Increasing future human-induced nitrogen exports to rivers and sea in the Zambezi river basin

Tang, T. ORCID: https://orcid.org/0000-0002-2867-9241, Strokal, M., Burek, P. ORCID: https://orcid.org/0000-0001-6390-8487, Leclere, D., Kroeze, C., Havlik, P. ORCID: https://orcid.org/0000-0001-5551-5085, Langan, S. ORCID: https://orcid.org/0000-0003-0742-3658, & Wada, Y. ORCID: https://orcid.org/0000-0003-4770-2539 (2018). Increasing future human-induced nitrogen exports to rivers and sea in the Zambezi river basin. In: AGU Fall Meeting, 10-14 December 2018, Washington DC,USA.

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Abstract

In the past decades, nutrient enrichment in African water bodies has been frequently reported and lead to water security challenges, such as unsafe drinking water and compromised local livelihood. Meanwhile, rapid population growth and land-use change towards intensified food production are projected in Africa. Substantial increases in anthropogenic nutrient inputs (e.g. human waste and fertilizer) to the terrestrial and aquatic environments are therefore expected. This may further deteriorate African water bodies and threaten water security.

As part of the Integrated Solution for Water, Land and Energy (IS-WEL) project funded by Global Environmental Facility and IIASA, this study aims to assess the status and projected changes of nitrogen (N) sources, associated inputs to rivers and export to sea. The study focuses on the Zambezi river basin, the 4th largest transboundary basin in Africa draining through 8 countries. N inputs to rivers and export to sea are estimated using the MARINA model (Model to Assess River Inputs of Nutrients to seAs) under current conditions and future climate, land use and socio-economic scenarios towards 2050. In addition to global climate (Representative Concentration Pathways) and socioeconomic (Shared Socioeconomic Pathways) scenarios, the study co-developed regional scenarios through stakeholder engagement in cooperation with the Zambezi Watercourse Commission. The regional scenarios, especially for sanitation and agricultural development, will later be incorporated in the model.

Preliminary results show that for the current period (2010), N input to rivers and export to sea are mainly from natural sources, namely N fixation by the natural ecosystems and organic N leaching from non-agricultural areas. By 2050, N sources in the basin will be more than doubled due to anthropogenic inputs based on the global scenarios. Consequently, the fraction of human-induced N export is projected to increase considerably. Additionally, N export to sea is strongly influenced by the intra- and inter-annual climate variabilities in the region. The study highlights the need to simultaneously consider source control and climate adaptation in the regional contexts to minimize further N-induced deterioration of water bodies and ensure regional water security.

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