CHARACTERIZATION OF STABLE CARBON ISOTOPES FROM SOILS DEVELOPED IN LOESS

Soils are an interface between the atmosphere, biosphere, geosphere, and hydrosphere, providing life sustaining ecological services such as buffer and filter for the air we breathe and the water we drink. As such, soil plays a critical role in the carbon and nitrogen cycles. Changes to the natural carbon and nitrogen cycles due to anthropogenic activities are of great ecological concern because of their influence on greenhouse gases, and on the sustainability of agricultural productivity. Understanding how these activities affect organic carbon pools in soils provides valuable information for sustaining this critical resource. This study presents data from multiple soil profiles at two Midwestern sites: New Philadelphia Historical Landmark (NPHL), and Plum Grove Historical Farmstead (PGHF), which illustrate the effects of natural and anthropogenic impacts on soil organic carbon. Depth profiles of stable carbon isotope (δ¹³C) values show no significant difference amongst sampling locations within each site. This indicates that either there has been no significant erosion or deposition, or the locations within each site have similar erosion/deposition histories. Stable carbon isotope values of soil organic matter near the surface of cores at both NPHL and PGHF illustrate the effect of modern inputs from burning fossil fuels, known as the Seuss effect, accounting for a shift in δ¹³C values 1-2‰ more negative. An additional influence on δ¹³C values from SOM resulting in a 1-2‰ increase has been attributed to microbial decomposition processes between the surface and subsurface horizons. The larger increase in δ¹³C values from soils at PGHF is supported by higher the C/N ratio which would support increased microbial activity. Taking these factors into consideration, the δ¹³C values from both sites suggest that pre-settlement the vegetation was mixed C₃/C₄.