Deliverable D2.4. Modelling module for biological diversity and functions in land surface water balance

The WP2 "Soil Functioning and Ecosystem Services", of the EcoFINDERS project, has produced a modelling module linking soil biodiversity and its functioning to hydrological properties of agricultural soil. The scope is of a proof-of-concept, including only earthworm burrows as a proxy for cropping systems. The biodiversity focus is on anecic earthworm burrows, which traverse vertically into the deep soil. At the LTO Lusignan this group of earthworms dominates the cropping systems of permanent grass (T5) and of three years of grass in a sequence with three years of annual crops (T2). In contrast, a cropping system without grass and with frequent tillage (T1) is dominated by the soil dwelling endogeic earthworms. The hydrological modelling starting point was the Joint UK Land Environment Simulator (JULES), but the soil hydrology module in JULES only considers water-flow through the soil matrix. Hence, we incorporated a representation of the water flow through macropores made by earthworms by adopting representation of macropore soil water flow in the open source soil-plant-atmosphere model, DAISY. The macropore parameters used for this module are: density, diameter, depth, conductivity of the macropore wall and soil water pressure. The approach has enabled the assessment of events of waterlogging and water deficiency in agricultural soils in real case scenarios, identifying the periods of risk in relation to earthworm burrowing. Two metrics were calculated from the simulated soil water contents: trafficability and vegetation soil water stress, corresponding to detrimental effects of water logging and insufficient plant accessible water. The presence of burrows could somewhat mitigate the risks for soil water logging and hence increase trafficability of the land. However, a trade-off was observed in a corresponding increase of the risk for water deficiency, although this may be a model artefact as water uptake related to crop type was not included in the model. A sensitive aspect in our data is the number of hydrologically active earthworm burrows which vary by season. The results of this study should not be extrapolated to other soil types or land uses and management. For extrapolation purposes, further research would be required. The output of the modelling is input to an economic assessment, e.g. by quantitatively assessing the occurrences of soil water deficiency and water logging as risk to farmers’ income stability as a result of reduced yields or loss of entire crops.