Environmental News

Earth’s Nutrient Cycle Is Being Disrupted By Humans

Biologists have identified an increasing threat to the Earth’s ecosystem. Surprise, surprise: it’s humans.

Whales, elephants, rhinos, birds, fish, and many other animals are vital to the Earth’s ecosystem because of their ability to transport vital nutrients away from concentrated naturally occurring areas.

Anadromous fish, for example, are born in fresh water locations, though they spend most of their lives in the salty ocean, returning only to find a mate. Nutrients they consume on their journey, such as ones found at the bottom of the ocean, are deposited elsewhere when they defecate, urinate, and ultimately when their bodies decompose after death.

The process is not unique to fish, and is especially significant in larger land mammals that eat huge amounts of food and leave an equally large amount of dung. Nutrients are transported in this manner from the ocean’s depths to the mountain peaks, up the rivers and across the valleys, far inland.

The process plays an important role in keeping the entire planet fertile, but it’s also being disrupted thanks in part to human influence.

A new study published in the Proceedings of the National Academy of Sciences (PNAS) warns that some of these cycles have been dealt serious blows over Earth’s history, from the extinction events that killed off the dinosaurs and other megafauna in the distant past, to the massive amount of hunting and poaching over the last few centuries.

Whales in particular have seen a dramatic decline in population over the past hundred years, as hunting and a disruption of their habitat have decimated their numbers. The Washington Post reports that before this occurred, whales redistributed an estimated 750 million pounds of phosphorus from the bottom of the ocean, where they feed, to the surface where the animals breathe and poop.

Today, the amount of phosphorus transported through this method is much lower. Researchers noted an 88 percent decline, as an estimated 165 million pounds of phosphorus was measured to be recycled in this manner.

The anadromous fish mentioned earlier were found to have been hit even harder, experiencing a 96 percent decline in the nutrient distribution process.

The lead author of the study, Christopher Doughty, said that before the study took place, scientists believed other natural events were responsible for the movement of nutrients on Earth.

Previously, animals were not thought to play an important role in nutrient movement

The prior belief was that the nutrient cycle was based on the weathering of rocks and nitrogen collection by some bacteria. The findings, however, clearly indicate that animals, particularly large ones, act as a “distribution pump” in which nutrients are consumed, transported, and then deposited in the form of poop.

The good news is that environmental activism is working. Efforts to restore whale populations have experienced some success, though not enough time has gone by to ensure their complete recovery — as demonstrated by the struggling blue whales. The blue whale population has been particularly devastated over the last few centuries, falling from 350,000 to just a few thousand, according to Phys.org.

Restoring the populations of these animals — some of which are endangered — is as simple as not killing them anymore, according to the study’s co-author, Joe Roman. “We can turn these effects around by restoring native populations of large vertebrates around the globe”, he told The Washington Post.

The study notes that the increase in domesticated animals, such as cows, has not counterbalanced the disruptions caused by humans. This is because their movement is restricted, and since they are not permitted to roam freely, the nutrients from their poop will always go one way: downstream.

If, however, foraging animals are given an opportunity to thrive and no longer face the threat of extinction, the world could experience a very positive environmental impact. “They’re bringing nutrients from the deep sea that could eventually reach a mountain in British Columbia”, said Roman.

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