By measuring soil carbon flux, researchers can obtain information concerning the health of forest ecosystems and measure the impact of global warming. This article explores how soil CO2 efflux is measured and how soil carbon flux is used in research.
Figure 1. Soil is an important part of the Earth’s carbon cycle. Image credit: pixabay.com/Picography
The Earth’s carbon cycle maintains a steady balance of carbon in the atmosphere that supports animal and plant life. The rising levels of CO2 in the atmosphere has become a growing concern in recent years, as it indicates that there is a problem with the Earth’s carbon cycle.1,2
When the carbon cycle is stable, a process called carbon flux operates via the exchange of carbon between carbon pools such as the ocean, the atmosphere, the land, and living things. Typically, carbon exchange occurs as a result of natural processes such as decomposition, photosynthesis, and respiration.
Since the industrial era, human activities such as fuel burning and the initiation of chemical processes have heavily contributed to carbon exchange. This has led to rising concentrations of CO2 in the atmosphere and increasing temperatures worldwide.1-3
Soil Carbon Flux Provides Feedback on Environmental Conditions
Soil is a vital component in Earth’s carbon cycle, as it contains nearly three times as much carbon as the atmosphere. Carbon is present in soil as ‘solid organic carbon,’ which includes decomposing animal and plant matter. As time passes, carbon is released into the atmosphere in the form of CO2 as a result of the microbial decomposition of the organic components in soil.4,5
Soil fertility, microbial activity, water quality, and plant growth are all affected by the amount of carbon present. Scientists can gain insight into an ecosystem as a whole by studying the carbon flux of soil and specific information concerning plant growth and microbial activity.4-6
Soil carbon flux can also help researchers understand and predict the effects of global warming. Microbial activity is likely to increase as global temperatures rise, which will lead to faster plant decomposition and increased CO2 efflux into the atmosphere.5,6
Measuring Soil CO2 Efflux
It can be difficult to determine soil-surface CO2 efflux. One common method employed by researchers to determine CO2 efflux involves combining a chamber with CO2 concentration measurements. Several different chambers have been designed for this kind of research, some of which are available commercially.7-10
In a closed-chamber system, air is usually pumped through a gas analyzer. This measures CO2 concentration and then returns the air to the chamber. The rate of increase of CO2 concentration in the chamber is then used to estimate soil CO2 efflux.
In an open-chamber system, ambient air is pumped into the chamber. The change in CO2 concentrations between the air which enters the chamber and the air that evacuates is measured and compared to ascertain the soil CO2 efflux.
Open-chamber systems are considered the more accurate of the two systems, as closed chambers tend to underestimate CO2 efflux. This is because less CO2 diffuses out of the soil while the chamber is in place, due to the increased CO2 concentrations in the chamber.10,11
Frequently, an estimate of CO2 efflux is attained by periodically measuring CO2 concentrations in chambers and then extrapolating the data. As CO2 efflux can vary widely between measurements (as a result of alterations in environmental conditions), this can be an inaccurate method.
Another limitation of the chamber-system of measuring CO2 efflux is that chambers usually only provide measurements in one location. This is an issue because CO2 efflux has been found to vary significantly, even in reasonably homogeneous environments. The overall outcome is CO2 efflux data with limited spatial and temporal resolution, which does not reflect the overall environmental situation.10,12,13
A group of researchers from the National Institute for Environmental Studies, led by Naishen Liang, has designed an automated, multi-chamber system of soil-surface CO2 efflux measurement.
As CO2 concentrations are measured automatically (using an infrared gas sensor), CO2 efflux can be determined accurately throughout the experiment. The improved temporal resolution, combined with increased spatial detail result for using multiple chambers, provides a clearer overview of how CO2 efflux fluctuates over time, location and environmental conditions within an ecosystem.10
Liang and his team employed this method to obtain information relating to a number of forest ecosystems. High-resolution, long-term data concerning the effects that global warming has on CO2 efflux and microbial activity has also been gathered using the team’s combination of automated chambers and heat lamps in various forest locations.
Liang’s research has shown that, in a significant number of forest environments, soil temperatures do have a significant effect on CO2 efflux. This information is crucial to scientists’ understanding of the impact that global warming has on forest ecosystems and the Earth’s carbon cycle in general.14-17
Figure 2. CO2 efflux measurements with Liang’s automated multichannel chamber system. Image credit: Naishen Liang.
