Deltalife 13

29 Deltares, spring 2020 The numbers tell the story A revolutionarymethod will be tested in a traditional Dutch tulip field to monitor the leaching of nutrients that dissolve in water. For the first time, we have an environment-friendly way to record the path taken by these substances and how long they take to spread. All using amicroscopic tracer with synthetic DNA. By Astrid van Bragt Photo Welmoed Jilderda 'W e already use tracers a lot in water science to study how water, and the substances dissol- ved in it, move through the subsurface, groundwater, brooks and rivers. A tracer can be a dye or a salt but, in this case, we use a tiny grain of sand enco- ded with a piece of synthetic DNA that isn't left behind in the environment. In this field trial, we will look at how nutrients and pesticides may move into ditch water from tulip fields.' Joachim Rozemeijer, a specialist in soil and groundwater quality at Deltares, explains. 'The great thing is that the DNA code allows you to use an infinite number of unique tracers. You can then retrieve the tracers to see which route they have taken and how fast they have reached the ditch. You can use the results to design efficient ways of improving water quality. In the case of tulips, you can make changes to the regulations for fertilisers. On the other hand, a filter on the pipes used for drainage may be just as effective. In that case, you do have to be sure that most of the substances pass along that route. Our approach allows us to provide that certainty.' Tulip field The unique trial in a tulip field near Noordwijkerhout will be conducted by Deltares in collaboration with Delft University of Technology, IHE, Utrecht University, KWR (drinking water research institute) and Biolegio (DNA). The sandy ground near the coast is ideal for the tracers. 'They can move around here more easily than, for example, in clay,' says Rozemeijer. 'Hydrology in a tulip field is also relatively simple. The tracers will be transported quickly and easily. Because the water in the field is drained off through pipes, there are clear drainage points where we col- lect the tracers for analysis. In short, this is the perfect location for a first field trial.' What will be possible in the future with these new DNA tracers? Rozemeijer explains: 'I expect the tracers to work well in hydrodynamics, too. For example where water flows meet in confluences or the flushing of polders to prevent salinisation. And it's possible that we might be able to attach tracers to sediment or plastics to monitor transport to the sea. DNA is getting better and cheaper to measure and this tracer technology will certainly help research in delta areas.' For more information: joachim.rozemeijer@deltares.nl