Climate shock: Lakes are losing oxygen faster than expected

Climate change is reshaping our planet, and lakes are not spared from its effects. Many people worry about vanishing ice caps or dying coral reefs, but shrinking oxygen levels in freshwater may be an equally serious concern.

In recent study led by Professor Shi Kun and Professor Zhang Yunlin from the Nanjing Institute of Geography and Limnology, a team of researchers set out to understand how warming trends affect more than 15,000 lakes across the world.

The findings point to a steep drop in dissolved oxygen in over four-fifths of these lakes.

“A widespread decline in dissolved oxygen (DO) has been observed in rivers, temperate lakes, and oceans, yet the impacts of climatic warming on global lake deoxygenation remain unclear,” noted the researchers.

Understanding changes in lake oxygen

Lake water holds oxygen that fish, plants, and other organisms need. The oxygen usually comes from contact with the atmosphere or from photosynthesis. Warmer conditions reduce how much oxygen water can contain, and shorter winters mean less cold water mixing from top to bottom.

The researchers noticed that lake oxygen loss is occurring even faster than what’s been recorded in oceans or rivers. The results of the study suggest that around 55% of surface oxygen decline in lakes is tied to rising temperature, while nutrient overloads, also called eutrophication, explain about 10 percent.

Why heat waves raise concerns

Short bursts of hot weather affect lakes differently than year-round warming. A recent analysis found that temperatures soaring above normal speed boost oxygen loss by about 7% to 8%. More frequent heat waves could intensify these patterns and harm fish populations in unexpected ways.

Some areas seem more vulnerable because they already deal with high nutrient levels and thick algae growth. In these places, sudden temperature spikes push oxygen even lower.

Impacts on aquatic life and beyond

Fish and other animals suffer when oxygen dips below critical levels. Low-oxygen zones reduce habitat space, affect breeding cycles, and sometimes kill entire populations of sensitive species. Large fish die-offs draw headlines, but even smaller organisms and plants feel the strain.

Local communities may see declines in water quality, too. Murky, low-oxygen water can encourage bacterial blooms and alter the taste and smell of drinking water. Economic repercussions often follow, especially in regions relying on tourism or commercial fishing.

Surprising twists in tropical lakes

Scientists highlight that warming might boost the photosynthetic processes in some tropical lakes. Oxygen produced by algae in these warm spots can offset some of the losses that are tied to reduced solubility.

Still, conditions are unpredictable. Dense algae blooms can surge, then suddenly die off, leaving behind decomposing matter and driving oxygen levels down.

This seesaw effect keeps scientists on alert. In some tropical zones, the balance temporarily tilts toward higher oxygen from heavy algae growth. Over time, these blooms can trigger more harm than good if they deplete oxygen once they begin to decay.

Broader implications for communities

Experts point out that declining oxygen in freshwater could worsen greenhouse gas emissions. When lakes lack adequate oxygen, they can release more methane and nitrous oxide, gases that trap heat in the atmosphere. That creates a feedback loop, leading to more warming and further declines in oxygen.

Local economies also face pressures. Regions that depend on fishing might see less catch and more restrictions on harvests. If oxygen-starved waters become common, aquatic diversity could shrink, and entire food webs might shift.

Where do we go from here

Researchers stress that reversing some trends might be challenging, but there is room for action. Better nutrient management is a top priority. Agricultural runoff can be minimized with smarter fertilizer use, and communities can invest in wastewater treatments.

Heat waves are expected to become more frequent in the coming decades, so improved forecasting could help local managers plan for temperature spikes that may affect oxygen levels.

Protecting watersheds with efforts such as tree planting and wetland restoration can also buffer lakes against the hazards of warming.

The study is published in the journal Science Advances.

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