China's mysterious 'river of blood'

The Yangtze River, China’s longest river, suddenly turned a red colour over the last few days. As of yet, scientists are unsure as to why. Although the source of the problem is unknown, I think we can rule out a couple of possible explanations. For instance, biological activity is often offered as a cause of discolouration of water bodies. However, in this instance, I would be inclined to say that this is not the problem. Intrusion of colour causing bacteria is usually the result of a decrease in oxygen concentration of a water body. But, as this is a river, and by definition is free moving, a significant decrease in oxygen levels on this scale is unlikely. I would also think an algal bloom is an unlikely cause, the main microorganisms that cause large discolourations or “red tide” are predominantly marine based, and of course, this is fresh water.

On the other hand, one cause that could most certainly be valid is industrial pollution; the surrounding area of the river is home to China’s largest industrial centre. Since the phenomenon has happened so quickly, it is possible that it is the result of a large release of chemical dyes into the river at some point upstream. But this will not be confirmed till analysis is complete.

If it is not found to be the direct result of a pollutant release, I would be inclined to attribute the problem to Acid Mine Drainage. AMD, can occur when water flows over or through sulphur-bearing materials forming solutions of net acidity. It is mainly associated with abandoned coal mines and currently active mining. An iron percipitate is formed and is the cause of a red/orange discolouration. Of course, there are many other probable causes; the addition of red clay to the water is one. But, whatever the prognosis, this event shows how sensitive water bodies are to changes in their environment.