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

Abstract

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.

Mammalian bioturbation amplifies rates of both, hillslope sediment erosion and accumulation, in coastal Chile

“…Lastly, we also included the vertical movement of sediment particles from deeper soil layers to the surface in dependence on climate. The animals were found to reconstruct their burrows after each rainfall event (Grigusova et al, 2022). Corresponding with these findings, we increased the entrance depth and mound height by 30% after each rainfall event.…”

“…The adaptations varied with climate zone and burrow size. The size, geometric structure and excavation rates of burrowing animalswere previously estimated at a high spatial and temporal resolution (Grigusova et al, 2022). Based on this results, we firstly adjusted the microtopography.…”

“…Burrow aggregation describes at least 4 neighboring pixels with predicted burrows. We calculated the amount of excavated sediment as a sum of burrow density and the burrow excavation rate as estimated in Grigusova et al (2022).…”

“…Similarly, the highest volume of excavated sediment at the beginning of the modelling period was in LC and PdA. After each rainfall event, the animals reconstructed their burrows as described in Grigusova et al 2022. Due to various number of rainfall events, the volume of excavated sediment during our modelling period was the highest in NA, followed by LC, SG and PdA.…”

“…Previously used methods have, however, several limitations when studying bioturbation. Field measurements likely lead to an underestimation of sediment fluxes, as they are one-time or seasonal measurements, and thus do not capture the continuous excavation of the sediment by the animal (Grigusova et al, 2022) at a high temporal resolution. Box experiments and from them derived mathematical equations describe bioturbation as an isolated process and ignore surrounding environmental parameters (such as climate or vegetation).…”