easy fixes. Hence, if sustainable progress is to be achieved, the responsibility for change must be in the hands of the communities and household themselves. Pastoral communities, in collaboration with CARE-Ethiopia, local government and other partner NGOs embarked on grassland improvement activities that were based on traditional activities. The objective of this study was to assess the condition of the traditionally-improved grazing lands

Factors that transformed maize productivity in Ethiopia

Published online: 26 July 2015Maize became increasingly important in the food security of Ethiopia following the major drought and famine that occurred in 1984. More than 9 million smallholder house- holds, more than for any other crop in the country, grow maize in Ethiopia at present. Ethiopia has doubled its maize produc- tivity and production in less than two decades. The yield, currently estimated at >3 metric tons/ha, is the second highest in Sub-Saharan Africa, after South Africa; yield gains for Ethiopia grew at an annual rate of 68 kg/ha between 1990 and 2013, only second to South Africa and greater than Mexico, China, or India. The maize area covered by improved varieties in Ethiopia grew from 14 % in 2004 to 40 % in 2013, and the application rate of mineral fertilizers from 16 to 34 kg/ ha during the same period. Ethiopia ’ s extension worker to farmer ratio is 1:476, compared to 1:1000 for Kenya, 1:1603 for Malawi and 1:2500 for Tanzania. Increased use of im- proved maize varieties and mineral fertilizers, coupled with increased extension services and the absence of devastating droughts are the key factors promoting the accelerated growth in maize productivity in Ethiopia. Ethiopia took a homegrown solutions approach to the research and development of its maize and other commodities. The lesson from Ethiopia ’ s experience with maize is that sustained investment in agricul- tural research and development and policy support by the national government are crucial for continued growth of agricultur

Mixing and crystal scavenging in the Main Ethiopian Rift revealed by trace element systematics in feldspars and glasses

For many magmatic systems, crystal compositions preserve a complex and protracted history which may be largely decoupled from their carrier melts. The crystal cargo may hold clues to the physical distribution of melt and crystals in a magma reservoir and how magmas are assembled prior to eruptions. Here we present a geochemical study of a suite of samples from three peralkaline volcanoes in the Main Ethiopian Rift. Whilst whole-rock data shows strong fractional crystallisation signatures, the trace element systematics of feldspars, and their relationship to their host glasses, reveals complexity. Alkali feldspars, particularly those erupted during caldera forming episodes, have variable Ba concentrations, extending to high values that are not in equilibrium with the carrier liquids. Some of the feldspars are antecrysts, which we suggest are scavenged from a crystal-rich mush. The antecrysts crystallised from a Ba-enriched (more primitive) melt, before later entrainment into a Ba-depleted residual liquid. Crystal-melt segregation can occur on fast timescales in these magma reservoirs, owing to the low viscosity nature of peralkaline liquids. The separation of enough residual melt to feed a crystal-poor post caldera rhyolitic eruption may take as little as months to tens of years (much shorter than typical repose periods of 300-400 years). Our observations are consistent with these magmatic systems spending significant portions of their life cycle dominated by crystalline mushes containing ephemeral, small (< 1 km3) segregations of melt. This interpretation helps to reconcile observations of high crustal electrical resistivity beneath Aluto, despite seismicity and ground deformation consistent with a magma body

Understanding the effects of dichotomization of continuous outcomes on geostatistical inference

Diagnosis is often based on the exceedance or not of continuous health indicators of a predefined cut-off value, so as to classify patients into positives and negatives for the disease under investigation. In this paper, we investigate the effects of dichotomization of spatially-referenced continuous outcome variables on geostatistical inference. Although this issue has been extensively studied in other fields, dichotomization is still a common practice in epidemiological studies. Furthermore, the effects of this practice in the context of prevalence mapping have not been fully understood. Here, we demonstrate how spatial correlation affects the loss of information due to dichotomization, how linear geostatistical models can be used to map disease prevalence and thus avoid dichotomization, and finally, how dichotomization affects our predictive inference on prevalence. To pursue these objectives, we develop a metric, based on the composite likelihood, which can be used to quantify the potential loss of information after dichotomization without requiring the fitting of Binomial geostatistical models. Through a simulation study and two applications on disease mapping in Africa, we show that, as thresholds used for dichotomization move further away from the mean of the underlying process, the performance of binomial geostatistical models deteriorates substantially. We also find that dichotomization can lead to the loss of fine scale features of disease prevalence and increased uncertainty in the parameter estimates, especially in the presence of a large noise to signal ratio. These findings strongly support the conclusions from previous studies that dichotomization should be always avoided whenever feasible

The impact of water hyacinth biochar on maize growth and soil properties: The influence of pyrolysis temperature

