SOIL EROSION AND ORGANIC CARBON SEQUESTRATION FROM AGRICULTURAL DOMINATED LANDSCAPES

Quantification of the terrestrial carbon budget is important to understanding global carbon dynamics and the fate of anthropogenically induced CO₂. There has been much conjecture over the magnitudes of various sedimentary terrestrial carbon “sinks.” However, the impact of humans on soil loss from agricultural lands is very well documented, especially in the USA. Recent global estimates by Wilkinson and McElroy (2007) suggest farmland denudation of 63–75 Gt yr^-1. The majority of this soil loss does not move very far from its source. This post-settlement alluvium has been mapped and reported in many locations in the Midwest and Mid-Atlantic states. To determine the importance of this material in sequestering carbon, we have measured the organic carbon and total N concentrations in samples of alluvium/colluviums from two locations, one in Illinois and one in Ohio. Organic carbon concentrations ranged from 0.42–2.42% with means of 1.19% and 0.81%. These values are slightly lower than those for similar deposits in Pennsylvania. If these values are extrapolated to the US as a whole, the amount of C in these deposits currently is ~1.6 to 3.0x10¹³ g yr^-1 or only ~5% of the annual photosynthetic uptake of CO₂ in North America. Clearly more field work and sample collection and analysis are need from other locations to confirm this preliminary result.