Author(s): E. Calamita; R. Scott Winton; B. Wehrli; M. Schmid

Linked Author(s):

Keywords: Water temperature; Oxygen dynamics; Zambezi River; Water-energy-food nexus; Dam management

Abstract: Major anthropogenic activities are affecting many tropical areas and we have poorly understood how those changes might alter freshwater ecosystems. In this study we aim to model how catchment changes in the Zambezi River Basin lead alterations of river thermal and oxygen regimes. Developing countries are experiencing major anthropogenic changes of their landscapes that are driving diverse ecohydrological alterations. Africa will experience one of the highest population growth rates over the coming decades, which precipitate changes in land use, water resource management and local climate. These catchment modifications might cause different shifts of ecologic, hydrologic, and biogeochemical fluxes. Thus, it is urgent a better understanding of the interconnection of anthropogenic and ecohydrological changes in tropical contexts. Among other changes, a boom of new hydropower dams is altering the natural hydrology of tropical catchments. The increased hydrologic residence time imposed by dams and the potential for stratification of their reservoirs can lead to major shifts in the temperature and oxygen content of outflowing water. Therefore, a switch in the operation rules of reservoirs can lead to downstream water quality changes, particularly for temperature and oxygen. Temperature and oxygen are fundamental to the functioning of aquatic ecosystems. Thermal regime plays a crucial role in several environmental compartments; among the others, it affect fecundity and eggs incubation period, hence species distribution patterns and competition. Oxygen dynamics has also direct impacts aquatic ecosystems, influencing several biogeochemical processes. In particular, hypoxia can cause the collapse of typically oxic river ecosystems, leading to potential extirpation of fish and other fauna. Artificial alterations of temperature and oxygen dynamics can have cascading effects on other water quality parameters, on the integrity of aquatic ecosystems and therefore on associated services. In this study we aim at investigating the alterations of thermal and oxygen regimes of a tropical river system related to changes in catchment-scale drivers. This study is part of an Horizon 2020 project called DAFNE: A Decision-Analytic Framework to explore the water-energy-food Nexus in complex and transboundary water resources systems of fast growing developing countries. The case study for this investigation is the Zambezi River Basin, located in south-eastern Africa. More than 15 dams are already planned or under construction in this catchment and further actions are planned to expand irrigated agriculture. We used a numerical model to simulate the influence of the artificial reservoir on the natural thermal and oxygen regimes of the Zambezi River. We compared a baseline scenario to three possible management scenarios for Kariba Dam. Moreover, we investigated how different dam operations might reduce the thermal and oxygen impacts on downstream aquatic ecosystems and hence improve the downstream ecosystem quality while providing energy and water availability.

DOI: https://doi.org/10.3850/978-981-11-2731-1_323-cd

Year: 2018