Geomorphic connectivity as a driver for the soil bioindicator distribution, implications for future research and modeling

Abstract

Hydrological structural connectivity, the degree to which water can move across a landscape, significantly influences water and sediment transport. While its impact on these processes is well established, the extent of its influence on soil biological activity is still being researched. This study examines the link between geomorphic connectivity (CI) and soil microbial functional indicators in the Greve watershed, Tuscany (Italy), by developing a new weighted connectivity index (CIFB) that inte grates the fungi-to-bacteria (F:B) abundance ratio as a bioindicator. Using high-resolution geospatial data, rare earth elements (REEs), satellite indices (NDVI, NDWI), and machine learning (Stochastic Gradient Boosting, SGB), were modeled relationships between geomorphic variables, soil erodibility (K factor), and microbial indicators. Results showed that CI ranged from -9.0 and +0.6, but the weighted index, CIFB, ranged from -10.0 and +4.0. This showed that the F:B ratio weighting caused an increase in the range of connectivity values between landform units, which implies it strengthened the relationships between them. The key finding is that CIFB can better identify hidden areas of sediment coupling and decoupling within a landscape. Under the physiographic environmental variables of the study area, the spatial distribution of F:B ratio was mainly related to CI, flow path length and K factor. The proposed approach, while requiring further development, show great potential for monitoring and conserving ecosystems, especially within watersheds, not just in the Mediterranean region but also in other vulnerable areas.