Green Roofs & Carbon Sequestration
HiveMind sequestered 135 metric tons of CO2e in four inches of soil on a 500 square feet green roof for our Cummins pilot project. That’s 67.5 tons of CO2 over ten years. Our data from over three-dozen sites in the U.S., U.K., and Europe show an average of 100 tons of CO2 sequestered per 1,000 square feet on a standard sedum roof over ten years. Our average cost is$35 per ton of CO2 sequestered so at a cost for 1,000 square feet is $3,500. See Note 1.
The Vital Role of Mycelium in Carbon Sequestration: Plants convert CO2 into carbon through photosynthesize turning 3.67 tons of atmospheric CO2 into 1 ton of carbon that the plant uses for its structure. That carbon is secure until the plant dies, decays, or burns, and then is released back into the atmosphere. Mycelium takes that carbon sequestration one step further by pushing it into a carbon matrix in the soil that is resistant to release back into the atmosphere even after the plant dies. Plants give mycelium 40-70% of their total carbon in exchange for increasing their root system a thousand fold and allowing them to access water and rate liming nutrients.
The easiest way to envision this is a giant sponge of mycelium composed of fibers 1/10 the diameter of a human hair with one cubic inch of soil containing enough to stretch eight miles.
See Note 2.
Off The Roof Carbon Banks: Off the roof results are greater overall because there is more volume of soil to sequester carbon in, but less dense as we use a smaller amount of mycelium (10% to 50% depending on the site) inoculant per square feet. We have achieved consistent results of 435.6 tons per acre over ten years at a 10% ratio compared to green roofs. Our costs lower to $11 per ton on large-scale projects so can deliver at $4,791 per acre. We can moderate the composition and amount of our mycelium blend to achieve more or less CO2 sequestration and stay within the client’s budget.
See Note 3.
Glomalin: From Carbon Bank to Carbon Vault:
Arbuscular mycorrhizal fungi appear to be the only producers of Glomalin. The substance is a key in Wright, a scientist at the USDA Agricultural Research Service. She describes the chemical composition as: “A clump of small glycoproteins with iron and other ions attached.” The iron ions seal in the carbon and also allow the mycelium to move nutrients back to the plants’ root system without leakage.
Carbon sequestered in Glomalin is extremely “recalcitrant’ or resistant to being respired back into the atmosphere. The Glomalin also holds soil together against erosion and is thus is a type of “soil glue.” Wright states, “It requires an unusual effort to dislodge Glomalin: a bath in citrate combined with heating at 250F (121 C) for at least an hour. Glomalin contains from 1 to 9% tightly bound iron.
We’ve seen Glomalin on the outside of hyphae, and we believe this is how the hyphae seal themselves so they can carry water and nutrients. Glomalin-related soil proteins (GRSPs), along with humic acid are a significant component of soil organic matter and act to bind mineral particles together, improving soil quality. Glomalin is unique among soil components for its strength and stability.”
Other soil components that contain carbon and nitrogen, as glomalin does, don’t last very long. As microbes quickly break them down into byproducts that are then released back into the atmosphere. Because much of modern industrial agriculture employs fungicides there is very little or no mycelium or glomalin in most soils.
Note 1: 100 tons over ten years equals 10 tons per year. Atmospheric CO2 converts to soil-bound carbon at a ratio of 3.67 so that’s an additional 2.72 tons per 1,000 square feet per year or 5,440 pounds. Spread over 1,000 feet that’s 5.45 pounds per square feet and well within an industrial roof’s capacity.
Note 2: The best overview of how mycelium forms symbiotic relationships with plants is Suzanne Simard’s Ted Talk: How Trees Talk to Each Other. https://www.ted.com/talks/suzanne_simard_how_trees_talk_to_each_other?language=en
These two short videos give a sense of how quickly and comprehensively mycelium spreads in soil.
Note 3: Articles on Mycelium & Carbon Sequestration:
Articles on Glomalin: