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Triggering fish of Hippo excrement kill in African rivers



sixteenth May (UPI) – Hippo excrements are held responsible for fish mortality in the Kenyan Mara River.

According to a new study of the hippopotamus population and river health in the Maasai Mara National Reserve, the mammals excrete 9.3 tons of waste into the Mara River each day.

Researchers suggest that the massive influx of waste can lead to fish death, as the semi-digested plant material decomposes and robs large amounts of oxygen flux. When microbes degrade the excrement, they produce ammonium and sulfide – toxins that are harmful to fish and other aquatic life.

At night, hippos graze in the savannah. During the heat of the afternoon, they rest in the river.

"During dry periods, low-oxygen water accumulates in hippos," said Emma Rosi, freshwater ecologist at the Cary Institute of Ecosystem Studies, in a press release. "Periodically intense rains eventually flush the water downstream, and this sudden pulse of deoxygenated water can cause transient hypoxia and fish death."

For more than three years, scientists observed water chemistry downstream from 1

71 hippopotamus pools. During this time, the scientists observed 55 flushing events when rain doubled the volume of the river. Of the 55, 49 lowered oxygen levels. Of the 49, 13 compressed levels low enough to kill fish.

Laboratory experiments allowed researchers to replicate the biochemical processes that occur in hippopotamuses and to confirm the causes of low-oxygen water. Flushing events not only drain water that is low in water, but also stimulate sediments that are rich in hippo waste that continues to decompose and break down oxygen further downstream. In the Mara River system, flushing flows are important for cleaning hippopotamus in pools, but Accumulated toxic chemicals and deoxygenated water have serious downstream effects on aquatic life, "said David Post of Yale University.

While the new findings – published this week in Nature Communications magazine – may seem like a negative, dead fish provided fishing opportunities for birds and crocodiles.

"There is the idea that pristine rivers should not have dissolved oxygen quenching, but we think that's because generations of scientists have investigated places where there are no longer large intact wild animal populations, whereas the Mara River ei This is not the case, "said Yale researcher Christopher Dutton. "This system provides a window into the past and illustrates how ecosystems might have worked against human impact."


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