Every chamber system that is used for determining CO2 efflux relies on the accurate analysis of CO2 concentration. The methods of instrumentation that are most widely employed to determine the CO2 concentrations in soil CO2 efflux measurement chambers are infrared gas analyzers.8,10,18
Liang and his team used infrared gas sensors - similar to the sensors produced by Edinburgh Sensors - because they are ideally suited to provide CO2 concentration measurements in soil chambers.
When compared with other sensors, gascard sensors are simple to use, robust, and low-maintenance. They are available as either individual sensors for simple integration into automated chambers (such as the Gascard NG) or as complete boxed sensors (such as the Boxed Gascard). Both choices provide quick and easy-to-interpret results.19,20
Figure 3. Boxed Gascard (left) and Gascard NG (right) from Edinburgh Sensors. Image credit: Edinburgh Sensors.
References and Further Reading
- ‘The Carbon Cycle’
- ‘Global Carbon Cycle and Climate Change’ — Kondratyev KY, Krapivin VF, Varotsos CA, Springer Science & Business Media, 2003.
- ‘Land Use and the Carbon Cycle: Advances in Integrated Science, Management, and Policy’ — Brown DG, Robinson DT, French NHF, Reed BC, Cambridge University Press, 2013.
- ‘Soil organic matter and soil function – Review of the literature and underlying data’ — Murphy BW, Department of Environment and Energy, 2014
- ‘The whole-soil carbon flux in response to warming’ — Hicks Pries CE, Castanha C, Porras RC, Torn MS, Science, 2017.
- ‘Temperature-associated increases in the global soil respiration record’ — Bond-Lamberty B, Thomson A, Nature, 2010.
- ‘Measuring Emissions from Soil and Water’ — Matson PA, Harriss RC, Blackwell Scientific Publications, 1995.
- ‘Minimize artifacts and biases in chamber-based measurements of soil respiration’ — Davidson EA, Savage K, Verchot LV, Navarro R, Agricultural and Forest Meteorology, 2002.
- ‘Methods of Soil Analysis: Part 1. Physical Methods, 3rd Edition’ — Dane JH, Topp GC, Soil Science Society of America, 2002.
- ‘A multichannel automated chamber system for continuous measurement of forest soil CO2 efflux’ — Liang N, Inoue G, Fujinuma Y, Tree Physiology, 2003.
- ‘A comparion of six methods for measuring soil-surface carbon dioxide fluxes’ — Norman JM, Kucharik CJ, Gower ST, Baldocchi DD, Grill PM, Rayment M, Savage K, Striegl RG, Journal of Geophysical Research, 1997.
- ‘An automated chamber system for measuring soil respiration’ — McGinn SM, Akinremi OO, McLean HDJ, Ellert B, Canadian Journal of Soil Science, 1998.
- ‘Temporal and spatial variation of soil CO2 efflux in a Canadian boreal forest’ — Rayment MB, Jarvis PG, Soil Biology & Biochemistry, 2000.
- ‘High-resolution data on the impact of warming on soil CO2 efflux from an Asian monsoon forest’ — Liang N, Teramoto M, Takagi M, Zeng J, Scientific Data, 2017.
- ‘Long‐Term Stimulatory Warming Effect on Soil Heterotrophic Respiration in a Cool‐Temperate Broad‐Leaved Deciduous Forest in Northern Japan’ —Teramoto M, Liang N, Ishida S, Zeng J, Journal of Geophysical Research: Biogeoscience, 2018.
- ‘Sustained large stimulation of soil heterotrophic respiration rate and its temperature sensitivity by soil warming in a cool-temperate forested peatland’ — Aguilos M, Takagi K, Liang N, Watanabe Y, Teramoto M, Goto S, Takahashi Y, Mukai H, Sasa K, Tellus Series B : Chemical and Physical Meteorology, 2013.
- ‘Liang Automatic Chamber (LAC) Network’
- ‘Interpreting, measuring, and modeling soil respiration’ — Ryan MG, Law BE, Biogeochemistry, 2005.
- ‘Boxed Gascard’
- ‘Gascard NG’
This information has been sourced, reviewed and adapted from materials provided by Edinburgh Sensors.
For more information on this source, please visit Edinburgh Sensors.