• Energy Research

AbstractNuclear energy is a potential solution to electricity demand but also entails risks. Policy debates on nuclear accidents have focused primarily on negative impacts on humans. Although such impacts are important, we argue that policy debates must also consider the consequences for biodiversity and ecosystem services. We reviewed 521 studies conducted after the Chernobyl accident, the most severe nuclear accident in history. Elevated radiation levels have been recorded among a diversity of species, even up to thousands of kilometers away from the meltdown site, and after more than two decades following the accident. Close to the reactor, physiological and morphological changes have occurred. Negative effects on ecosystem services have been observed, including the contamination of water, soils, and wild food supplies. Informed policy decisions on nuclear energy require a greater understanding of the consequences of accidents, including effects on biodiversity and ecosystem services. Based on our review, we recommend to (1) fully incorporate risks for biodiversity and ecosystem services into policy debates; (2) develop a coherent information chain regarding such risks; (3) use proactive planning strategies to be prepared for potential accidents; and (4) develop a coherent research agenda on the consequences of nuclear accidents for biodiversity and ecosystem services.

La ganadería está poco representada en los presupuestos de N para el continente africano, aunque algunos estudios han examinado los flujos de N relacionados con la ganadería a diferentes niveles. La ganadería desempeña un papel importante en el ciclo del N y, por lo tanto, en los presupuestos del N, incluidos los flujos relacionados con el ganado. Este estudio revisa la literatura sobre los presupuestos N para África para identificar los factores que contribuyen a las incertidumbres. Las densidades de ganado suelen modelarse debido a la falta de datos espaciales observables. A pesar de que la disponibilidad y calidad de los alimentos varía según las estaciones, la mayoría de los estudios utilizan tasas constantes de excreción de ganado, y generalmente se supone que los excrementos se distribuyen uniformemente en la tierra. Las principales incertidumbres se originan en la fracción de estiércol gestionado y los factores de emisión que pueden no reflejar la situación de África. Los presupuestos N utilizan supuestos aproximados sobre la producción, disponibilidad y uso de residuos de cultivos como alimento para el ganado. No hay flujos entre las tierras de cultivo: el ganado y los pastizales reflejan la falta de datos. Se necesitan esfuerzos conjuntos para la recopilación de datos espaciales de datos ganaderos, el crowdsourcing parece ser una opción prometedora. El enfoque de la evaluación de los presupuestos N debe ir más allá de las tierras de cultivo para incluir el ganado y los flujos de cultivos y ganado. Proponemos una definición de sistemas anidados de sistemas ganaderos para vincular el nivel local, regional y continental y para aumentar la utilidad de las mediciones puntuales de las pérdidas de N. Los científicos que trabajan en todos los niveles deben generar datos para calibrar los modelos basados en procesos. Las mediciones en el campo no solo deben concentrarse en las emisiones de gases de efecto invernadero, sino que también deben incluir mediciones de la producción agrícola y ganadera, cambios en las existencias de suelo y otras vías de pérdida de N, como la lixiviación, la escorrentía y la volatilización, para evaluar las prácticas de gestión y las compensaciones. En comparación con la investigación realizada en otros continentes sobre los flujos de N en los sistemas ganaderos, hay pocos datos para África y, por lo tanto, se necesitará un esfuerzo concertado para generar datos suficientes para la modelización. L'élevage