Multi-scale evaluation of soil functional indicators for the assessment of water and soil retention in Mediterranean semiarid landscapes

Abstract

Ecosystem monitoring and assessment are often based on functional indicators, which provide integrated and yet simple and affordable measures of key ecosystem functions. The landscape function analysis (LFA) assesses ecosystem functioning through three indices that represent basic soil functions: surface stability, infiltration, and nutrient cycling. Given the high scale-dependency of hydrological and erosion processes in semiarid ecosystems, the validation of the stability and infiltration indices requires a multi-scale approach, which has not been applied by previous works. Using records from a four-year monitoring of a semiarid landscape in SE Spain, we evaluated the LFA infiltration and stability indices against quantitative measurements of water and sediment flows at multiple scales. At the finest scale, the indices correctly reflected the higher infiltration and lower sediment production of plant patches as compared with bare-soil interpatches. The infiltration index also captured the spatial variation in the infiltration capacity of bare-soil interpatches. At the hillslope scale, total runoff was inversely related to the average infiltration index for bare-soil interpatches, but it was not related to the global infiltration index, which combines the values from both bare-soil interpatches and plant patches. These results suggest that the hydrological response of semiarid hillslopes depends mainly on the variation in the functioning of bare-soil interpatches. Total sediment yield from the hillslope plots was not related to the stability index. At the catchment scale, both the bare-soil interpatch and the global infiltration indices correctly captured the variability in total runoff produced by three micro-catchments of comparable size. The bare-soil infiltration index predicted bare-soil infiltration rate and hillslope runoff better than common simple indicators of soil functioning such as soil organic carbon, stone cover, crusted bare-soil cover, bulk-density and plant cover, and exhibited a similarly high indicatory potential that a variety of plant spatial-pattern indicators. In contrast to the multi-scale validation of the infiltration index, the indicatory potential of the stability index was only proved for the most contrasting soil conditions in the study site, pointing to a lower sensitivity of this latter index.