It is obvious that baby's poop causes death of fish

Hippo eats about 40 kg of food a day and put out the same amount of poop. Also, since hippopotamus lives in a group of 10 or more herds, popping up in a water field that is normally inhabited becomes an enormous amount. Research teams such as Christopher Dutton and others, who are ecologists at Yale University, revealed that this hippopotamus of poop is responsible for the mass mortality of fish.

Organic matter loading by hippopotami causes subsidy overload generated in downstream hypoxia and fish kills | Nature Communications
https://www.nature.com/articles/s41467-018-04391-6

Hippos poop so much, sometimes their waste kills all the fish
https://www.sciencealert.com/hippopotamus-faeces-causes-water-hypoxia-kills-fish

Hippo waste causes fish kills in Africa's Mara River | Cary Institute of Ecosystem Studies
http://www.caryinstitute.org/newsroom/hippo-waste-causes-fish-kills-africa-s-mara-river

The research team of Dutton et al.Mara RiverI witnessed the situation where dead fish was flowing on the banks of the river when the water level rose, confirmed the existence of this phenomenon.


The research team started investigating to ascertain this cause. As a result of taking three years to investigate, it turned out that the cause of killing the fish was hippopotamental. Emma Rossey, one of the research teams, said about the amount of hippopotamus actually, "There are more than 4000 hippopotamus in the Mala, about 9.3 tons of poo in a day" I will.

Actually when the birth defecates, the poop will sink to the bottom of the river. And oxygen in the water is consumed by microorganisms eating that poop, oxygen concentration in water drops. Furthermore, microbial activities produce chemicals that are toxic to fish such as "ammonium" and "hydrogen sulfide".

Even if water is in this state, there is no problem when staying in the water field where hippo lives. However, when the water level in the river rises and anoxic water in the bird's water field flows into the downstream, problems arise. When oxygen-free water flows in, the downstream water falls into a temporary hypoxic state. And, due to the presence of poor breaking pans, a small amount of oxygen remaining in the microorganisms will be exhausted, and the fish will suffocate death.

Bymuffinn

According to Mr. Dutton's research team, during the three years of investigation, the water level of the Mala River rose doubled, and there were 55 cases where the water of the Hippopotamus water flowed into the downstream. Of these, 49 times confirmed the decrease in the oxygen concentration in water, 13 times it actually decided to kill the fish suffocation.

Mr. Dutton says, "This system shows how the ecosystem before human influence was functioning." The flow of a river that sometimes causes suffocation death of fish also plays a role of supplying food to animals such as birds and crocodiles that live in the surroundings.