Measuring Carbon Exchange on Extensive Green Roofs

Introduction to Green Roofs

Green roofs involve layers of vegetation and growing medium over regular roof membranes. These “built habitats” are usually constructed for energy conservation (the soil and vegetation lead to reduced building energy costs) and to reduce storm water outputs from urban systems. The Lundholm Lab at Saint Marys University, in Halifax, Nova Scotia, is trying to determine whether native plant species outperform non-natives on green roofs in Atlantic Canada.

Most of the Lundholm lab’s green roof research involves extensive green roofs. Extensive green roofs typically have shallow substrates (usually 20cm or less of growing medium) thereby offering greater potential application on a range of buildings by minimizing additional load on the building. On the Atrium roof (an extensive green roof) at Saint Marys University, the Lundholm lab is further quantifying the ecosystem services provided by green roofs, and testing the role of habitat heterogeneity on biodiversity.

Saint Marys University Atrium Green Roof

Saint Marys University Atrium Green Roof

Eosense’s Green Roof Monitoring

While the carbon sequestration potential of green roofs is often cited as one of the key benefits; few measurements have been taken that quantify the exchange of carbon between green roof ecosystems and the atmosphere. Eosense teamed up with the Lundholm lab to gather some preliminary data to start to address these C-sequestration questions.

We deployed two C-exchange systems on the Atrium green roof, with measurements starting on October 5, 2016. The first system consisted of 4 eosAC automated chambers, which were connected to an LGR UGGA via the Eosense eosMX-P multiplexer. This system allowed us to monitor the total emissions of carbon dioxide and methane from the green roof with each of the 4 chambers collecting a measurement once per hour. After consulting with the Lundholm lab team, we decided to deploy the chambers over parts of the green roof that were dominated by vascular plant species versus mosses, with 2/4 chambers being deployed on each dominant type.

Four eosAC automated soil flux chambers deployed on the Atrium green roof with the eosMX-P portable multiplexer and the LGR UGGA CO2 and CH4 analyzer.

Four eosAC automated soil flux chambers deployed on the Atrium green roof with the eosMX-P portable multiplexer and the LGR UGGA CO2 and CH4 analyzer.

During the same visit, we also deployed an eosFD automated soil flux chamber on the green roof in an area that receives about 50% sun and 50% shade during the diel cycle due to shading by the building. This eosFD unit will monitor carbon dioxide emissions from the site continuously, and remain on the roof through the winter season to quantify winter CO2 emissions.

Chance Creelman (VP R&D) waiting intently for the eosFD to start up after installing on the green roof.

Chance Creelman (VP R&D) enjoying the sun and waiting patiently for the eosFD cable to arrive.

Stay tuned for GHG data!

In our next blog post, we’ll be highlighting a week of data from the LGR UGGA and eosAC system. Excitingly, we happened to deploy in time to catch Hurricane Matthew as it passed Nova Scotia, which brought high winds and rainfall to the green roof after a long, dry summer. We’ll also talk about the differences observed between the two different plant types, and potential for future work on extensive green roofs.

And, as the winter trudges on in Nova Scotia you can expect to hear more about how the eosFD is performing on the green roof, and how the green roof soils are responding to winter conditions.

Finally, special thanks to the Lundholm lab’s research associates Caitlin Porter, Emily Walker and PhD student Amy Heim for access to the green roof research site, and their assistance with setup and site selection.

Left to Right: Caitlin Porter, Amy Heim, Chance Creelman, Nick Nickerson. Photo by Emily Walker.

Left to Right: Caitlin Porter, Amy Heim, Chance Creelman, Nick Nickerson. Photo by Emily Walker.