Scientists are well aware of how just how polluted the German seaside is. But less-known is how much garbage ends up in the sea via rivers.

To close this knowledge gap, thousands of students aged 10 to 16 have worked together with scientists from the north German research lab Kieler Forschungswerkstatt.

Over the last two years, the children and teenagers, from 300 different schools, applied scientific methods to collect trash in and along rivers, documenting their findings along the way.

Scientists have now analyzed the data, which represents the largest study of waste in German rivers to date. The results are alarming, says teacher and scientist Katrin Kruse, and paint a different picture than most Germans have of their environment.

DW spoke with Kruse, who works at the Kieler Forschungswerkstatt and at a German high school where she supervised the project "Plastikpiraten," or plastic pirates.

DW: What's the state of German rivers?

Katrin Kruse: They are not as tidy and clean as one would like to think. Our results debunk the myth that Germany isn't responsible for the garbage in the oceans. We are responsible - because trash in rivers ends up at the seaside. It doesn't matter whether you live in Schleswig-Holstein [a state in northern Germany bordering the North Sea and the Baltic Sea] or in Bavaria [a state in southern Germany].

The students found an incredible amount of trash on German riverbanks

How much trash did the students find in the rivers?

The students collected in total 10,897 pieces of rubbish in an area of 16,611 square meters on the riverbanks. Let's illustrate it like this: If you imagine a classroom of 50 square meters, this would mean that 33 garbage pieces would be lying on the floor.

We are still analyzing how much microplastic is in the rivers. The students collected more than 200 samples; we have evaluated 50 of them. What we can tell so far is that half of these samples contain microplastics — around five plastic particles per cubic meter.

This doesn't sound like a lot. But the Rhine River, for example, sends 2,900 cubic meters of water per second into the North Sea. If you extrapolate our findings, this would mean that 14,500 pieces of microplastic ends up in the ocean — per second. That's an entirely different scale.

It does sound like a lot of garbage. Were you and the students surprised by the results?

My colleagues and I at the Kieler Forschungswerkstatt have been researching plastic waste in the ocean for the last five years. A while ago, sperm whales were stranded on the shores of the North Sea, and they had a lot of plastic waste in their stomachs. We are increasingly aware that in Germany, a lot of garbage ends up in our oceans.

Fathoming a whale's death Unfortunate news Why did 12 sperm whales end up on German and Dutch beaches last week? What caused them to die? An autopsy of the more than 10-meter-long (33-foot-long) carcasses is supposed to reveal answers.

Fathoming a whale's death Heavy burden For the autopsy, the whales were transported from the beach to mainland Germany. "Difficult and fascinating at the same time," Almut Kottwitz - the deputy environment minister of the German state of Lower Saxony - told DW. A female sperm whale weighs 15 metric tons (16.5 tons), a male up to 60 tonnes. Even though the beached whales were still quite young, they had to be moved with cranes.

Fathoming a whale's death Getting to the skeleton First, the whale's skin is cut into strips and peeled from the body. Preparers removed its muscles and ligaments, and gathered up the innards. "It cut me to the quick to see how these beautiful animals were being skinned and torn apart," an observer of the procedure told DW.

Fathoming a whale's death Museum as final resting place One of the skeletons was brought to Giessen University. Visible here is the whale's jaw - the bones will be treated for display. Another skeleton will be exhibited at a marine museum in Stralsund.

Fathoming a whale's death Lack of food Some of the beached whales seem to have been undernourished, the atopsies found. No wonder: sperm whales feed on giant squids. And these don't live in the North Sea. "Their stomachs and their bowels were entirely empty," Almut Kottwitz told DW, adding that undernourishment seems to be "at least one of the reasons why they died." When whales are hungry and weak, they can get more easily lost.

Fathoming a whale's death Too heavy for land Others among the sperm whales, however, seem to have been well-fed before they ended up on the beach, Ursula Siebert of the University of Veterinary Medicine in Hannover told DW: "They still had undigested beaks of giant squids in their stomachs, and feces in their bowels." Once on the beach, their weight compresses their blood vessels and lungs, causing them to die.

Fathoming a whale's death Champions in deep-sea diving Sperm whales are not made to live in the shallow North Sea. They mostly live thousands of meters under water. In the North Sea, their echolocation doesn't work correctly. "When they arrive at the North Sea, they don't have muchof a chance of finding their way out of it again," vet and zoologist Siebert said. Ultimately, they beach and die.

Fathoming a whale's death Mass beachings A week ago, more than 80 short-finned pilot whales got stranded on the beach of the Indian state of Tamil Nadu. Conservationists managed to push some animals back into the sea, but most of them died. Fabian Ritter of the Whale and Dolphin Conservation estimates that thousands of whales beach every year.

Fathoming a whale's death You beach, I beach The more socially minded a whale species is, the higher the number of whales that beach from that group. The long-finned pilot whale is one of these species, Fabian Ritter says. These whales have a very strong connection within their family group, or pod. "When the leader is ill or out of sorts, and swims onto the beach, the other group members follow - out of loyalty."

Fathoming a whale's death Too much noise Conservationists warn that underwater noise is dangerous for marine mammals. "Whales have a very sensitive sense of hearing and communicate via sound with each other," Fabian Ritter says. "Loud noise such as from military exercises disorients them." Especially beaked whales are known to beach more often when there is too much noise underwater, Rittter says.

Fathoming a whale's death Is the sun at fault? Solar winds disturb the Earth's magnetic field. Whales might get confused and beach more frequently, researchers found. At the end of December 2015 were three major solar winds, physicist Klaus Vanselow of Kiel University told DW. This might have led the 12 sperm whales to take a wrong turn into the North Sea - and end in death on its beaches. Author: Brigitte Osterath



But for the students, this was totally new. They usually think that we don't have this problem in Germany. Our streets, riverbanks and beaches get regularly cleaned.

But our results painted a different picture. The students were very alarmed by how much garbage they found – especially how much plastic. I think that the research will leave a lasting impression on them.

"Plastic pirates" is a citizen science project. How did the students and scientists work together?

The students learned scientific methods in the classroom and then went out to the rivers to apply them. They documented everything and took photos. Then, they uploaded their results to a website, where they could compare their findings with the findings of their peers from other schools.

The students sent their microplastic samples to the Kieler Forschungswerkstatt. Based on these samples and the uploaded photos, the scientists could double-check the results. This step is critical in citizen science projects in order to guarantee the quality of the data.

In all, 5,500 teenagers participated in the scientific study. This is simply amazing if you consider how long a small group of researchers would have taken to collect this amount of data. The students did a great job.

What was the feedback from the students?

They were totally thrilled that they were taken seriously by scientists, and that they could work as scientists themselves. On the other hand, they were also shocked to see how much garbage they collected. One group even witnessed how animals were entangled in plastic waste and or were eating trash.

We hope that students learn from this experience and change their habits. That they don't litter. That they go home and tell their parents they don't want to buy products packed in plastic anymore.

Will the plastic pirate project continue?

We would very much like to continue it. The project was part of the Science Year Seas and Oceans that ended in 2017 [an initiative by the German Education Ministry]. So we need to see how to finance it further. We are positive we can continue, since we collected such a huge amount of data that is significant for Germany and for the rest of the world. The students also said they would like to continue. They are very motivated to do their bit against garbage in the oceans.

Katrin Kruse is a biology and chemistry teacher at the Selma Lagerlöf high school in the northern German town of Ahrensburg. She is also a scientist at the Leibniz Institute for Science and Mathematics Education, conducting research into citizen science projects around microplastics.

The interview was conducted by Katharina Wecker and has been translated from its original German.