[A] Feedbacks between soils, biota, land management and hydrological processes at different spatiotemporal scales

Biotic processes influence soil structure and thereby soil physical processes at different spatial and temporal scales 1. Simultaneously the local dynamics in soil moisture content, aeration and temperature influence the bioactivity of soil organisms 2. At catchment scale, the spatial distribution of favorable habitat characteristics influences the species' distributions. The interactions between these biotic and abiotic processes act over different spatiotemporal scales: short macropores with varying depth distribution created by earthworms and vegetation mainly influence the local depth distribution of infiltration, i.e. at EFU scale, while at hillslope scale these short macropores can be connected into larger scale macropore networks 3, possibly through lateral rodent burrows, old root networks or soil pipes. Thus the spatial distribution of species abundance and composition can be used on the one hand to extrapolate knowledge on local infiltration patterns to the catchment scale and on the other hand to describe the connectivity of macropores at hillslope scale.

Fig. 1: Task of subproject A

Soil organisms and vegetation play a leading role in soil structure formation and thereby regulate soil hydrological processes, at the same time these organisms depend on the soil moisture regime. Including these feedbacks in models may be crucial for obtaining reliable predictions of change in hydrological processes under changing climate or land-use. The main objective of this subproject is to improve the understanding and quantification of these feedbacks between abiotic and biotic processes, including human influence, at different spatiotemporal scales.

In the light of our achievements of the first phase, we aim at a quantification of temporal variability in the abiotic and biotic processes considering seasonal and management controls on soil structure and biota as well as the translation of soil organism distributions into hydrological functioning of soils by developing coupled species distribution models and hydrological models. Hereto we propose to use the spatial distribution patterns of soil organisms to describe the spatial differences in soil structure and support the parameterization of hydrological models from plot scale to catchment scale. Finally we seek to apply this knowledge in widening also the temporal scale by starting to consider the effects of these feedbacks on landscape evolution.

1. Lavelle et al.: Soil function in a changing world: the role of invertebrate ecosystem engineers, Editions scientifiques et médicales Elsevier, Paris, FRANCE, 1997.
2. Lavelle, P.: Earthworm activities and the soil system, Biology and Fertility of Soils, 6, 237-251, 1988.
3. Tsuboyama, Y., Sidle, R. C., Noguchi, S., and Hosoda, I.: Flow and solute transport through the soil matrix and macropores of a hillslope segment, Water Resources Research, 30, 879-890, 1994.