Influence of bioturbation on sediment redistribution along climate gradient in Chile estimated by combining semi-empirical modelling, remote sensing and machine learning

Soil bioturbation activity affects soil texture, bulk density, soil water content and redistribution of nutrients. All of these factors influence surface and subsurface sediment and hydrological processes, and thus are expected to shape the surface on large temporal scales. Previous studies have shown that the impact of bioturbation on these processes is not homogenous.

However, the factors, which determine if bioturbation will positively or negatively affect the named processes, remain unknown. For this reason, the inclusion of bioturbation into erosion and landscape models have up until now been limited. The few models which include it in their algorithms assume a linear positive relationship between bioturbation rates, and erosion, soil mixing and vegetation cover.

In our study, we tested the possibilities and limitations of including bioturbation into soil erosion modelling. We modelled the impact of bioturbation on sediment redistribution, surface runoff, subsurface runoff and infiltration capacity within several climate zones and identified environmental parameters determining the positive or negative impact of bioturbation on surface processes.

Our study area was located along Chilean climate gradient. We measured the needed soil properties and location of burrows created by bioturbating animals in the field. Then we applied machine learning algorithms and used satellite data as predictors to upscale the soil properties and burrow distribution into the catchment. At each of the predicted burrow locations we adjusted the topography, soil properties and vegetation cover accordingly. We implemented the predicted parameters into a semi-empirical model and ran the model for a time period of 3 years under two conditions: With and without integrated bioturbation. We validated the model using sediment fences located at the base of each catchment.

Model with integrated bioturbation activity had an R² of 0.71 while a model without bioturbation activity had an R² = 0.45. Bioturbation increased sediment redistribution in all but humid climate zone. The surface runoff increased in semi-arid zone while the infiltration capacity and subsurface runoff increased in the mediterranean and humid climate zone. Bioturbation increased sediment erosion at high and middle values of elevation, at high values of inclination and connectivity, and at low values of profile curvature. Bioturbation increased sediment accumulation at high values of surface roughness and topographic wetness index and at low values of vegetation cover.