Comparison of water-stable aggregates on different soil types and land-uses in a Portuguese Mediterranean catchment

Erosion is one of the main soil threats in the Mediterranean region, leading to degradation and desertification of several areas. Water stable aggregates (WSA) is a rate of the extent to which soil aggregates resist falling apart when wetted and hit by rain drops, indicating also the resistence of soil to compaction and soil quality status. This study aims to determine the WSA in differrent soils, characterized by distinct land-uses and soil types. This work is part of Ribeira dos Covões catchment research, in the suburbs of Coimbra, the largest city of central Portugal, where research dealing with soil and hydrological properties has been developed for long time. WSA were investigated for agricultural and forest soils, on both sandstone and limestone. Soil surface samples (0-10cm) were collected in December 2020, and analysed through wet sieving method which quantifies the amount of water-stable soil aggregates fractions.

Not surprisingly, the results showed that forest soils contain a much higher proportion of water-stable soil aggregates of larger fractions than agricultural soil, where the smaller fractions prevailed. Similar results have been also reported in previous studies and found during our previous research at Praha-Suchdol locality (Housle), in Czech Republic. The fraction distribution of WSA in sandstone and limestone was comparable for forest soils. In case of agricultural soils, distribution of WSA was slightly different. WSA are a relevant part of soil surface layer, with important impacts on other soil properties (e.g. soil moisture, hydrophobicity, infiltration), thus affecting the rainfall-runoff-erosion processes, previously investigated in the study area. Further research will be developed to better assess WSA differences between distinct forest types, given the relevance of vegetation species for example on hydrophobicity and WSA dynamics. A better understanding of WSA in different soil types will be useful to support improved soil management and mitigate land degradation.