Groundwater pollution

As I pointed out in my last post, the groundwater recharges dependents on the surface water inflows and the river recharges from upstream. And at the same time it is a closed system, on that account the vulnerability for pollution could be immense, because every contamination will accumulate over the time. In particular, because of a growing population, there is a growing demand for food, therefore more production and more fertilization. Which implicates a great threat to the groundwater. While working on the project ‘Advice on groundwater resources for the Lake Chad Basin Commission’, the BGR published several reports on the quality of water in this area. I will give you a brief summary on that.

In their most recent report (Nr. 4, 2012), they used data from 441 water samples, 19 from surface water and 422 from groundwater. They looked at the anion and cation species and trace elements by measuring temperature, pH and electric conductivity. In general, groundwater quality depends on the paste of infiltration. To put it simply, fast infiltration means less minerals and less filtering than slow infiltration. The paste of infiltration depends on the flow features and thickness of the unsaturated zone. As you can see on the figure below the light-colour areas are characterized by direct recharge and therefore low in minerals, whereas the dark-colour areas are marked by low flow velocity, so the water had time to mineralize.

Figure 7: BGR Nr. 4, 2012

The danger of pollution is immense higher with a direct recharge of water than with a long time of filtration through the ground. Therefore, hand dug open wells are a particular threat to the groundwater. The next figure is showing the nitrate pollution, a pollution, which is caused by agricultural fertilizers and human or animal faeces. With more than 50mg/l nitrate (US and WHO limit, the European limit is 25mg/l) the water can harm the health of a human body. In 59 samples of water were the limit exceeded.

Figure 8: BGR Nr. 4, 2012

To conclude, there is a punctual pollution of nitrate in some areas. Mainly caused by livestock and farming and open contact to the groundwater. On that account, the BGR strongly recommend a better protection of the groundwater, especially concerning open hand dug wells. But in general the pollution of water is at the moment not the greatest threat for this area. More important is a constantly water supply to save lake Chad from drying and keep a basis of existence for all the people living there.