Healthy Trees need Oxygen, not Natural Gas in their soil – Case Study in Chelsea, MA

Schollaert, C., R. C. Ackley, A. DeSantis, E. Polka, M. K. Scammell. 2020. Natural gas leaks and tree death: a first-look case-control study of urban trees in Chelsea, MA USA. Environmental Pollution 263:114464. https://doi.org/10.1016/j.envpol.2020.114464

Everyone loves the trees in our cities. They give us relief in the shade on a hot day, work to clean our air by removing pollutants, and provide beauty on our walk to and from the bus station. Unfortunately, our urban trees face a lot of challenges that threaten their livelihood and health in urban areas. One team of researchers decided to explore one of the lesser known threats to urban trees: natural gas leaks.

Natural gas is not a green energy

Natural gas is one of the leading fuels for creating electricity in cities across the world. Many home owners and renters have gas stoves that use natural gas, natural gas clothes dryers, and use natural gas to cool/heat their houses and businesses. Natural gas energy was originally created as a bridge fuel to help people transition from environmentally-damaging fuel sources, such as oil and coal, to renewable energy from sources such as the wind and the sun. Unfortunately, several decades later, we are still using natural gas in many countries and the transition to renewable energy sources has become increasingly difficult.

Gas burning from a gas stove burner. https://commons.wikimedia.org/wiki/File:Gas-natural.jpg

Using natural gas so extensively has caused the scientific community to explore some of the environmental consequences associated with natural gas energy. One group of researchers has decided to explore the relationship between the infrastructure that distributes the natural gas we burn for electricity underneath city streets and the urban street trees that we all love. A lot of the infrastructure buried under city streets to distribute natural gas to homes and businesses is quite old and there has been increasing concern regarding this infrastructure springing leaks and polluting the environment with un-combusted natural gas. One of the primary components of natural gas is methane, which is a very potent greenhouse gas that contributes to climate change. When this methane leaks from the aged and leaking natural gas distribution infrastructure, it can harm the environment.

Aging natural gas infrastructure

The team of researchers decided to explore how this leaking natural gas affects urban street trees in Chelsea, Massachusetts. Chelsea is one of the most densely populated and diverse cities in the United States and the natural gas infrastructure is quite old, like a lot of municipalities across MA. When natural gas leaks from underneath the street, the gas is looking for an easy way to escape from underneath the pavement of the street. One area of least resistance for the leaked natural gas to escape is through the soil in a street tree pit.

Gas pipelines at a construction site. https://www.geograph.ie/photo/5767415

Researchers in Chelsea wanted to find out the impacts of this gas on the health and integrity of their street trees. To do this, they measured the concentration of methane in the soil of the tree pit in nearly 200 street trees across Chelsea, 84 of which were very close to dying or dead. Results from their study found that these unhealthy or dead trees were 30 times more likely to have detectable methane in their soil than other healthy trees. The research team also measured the concentration of methane in the soil on all four sides of the tree pit. The side with the highest concentration of methane was the side adjacent to the road, right next to the buried leaking gas infrastructure. These soil concentration measurements provided support for the researchers that the methane was coming into the soil from a pipe under the street.

A sunny day in Chelsea, MA. https://commons.wikimedia.org/wiki/File:Chelsea_Clock_Company,_Chelsea_MA.jpg
What does natural gas mean for trees?

So, we ask, what happens to the soil and the tree when there is methane in the soil? Methane gas is not commonly found in tree pits and nearly any concentration can cause concern for the soil community. Previous research has found that when methane enters the soil in a tree pit it pushes out the oxygen in the soil. Unfortunately, trees rely on that oxygen in their to grow and to live. Increased methane also leads to changes in the microbes that live in the soil, causing microbes that use oxygen to eat the methane to start to outcompete other microbial communities. The combination of these phenomena mean that there is far less oxygen available for the tree to use, causing damage to the tree that can lead to declining health and even death.

Mature trees line a neighborhood street. https://commons.wikimedia.org/wiki/File:Burlingame_city_of_trees.JPG
Next steps

The more scientists learn about the environmental consequences of natural gas, the more it seems that we need to start moving off of natural gas energy and onto renewable energy technologies for our towns and cities. This study was the first to quantify the effects of natural gas leaks on urban tree health and helps to demonstrate the negative effects of methane on trees. The authors of this paper are helping to spread awareness of the threat natural gas energy has to our urban environments.

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Jessica Wright

Jessica Wright

I am a third year PhD. student in earth sciences at Boston University in the Department of Earth and Environment. My research focuses on urban infrastructure systems and energy transition policy, specifically focusing on the role of natural gas. I completed my undergraduate studies at Connecticut College in Biology and have worked with a lot of non-profits in and around the Greater Boston area on energy transition policy-making. I love to swim, do yoga, and travel!

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