Essay on Soil Carbon

Caitlin Hicks Pries and colleagues conducted research to determine how much carbon was generated when soil was warmed at different depths. Deep soil profiles harbor thrice as much carbon as the atmosphere, and the emission of soil carbon affects climate (Hicks Pries et al., 2017).

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Methods and procedures

Radiocarbon sampling was conducted to determine whether warming fueled decomposition of old carbon deposits in the soil. The researchers used a control experiment. Three pairs of 3m diameter circular plots consisting of one experimental and one control plot each were set up. A perimeter set up for both plots had sand-filled steel pipes where pipes in the experimental plots were fitted with heat resistant cables (Hicks Pries et al., 2017)

To make up for lost surface heat, the researchers placed heated cables in two concentric circles at 1 and 2m diameter, 5cm below the surface and unheated cables similarly in the control plots. Recording of soil temperature occurred every 30 minutes using various electronic thermometers. Moisture levels came from comparing soil samples within 500m of the experiment. This sampling was repeated both in dry and wet seasons every 6 months for two and a half years. Each plot had five gas wells from which 25 ml of gas were collected to determine the level of carbon dioxide generated by diluting the sample with ultra-zero air (Hicks Pries et al., 2017).

Results

Soil temperature on the experimental plot was about 2.4o C warmer than in the control plots. The volumetric content of soil moisture was lower in the heated plots by 1.5-3.5%. In-depth warming was by 4oC, and it resulted in a 34-37% whole profile soil respiration increment. The temperature coefficient was determined by comparing respiration and soil temperature of 10cm depth between the heated and control plots to avoid confusing the temperature response to the seasonal change in moisture.

Consequently, about 50% of soil respiration and 40% of the warming response occurred 15cm below the surface. Soil profiles that are 1m below the surface contained 63% of soil organic carbon and accounted for 20% of soil respiration and 10% warming response below 30cm which holds 32% of the carbon stock (Hicks Pries et al., 2017).

Interpretation

The study concluded that temperature sensitivities across soil horizons are the same. In all depths, respiration was dominated by carbon fixed within the past 50 years when compared with carbon dioxide values in other soil samples. Decomposition of old carbon deposits was not significantly affected by soil warming. The increased respiration, however, was caused by the light fraction occurring at all depths (Hicks Pries et al., 2017).

Significance

The study helps to determine whether global warming releases soil carbons and thus puts forth a new question; from where do the increased carbon levels in the atmosphere come. Atmospheric carbon levels are rising and causing pollution, and this is an urgent issue that should be addressed.

Evaluation

The authors propose that soil warming accounts for about 30% of global carbon emissions. I agree with them that this is a big percentage that cannot be ignored as it is adding to the adverse effects of carbon pollution (Hicks Pries et al., 2017). Too much carbon dioxide in the atmosphere is the leading cause of extreme weather conditions like severe floods and dry spells. It is true that plants should take in carbon dioxide, but the world's vegetation cover is not enough to expel all the carbon emitted by factories.

References

Hicks Pries, C., Castanha, C., Porras, R., & Torn, M. (2017). American Association for the Advancement of Science.