NitroAfrica

Nitrogen, N, represents 78% of the air we breathe, under the stable and inert form of N2, and once N2 is converted into reactive forms (Nr), it becomes a key nutrient that strongly influences ecosystem functioning and food production. The quantification of N budgets (N inputs and outputs) between the surface and the atmosphere is a prerequisite to understand the N biogeochemical cycle. In Africa, the increase in demography and the associated increased fertilizer inputs (to supply growing food and energy demands) will lead to increased emissions from amended soils, which will increase atmospheric N deposition and induce feedbacks to the ecosystems and the atmosphere. In Sub Saharan Africa, Low N contents in soils make natural ecosystems very vulnerable to the potential increase of N deposition induced by large scale anthropogenic activity development. Indeed, N in excess may lead to changes in biodiversity. But West African research institutes lack resources and ecosystems have not been as well monitored as in temperate regions. In this context, the overall objective of NitroAfrica is to study –coupling field experiments and different modelling approaches– the relationships and retroactions between atmospheric N deposition, N cycling in the soil-vegetation system, emissions of reactive N forms by the surface to the atmosphere, atmospheric chemistry and regional climate. NitroAfrica will focus on wet N deposition, because in Africa it is expected that N deposition on ecosystems, particularly in wet form, will increase by 50% by 2100. We will test two main hypotheses: (1) an increase in wet N deposition, as already observed in some regions of SSA and predicted in the future for many regions of SSA will significantly affect the ecosystem functioning (including agro-ecosystems), in terms of N processes in the soil (nitrification, denitrification, mineralization), and subsequent N compound emissions; and (2) these changes in emissions of N chemical compounds to the atmosphere will significantly impact regional atmospheric chemistry and regional climate over West Africa, ultimately influencing further N. The project is highly original because there is for now no such study for Africa addressing these feedbacks in a comprehensive way, linking N deposition, ecosystem processes, surface atmosphere N compound exchanges, atmospheric chemistry and climate, allowing to link alterations of local ecosystem processes to modifications of atmospheric chemistry at the regional scale. A French-Senegalese-Ivorian multidisciplinary consortium will bring expertise on atmospheric physical chemistry, microbiology, biogeochemistry and ecology in the soil-plant-atmosphere continuum. The project is based on a close interconnection between experimental and modeling tasks, at the local and regional scales. Experiments will take place in 3 representative West African biogeographic zones (savanna and cropland sites located in Sudanian, Guinean and Sahelian zones). Local scale modelling will be performed to capture relevant soil-vegetation N-C processes leading to emissions, and surface atmosphere nitrogen fluxes will be upscaled to study the impacts at the regional climatic scale. The impacts of NitroAfrica will be measurable in terms of academic research, communication to different publics (large public, stakeholders, policy makers), training and education, and capacity building.