Seeds from the sewage treatment plant Tomatoes are growing in Bonn’s Rhine riverbed

Bonn · If you walk along the Rhine at the moment you can see tomatoes growing. Hundreds of them are sprouting in the Rhine riverbed below the Rheinaue sewage treatment plant.

“Silt is a particularly fertile soil, the warm temperatures have encouraged growth,” explains Markus Radscheit from the Botanical Gardens at the University of Bonn. However, experts are divided about how the seeds got there.

Peter Esch, head of the Civil Engineering Department, under whose responsibility the operation of the sewage treatment plant falls, has also discovered tomato plants in the containers in which the sand contained in waste water is collected. “This sand settles in the so-called sand-trap, which is part of the mechanical treatment stage,” explains Esch.

It is then regularly removed and ends up in the containers. This suggests that the tomatoes on the Rhine actually do come from the sewage treatment plant. “However, it is unlikely that the seeds will survive the biological treatment stage,” says Esch. At the latest in the last stage, filtration, no more seeds pass through.

Markus Radscheit, on the other hand, does not think the explanation, which GA reader Matteo Pedicillo also gives, is so far-fetched. “Tomato seeds are very adaptable and hardy,” says Radscheit. They would easily survive the treatment stages of the sewage treatment plant and then thrive in front of the runoff leading into the Rhine.

The sewage treatment plant discharges treated water into the river. However, these could also be seeds that have been in the Rhine’s silt for a long time. “I’ve also seen the fast-growing tomato plants in Bad Honnef.” Biologically speaking, the most exciting time of the year for botanists is when water levels are low, as the silt, which lies hidden under many stones, is extremely fertile soil. “Even the ancient Egyptians took advantage of it,” explains Radscheit.

Type of tomato cannot be identified

They sowed their rice whenever the Nile had flooded and left mud behind when it retreated. For the Rhine, this means that “interesting pioneer species” form when water levels are low in the late summer. These also include tomatoes, chestnuts and even lilacs.

According to Radscheit, the tomato species now growing there cannot be identified. “Nevertheless, you can eat the tomatoes growing on the Rhine without hesitation,” says Radscheit. However, there is not much time left to do so. The Rhine level will rise again in the coming days. It will be a few weeks until the tomatoes are ripe. “And as soon as the first frost arrives, the tomato plants will die.”

8Original text: Nicolas Ottersbach / Translation: kc)