Afroalpine Wetlands of the Bale Mountains, Ethiopia: Distribution, Dynamics, and Conceptual Flow Model

Abstract

The Bale Mountains of Ethiopia contain the largest contiguous area of alpine habitat in Africa. The region provides critical water resources and other essential environmental services to highland communities, endemic wildlife, and millions of downstream people in East Africa. Increasing land use change has created concern over degradation to headwater wetlands and potential impacts on hydrologic regimes. Baseline understanding of wetland dynamics is lacking, however, and little is known about their function in the regional hydrologic system. We used remote sensing, machine learning, and field surveys to map the distribution of Afroalpine wetlands in the Bale Mountains. We developed a wetland typology based on hydrogeomorphic characteristics and a conceptual model of surface-groundwater flow. Our results show that wetland extent more than doubles between wet and dry seasons and that only 4 percent of the Afroalpine zone is saturated year-round. We also found evidence of a hydrologic continuum based on volcanic and glacial legacies, with wetlands at elevations above approximately 3,800 m asl likely to be ephemeral and wetlands at lower elevations tending to be perennial. Further interpretation suggests that local geology is a principal control on wetland distribution and hydrologic attenuation in the Bale Mountains. This lays the foundation for further research into surface–groundwater connectivity, climate change impacts, and conservation planning. Key Words: Afroalpine, Ethiopian highlands, HGM classification, mountain water tower, tropical alpine.

埃塞俄比亚的贝尔山群包含非洲最大的连续高山栖地。该区域为东非的高原社群、该地特有的荒野生活，以及数百万居下游居民提供关键的水资源与其他重要的环境服务。逐渐改变的土地使用，已造成对河流源头湿地的侵蚀以及对水文体制的潜在冲击之隐忧。但我们却缺乏对湿地动态的基本理解，而其在区域水文体制中的角色亦鲜为人知。我们运用遥测、机器学习、以及田野调查，绘製贝尔山群非洲高地湿地的分佈。我们根据水文地貌特徵与地表与地下水迳流的概念模型，发展出湿地地形学。我们的研究结果显示，湿地范围在乾季与雨季之间增加两倍以上，且仅有百分之四的非洲高地地带终年呈现饱和。我们同时根据火山和冰河遗迹，发现水文持续性的证据，其中高于海拔约三千八百公尺的湿地，可能仅只是短暂存在，而位于低海拔的湿地则倾向终年存在。进一步的诠释显示，在地的地质，是贝尔山群的湿地分佈与水文减弱的的主要控制。此一发现为有关地表与地下水连结、气候变迁冲击，以及保育计画之未来研究打下基础。关键词：非洲高山地带，埃塞俄比亚高地，HGM分类，山区水塔，热带高山地带。

En las Montañas Bale de Etiopía se halla el área contigua más grande de hábitat alpino en África. Esta región genera los recursos hídricos críticos y otros servicios ambientales esenciales para las comunidades de montaña, la vida silvestre endémica y para millones de personas que viven aguas abajo en África Oriental. El incremento de cambios en el uso del suelo ha causado preocupación por la degradación que sufren las cabeceras húmedas y por los impactos potenciales sobre los regímenes hidrológicos. Sin embargo, se carece de conocimientos básicos sobre la dinámica de los humedales y poco se sabe de su función en el sistema hidrológico regional. Usamos percepción remota, aprendizaje con máquina y estudios de campo para mapear la distribución de los humedales afroalpinos en las Montañas Bale. Desarrollamos una tipología de humedales con base en las características hidrogeomórficas y en un modelo conceptual del flujo de aguas superficiales y freáticas. Nuestros resultados indican que la extensión de los humedales es más del doble entre las estaciones de lluvias y de sequía, y que tan solo un 4 por ciento de la zona afroalpina se satura durante todo el año. También hallamos evidencia de un continuo hidrológico basado en herencias volcánicas y glaciales, con humedales a elevaciones aproximadamente por encima de los 3.800 m sobre el nivel del mar, probablemente efímeros, y humedales a elevaciones inferiores que tienden a ser perennes. Una interpretación adicional sugiere que la geología local es el control principal de la distribución de los humedales y de la atenuación hidrológica en estas montañas. Esto sirve de base para una mayor investigación de la conectividad del agua de superficie y la subterránea, los impactos del cambio climático y los planes de conservación. Palabras clave: afroalpino, tierras altas etíopes, clasificación HGM de la torre de agua montañosa, alpino tropical.

Acknowledgments

The authors thank Joanna Lemly, Sarah Marshall, and two anonymous reviewers for their feedback in improving the final article.

Supplemental Material

Supplemental data for this article can be accessed on the publisher’s website.

References

Additional information

Funding

This research was supported by the National Science Foundation (Award No. 1313728), The Murulle Foundation, and a travel grant from the International Development Interdisciplinary Studies Program at Colorado State University. A portion of the material is based on work supported by the National Aeronautics and Space Administration under award No. NNX14AB60A.

Notes on contributors

Stephen M. Chignell

STEPHEN M. CHIGNELL is a Research Assistant in the Department of Ecosystem Science and Sustainability at Colorado State University, Fort Collins, CO 80523. E-mail: [email protected]. He is interested in understanding coupled human–environmental systems, particularly related to land and water development, using geospatial modeling, participatory mapping, political ecology, and environmental history.

Melinda J. Laituri

MELINDA J. LAITURI is a Professor in the Department of Ecosystem Science and Sustainability at Colorado State University, Fort Collins, CO 80523. E-mail: [email protected]. She has worked with indigenous peoples throughout the world on issues related to natural resource management, disaster adaptation, and water resources using geographic information systems that integrate cultural and ecophysical data.

Nicholas E. Young

NICHOLAS E. YOUNG is a Research Associate in the Natural Resource Ecology Laboratory at Colorado State University, Fort Collins, CO 80523. E-mail: [email protected]. He has extensive experience with species distribution modeling and prediction, with interests that include habitat modeling, wildlife movement, and risk prediction and assessment.

Paul H. Evangelista

PAUL H. EVANGELISTA is a Research Ecologist in the Natural Resource Ecology Laboratory and Assistant Professor in the Department of Ecosystem Science and Sustainability at Colorado State University, Fort Collins, CO 80523. E-mail: [email protected]. His research combines field data, traditional and expert knowledge, and geospatial modeling to examine a broad array of environmental issues.