Of course, river salinity can be natural. The geology of the area where a river flows may contain salt minerals such as gypsum or halite that are preferentially and easily dissolved by flowing water, or by the climate. However an increasingly large amount of the salinity in our river systems is coming from anthropogenic forces; industrial and agricultural activity, mining, and waste discharge from domestic sites.
In all of the Earth’s river systems, the additional salinity from man-made situations is threatening not just the ecosystems in the natural world that depend on the rivers for survival, but ultimately also the human race, who at the end of the scale depend on the rivers for drinking water. The additional salinity caused by our own doing is giving us an economic headache, as well as being a threat to the health of the public. Many of the chemicals used to make saline water drinkable are harmful to human health, as well as being poisonous to many plants and animals; this affects the long term food-web.
The worst cases of salinisation come from Australian rivers, and as yet there is an unclear reason why. It does however appear that local groundwater systems respond rapidly to the recharge of water, taking perhaps 30-50 years to dispel highly saline water after the clearing of ground for agricultural reasons. In Australia however there is a great collaborative effort between both the scientists and the local farmers to try to discover exactly what is happening, as well as why and what can be done to prevent the disruption of what is obviously a fragile balance. Europe also faces the same problem, with Spain being one of the worst hit countries- the land is arid, but the water sources have been over exploited by the people, and high salinity is the result.
So what can we do about it?
Well in Europe at least until new legislation is introduced, not a lot. Salinity is not a factor that has tight environmental controls, meaning there is no universal “safe” level of salinity, and until legislation comes into place it can be difficult to set boundaries for the mining and agricultural industry. There is also a public awareness issue. Many people do not understand how excess salinity can be detrimental to the fragile ecosystems that rely on the worlds river systems.
There is some good news though. There has been a successful salinity management programme: the Hunter River in New South Wales, Australia. The programme is called Hunter River Salinity Trading Scheme, and in simple terms works by discharging water into areas that are low saline-high fresh water, and by not discharging any water where there is low flow along the river. To read fully how the scheme works head here: http://bit.ly/XHBSzI.
In the future, with an uncertain climate, the issue is likely to get worse. In order to tackle the issue the leaders of the world must come together to introduce legislation to control and try to reverse the issue before it becomes too late.
Much more information can be found in the links below.
Image: Jason Pemberton