Oxygen is falling in inland waters – and human activity is responsible

Rivers, streams, lakes and reservoirs are not just the scenic parts of our landscape. It is also an important engine for life on Earth. Just like us, these inland oceans “breathe” oxygen. However, new research led by researchers at Utrecht University shows that we have suffocated them in the last century, an era known as the Anthropocene. The study, published today in Science Advances, reveals that the way oxygen is produced and used in inland waters has changed dramatically since 1900. Human activity.

Oxygen, the most important resource on the planet, plays an important role in other nutrient cycles, such as carbon and nitrogen. Oxygen depletion in the water, known as hypoxia, is causing problems. They are stacked on various coastal and freshwater systems. result? It already affects freshwater ecosystems around the world, including dying fish, food webs and poor water quality. This study shows that it is not just a local issue, but a planetary issue.

Behind oxygen depletion: Accelerated oxygen cycle

A group of researchers led by Utrecht Earth scientists Junzie Wang and Jack Middelberg have developed the first global model that explains the entire oxygen cycle in inland waters around the world. “Using this model provides a large-scale, providing oxygen-related problems that can reveal the cause and intervene in time if possible,” explains Middelburg.

When it comes to oxygen, inland waters have become a much busier place. The team discovered that global “oxygen turnover” (i.e. how much oxygen is produced and consumed increases. But here’s a twist: these waters consume more oxygen than they produce, making them the sink for atmospheric oxygen.

“More agriculture, more wastewater, more dams, and warmer climates — they all change how our freshwater ecosystem works,” Wang says. As more nutrients flow into rivers, lakes, and reservoirs, algae grow faster, but when they die and break down, they run out of vast amounts of oxygen.

“We found that the main cause lies in these direct human activities. First, we found that nutrient inputs are, for example, a major driver of excessive bloat. Second, longer travel times for freshwater to the sea through the construction of dams and reservoirs have been proven equally important,” says Midelber.

At the same time, due to indirect human impacts such as rising temperatures, oxygen reduces the solubility of water, transporting the water column vertically, speeding up the process of burning faster. “To date, the consensus in the scientific literature has been that temperature rises is primarily causing this acceleration. However, our model shows that warming contributes only about 10-20% to this phenomenon,” Wang says.

Anthropocene fingerprints

This study showed that modern oxygen cycles in inland waters can be seen, as in the early 1900s. “These waters cover only a small part of the Earth’s surface, but now they remove nearly 1 billion tons of oxygen from the atmosphere every year.

“We can no longer ignore the global climate and inland waters of oxygen budgets,” adds Wang. “They are changing faster than we thought, and they’re an important part of the Earth System puzzle.”