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An aerial view of Hartsfield-Jackson International Airport south of Atlanta

Helping land help you: The role carbon plays in ecosystem services

Note: This story is part of a special issue of The Warnell Log focused on carbon.

There’s a good chance you’ve been to the head of the Flint River and didn’t know it.

Just south of downtown Atlanta, its starting point sits underneath Hartsfield-Jackson International Airport, the world’s busiest airport. As its waters emerge from underground pipes and through south Fulton County, it flows past developed and undeveloped land.

Warnell doctoral student Behnoosh Abbasnezhad has mapped this land using a method called “land use land cover projection,” projecting changes to 2040 that could affect the headwaters of the Flint. By developing a series of detailed maps, Abbasnezhad can show carbon sequestration, along with a host of other ecosystem services such as water purification, sediment runoff and wildlife habitat. Her calculations also show land that is likely to become developed, the outcomes of this development, and identify parcels that could be the most beneficial to the watershed if they are conserved.

“Because of this metropolitan area, all of these areas are subject to conversation to urban areas,” said Abbasnezhad as she pointed to shaded areas on a complex map on her computer screen. “So not only are we losing forest lands, but we are losing a lot of carbon storage and also water” due to pollution from developed areas around the airport, she said. 

Losing forestland means losing carbon storage. It also increases flood risk, soil erosion and water pollution risks.

“When it is converted to urban areas, there is no way back; it remains as urban.”


Drawing the maps

To understand how land is used, Abbasnezhad first needed to map the area. She had a couple federal government databases collected by USGS to get her started: the National Land Cover Database (NLCD) and Landsat images collected by the agency. Images from the NLCD are images that are categorized, pixel-by-pixel, by certain land use categories such as forestland, grassland, roads or built environments. Landsat images show detailed land areas but don’t include the classifications in their data.

Abbasnezhad wasn’t sure if it was better to use the pre-programmed land-use data or create a custom system for the small area she was focusing her work, so she used both sets of images to compare their accuracy. “So, I gathered all of the satellite images from Landsat and did the classification and image processing. But at the end of the day, I didn’t add more accuracy,” she said. “Based on my approach, it’s better to use the data that’s publicly available for other regions, too. I did my due diligence, but at the end of the day, now I have more confidence to use and suggest using the NLCD maps.”

The process gave her deep knowledge of the upper Flint River watershed, though, including the changes it’s seen over the years. For example, one set of images from 1995 showed a deciduous and evergreen forest; by 2020, the same area was covered by Lake McIntosh, which was formed in 2007. Other areas appeared to have been converted to urban areas, but upon closer inspection, Abbasnezhad realized they were solar panel farms. Suburban neighborhoods were sometimes classified as “grasslands,” given the size of mowed yards—evidence of the urban sprawl that’s taken place in the past few decades.

Studying the history of land conversion helps to anticipate the trend of future changes, but urbanized watersheds like the Upper Flint are complex ecosystems, with drivers that include population growth, income, conservation politics and even broadband coverage. Because of this, Abbasnezhad incorporated these factors while calculating the probability of urban developments.

“I’m trying to map the probability of conversion,” she said, pointing to shaded areas over sections defined on the map. “These dark spots show lands with almost zero possibility to get converted, such as lands under conservation easements. Then it goes to red, which means it’s going to get converted. And you see most of the conversions are near metro Atlanta.”

She used this information to calculate a model for future land use out to 2040. Then, she created another model that calculates the amount of ecosystem services provided by parcels—and projections over the coming decades.

“We are calculating the amount of ecosystem services separately—for example, how much carbon is sequestered in 2019 and how much will it be by 2040 if the land use and land cover got changed as we projected,” she added. “And these conversions can affect the availability of ecosystem services within the next 20 years—and we can project it for the next 200 years from now.”


Regional benefits

Abbasnezhad is aware of the irony embedded in her maps: The idea that Delta Airlines, headquartered in Atlanta with pledges to work toward fewer carbon emissions, might also be influencing the conversion of forests to developed areas. But the maps also reveal an opportunity: while areas around the airport are heavily developed, forestland still exists.

By investing in these parcels and committing to conservation, it could benefit not just the company, but also users of the Flint River.

According to her maps, these benefits could also extend into water purification, sediment, carbon sequestration and habitat fragmentation—all ecosystem services she is calculating. Not only is this information useful to property owners, but it’s also valuable for municipalities and regional planners. Using the forecasting models in Abbasnezhad’s maps, it’s possible to identify areas of concern or potential development, then take a proactive approach by identifying landowners about conservation easements and other tools to preserve undeveloped land.

The upper parts of the Flint river are located in four out of 12 Georgia Regional Commissions. Abbasnezhad approached these planning organizations and gathered information about their future development plans for roads and urban expansions in the area. She was able to overlay this information onto her own maps.

“It was valuable to me that members of the regional commissions generously shared their data with me and seemed very interested in the results,” she said.

It’s important to consider these ecosystem services as large tracts of land change hands over the years, she added. The majority of these forests are owned and managed by families and individuals. Too often, the death of a family member means large forests are divided among their heirs and sold, leaving them vulnerable to development.

“And when it is a smaller parcel, like less than 50 acres, forestry practices in these regions get so costly and so hard that most people cannot maintain their forest lands,” she said. “And part of this research helps to prioritize those areas where they can do conservation. We cannot protect everything, but we can protect those areas that can have a bigger effect with higher conservation values and at the risk of urbanization. So part of this research helps to identify those regions. It can be beneficial for organizations such as land trusts to be proactive about protecting forests rather than waiting for family members to approach them after the death of a loved one.”


Carbon as a ‘service’

Abbasnezhad began this research in her home country of Iran, where she became fascinated with urban forests’ carbon sequestration services. But she soon realized that carbon is just one of several “services” that undeveloped land provides.

When she arrived at Warnell, she and her advisor, associate professor Jesse Abrams, began digging into the research on carbon sequestration modeling.

“When I was reading about forest carbon stocks, I learned about ecosystem services, a term coined 20 years ago and is still developing to address all sorts of benefits that natural ecosystems provide to humans,” she said. From there, she decided to expand her research to focus on more ecosystem services than just carbon. “So, it’s better to combine all of these things and have a bigger picture.”

But if, for example, a large airline wanted to invest in forestlands as part of its corporation’s social responsibility to sequester carbon, Abbasnezhad’s calculations could help identify the best place to do that and the benefits they might receive in the future. She also uses current carbon market data to calculate carbon values, now and into the future.

The work is more than a dissertation, Abbasnezhad said. She feels personally connected to it. On a recent trip, she happened to pass a poster at Hartsfield-Jackson hung above a water fountain. “I took a picture and sent it to Jesse and I was like, ‘You see this?’” 

The poster read, “Let’s Protect the Flint River.”

To Abbasnezhad, it was a sign that people were aware of the river and its perils. And the importance of her project.

“I feel a connection to it,” she said. “I want to have an impact. I want this project to have a broader impact than just publishing some papers. I want to see results in the real world.”


Associate Professor, Natural Resource Policy and Sustainability

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