• Energy Research

Il existe actuellement un manque d'observations représentatives, systématiques et harmonisées des gaz à effet de serre (GES) couvrant la variété des biomes naturels et modifiés par l'homme qui se produisent en Afrique. Cela entrave l'évaluation à long terme des moteurs du changement climatique, en plus de leurs impacts et de leurs boucles de rétroaction à l'échelle continentale, mais limite également notre compréhension de la contribution du continent africain au cycle mondial du carbone (C). Compte tenu de la transformation actuelle et prévue des conditions socio-économiques en Afrique (c'est-à-dire la tendance croissante de l'urbanisation et de la croissance démographique) et des impacts négatifs du changement climatique, le développement d'une infrastructure de recherche (IR) sur les GES est nécessaire pour soutenir la conception de stratégies d'atténuation et d'adaptation appropriées nécessaires pour assurer la sécurité alimentaire, énergétique, nutritionnelle et économique de la population africaine. Ce document présente les premiers résultats du projet SEACRIFOG UE-Afrique, qui vise à concevoir une IR d'observation des GES pour l'Afrique. Les premières étapes de ce projet comprenaient l'identification et l'engagement des principales parties prenantes, la définition du cadre de suivi conceptuel et une évaluation des capacités infrastructurelles existantes. Les commentaires des secteurs des parties prenantes ont été obtenus lors de trois ateliers de consultation des parties prenantes tenus au Kenya, au Ghana et en Zambie. Les principales préoccupations identifiées étaient la qualité et l'accessibilité des données, le besoin de renforcement des capacités et de mise en réseau de la communauté scientifique, et l'adaptation au changement climatique, qui a été confirmée comme une priorité pour l'Afrique. Ces commentaires, en plus des contributions d'experts dans les domaines thématiques atmosphériques, terrestres et océaniques, ont facilité la sélection d'un ensemble de « variables essentielles » qui doivent être mesurées dans le futur IR environnemental. Un inventaire de 47 réseaux existants et prévus à travers le continent a permis d'évaluer les besoins et les lacunes actuels des IR en Afrique. Dans l'ensemble, le développement d'un IR panafricain harmonisé et standardisé servira à relever les principaux défis sociétaux et scientifiques du continent grâce à une synergie intersectorielle potentielle entre les réseaux existants et prévus aux échelles régionale, continentale et mondiale. Actualmente hay una falta de observaciones representativas, sistemáticas y armonizadas de gases de efecto invernadero (GEI) que cubran la variedad de biomas naturales y humanos alterados que se producen en África. Esto impide la evaluación a largo plazo de los impulsores del cambio climático, además de sus impactos y ciclos de retroalimentación a escala continental, pero también limita nuestra comprensión de la contribución del continente africano al ciclo global del carbono (C). Dada la transformación actual y proyectada de las condiciones socioeconómicas en África (es decir, la tendencia creciente de la urbanización y el crecimiento de la población) y los impactos adversos del cambio climático, se necesita el desarrollo de una infraestructura de investigación (IR) de GEI para apoyar el diseño de estrategias adecuadas de mitigación y adaptación necesarias para garantizar la seguridad alimentaria, energética, nutricional y económica de la población africana. Este documento presenta los resultados iniciales del proyecto SEACRIFOG UE-África, que tiene como objetivo diseñar un RI de observación de GEI para África. Las primeras etapas de este proyecto incluyeron la identificación y participación de las partes interesadas clave, la definición del marco conceptual de monitoreo y una evaluación de la capacidad de infraestructura existente. Los comentarios de los sectores interesados se obtuvieron a través de tres talleres de consulta a las partes interesadas celebrados en Kenia, Ghana y Zambia. Las principales preocupaciones identificadas fueron la calidad y accesibilidad de los datos, la necesidad de desarrollar capacidades y establecer redes entre la comunidad científica, y la adaptación al cambio climático, que se confirmó como una prioridad para África. Esta retroalimentación, además de los aportes de expertos en las áreas temáticas atmosférica, terrestre y oceánica, facilitó la selección de un conjunto de "variables