To celebrate World Soil Day, an international observance intended to draw attention to the importance of healthy soils, we are going to take a look at the hidden world beneath our feet.
The Ground is Alive
We stop to marvel at a blooming wildflower and to rest below the canopy of magnificent trees. In doing so, we may contemplate the wonderful world of plants around us, but rarely do we consider the soil conditions that give rise to and support these communities.
Soil escapes our attention largely because it’s underground -- hidden from our view. When we do see soil, overturned in a freshly tilled field or otherwise, the complex community of fungi, bacteria, insects, and other living organisms within is too small for our eyes to discern. Further, “soil” and “dirt” can be misleading words. The fascinating world under foot is reduced to a singular and contained whole. In reality, what we call soil is a fecund and thriving multiplex of organisms and relationships.
Recent research has revealed the vast, symbiotic network that trees and fungi (mycorrhizae) form in the forest floor. Hilariously named “The Wood Wide Web,” this network is cooperative; trees send danger signals when attacked so other trees can prepare and share carbon amongst themselves. In light of it’s underground life, a forest can be considered one large, cooperating organism. Soil and the life it contains is far more complex, and definitely more interesting, than we give it credit for.
Healthy Soil @ OSGF
At the Oak Spring Garden Foundation, we take our soil pretty seriously. After all, plants can only be as healthy as the soil they are grown in. We are working to implement ecological restoration to reduce soil pollution and improve soil health.
A recent example: Over the last month, the land management team at OSGF as been planting hundreds of native tree species as part of a long-term reforestation plan. By planting native species, we are hoping to tap into the unseen world of mycorrhizae and extend the current forest network into a larger area. Black locust (robinia pseudoacacia) and honey locust (Gleditsia triacanthos) are among the seedlings. Though both are thorny and nobody’s favorite to handle, these trees have a useful characteristic -- they fix nitrogen. Nitrogen is all around us, making up about 78% of our atmosphere, and it is essential for plant growth. However plants are unable to utilize atmospheric nitrogen. Black locust and honey locusts convert atmospheric nitrogen into other forms that plants can uptake. Other native nitrogen fixers include lupine (Lupinus perennis) and false indigo (Amorpha fruticosa). The ability to restore nitrogen to the soil is what makes varieties of peas and clovers such good cover crops!
Remediation: Beyond Preventing Pollution
Soil pollution can seem like a done deal. When soil is contaminated, the rich life it contains dies and the plant communities it supports perish. Without root structures and ground cover, contaminated soils erode into local water sources. This feedback loop only spreads and worsens the initial pollution.
In honor of World Soil Day’s 2018 theme, Stop Soil Pollution, we wanted to highlight some encouraging efforts to clean up contaminated soils with bioremediation and phytoremediation, the use of living organisms to aid in the remediation of a contaminated medium, be it soil, water, or air. In bioremediation fungi and bacteria are put to work to catalyze the breakdown and digestion of harmful substances. Phytoremediation is a form of bioremediation that specifically uses plants to sequester toxins. The main difference is bioremediation organisms degrade and transform toxins, whereas in phytoremediation plants draw toxins out of the soil and hold them in their biomass, in “storage.”
Bioremediation and phytoremediation are increasingly being utilized to restore degraded post industrial sites and other brownfields. The following examples hint at the power of plants to remediate polluted soil:
Gas Works Park, by Richard Haag, Seattle, WA
Along the shore of Lake Union in Seattle, Gas Works Park occupies land that was previously host to a coal gasification works. When the gasification works left the site, the land was so toxic and disturbed that no plants grew. Enter visionary Landscape Architect Richard Haag. Haag was adamant about dealing with all toxic material and soil on site. This approach was revolutionary. At this time, standard practice for cleaning up post-industrial sites involved trucking out contaminated soil and trucking in new soil. Instead, Haag launched a process of mixing sawdust, straw, and compost into the toxic mess and turning it regularly. By the end of the summer plants were popping up where none had grown for 10 years.
Bioremediation continued to dictate the park, all the way to form. The iconic Kite Hill offers breathtaking views of Downtown Seattle while also sequestering remaining toxic site materials. Anything that could not be remediated was packed into a hill and capped with 18 inches of hard packed clay. The hill is engineered with a slope that ensures water will runoff at a rate faster than it can infiltrate through the dense clay layer. Gas Works Park took a contaminated, lifeless site and created a scenic, revolutionary park.
Haag presented an alternative approach for managing post-industrial sites. He refused to blanket the site’s history with a picturesque landscape, instead opting to remediate the soil and retain surviving buildings. Gas Works Park exists as a monument of sorts, constantly confronting our industrial past and the landscapes left behind.
Revival Field, by Mel Chin, 1991 - ongoing, Plants, industrial fencing on a hazardous waste landfill
In 1991 artist Mel Chin launched his Revival Field, a place-based work “with the intent to sculpt a site’s ecology.” The work, or “experiment” as Chin calls it, was located at the Pig’s Eye Landfill, a Minnesota Superfund Site. The field is demarcated with a fence in the shape of a square, in which sits a fenced off circle, divided into four equal portions. In conjunction with USDA agronomist Dr. Rufus Chaney, Chin planted the quadrants with “hyperaccumulator” plants. Varieties of pennycress (Thlaspi spp.) were used specifically for their ability to extract heavy metals from the soil. Later samples of the plants revealed excess cadmium. Thereby offering phytoremediation as a viable, site based solution for cleaning up the toxic soil. Revival field is fascinating work that blends ecology and artistic practice to realize a site-specific intervention.
Mycoremediation, using mushrooms to bioremediate, is a fascinating field of study. Certain fungi are capable of metabolizing and breaking down the most toxic and synthetic of substances, including hydrocarbons.
Paul Stamets, myco-enthusiast and expert, is currently researching the potential of mushrooms to help clean up oceanic oil spills. Oyster mushrooms (Pleurotus ostreatus), the most common culinary mushroom in the world, is also a voracious metabolizer of hydrocarbons. Over 120 enzymes have been identified in oyster mushroom mycelium (analogous to the roots of a plant) and many of these enzymes break down hydrocarbons.
In another experiment, Stamets and a team of scientists at Battelle Laboratories found that after 16 weeks of growing oyster mushrooms in diesel contaminated soil, the number of TAH’s (Total Aromatic Hydrocarbons) was reduced from 10,000 ppm to around 200 ppm, a remarkable reduction.
In action, Stamets has been part of efforts to clean up oil spills in Ecuador, waterways in Oregon, and a 2007 oil spill in San Francisco. Though still under development, mycoremediation is a promising tool for remediating hydrocarbon contamination in soils and water.
Three Cheers for Soil
The ground beneath our feet is more productive and intriguing community than we give it credit for -- and also far more important. Soil health dictates plant and ecosystem vigor. Food is only as healthy as the soil in which it is grown and streams are only as clean as the land through which they travel. Plants and fungi have a remarkable ability to restore devastated soils and remedy pollution. We hope we honored World Soil Day by enlivening the fascinating world beneath our feet and giving soil, an unsung hero, some well deserved praise.
Soil in Art: These earlier botanical paintings, circa 1630, are from an apothecary shop in Saumur, France and depict medicinal plants. The building these paintings were in was burned during the French Revolution. Fortunately, the paintings were saved. Mrs. Mellon later purchased all eight painting in the set. The paintings now hang in the Oak Spring Garden Library.