Climate change creates environmental effects that are both visible and invisible to the public eye. One of its less visible consequences is the degradation of carbon-rich materials in soil organic matter in northern cold-region soils. In a recent study to understand how environmental changes attributed to climate change influence organic matter decomposition and soil carbon levels, EVS researchers have identified diffuse reflectance Fourier transform mid infrared (DRIFT) spectroscopy as an efficient and cost-effective tool for analyzing physical and chemical composition of soils.
Soil organic matter is the element of soil comprised of decomposing plant and animal remains, soil organisms' cells and tissues, and the substances these organisms synthesize. The amount of organic matter within a given region defines the health of that soil and determines its ability to retain water, amass nutrients, and store carbon extracted from the Earth's atmosphere moving through the carbon cycle.
Climate has a significant impact on the composition of northern soils. Low temperatures in this region greatly influence soil through freeze‑thaw cycles in a process known as cryoturbation. This process allows fresh organic materials to become buried deep below the surface, slowing their rate of decomposition. The rising temperatures, permafrost degradation, and hydrologic changes that accompany climate change have disturbed these natural soil processes.
Focusing their research over a 2,800-km transect of land in Alaska, EVS researchers collected 119 soil samples from 28 different sites. This variation allowed researchers to observe a wide range of soil types and note the variation in DRIFT spectra results. The researchers found that DRIFT spectroscopy provides a noninvasive way to identify variations in the physical and chemical properties of soil, revealing details including the quantity of carbon it has stored and the rate of organic matter decomposition. This study further showed that the information provided by DRIFT spectra of the northern cold-region soils also takes into account the soil's site-specific environmental conditions—topography, parent material, and weathering processes—that often factor into organic material composition and stability.
Using this technique, EVS researchers discovered that a single spectral band can provide a quick estimate of soil organic carbon and total nitrogen concentrations by highlighting increases in aromaticity and functional group presence, signs of higher decomposition rates. The chemical composition of soil organic material with less carbon decomposition has a greater amount of fresh materials, such as aliphatics and carbohydrates. Highly decomposed soils or those with lower carbon levels (and more minerals) contain a great deal of inorganic materials like clay and silicates.
This new technique comes as a welcome advancement to environmental research, as previous methods have proven time-consuming, very costly, and have required a large soil sample to work properly. DRIFT spectroscopy requires less time and money, and less soil and it also offers promising detailed characterizations of soil physical and chemical compositions. This study demonstrates that DRIFT spectroscopy can serve as a valuable tool for quickly and reliably assessing variations in the organic matter of northern cold-region soils.
This research was supported by DOE's Biological and Environmental Research program and published in Geoderma. Learn more about the work of DOE and Argonne's scientists in the Arctic on Argonne's Terrestrial Ecosystem Science (TES) Scientific Focus Area (SFA) website.
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