Creatures buried in soil for over a century burst back to life in Toronto waterfront

When Shelby Riskin was handed disk-shaped samples of century-old soil from Toronto’s waterfront, the ecosystem ecologist was hopeful she might find trace evidence of plants – cattails, bulrushes, water lilies and irises – that had once populated a long-destroyed wetland. But when she and a graduate student peered through a microscope, they watched in astonishment as a brown wormlike creature greedily munching through green clumps of algae as if more than 130 years hadn’t passed since its last meal. Equally oblivious, a host of life – water fleas, worms, plankton – danced and spun around it. “We’ve been able to resurrect some of the ancient life that shows what this wetland was like prior to urbanization,” said Riskin, an soil expert at the University of Toronto who was called in to analyze the samples. “It’s hard not to get really excited about this.” Riskin’s work and separate research from a paleoecologist, have contributed towards two peer-reviewed studies due to be published soon on the team’s findings. For the researchers, the discoveries do more than just serve as a novel time capsule. Toronto’s multibillion-dollar effort to re-naturalize a major river and the surrounding lands, was advertised as one of the “largest waterfront revitalization projects” in the world. As the project nears completion, the discoveries have underscored the resilience of ecosystems in the face of human-led destruction. Interactive A possible chironomid larvae discovered in the soil. Source: Hana Cho The samples that came to Riskin had themselves been the source of disbelief three years before, when heavy machinery was excavating vast amounts of dirt and debris from Toronto’s waterfront in an effort to re-route the Don River. When one of the bulldozers was halted by thick green shoots, the machine operator soon realized that the sedges and cattails looked nothing like the other weeds at the site. Scientists soon knew they were witnessing something both unexpected and profound: seeds and plant scraps, trapped underground for more than a century, had roared back to life. The peat bogs and wetlands had been buried under nearly 25ft of dirt and gravel more than a century ago, in an attempt to pacify the remaining scraps of wild around what is now one of North America’s largest cities. Decades later, in the 1920s, engineers applied a “straitjacket” to the Don River, when they built a concrete canal, wresting control from the body of water as they realized a vision of a heavily industrialized district known as the Port Lands. But while the river’s flow was largely predictable, the over-engineering of the river meant storms would lead to costly flooding events. In response, a project first envisioned in 2007 to restore the area is nearing completion. Three hectares of new coastal wetland and four hectares of wildlife habitat have been added to a space that was once a post-industrial wasteland – a rare victory in an era of environmental degradation. The construction of a marshier, more natural meander to the river has also led to creation of a new island, Ookwemin Minising, where the discovery of century-old plants unfolded. “When the project started, it was like being on the moon. The space was so just barren, so awful, dusty. It was bereft of any life,” said Melanie Sifton, a horticultural expert who was on site at the time the cattails and sedges were spotted. She helped with the careful extraction of 50 pancake-shaped samples of soil bound for the University of Toronto’s labs. “To find what we did – it was like finding buried treasure.” Once in the lab, the team eagerly scoured the clods of dirt, and the excitement deepened. “What is still alive, and what’s revivable and what we can learn from all of this is far deeper than what was initially thought,” said Sifton. The century-old plants bursting from newly exposed soil initially made headlines, but it was only the first of a string of extraordinary discoveries. Pollen from the American chestnut, a tree now extinct in the area, was discovered in the dirt. So too was a seed from the 1500s. The remains of one of the largest and most important peat bogs in the region were rescued. Then, last year, the team submerged soil samples and made the astounding discovery of water fleas, trapped in the soil since at least the late 1800s, which had sprung back to life. So too had worms, larvae and zooplankton. “In general, humans have actually been very bad at recreating wetlands. It’s a really common mitigation tool for environmental damage [but] the problem is, [relocated] wetlands have very rarely functioned in the way that we hope they will.” Riskin says the complex feedback loops that underpin the ecosystems have long baffled experts. But in the recovery of plants and water fleas, the power, mystery – and even the the magic, of dirt has astounded veterans of ecosystem study. “The soil was ready to turn on. And that’s what I love so much about it. The microbes, the nutrients, all of those pieces that are so small and outside of the human scope of vision, that we don’t totally understand as well, were ready to make the soil into a thriving ecosystem.” said Riskin. The discoveries might also hint at the power of using native soils in restoration efforts to “enhance” ecosystems, says Riskin. Riskin and the University of Toronto paleoecologist Sarah Finkelstein plan to publish their study into the carbon dating of the seeds, the pollen assemblage discovered in the soil and the results of germination experiments. For Shelley Charles, an Anishinaabe elder who helped name the newly formed island Ookwemin Minising – an Anishnaabe name meaning “Place of the black cherry trees” – the findings vindicate a more holistic Indigenous world view of ecosystems. “We knew instinctively that seeds were there and but we didn’t realize the immensity of it all,” she said. “Traditional knowledge really has a story of today and the future, but it also connects us to the past. So when the first plants started reviving themselves, we realized something much bigger and more interconnected was unfolding.” To the surprise for those toiling on the grounds and waters, the replanting of native plant species has been followed by the return of beavers, muskrats, fish, turtles, snowy owls and eagles – species which Charles calls the “natural engineers of the ecosystem”. “There was a real feeling of validation that Indigenous knowledge could contribute in a very meaningful way to revitalization efforts. And this spread to most people that have been working on the project – those doing the planting or the engineering hydrology,” said Charles. For more than a century, the lands that would become Ookwemin Minising were a barren industrial zone. Today, children clamber through a new park and a peaceful watershed, where paddlers and joggers ease along the thick greenery. “I still think back to the moment when those plants were discovered. It was joyful. I actually cried when I heard about it and when I heard of the care that the machine operators took. In other projects, everything is just scraped away. But the people working on the machines were so very kind,” said Charles. “This whole project has become a celebration, because who would have thought that underneath meters and meters of contaminated soil were these seeds waiting to come back to life? It’s a reminder to us all of what is possible.”