Original Title: ¹⁴C distribution in soils with different history of land use, Calhoun CZO, USA
The soil organic matter (SOM) is the major carbon reservoir in terrestrial ecosystems. The understanding of potential impact of soil and anthropogenic processes on biogeochemical cycling remains one of the great uncertainties. Radiocarbon measurements of SOM provide powerful constraints for determining carbon dynamics and the magnitude and rates SOM response to the environmental changes. The performed experimental tests were aimed to find out the distribution of ¹⁴C in Ultisols with different history of land use located in the Sumter National Forest. We analyzed: a) reference hardwood stands, mainly of oak and hickory that are taken to be never cultivated; b) pine stands, which had been used for growing cotton from beginning of the 19th century and then was abandoned in the beginning of 20 century and naturally reforested; c) currently cultivated plots, which were also used growing cotton prior to the 1950’s but for the last 50-60 years for growing corn, wheat, legume, sorghum, and sunflowers. There were analyzed 3 profiles for each - reference hardwood and pine reforested sites and 2 profiles for cultivated sites. There were obtained 53 radiocarbon AMS dates.
The top AO and A horizons in all soils have very close ¹⁴C concentration between 25-65‰, which mostly controls by quality (e.g. pine needle vs wheat) and quantity of the carbon input. However starting from AB horizon we have observed the huge differences even inside the sites with similar land use history. The AB, Bt, Bt2, and BC horizons have got ¹⁴C concentrations under hardwood in the ranges -32- -140‰ -270- -480‰, -400- -530‰, and -320- -610‰, correspondently. Soil under reforested sites also has wide ranges of variations with the slightly lower ¹⁴C concentrations as a result of previous erosion of the top horizons during their cultivation with lowest concentration in Bt2 horizon about -700‰. The cultivated sites have got the lower concentration compare to the undisturbed hardwood soil starting from Bt2 horizon.
It varies from -460 to- 670‰ and depends from the geomorphological position. As the rule the profiles in the low part of the slope have lower ¹⁴C concentration in under surface horizons for any type of land use so the soil hydrology and input of carbon with the vertical and lateral transport could also affect ¹⁴C concentration. As a result we can observe some inversion of ¹⁴C concentration in BT and BC horizons when the ground water gives some input of modern carbon in the underlying horizons.
The ¹⁴C distribution in the top 60-80 cm of the cultivated soils clears sings of the erosion when underlying horizons with lower ¹⁴C concentration appear closer to the surface. In the case of the reforested sites we also can observe the similar phenomena, however this process is smoothed out by higher biological productivity of the pine forest compare to the cultivated sites.
Cherkinsky, Alexander, Ravi Prasad, Daniel Richter, Hai Pan (2018): Distribution of 14C and 137 Cs in the profile of Ultisol, Calhoun CZO. International Radiocarbon Conference, June 17-22, 2018, Trondheim, Norway.
This Paper/Book acknowledges NSF CZO grant support.