They projected that nitrogen pollution could render many sub-basins in South China, Central Europe, North America, and Africa to become water scarcity hotspots.
The team, led by Wageningen University in The Netherlands, has attributed the nitrogen pollution to urbanisation and agriculture. Their findings are published in the journal Nature Communications.
River sub-basins are smaller working units of river basins, which are a large source of drinking water but also remain locations of large scale urban and economic activities, potentially polluting local waterways through sewers. While nitrogen is a nutrient vital for plant and animal growth, its high concentrations can cause harmful algal blooms, disturbing ecosystems and leading to clean-water scarcity.
The researchers said that agriculture around rivers also contribute to non-point sources of pollution, which can come from many places all at once and are more difficult to control.
The international team of researchers analysed the sub-basins based on their river discharges (for water quantity) and nitrogen pollution levels (for water quality) and calculated the indicators for clean water scarcity for the years 2010 and 2050.
According to their assessment, in 2010, one-fourth of these sub-basins (2,517) faced severe scarcity of clean water, 88 per cent of which were “dominated by nitrogen pollution”.
“These water scarcity hotspots were mainly distributed in southern parts of North America, Europe, parts of Northern Africa, the Middle East, Central Asia, India, China, and Southeast Asia,” the researchers wrote.
Covering 32 per cent of the global land area, they said that about 80 per cent of the total population lived in these usually agriculture-intensive regions and contributed to 84 per cent of global total nitrogen losses to rivers from human waste.
In 2050, the authors projected that one-third of the 10,000 (3,061) sub-basins are at risk of being water quantity and quality scarce, risking the water resources of an additional 3 billion people. These basins would either not have enough water or have polluted water, they explained.
The team said that further deterioration of clean water scarcity could be stopped and even reversed, to some degree, if more efficient fertilisation practices as well as more plant-based diets were adopted.
They also recommended that a larger share of the world population be connected to sewage treatment, along with stressing the importance of policy makers incorporating water quality in their assessments of future water resources.