Today you tell us about the rain and the good weather
Mostly from the rain in fact, and above all from what remains of water after the rain. You will surely remember that for a large part of 2022 we had water restrictions, because of the drought, and moreover the latest bulletin from BRGM, the Bureau of Geological and Mining Research, which is in charge of groundwater monitoring, still reported at the beginning of this year a moderately low and stable level of groundwater in the Nord – Pas-de-Calais region, in any case below average.
However, it seems that it rains a lot in the region
Yes, but with us, more than 90% of the water used comes from underground. We pump a lot into the aquifers in the spring and summer, and then they take several months to recharge. In addition, with global warming, we have more and more violent natural phenomena that cause heavy rains. But heavy rains aren’t ideal for replenishing water tables, because the ground can’t absorb all the water. Suddenly, the water runs off, it joins the rivers, but not the water tables. In addition, in passing, it is loaded with pollutants, and when this poisoned water reaches the rivers, it can harm the local fauna and flora.
But where do these pollutants come from?
Well, for years the North was a very industrialized region with intensive agriculture. The pesticides used by this agriculture have accumulated in the soil, and have even reached the water tables closest to the surface. And so we must not only be interested in the quantity of water available, but also in its quality!
All this is not very pleasant. Can we at least improve this quality?
So precisely, researchers from the Physico-Chemistry of the Environment team at LASIRE, a laboratory of the University of Lille and the CNRS, are currently working on this contamination and its transfer into rivers and groundwater. For example, they measure the rate of contamination of waterways in the Scheldt basin, such as the Marque or the Deûle.
And how do they proceed?
Well they recently developed a mobile laboratory deployed in the field. It measures physico-chemical parameters, such as pH and temperature, and is equipped with an automated filter sampler which allows samples to be taken which are then analyzed at the university. There are all kinds of contaminants: pesticides, metals, drug residues… We are talking about a cocktail of pollutants, which change according to the weather.
How so ?
Yes, river pollution is not constant, it changes with the weather. For example, a rainy episode drastically changes the chemical quality of watercourses. To better understand the effect of meteorological conditions on the presence of pollutants, measurements are taken during periods of rain or drought. But the quality of the water is also not the same between day and night, for example, and the mobile laboratory therefore makes it possible to learn a lot about these fluctuations.
And these researchers are also working on ways to clean the water?
Of course, they seek to improve the water treatment processes at the source, to clean it up before it reaches the natural environment. Some materials retain pollutants well, but we can also work on their elimination using treatments with UV radiation, for example. The objective, in the end, is to seek to respond to these environmental problems and to provide sustainable solutions to have good quality water in the natural environment and also at the tap.