esenciales" que deben medirse en la futura IR ambiental. Un inventario de 47 redes existentes y planificadas en todo el continente permitió evaluar las necesidades y brechas actuales de RI en África. En general, el desarrollo de una IR panafricana armonizada y estandarizada servirá para abordar los principales desafíos sociales y científicos del continente a través de una posible sinergia entre dominios entre las redes existentes y planificadas a escala regional, continental y global. There is currently a lack of representative, systematic and harmonised greenhouse gas (GHG) observations covering the variety of natural and human-altered biomes that occur in Africa. This impedes the long-term assessment of the drivers of climate change, in addition to their impacts and feedback loops at the continental scale, but also limits our understanding of the contribution of the African continent to the global carbon (C) cycle. Given the current and projected transformation of socio-economic conditions in Africa (i.e. the increasing trend of urbanisation and population growth) and the adverse impacts of climate change, the development of a GHG research infrastructure (RI) is needed to support the design of suitable mitigation and adaptation strategies required to assure food, fuel, nutrition and economic security for the African population. This paper presents the initial results of the EU-African SEACRIFOG project, which aims to design a GHG observation RI for Africa. The first stages of this project included the identification and engagement of key stakeholders, the definition of the conceptual monitoring framework and an assessment of existing infrastructural capacity. Feedback from stakeholder sectors was obtained through three Stakeholder Consultation Workshops held in Kenya, Ghana and Zambia. Main concerns identified were data quality and accessibility, the need for capacity building and networking among the scientific community, and adaptation to climate change, which was confirmed to be a priority for Africa. This feedback in addition to input from experts in the atmospheric, terrestrial and oceanic thematic areas, facilitated the selection of a set of 'essential variables' that need to be measured in the future environmental RI. An inventory of 47 existing and planned networks across the continent allowed for an assessment of the current RIs needs and gaps in Africa. Overall, the development of a harmonised and standardised pan-African RI will serve to address the continent's primary societal and scientific challenges through a potential cross-domain synergy among existing and planned networks at regional, continental and global scales. يوجد حاليًا نقص في الملاحظات التمثيلية والمنهجية والمنسقة لغازات الدفيئة (GHG) التي تغطي مجموعة متنوعة من المناطق الأحيائية الطبيعية والمعدلة بشريًا التي تحدث في إفريقيا. وهذا يعيق التقييم طويل الأجل لدوافع تغير المناخ، بالإضافة إلى آثارها وحلقات التغذية الراجعة على المستوى القاري، ولكنه يحد أيضًا من فهمنا لمساهمة القارة الأفريقية في دورة الكربون العالمية. بالنظر إلى التحول الحالي والمتوقع للظروف الاجتماعية والاقتصادية في أفريقيا (أي الاتجاه المتزايد للتحضر والنمو السكاني) والآثار السلبية لتغير المناخ، هناك حاجة إلى تطوير بنية تحتية لبحوث غازات الدفيئة (RI) لدعم تصميم استراتيجيات التخفيف والتكيف المناسبة المطلوبة لضمان الغذاء والوقود والتغذية والأمن الاقتصادي للسكان الأفارقة. تعرض هذه الورقة النتائج الأولية لمشروع SEACRIFOG المشترك بين الاتحاد الأوروبي وأفريقيا، والذي يهدف إلى تصميم مؤشر مرجعي لرصد غازات الدفيئة في أفريقيا. تضمنت المراحل الأولى من هذا المشروع تحديد أصحاب المصلحة الرئيسيين وإشراكهم، وتحديد إطار الرصد المفاهيمي وتقييم قدرات البنية التحتية الحالية. تم الحصول على تعليقات من قطاعات أصحاب المصلحة من خلال ثلاث ورش عمل تشاورية لأصحاب المصلحة عقدت في كينيا وغانا وزامبيا. وتمثلت الشواغل الرئيسية التي تم تحديدها في جودة البيانات وإمكانية الوصول إليها، والحاجة إلى بناء القدرات والتواصل بين الأوساط العلمية، والتكيف مع تغير المناخ، الذي تأكد أنه يمثل أولوية بالنسبة لأفريقيا. هذه التغذية الراجعة بالإضافة إلى مدخلات الخبراء في المجالات المواضيعية الجوية والبرية والمحيطية، سهلت اختيار مجموعة من "المتغيرات الأساسية" التي يجب قياسها في RI البيئي المستقبلي. أتاح جرد 47 شبكة قائمة ومخططة في جميع أنحاء القارة إجراء تقييم لاحتياجات منظمات الإغاثة الدولية الحالية والثغرات في أفريقيا. بشكل عام، سيعمل تطوير RI متناسق وموحد لعموم إفريقيا على معالجة التحديات المجتمعية والعلمية الأساسية للقارة من خلال التآزر المحتمل عبر المجالات بين الشبكات القائمة والمخطط لها على المستويات الإقليمية والقارية والعالمية.

