We test the hypothesis that erosion driven soil movement on hillslopes results in an increase in new organomineral associations and overall organic matter storage in colluvial deposits within a forested hillslope. We measured mineral specific surface area (SSA), organic carbon (OC), meteoric radioisotopes (210Pb, 137Cs, 10Be), soil physical properties, C/N, δ15N, δ13C, and ∆14C in bulk soil and density fractions in a hillslope transect of soil pits. The quantity of OC per unit of mineral surface area (OC/SA) and OC inventories increased by a factor of 2–3 in depositional sites as result of soil mixing due to erosional movement as confirmed by 210Pb, 137Cs, and 10Be profiles and inventories. Soil mixing systematically decreased C/N and enriched stable isotopes of δ13C and δ15N, revealing that formation of organomineral associations instead of microbial processing was responsible for depth trends in organic matter composition. Our findings indicate that the processes that associate organic matter and minerals are fundamentally linked with organic matter composition, and OC/SA, C/N, δ13C, and δ15N provide proxies for organic matter stabilization by soil minerals.
Bibliographical noteFunding Information:
The authors extend gratitude to the National Science Foundation for funding this work through the Christina River Basin Critical Zone Observatory [grant numbers 0724971 and 1331856 ]. We would like to thank Brandywine Conservancy, Dr. Phoebe Fisher, and the field team at Stroud Water Research Center, especially D. Montgomery, S. Hicks, J. Matkov, and S. Dix for immeasurable assistance with the field and lab components of this project.
© 2018 Elsevier B.V.
- Critical Zone
- Hillslope processes
- Mineral surface area
- Organic carbon