Lake Modeling Reveals Management Opportunities for Improving Water Quality Downstream of Transboundary Tropical Dams

Abstract

Sustainable solutions to meet the growing food, water and energy needs of the human population are urgently required, especially in developing countries. Demand for hydropower and irrigation water threatens large river systems with potentially irreparable environmental effects (Best, 2019). More than 3,700 dams are proposed in tropical and subtropical countries (Winemiller et al., 2016;Zarfl et al., 2015). The African continent still has a largely untapped hydropower potential: Only 10% of this potential has been exploited, the lowest of any of the world's regions (The World Bank, 2015). The imminent growth of hydropower projects at low latitudes calls for an examination of the environmental effects of tropical dams (Anderson & Veilleux, 2016).Dams disrupt the continuum of rivers, altering natural hydrological regimes . By storing water, dams inevitably increase water residence time. As a consequence, thermal stratification and, subsequently, chemical stratification can develop in a reservoir (Friedl & Wüest, 2002). Hence, downstream water temperature and chemistry depend on the withdrawal depth, and dams thus modify not only downstream water quantity, but also water quality (e.g., Moran et al., 2018;Winton et al., 2019).The alteration of river water quality might have cascading effects and implications for the entire river ecosystem. Water temperature and oxygen concentration, for instance, are key parameters for aquatic species (Caissie, 2006). Water temperature affects growth, metabolism, reproduction, emergence, and the distribution of aquatic organisms, including insects and fish (e.g., Schulte, 2015;Vannote & Sweeney, 1980). Thus, water temperature changes may lead to changes in community composition or even to extinction of some species (Best, 2019). Dissolved oxygen (DO) concentration is also a key parameter for aquatic life (e.g., Kramer, 1987). Low oxygen concentrations alter lifecycle performance, growth capacity, reproductive success and disease vulnerability of fish, whilst hypoxia leads to higher fish mortality (Winemiller et al., 2008).

Lake Water Temperature Modeling in an Era of Climate Change: Data Sources, Models, and Future Prospects

“…14 of 52 all pixels within a water body) (MacCallum & Merchant, 2012;Woolway & Merchant, 2017) and within-lake thermal patterns, as well as their responses to climate change (Calamita et al, 2021;Mason et al, 2016;Woolway & Merchant, 2018;Zhong et al, 2016). Specifically, studies that have investigated spatially resolved observations of LSWT demonstrated considerable within-lake warming patterns, with warming rates often differing at sub-basin scales (Kraemer et al, 2015;Mason et al, 2016;Zhong et al, 2016).…”

Anthropogenic influences on Zambian water quality: hydropower and land-use change

“…From sampling points further downstream on the Zambezi, we observed a trend of recovery towards near-saturation, though models have suggest that full recovery of dissolved oxygen will only occur aer 380 km at which point the river will have already reached the Cahora Bassa reservoir in Mozambique. 30 The severe hypoxia in the Kafue River below the Itezhi-Tezhi appears to be a new phenomenon driven by a recent change in dam operation. Previously, the Itezhi-Tezhi had served as a supply reservoir for downstream generation at the Kafue Gorge (located at the far end of the Kafue Flats) and discharged lake surface waters through spill gates.…”

“…Climate warming could also change strati-cation dynamics by disrupting seasonal re-mixing driven by cooler air temperatures and winds. Modeling the physical mixing, temperature and oxygen regimes in tropical reservoirs 30 such as Kariba and Itezhzi-Tezhi could quantify the projected effects of climate warming and increased fertilizer loads on water quality in downstream river reaches.…”

On the Spatial-Temporal Behavior, and on the Relationship Between Water Quality and Hydrometeorological Information to Predict Dissolved Oxygen in Tropical Reservoirs. Case Study: La Miel, Hydropower Dam

“…However, all those conclusions cannot be directly applied to tropical case studies where the hydrological regime is different (Winton et al, 2019). Nevertheless, based on the studies mentioned above, it is necessary to go deeper into studies that directly relate water quality to hydrological and meteorological factors in hydropower systems in tropical latitudes (Calamita, 2020).…”