Big scienceWith the first experiment now completed, the students join Lucien Biolley, employee at ETH’s Institute of Environmental Engineering. Together with Marius Floriancic, he is responsible for ensuring that field instruments remain in perfect working order throughout the year. It’s also his job to prepare the equipment required for the present module: two vans and two fully packed trailers are dispatched each year from Hönggerberg campus to Kappelen. Biolley explains to the students how they can use a pressure sensor to continuously monitor the level of the water table. Inside the blue tubes that pass through the borehole caps are cables that transmit the measurements to a data box. This collates all the data and can also be accessed remotely from Zurich. Later on, the students will have a chance to crunch data collected over the past five years. Right now, however, there’s more immediate work to be done.
Carole, Gianna, Raffaele and Robyn use a wheelbarrow to fetch a 1,000-litre water tank - still empty, fortunately. They position it next to one of the boreholes and fill it with groundwater using a pump. That evening, marker dye will be added to the water to prepare it for another experiment. "The great thing about fieldwork is that everything’s on a big scale, including the equipment," says Biolley. "That makes it much easier to figure out what’s going on."
The four students are equally enthusiastic. Robyn and Carole completed a Bachelor’s in Environmental Sciences before switching to Environmental Engineering for their Master’s. "I’m interested in technical solutions to environmental issues," Carole explains. "I like the hands-on approach." And for Robyn, what counts is not only "what we learn while studying, but also the insight we get into environmental engineering as a profession."
Forest or meadow?For the next experiment, the students meet up with Marius Floriancic. His job is to teach them how to measure the amount of water the soil can hold. For this purpose, tensiometers are used. The students take the small tubes, fit a ceramic cap to the bottom and then fill them with water. The drier the soil, the greater the amount of water that passes though the ceramic cap and into the ground. The students insert the tubes to different depths in the forest floor. The readings show the water retention curve, a measure of the soil’s ability to absorb water.
A second instrument, shaped like a large fork, measures soil moisture. Floriancic asks where we think soil moisture will be higher: in the forest or in the open meadow? The answer is unanimous: the forest! To our great surprise, the measurements show the exact opposite. Together with the students, Floriancic explores the reasons why: when it rains, the tree canopy and natural debris on the forest floor prevent some of the water entering the soil; also, trees extract more moisture from the soil than grass does; and, finally, forest soil is more permeable than compact meadow soil, which means it lets through more water. "Computing and modelling - that’s something ETH students are good at. But working out here in the field gives them a practical edge to that knowledge," says Floriancic with a grin. "It’s an expensive module, but definitely worth the investment," he adds, on a more serious note. As evening falls, the group returns to the water tank in the forest, where Biolley pours in the marker dye. The coloured water flows from the tank through a thick hose into one of the boreholes, where it mixes with the groundwater below. Some 30 metres away, groundwater is pumped to the surface from another borehole and fed through a monitoring device. It will take some time before any coloured water is detected.
The students have completed enough practical work for the day. Later on, they’ll be taking a closer look at the data on a laptop. It’s precisely this combination of field and desk work that Raffaele finds so rewarding. Gianna, who holds a scholarship from the ETH Excellence Scholarship & Opportunity Programme, also likes the variation. For her, it’s "the combination of technology and nature that makes environmental engineering so appealing".