Abstract
Paleosols are formed when the topsoil gets buried by the lateral distribution of soil and can store large quantities of soil organic matter (SOM) that may persist over millennial timescales due to its detachment from the disturbances at the surface. We studied buried SOM dynamics in the Brady paleosol, a deep loess (aeolian) deposit in Nebraska, USA, where climate has historically driven varying rates of loess deposition during the late Pleistocene and Holocene, burying soils up to 50m below the surface. Soils were sampled
along the depositional and erosional transects at depths from 0.2 to 5.5m to understand the variability in the physical and chemical composition of the soils. We used elemental and isotopic compositions of C, N, 13 C, and 15 N, along with radiocarbon, base cation concentrations, and Fourier Transformed Infrared Spectroscopy (FTIR) to determine the distribution, stabilization, and composition of SOM and organic carbon in the soil profiles. Our results show a general decreasing trend of d 13 C and d 15 N values with depth,
suggesting root input to soil carbon pools and the presence of less decomposed SOM in the deeply buried soil layers. Radiocarbon analysis of bulk soil indicated a loss of ancient carbon and incorporation of new organic carbon in the eroding transect. To determine the vulnerability of the SOM to the addition of moisture, we added water to soil from the different transects and depths at 60% pore space capacity in two different experimental setups repeated wet and dry cycles and continuously wet. We found that repeated wetting and drying led to higher CO 2 efflux for buried Brady soils from erosional transects compared to the modern soils collected from the depositional transects. Our findings indicate that change in soil moisture status can play a critical role in destabilizing previously protected ancient carbon. Finally, our study highlights the need for furthering our understanding of how a predicted increase in precipitation quantity and intensity coupled with accelerated erosion can release large quantities of greenhouse gases by mineralization of previously protected old carbon stocks.

Biography

Manisha Dolui grew up in India, Kolkata. She did her MS at Tennessee State University in Agricultural Science before joining UC Merced in 2017 at Professor Berhe’s biogeochemistry lab and eventually moved to Professor Ghezzehei’s lab in 2022. She received her undergraduate degree in zoology and a post graduate degree in environmental science from the University of Calcutta before coming to the USA. She enjoys nature and cooking during her spare time.