est peu représenté dans les budgets de l'azote pour le continent africain bien que certaines études aient examiné les flux d'azote liés à l'élevage à différents niveaux. L'élevage joue un rôle important dans le cycle de l'azote et donc dans les budgets de l'azote, y compris les flux liés à l'élevage. Cette étude passe en revue la littérature sur les budgets d'azote pour l'Afrique afin d'identifier les facteurs contribuant aux incertitudes. Les densités de bétail sont généralement modélisées en raison du manque de données spatiales d'observation. Même si la disponibilité et la qualité des aliments varient selon les saisons, la plupart des études utilisent des taux d'excrétion constants du bétail, et les excréments sont généralement supposés être uniformément distribués sur la terre. Les principales incertitudes proviennent de la fraction de fumier gérée et des facteurs d'émission qui peuvent ne pas refléter la situation de l'Afrique. Les budgets de l'azote utilisent des hypothèses grossières sur la production, la disponibilité et l'utilisation des résidus de culture comme aliments pour le bétail. Aucun flux entre les terres cultivées, l'élevage et les parcours ne reflète le manque de données. Des efforts conjoints sont nécessaires pour la collecte de données spatiales sur le bétail, le crowdsourcing semble être une option prometteuse. L'objectif de l'évaluation des budgets d'azote doit aller au-delà des terres cultivées pour inclure les flux de bétail et de cultures-élevage. Nous proposons une définition des systèmes d'élevage imbriqués pour relier les niveaux local, régional et continental et augmenter l'utilité des mesures ponctuelles des pertes d'azote. Les scientifiques travaillant à tous les niveaux devraient générer des données pour calibrer les modèles basés sur les processus. Les mesures sur le terrain ne doivent pas seulement se concentrer sur les émissions de gaz à effet de serre, mais doivent inclure des mesures de la production végétale et animale, des changements dans les stocks de sol et d'autres voies de perte d'azote telles que le lessivage, le ruissellement et la volatilisation pour évaluer les pratiques de gestion et les compromis. Par rapport aux recherches effectuées dans d'autres continents sur les flux d'azote dans les systèmes d'élevage, il existe peu de données pour l'Afrique, et un effort concerté sera donc nécessaire pour générer suffisamment de données pour la modélisation. Livestock is poorly represented in N budgets for the African continent although some studies have examined livestock-related N flows at different levels. Livestock plays an important role in N cycling and therefore on N budgets including livestock-related flows. This study reviews the literature on N budgets for Africa to identify factors contributing to uncertainties. Livestock densities are usually modelled because of the lack of observational spatial data. Even though feed availability and quality varies across seasons, most studies use constant livestock excretion rates, and excreta are usually assumed to be uniformly distributed onto the land. Major uncertainties originate in the fraction of manure managed, and emission factors which may not reflect the situation of Africa. N budgets use coarse assumptions on production, availability, and use of crop residues as livestock feed. No flows between croplands–livestock and rangelands reflect the lack of data. Joint efforts are needed for spatial data collection of livestock data, crowdsourcing appears to be a promising option. The focus of the assessment of N budgets must go beyond croplands to include livestock and crop–livestock flows. We propose a nested systems definition of livestock systems to link local, regional level, and continental level and to increase the usefulness of point measurements of N losses. Scientists working at all levels should generate data to