HILLSLOPE ASPECT CONTROLS ON BIOTURBATION IN THE BLUE OAK RANCH RESERVE, CALIFORNIA TRACED WITH 137CS

Hillslope aspect is known to affect microclimate conditions in soils worldwide. On semi-arid landscapes, in particular, hillslope aspect controls soil moisture, affecting vegetation cover and thus sediment transport. However, the specific effects that hillslope aspect has on bioturbation, a key driver of hillslope diffusion and thus landscape evolution, have not been measured. Here we study how burrowing mammals, such as tunneling ground squirrels, affect the transport and diffusion of ¹³⁷Cesium on hillslopes in the Blue Oak Ranch Reserve, California. Eight total soil cores were collected from a north and a south-facing slope; two were collected on each hill's ridge, one at each mid-section, and one at each toe. The cores were then sub-sectioned based on depth, packed, and analyzed for ¹³⁷Cs activity using gamma spectrometry, as ¹³⁷Cs is a powerful tracer of soil transport. Results so far show sharper ¹³⁷Cs peaks in the top 10 cm of soil on south-facing slopes, indicating reduced diffusion, possibly from reduced burrowing activity. North-facing slopes show more variability in ¹³⁷Cs activity through the vertical profile, likely due to bioturbation. These findings may suggest aspect-driven variation in bioturbation and sediment transport mechanisms in a local system. This research will be advanced by analyzing more soil profiles, coupling ¹³⁷Cs measurements with soil carbon, and comparing diffusion rates across slopes and varying parts of the hills. Studying these processes in a semi-arid region prone to increased drought and wildfire frequencies is critical for understanding landscape evolution and predicting responses to climate change.