Abstract:
Animal burrowing activity affects soil texture, bulk density, soil water content and redistribution of nutrients. All of these parameters influence sediment redistribution, which shapes the earth surface. Hence it is important to include bioturbation into erosion models. However, up to present, the inclusion of terrestrial burrowing animals into catchment-wide models has been limited to invertebrates, single species, and animal triggered sediment redistribution. However, an inclusion of all burrows created by vertebrate bioturbators into an erosion model to estimate their impact on rainfall triggered erosion is missing.
Here, we included vertebrate bioturbator’ burrows into a soil erosion model and interpreted the impacts of bioturbation on sediment redistribution. To do this, we measured the needed soil properties and location of burrows created by bioturbating animals in four research sites located along the Chilean climate gradient. Then, we parametrized a semi-empirical erosion model by applying machine learning algorithms to upscale soil properties and integrated the burrows into the model. We validated the model using several sediment fences in the field. We estimated the modelled sediment redistribution and surface runoff in all climate zones. Lastly, we identified environmental parameters determining the impact of burrows on sediment accumulation or erosion.
The model including bioturbation performed much better (R2 = 0.71, RMSE = 0.63 kg ha-1 year-1) than the model without bioturbation (R2 = 0.17, RMSE = 1.18 kg ha-1 year-1). Burrows increased sediment accumulation by 137.8 % ±16.4 % in the arid zone (3.53 kg ha-1 year-1 vs. 48.79 kg ha-1 year-1), sediment erosion by 6.5 % ±0.7 % in the semi-arid zone (129.16 kg ha-1 year-1 vs. 122.05 kg ha-1 year-1) and sediment erosion by 15.6 % ±0.3 % in the Mediterranean zone (4602.69 kg ha-1 year-1 vs. 3980.96 kg ha-1 year-1). Bioturbating animals seem to play only a negligible role in the humid zone. The fraction of sediment excavated by the animal to sediment redistributed during rainfall events was 128 % in arid, 24 % in semi-arid, 33.5 % in Mediterranean and 5.6 % in humid zone. Bioturbation increases erosion with increasing slope, sink connectivity and topography ruggedness, decreasing vegetation cover and soil wetness. Bioturbation increases sediment accumulation with increasing surface roughness, soil wetness and vegetation cover.