Introduction: Options for managing water hyacinths (WHs) include converting the biomass into biochar for soil amendment. However, less has been known about the impact of WH‐based biochar developed in varying pyrolysis temperatures on plant growth and soil qualities. Materials and Methods: A pot experiment was undertaken in a factorial combination of WH biochars (WHBs) developed at three temperatures (350°C, 550°C and 750°C) and two application rates (5 and 20 t ha−1), plus a control without biochar. Maize was grown as a test crop for 2 months under natural conditions. Results: Our study showed that applying WHB developed between 350°C and 750°C at 20 t ha−1 increased maize shoot and root dry biomass by 47.7% to 17.6% and 78.4% to 54.1%, respectively. Nevertheless, raising the biochar pyrolysis temperature decreased maize growth, whereas increasing the application rate displayed a positive effect. The application of WHB generated at 350°C and 550°C at 20 t ha−1 resulted in significant improvements in soil total nitrogen (17.9% to 25%), cation exchange capacity (27.3% to 20.2%), and ammonium‐nitrogen (60.7% to 59.6%), respectively, over the control. Additionally, applying WHB produced from 350°C to 750°C at 20 t ha−1 enhanced soil carbon by 38.5%–56.3%, compared to the control. Conversely, applying biochar produced at 750°C resulted in higher soil pH (6.3 ± 0.103), electrical conductivity (0.23 ± 0.01 dSm−1) and available phosphorus (21.8 ± 2.53 mg kg−1). Conclusion: WHBs developed at temperatures of 350°C and 550°C with an application rate of 20 t ha−1 were found to be optimal for growing maize and improving soil characteristics. Our study concludes that pyrolysis temperature significantly governs the effectiveness of biochar produced from a specific biomass source

Sustainable weed management and soil enrichment with water hyacinth composting and mineral fertilizer integration

Composting water hyacinth (Eichhornia crassipes) presents a promising approach for managing the weed and the aquatic environment while increasing agricultural production and soil fertility. However, limited research reported on the impact of water hyacinth compost on soil properties and crop production under field conditions. This study aimed to evaluate impact of water hyacinth compost and its combined application with mineral fertilizer on soil properties and crop production. Before field experiments, the compost's phytotoxicity was assessed through bioassays, confirming it was safe for agricultural use with a seed germination index exceeding 80 %. Field trials were conducted using a factorial design with four application rates of water hyacinth compost (0, 8, 16, and 24 t ha-1) and three rates of the recommended mineral fertilizer for teff production (0/0, 40/23, and 80/46 kg N/P2O5 ha-1). The results indicated that compared to the control group, applying water hyacinth compost increased soil pH by up to 0.69 units and reduced bulk density by 10.3 %. Soil organic carbon, total nitrogen, available phosphorus, cation exchange capacity, and exchangeable potassium increased by 24.3 %, 28.6 %, 80.2 %, 26.2 %, and 112.7 %, respectively. Furthermore, exchangeable acidity and aluminum were reduced by 72.5 % and 78.6 %, respectively. The maximum grain yield (1826 kg ha-1) and total biomass (8020 kg ha-1) of teff were achieved by applying 24 t ha-1 of water hyacinth compost coupled with the full rate of mineral fertilizer. However, compared to adding only full fertilizer, the grain yield that resulted from applying water hyacinth compost at 16 and 24 t ha-1 along with half of the suggested mineral fertilizer was superior. This implies that water hyacinth compost could substitute 50 % of the mineral fertilizer required. In conclusion, composting water hyacinth offers a dual benefit of weed management and soil enrichment. This could be a sustainable strategy to mitigate weed proliferation while improving soil quality and crop production

Magma storage conditions beneath a peralkaline caldera in the Main Ethiopian Rift

The numerous volcanic centres in the Main Ethiopian Rift (MER) present significant but poorly understood hazards to local populations. The MER is also an important site to gain insights into tectonic processes as it captures the transition from continental rifting (to the south) to incipient seafloor spreading (to the north). Peralkaline magmas account for around 90% of the volcanic products found in the MER. Determining the conditions under which these magmas evolve is critical to understanding rift-related volcanism and its associated hazards. Corbetti Caldera has an extensive record of large-scale, predominantly aphyric, peralkaline rhyolite eruptions. However, little is known about the mafic magmas from which these highly differentiated melts have evolved. Here we present data from the only basaltic deposit found within the caldera, coupled with whole rock, glass and mineral analysis of the peralkaline products, to investigate magma storage conditions at Corbetti. We demonstrate that magma mixing played a role in the evolution of the basaltic magmas and use RhyoliteMELTS modelling to show Corbetti's peralkaline magmas likely evolved at pressures between 100 and 250 MPa, from a magma with an initial water content of 0.5–1 wt%, at or below the QFM buffer. Mineral hygrometry on the sparse crystal populations corroborates the RhyoliteMELTS modelling, suggesting that the basaltic magma had 0.1–1.2 ± 0.32 wt% H2O, and the peralkaline magmas an average of ~5.5 ± 1.25 wt% H2O. These results also match melt inclusion data for Corbetti and other peralkaline systems. We also provide new 40Ar/39Ar sanidine ages for two eruptions, a pre-caldera rhyolitic lava flow (206.7 ± 0.9 ka) and a post-caldera peralkaline ignimbrite (160 ± 0.8 ka). These results add to our understanding of the history of Corbetti and the storage conditions of peralkaline magmas within a continental rift setting and highlight the hydrous nature of Corbetti's magmas and the role that H2O plays during explosive eruptions