Science - May 17, 2012

Pollution in big rivers going up

The world's major rivers are getting more polluted with nitrogen and phosphorus. This is shown by a grey water footprint used by the Environmental Systems Analysis Group to evaluate water pollution levels of the one thousand biggest rivers.

The Ganges, the holy and most polluted river
We already have an ecological footprint. Twente environmental experts have now developed an indicator for water pollution, called the 'grey water footprint'.  Cheng Lui and Carolien Kroeze of Environmental Systems Analysis used this to determine how much pollutants end up in the big rivers and what the carrying and discharge capacities of these rivers are.  They found that two thirds of the one thousand largest rivers in the world have more nitrogen and phosphorus than they can discharge, leading to eutrophication.
The Ganges in India  is the most polluted river. The amounts of nitrogen and phosphorus in this river are four times higher than what it is able to handle. Most of the other heavily polluted rivers are located in China, India and Europe. The most polluted rivers are in the Tropics and Subtropics, but even the Rhine in the Netherlands gets more nitrogen than it can discharge. The biggest river on the earth, the Amazon River, hardly gets polluted because of its enormous discharge capacity although most of the farm effluents are being washed out there. At least, that appears to be the case based on annual measurements. Rivers can also get polluted if less nitrogen and phosphorus leach into them than what they can handle, as when pollution levels in dry periods are higher than the discharge capacity of these rivers.
The researchers have established that the percentage of pollutants has increased in almost all rivers between 1970 and 2000. They expect pollution to increase further by 2030. Kroeze, Cheng Liu and the Twente researchers use a global model which calculates nutrient transport from land to sea. This Global NEWS model, partially developed by Environmental Systems Analysis, was the basis for determining the grey water footprint for rivers. They will publish their results shortly in Ecological Indicators.