RUDN ecologists: 1 hectare of urban soil emits an additional 0.2 tons of CO2 per year due to elevated temperatures

Carbon dioxide is one of the main greenhouse gases that cause global climate change. It is released from the soil because of microbial activity, among other things. This process is called soil microbial respiration. Dependence of soil respiration on climatic conditions is well studied only for unpopulated areas. Urban conditions change increase heat capacity, decrease average wind speed and relative humidity. All this leads to a special meteorological phenomenon — urban heat island. Inside the city, the temperature turns out to be higher than in the surrounding areas. Soil scientists at the RUDN studied for the first time how an urban heat island affects soil microbial respiration.

RUDN scientists for the first time calculated how carbon dioxide emission from soil increases due to rising temperatures within the city limits.

Carbon dioxide is one of the main greenhouse gases that cause global climate change. It is released from the soil because of microbial activity, among other things. This process is called soil microbial respiration. Dependence of soil respiration on climatic conditions is well studied only for unpopulated areas. Urban conditions change increase heat capacity, decrease average wind speed and relative humidity. All this leads to a special meteorological phenomenon — urban heat island. Inside the city, the temperature turns out to be higher than in the surrounding areas. RUDN soil scientists studied for the first time how an urban heat island affects soil microbial respiration.

“Urban heat island is a known urban climate anomaly. At the same time standard monitoring overlooks its impact on microbial respiration of urban soils, although it is important for predicting the sustainability of carbon stocks in a changing climate. We decided to find out how heat island affects microbial respiration of soil on the example of Moscow”, — said Vyacheslav Vasenev, PhD in Biology, Associate Professor of the Department of Landscape Design and Sustainable development at RUDN University.

RUDN soil scientists studied Moscow’s soil in the summer of 2019. The researchers randomly selected 140 points, 74 of them were in New Moscow, a territory recently joined the city with lower population and building density. The paved surface area in New Moscow is 4 times less than in Moscow, but there are 33% more green areas. The samples collected were divided into two parts. Topsoil (up to 10 cm deep) was stored at 4℃ and used to study microbial respiration. The remaining samples were dried and sieved, and then their physical and chemical parameters were measured. The carbon content of all samples was determined, and a digital “map” was made of the resulting points, which simulates the amount of carbon in the soil of the entire city. The RUDN ecologists then compared the obtained measurements with data from meteorological stations in Moscow and the Moscow region.

On average, the temperature difference in the city and outside the city due to the urban heat island was 2.2℃. On some days in June and September it reached 5.5℃. Carbon content in the soil of New Moscow was 20% higher than in the city itself — 14.6 kg per square meter. Microbial respiration varied depending on temperature, 0.12 to 5.10 mg of carbon was released from 1 kg of soil in an hour at different points. Such a big difference shows how sensitive soil microbial respiration is to environmental conditions. In New Moscow microbial respiration was on average 60%-100% more intense than in Moscow.

However, the maximum values in New Moscow did not exceed 2 mg. per kilogram of soil per hour, while in Moscow they reached 2.45 mg. The historic center of the city, where the heat island is most pronounced, was also the point of most intense soil respiration. In general, according to the calculations of RUDN soil scientists, the urban heat island in Moscow increases microbial respiration up to 25% and causes the release of additional 0.2 tons of carbon dioxide per year from each hectare of soil.

“The associated economic and environmental risks are high and will increase further with climate change and ongoing urbanization. To reduce the risks, changes in urban soil management policies are needed — for example, by monitoring soil microbial respiration to determine its resistance to urban heat island effects,” — said Vyacheslav Vasenev, PhD in Biology, Associate Professor of Landscape Design and Sustainable Ecosystems Department, RUDN.

The results are published in Science of The Total Environment.