AbstractIn maize fields, few studies have been conducted to identify the temporal trend of soil salinity and formulate optimal irrigation plans under climate change. Therefore, the main goals of this study were to predict changes in soil salinity over 2022–2050 and to formulate an optimal supplemental irrigation plan preventing soil salinity in a South African rainfed maize field. The study used the Global Climate Model (GCM) MPI-ESM1-2-LR to obtain future climate data for the study area from 2022 to 2050 and applied the HYDRUS-1D model to project the effects of these future climate data on soil salinity over the same period and to identify the best irrigation plan under climate change. Two key findings were revealed: first, the combined use of GCMs (i.e., MPI-ESM1-2-LR model) and soil-water models (i.e., HYDRUS-1D) was a powerful tool to identify soil salinity trends and formulate optimal irrigation plan under climate change. Second, in addition to rainfall amount, supplying a limited supplemental irrigation amount equal to 8% of the actual evapotranspiration of maize at the mid-season stage of maize growth can significantly reduce soil salinity (<1.7 dS m−1) and enhance soil moisture under climate change by 2050. These findings will be useful for preventing soil salinity in rainfed maize fields.

Abstract. Denitrification within riparian buffers may trade reduced nonpoint source pollution of surface waters for increased greenhouse gas emissions resulting from denitrification-produced nitrous oxide (N2O). However, little is known about the N2O emission within conservation buffers established for water quality improvement or of the importance of short-term N2O peak emission following rewetting dry soils and thawing frozen soils. Such estimates are important in reducing uncertainties in current Intergovernmental Panel on Climate Change (IPCC) methodologies estimating soil N2O emission which are based on N inputs. This study contrasts N2O emission from riparian buffer systems of three perennial vegetation types and an adjacent crop field, and compares measured N2O emission with estimates based on the IPCC methodology. We measured soil properties, N inputs, weather conditions and N2O fluxes from soils in forested riparian buffers, warm-season and cool-season grass filters, and a crop field located in the Bear Creek watershed in central Iowa, USA. Cumulative N2O emissions from soils in all riparian buffers (5.8 kg N2O-N ha−1 in 2006–2007) were significantly less than those from crop field soils (24.0 kg N2O-N ha−1 in 2006–2007), with no difference among the buffer vegetation types. While N2O peak emissions (up to 70-fold increase) following the rewetting of dry soils and thawing of frozen soils comprised 46–70% of the annual N2O emissions from soils in the crop field, soils in the riparian buffers were less sensitive to such events (3 to 10-fold increase). The ratio of N2O emission to N inputs within riparian buffers (0.02) was smaller than those of crop field (0.07). These results indicate that N2O emission from soils within the riparian buffers established for water quality improvement should not be considered a major source of N2O emission compared to crop field emission. The observed large difference between measured N2O emissions and those estimated using the IPCC's recommended methodology (i.e., 87% underestimation) in the crop field suggests that the IPCC methodology may underestimate N2O emission in the regions where soil rewetting and thawing are common, and that conditions predicted by future climate-change scenarios may increase N2O emissions.

