A brand new study led by King’s College London has provided further evidence that the deaths of 350 African elephants in Botswana in 2020 were the result of drinking water from waterholes where toxic algae populations have exploded attributable to climate change.
The report’s lead creator says their evaluation showed the animals were most definitely poisoned by waterholes that developed toxic blooms of cyanobacteria, or cyanobacteria, after a really wet 12 months before a really dry one.
Davide Lomeo, a PhD student in the Department of Geography at King’s College London, supervised by the Plymouth Marine Laboratory (PML) and the Natural History Museum, said: “Botswana is home to a 3rd of all African elephants, and this unprecedented death – exclusion of the largest remaining population highlights the growing concerns about the impact of drought and climate change on the Okavango Delta, one of the world’s most vital ecosystems.
The elephant carcasses were first spotted in the northeastern sector of the country’s Okavango Delta between May and June 2020, but poaching was soon ruled out as the cause.
The event caused worldwide concern, with a complete of 350 elephants now known to have died.
One suspected cause was toxins produced by algae growing in watering holes, although the evidence remained inconclusive, partly because they occurred during the COVID-19 pandemic when movement restrictions were limited, making sampling inconceivable at the time.
The death of 25 elephants in neighboring Zimbabwe from septicemia the same 12 months raises questions on whether algal toxins were the cause of death in Botswana.
However, in a paper published in the journal, the team says their evaluation all but confirms that toxic algae is the cause.
Combining satellite data and spatial evaluation, the team investigated the relationship between roughly 3,000 watering holes and the locations of deceased elephants.
Their evaluation found that watering holes near the carcasses showed elevated levels of algae and recurring blooms in 2020 in comparison with previous years – particularly during a period related to mass mortality
The team also showed that decayed elephant carcasses were more scattered across the landscape than fresh ones, indicating that the 2020 die-off was different from typical elephant mortality patterns.
“We identified 20 watering holes near fresh carcasses that experienced increased algal blooms in 2020 compared to the previous three years combined. These waterholes also had the highest average algal biomass between 2015 and 2023,” Davide said.
After drinking, it’s estimated that the elephants walked a mean of 10 miles from the toxic watering holes and died inside about 88 hours of exposure.
These findings suggest an increased risk and likelihood of the presence of algal toxins in these watering holes, he added.
The team believes that the transition from a really dry 12 months in 2019 – the region’s driest in many years – to an exceptionally wet 12 months in 2020 can have led to the re-suspension of significant amounts of sediment and nutrients from the soil, promoting unprecedented algal growth.
Davide said: “As a result of climate change, South Africa is predicted to grow to be drier and warmer, and because of this, waterholes in the region are more likely to be drier for much of the 12 months. Our findings highlight the potential negative impact on water quantity and quality, and the disastrous effects this might have on animals.
“This work, conducted in partnership with local authorities, highlights the serious ecological consequences of the spread of toxic algae, highlighting the critical need for comprehensive water quality surveillance in all water bodies, including the smallest ones. Research demonstrates the effectiveness of satellite detection in identifying a variety of sources of contamination, underscoring the importance of expanding Earth observation applications to enable rapid intervention when similar environmental threats emerge.”
Colleagues from the University of Botswana, the Natural History Museum in London, Queen’s University Belfast and the Plymouth Marine Laboratory (PML) also participated in the research.
