Higher sediment redistribution rates related to burrowing animals than previously assumed as revealed by time-of-flight-based monitoring

Abstract. Burrowing animals influence surface microtopography and hillslope sediment
redistribution, but changes often remain undetected due to a lack of
automated high-resolution field monitoring techniques. In this study, we
present a new approach to quantify microtopographic variations and surface
changes caused by burrowing animals and rainfall-driven erosional processes
applied to remote field plots in arid and Mediterranean climate regions in Chile. We compared
the mass balance of redistributed sediment between burrow and burrow-embedded area, quantified the cumulative sediment redistribution caused by
animals and rainfall, and upscaled the results to a hillslope scale. The
newly developed instrument, a time-of-flight camera, showed a very good
detection accuracy. The animal-caused cumulative sediment excavation was
14.6 cm3 cm−2 yr−1 in the Mediterranean climate zone and 16.4 cm3 cm−2 yr−1 in the arid climate zone. The
rainfall-related cumulative sediment erosion within burrows was higher (10.4 cm3 cm−2 yr−1) in the Mediterranean climate zone than the arid
climate zone (1.4 cm3 cm−2 yr−1). Daily sediment
redistribution during rainfall within burrow areas was up to 350 %(40 %) higher in the Mediterranean (arid) zone compared to burrow-embedded
areas and much higher than previously reported in studies that were not
based on continuous microtopographic monitoring. A total of 38 % of the sediment
eroding from burrows accumulated within the burrow entrance, while 62 % was
incorporated into hillslope sediment flux, which exceeds previous
estimations 2-fold. On average, animals burrowed between 1.2–2.3 times a
month, and the burrowing intensity increased after rainfall. This revealed a
newly detected feedback mechanism between rainfall, erosion, and animal
burrowing activity, likely leading to an underestimation of animal-triggered
hillslope sediment flux in wetter climates. Our findings hence show that the
rate of sediment redistribution due to animal burrowing is dependent on climate and that animal burrowing plays a larger than previously expected
role in hillslope sediment redistribution. Subsequently, animal burrowing
activity should be incorporated into soil erosion and landscape evolution
models that rely on soil processes but do not yet include animal-induced
surface processes on microtopographical scales in their algorithms.