AbstractEcological sanitation combined with thermophilic composting is a viable option to transform human excreta into a stabilized, pathogen‐free, and nutrient‐rich fertilizer. In combination with suitable bulking materials such as sawdust and straw, and additives such as biochar, this could also be a suitable waste management strategy for reducing greenhouse gas (GHG) emissions. In this study, we conducted a 143‐days thermophilic composting of human excreta or cattle manure together with teff straw, organic waste, and biochar to investigate the effect that biochar has on GHG (CO2, N2O, and CH4) and NH3 emissions. The composting was performed in wooden boxes (1.5 × 1.5 × 1.4 m3), GHG were measured by using a portable FTIR gas analyzer and NH3 was sampled as ammonium in an H2SO4 trap. We found that the addition of biochar significantly reduced CH4 emissions by 91% in the cattle manure compost, and N2O emissions by 56%−57% in both humanure and cattle manure composts. Overall, non‐CO2 GHG emissions were reduced by 51%−71%. In contrast, we did not observe a significant biochar effect on CO2 and NH3 emissions. Previous data already showed that it is possible to sanitize human fecal material when using this composting method. Our results suggest that thermophilic composting with biochar addition is a safe and cost‐effective waste management practice for producing a nutrient‐rich fertilizer from human excreta, while reducing GHG emissions at the same time.

AbstractWetlands contain a large proportion of carbon (C) in the biosphere and partly affect climate by regulating C cycles of terrestrial ecosystems. China contains Asia's largest wetlands, accounting for about 10% of the global wetland area. Although previous studies attempted to estimate C budget in China's wetlands, uncertainties remain. We conducted a synthesis to estimate C uptake and emission of wetland ecosystems in China using a dataset compiled from published literature. The dataset comprised 193 studies, including 370 sites representing coastal, river, lake and marsh wetlands across China. In addition, C stocks of different wetlands in China were estimated using unbiased data from the China Second Wetlands Survey. The results showed that China's wetlands sequestered 16.87 Pg C (315.76 Mg C/ha), accounting for about 3.8% of C stocks in global wetlands. Net ecosystem productivity, jointly determined by gross primary productivity and ecosystem respiration, exhibited annual C sequestration of 120.23 Tg C. China's wetlands had a total gaseous C loss of 173.20 Tg C per year from soils, including 154.26 Tg CO2‐C and 18.94 Tg CH4‐C emissions. Moreover, C stocks, uptakes and gaseous losses varied with wetland types, and were affected by geographic location and climatic factors (precipitation and temperature). Our results provide better estimation of the C budget in China's wetlands and improve understanding of their contribution to the global C cycle in the context of global climate change.

Abstract. This paper summarizes currently available data on greenhouse gas (GHG) emissions from African natural ecosystems and agricultural lands. The available data are used to synthesize current understanding of the drivers of change in GHG emissions, outline the knowledge gaps, and suggest future directions and strategies for GHG emission research. GHG emission data were collected from 75 studies conducted in 22 countries (n = 244) in sub-Saharan Africa (SSA). Carbon dioxide (CO2) emissions were by far the largest contributor to GHG emissions and global warming potential (GWP) in SSA natural terrestrial systems. CO2 emissions ranged from 3.3 to 57.0 Mg CO2 ha−1 yr−1, methane (CH4) emissions ranged from −4.8 to 3.5 kg ha−1 yr−1 (−0.16 to 0.12 Mg CO2 equivalent (eq.) ha−1 yr−1), and nitrous oxide (N2O) emissions ranged from −0.1 to 13.7 kg ha−1 yr−1 (−0.03 to 4.1 Mg CO2 eq. ha−1 yr−1). Soil physical and chemical