Fecal waste culprit causes African river fish to suffocate

Fish stocks in the Mara River in Africa die massively each rainy season due to the huge amount of manure that hippos are emitting upstream.

The researchers found that the phenomenon of fish dying from hippopotamus when paying attention to fish bodies exposed on river banks when river water rises after heavy rain, according to Science Alert. After several years of conducting a series of tests, they could determine the cause of the water falling from upstream, where the hippo resided. The research results were published yesterday in Nature Communications.

Hippopotamus causes a lack of oxygen in the water, causing fish to die in mass on the Mara River.(Artwork: iStock).

"In total, hippopotamus on the Mara River discharges about 8,500 kilograms of fecal matter partially digested into the river every day ," explains Emma Rosi, an ecologist at the Cary Ecological Research Institute. care about the impact of this huge stream of organic and nutrient waste on aquatic life ".

The team took three years of observation, in which they monitored domestic chemicals from 171 live hippopotamus areas and the rest of the river, to find the answer. Because hippos are too dangerous for humans, they have to use remote control boats to carry sensors to check areas.

When the hippos excrete, their droppings sink to the bottom of the river. When large amounts of manure decompose, fecal digestive bacteria also use oxygen in the water, causing oxygen reduction. In addition, microbial activity also produces chemicals such as ammonium, hydrogen sulfide, methane, and carbon dioxide, two of which can be very toxic to fish.

This situation remains stable when the water does not flow from the river where the hippo lives. But the big problem occurs when heavy rains create a massive flow that washes oxygen-deficient water downstream, to fish habitats. The sudden flow of oxygen-deficient water can reduce oxygen in the river water downstream, causing fish to suffocate.

For three years, the team led by Yale University ecologist Christopher Dutton recorded the overflow when the river flowed twice as fast as usual, 49 of which had a dramatic decrease in oxygen. low enough to kill fish dozens of times. However, they also emphasize that this is a natural process. Not only cleaning the river, overflows also provide food for other animals living in the area such as birds and crocodiles.