calibrate process-based models. Measurements in the field should not only concentrate on greenhouse gas emissions, but need to include crop and livestock production measurements, soil stock changes and other N loss pathways such as leaching, run-off and volatilization to assess management practices and trade-offs. Compared to the research done in other continents on N flows in livestock systems, there are few data for Africa, and therefore concerted effort will be needed to generate sufficient data for modelling. الثروة الحيوانية ممثلة تمثيلاً ضعيفاً في ميزانيات N للقارة الأفريقية على الرغم من أن بعض الدراسات قد فحصت تدفقات N المتعلقة بالثروة الحيوانية على مستويات مختلفة. تلعب الثروة الحيوانية دورًا مهمًا في ركوب الدراجات وبالتالي في ميزانيات N بما في ذلك التدفقات المتعلقة بالثروة الحيوانية. تستعرض هذه الدراسة الأدبيات المتعلقة بميزانيات N لأفريقيا لتحديد العوامل التي تسهم في عدم اليقين. عادة ما يتم نمذجة كثافات الثروة الحيوانية بسبب نقص البيانات المكانية الرصدية. على الرغم من اختلاف توافر الأعلاف وجودتها عبر المواسم، إلا أن معظم الدراسات تستخدم معدلات إفراز ثابتة للماشية، وعادة ما يُفترض أن يتم توزيع الفضلات بشكل موحد على الأرض. تنشأ الشكوك الرئيسية في جزء السماد المدار، وعوامل الانبعاثات التي قد لا تعكس الوضع في أفريقيا. تستخدم الميزانيات افتراضات خشنة بشأن إنتاج وتوافر واستخدام مخلفات المحاصيل كعلف للماشية. لا توجد تدفقات بين الأراضي الزراعية والثروة الحيوانية والمراعي تعكس نقص البيانات. هناك حاجة إلى جهود مشتركة لجمع البيانات المكانية لبيانات الثروة الحيوانية، ويبدو أن التعهيد الجماعي خيار واعد. يجب أن يتجاوز تركيز تقييم ميزانيات N الأراضي الزراعية ليشمل تدفقات الثروة الحيوانية والمحاصيل والماشية. نقترح تعريفًا للأنظمة المتداخلة لأنظمة الثروة الحيوانية لربط المستوى المحلي والإقليمي والقاري وزيادة فائدة قياسات النقاط لخسائر N. يجب على العلماء الذين يعملون على جميع المستويات توليد بيانات لمعايرة النماذج القائمة على العمليات. يجب ألا تركز القياسات في هذا المجال على انبعاثات غازات الدفيئة فحسب، بل يجب أن تشمل قياسات إنتاج المحاصيل والثروة الحيوانية وتغيرات مخزون التربة ومسارات فقدان النيتروجين الأخرى مثل الرشح والجريان السطحي والتطاير لتقييم ممارسات الإدارة والمفاضلات. مقارنة بالبحوث التي أجريت في قارات أخرى حول تدفقات N في أنظمة الثروة الحيوانية، هناك القليل من البيانات لأفريقيا، وبالتالي ستكون هناك حاجة إلى بذل جهود متضافرة لتوليد بيانات كافية للنمذجة.

AbstractQuantifying and understanding the small‐scale variability of nitrous oxide (N2O) and carbon dioxide (CO2) emission are essential for reporting accurate ecosystem greenhouse gas budgets. The objective of this study was to evaluate the spatial pattern of soil CO2 and N2O emissions and their relation to topography in a tropical montane forest. We measured fluxes of N2O and CO2 from 810 sampling locations across valley bottom, midslope, and ridgetop positions under controlled laboratory conditions. We further calculated the minimum number of samples necessary to provide best estimates of soil N2O and CO2 fluxes at the plot level. Topography exhibited a major influence on N2O emissions, with soils at midslope position emitting significantly less than at ridgetops and valley bottoms, but no consistent effect of topography on soil CO2 emissions was found. The high spatial variation of N2O and CO2 fluxes was further increased by changes in vegetation and soil properties resulting from human disturbance associated with charcoal production. Soil N2O and CO2 fluxes showed no spatial pattern at the plot level, with “hot spots” strongly contributing to the total emissions (10% of the soil cores represented 73 and 50% of the total N2O and CO2 emissions, respectively). Thus, a large number of samples are needed to obtain robust estimates of N2O and CO2 fluxes. Our results highlight the complex biogeochemical cycling in tropical montane forests, and the need to carefully address it in research experiments to robustly estimate soil CO2 and N2O fluxes at the ecosystem scale.