properties, rewetting, vegetation type, forest management, and land-use changes were all found to be important factors affecting soil GHG emissions from natural terrestrial systems. In aquatic systems, CO2 was the largest contributor to total GHG emissions, ranging from 5.7 to 232.0 Mg CO2 ha−1 yr−1, followed by −26.3 to 2741.9 kg CH4 ha−1 yr−1 (−0.89 to 93.2 Mg CO2 eq. ha−1 yr−1) and 0.2 to 3.5 kg N2O ha−1 yr−1 (0.06 to 1.0 Mg CO2 eq. ha−1 yr−1). Rates of all GHG emissions from aquatic systems were affected by type, location, hydrological characteristics, and water quality. In croplands, soil GHG emissions were also dominated by CO2, ranging from 1.7 to 141.2 Mg CO2 ha−1 yr−1, with −1.3 to 66.7 kg CH4 ha−1 yr−1 (−0.04 to 2.3 Mg CO2 eq. ha−1 yr−1) and 0.05 to 112.0 kg N2O ha−1 yr−1 (0.015 to 33.4 Mg CO2 eq. ha−1 yr−1). N2O emission factors (EFs) ranged from 0.01 to 4.1 %. Incorporation of crop residues or manure with inorganic fertilizers invariably resulted in significant changes in GHG emissions, but results were inconsistent as the magnitude and direction of changes were differed by gas. Soil GHG emissions from vegetable gardens ranged from 73.3 to 132.0 Mg CO2 ha−1 yr−1 and 53.4 to 177.6 kg N2O ha−1 yr−1 (15.9 to 52.9 Mg CO2 eq. ha−1 yr−1) and N2O EFs ranged from 3 to 4 %. Soil CO2 and N2O emissions from agroforestry were 38.6 Mg CO2 ha−1 yr−1 and 0.2 to 26.7 kg N2O ha−1 yr−1 (0.06 to 8.0 Mg CO2 eq. ha−1 yr−1), respectively. Improving fallow with nitrogen (N)-fixing trees led to increased CO2 and N2O emissions compared to conventional croplands. The type and quality of plant residue in the fallow is an important control on how CO2 and N2O emissions are affected. Throughout agricultural lands, N2O emissions slowly increased with N inputs below 150 kg N ha−1 yr−1 and increased exponentially with N application rates up to 300 kg N ha−1 yr−1. The lowest yield-scaled N2O emissions were reported with N application rates ranging between 100 and 150 kg N ha−1. Overall, total CO2 eq. emissions from SSA natural ecosystems and agricultural lands were 56.9 ± 12.7 × 109 Mg CO2 eq. yr−1 with natural ecosystems and agricultural lands contributing 76.3 and 23.7 %, respectively. Additional GHG emission measurements are urgently required to reduce uncertainty on annual GHG emissions from the different land uses and identify major control factors and mitigation options for low-emission development. A common strategy for addressing this data gap may include identifying priorities for data acquisition, utilizing appropriate technologies, and involving international networks and collaboration.

Composting organic waste and human excreta could significantly reduce the amount of waste dumped and increase soil fertility and agricultural yields. However, studies focusing on the replacement of mineral fertilizer with compost from these resources are rare. The presented study quantifies the potential of human excreta and other organic waste for compost production. During wet and dry seasons, the generation and composition of household solid waste (HSW) was measured from three wealth categories: poor, medium, and rich, as well as the organic waste generated from 20 commercial facilities. Furthermore, the amount of human excreta, when converting unimproved into ecological sanitation facilities, was assessed. The HSW generation was significantly higher in the wet (0.77 ± 0.07 kg fresh weight (FW) cap−1 day−1) compared to the dry season (0.54 ± 0.04 kg FW cap−1 day−1). Organic waste was the main component of HSW in the dry and wet seasons, accounting for 84% and 76% of the total HSW, respectively. Annually, about 6824 Mg of organic dry matter could be collected from households, 212 Mg from commercial units, and 12,472 Mg from ecological sanitation. With these resources, 11,732 Mg of compost could be produced annually and used for fertilizing 470 ha of farmland, completely replacing mineral fertilizer.