World’s major rivers under threat from environmental stressors

New Delhi: Multiple environmental stressors such as agricultural runoff, pollution and invasive species threaten the world's major rivers that serve 80 per cent of the world's population, a new research report has warned.

The Ganges, India

Between them, these rivers provide water to over 5 billion people who live near them, besides providing a home to thousands of species.
These stressors endanger the biodiversity of 65 per cent of the world's river habitats and put thousands of aquatic wildlife species at risk. Also, over-development and excessive extraction as well as billions of dollars of investment by developed countries to avert water stress have damaged biodiversity of the rivers, the report published in the latest issue of journal Nature said.

Water gushes from the Xiaolangdi Reservoir on the Yellow River, China

The findings of the report follow the first global-scale initiative to quantify the impact of multiple stressors on humans and riverine biodiversity. The research team comprised scientists and experts from The City College (CCNY) of The City University of New York (CUNY), University of Wisconsin and seven other institutions.
The team produced a series of maps documenting the impact using a computer-based framework they developed.

The Niger river, West Africa

"We've integrated maps of 23 different stressors and merged them into a single index," said the report's lead author Peter McIntyre of University of Wisconsin-Madison. "In the past, policymakers and researchers have been plagued by dealing with one problem at a time. A richer and more meaningful picture emerges when all threats are considered simultaneously", he added.
Rivers in some of the world's most populated regions, including Yellow River in northern China, Ganges in India, Niger in West Africa, are losing water largely due to climate change.

The Manu River in Peru's southern Amazon region

Experts have warned that the changes taking place could threaten food and water supply of millions of people who live in some of the world's poorest regions.
The report stated that over 30 of the world's 47 largest rivers, which collectively account for half of the global runoff of freshwater, are under at least "moderate" threat. Eight of them are rated as being under very high threat in terms of water security for humans while 14 are rated as being under very high threat for biodiversity.

The Yenisei river in Siberia

What's worse is that the report said the estimates arrived at by the research team are most probably conservative as it was unable to take into account pollution from mining or the effects on biodiversity from rising levels of pharmaceutical products in river water.
At the same time, the report stated that some rivers were not yet threatened. The rivers of Scandinavia, Siberia, northern Canada and unsettled parts of the tropical zone in Amazonia and northern Australia have the lowest threat rating.
In rich countries, heavy investment in dams and reservoirs and diverting flows from wetlands has benefited 850 million people, reducing their exposure to extreme water scarcity by 95 per cent, the report said.

The Mekong river, Cambodia

The team noticed that rivers in different parts of the world were subject to similar types of stresses -- whether they were present in a developed or developing country -- such things as agricultural intensification, industrial development, river habitat modification and other factors.
"Flowing rivers represent the largest single renewable water resource for humans," said Charles J. Vörösmarty of the City University of New York, one of the report's co-authors. "What we've discovered is that when you map out these many sources of threat, you see a fully global syndrome of river degradation."
Source: India Water Review