Increasing demand for food and the shortage of arable land call for sustainable intensification of farming, especially in Sub-Saharan Africa where food insecurity is still a major concern. Kenya needs to intensify its dairy production to meet the increasing demand for milk. At the same time, the country has set national climate mitigation targets and has to implement land use practices that reduce greenhouse gas (GHG) emissions from both agriculture and forests. This study analysed for the first time the drivers of forest disturbance and their relationship with dairy intensification across the largest montane forest of Kenya. To achieve this, a forest disturbance detection approach was applied by using Landsat time series and empirical data from forest disturbance surveys. Farm indicators and farm types derived from a household survey were used to test the effects of dairy intensification on forest disturbance for different farm neighbourhood sizes (r = 2–5 km). About 18% of the forest area was disturbed over the period 2010–2016. Livestock grazing and firewood extraction were the dominant drivers of forest disturbance at 75% of the forest disturbance spots sampled. Higher on-farm cattle stocking rates and firewood collection were associated with 1–10% increased risk of forest disturbance across farm neighbourhood sizes. In contrast, higher milk yields, increased supplementation with concentrated feeds and more farm area allocated to fodder production were associated with 1–7 % reduced risk of forest disturbance across farm neighbourhood sizes. More intensified farms had a significantly lower impact on forest disturbance than small and resource-poor farms, and large and inefficient farms. Our results show that intensification of smallholder dairy farming leads to both farm efficiency gains and reduced forest disturbance. These results can inform agriculture and forest mitigation policies which target options to reduce GHG emission intensities and the risk of carbon leakage.

Plant oil is a key commodity in the global economy, particularly for food and bioenergy markets. However, current production practices often impair smallholder livelihoods, cause land use changes, and compete for food production. The neotropical palm Acrocomia aculeata is currently being promoted as a novel sustainable biomass feedstock, particularly for bioenergy, but only little is known about the palm's ecological requirements. Based on a comprehensive literature and database search for recorded occurrences of A. aculeata in Latin America, we computed an ecological niche modeling to determine the palm's potential distribution area based on climatic and soil variables. We subsequently considered current land cover and predicted future climate change scenarios to discuss the cultivation potential of A. aculeata within its possible distribution area. The results revealed a large potential to cultivate A. aculeata in Latin America under current abiotic environmental conditions. The two core distribution regions identified were (1) Central America including the Caribbean, northern Colombia and Venezuela, and (2) southern Brazil and eastern Paraguay. A considerable proportion of the medium to highly suitable growing areas were found to be currently used for agricultural production or covered by land types with high conservation and carbon sequestration value. Applying the model under the IPCC's A2A 'business as usual' emission scenario suggested that by 2080 the vast majority of suitable growing areas severely decline in extent or disappear entirely. Our ecological niche modeling thus shows that despite the palm's high cultivation potential, a sustainable deployment of A. aculeata requires a precautious, evidence-based approach.

AbstractSub‐Saharan Africa (SSA) could face food shortages in the future because of its growing population. Agricultural expansion causes forest degradation in SSA through livestock grazing, reducing forest carbon (C) sinks and increasing greenhouse gas (GHG) emissions. Therefore, intensification should produce more food while reducing pressure on forests. This study assessed the potential for the dairy sector in Kenya to contribute to low‐emissions development by exploring three feeding scenarios. The analyses used empirical spatially explicit data, and a simulation model to quantify milk production, agricultural emissions and forest C loss due to grazing. The scenarios explored improvements in forage quality (Fo), feed conservation (Fe) and concentrate supplementation (Co): FoCo fed high‐quality Napier grass (Pennisetum purpureum), FeCo supplemented maize silage and FoFeCo a combination of Napier, silage and concentrates. Land shortages and forest C loss due to grazing were quantified with land requirements and feed availability around forests. All scenarios increased milk yields by 44%–51%, FoCo reduced GHG emission intensity from 2.4 ± 0.1 to 1.6 ± 0.1 kg CO2eq per kg milk, FeCo reduced it to 2.2 ± 0.1, whereas FoFeCo increased it to 2.7 ± 0.2 kg CO2eq per kg milk because of land use change emissions. Closing the yield gap of maize by increasing N fertilizer use reduced emission intensities by 17% due to reduced emissions from conversion of grazing land. FoCo was the only scenario that mitigated agricultural and forest emissions by reducing emission intensity by 33% and overall emissions by 2.5% showing that intensification of dairy in a low‐income country can increase milk yields without increasing emissions. There are, however, risks of C leakage if agricultural and forest policies are not aligned leading to loss of forest to produce concentrates. This approach will aid the assessment of the climate‐smartness of livestock production practices at the national level in East Africa.