Lakes’ Capacity to Remove Pollution Declines as Global Temperatures Continue to Increase

 الأراضي المقدسة الخضراء / GHLands

A recent scientific study indicates that lakes are becoming less capable of purifying themselves from pollution as temperatures continue to rise due to climate change. This finding challenges the common assumption that warmer waters enhance microbial activity and therefore improve purification efficiency.

The study explains that most nitrogen removal processes in freshwater systems do not occur during summer, as previously believed. Instead, they depend primarily on winter conditions, a factor that weakens the ability of aquatic ecosystems to perform this essential function under ongoing global warming.

The research was led by ecologist Cameron M. Colbeck of the University of Basel in collaboration with the Swiss Federal Institute of Aquatic Science and Technology (Eawag). The team focused on Lake Baldegg in Switzerland, a nutrient-rich lake that undergoes a single seasonal mixing cycle each year.

The findings show that the lake remains stratified for most of the year, with a warm water layer near the surface and a colder layer below. During winter, falling temperatures trigger a complete mixing of these layers.

During this winter mixing period, nitrogen removal processes become significantly more active. The lake records purification rates approximately 50% higher than those observed in summer, making winter the most critical season for cleansing the lake’s ecosystem.

Lakes Rely on Winter Conditions to Remove Nitrogen, and Rising Temperatures Reduce Their Natural Capacity to Purify Water

This process relies on microorganisms living within the lake-bottom sediments, where they convert dissolved nitrogen into harmless nitrogen gas that is released into the atmosphere through a process known as denitrification.

The study also revealed a complex microbial interaction within the sediments. One group of bacteria breaks down chitin, a biological compound found in the remains of microorganisms and dead algae, thereby providing food sources that support another group of microbes responsible for completing the nitrogen-removal process.

The researchers tracked a radioactive nitrogen isotope within the aquatic sediments and combined these measurements with computer models designed to simulate the lake’s water cycle. The results showed a strong agreement between the field observations and the model predictions, confirming that winter represents the peak period of the lake’s natural purification activity.

Under a high-emissions climate scenario, the study predicts that rising temperatures could shorten the winter mixing period by approximately 27 days, resulting in the loss of a significant portion of the lakes’ natural purification season.

The Declining Capacity of Lakes to Remove Pollution as Temperatures Continue to Rise

The findings further showed that this reduction in winter mixing could decrease lakes’ nitrogen-removal capacity by approximately 10%, potentially affecting the health and stability of the ecosystems connected to them.

The researchers warn that nitrogen that is not removed does not simply disappear. Instead, it is transported through rivers into seas and oceans, where it contributes to harmful algal blooms. These blooms deplete oxygen levels in the water and can lead to the formation of coastal “dead zones,” areas where aquatic life struggles to survive.

The study emphasizes that climate change affects far more than temperature alone; it is reshaping the fundamental ecological processes that maintain the balance and functioning of aquatic ecosystems.

the study source : https://www.nature.com/articles/s41564-026-02349-9