Can Soil Organic Carbon Fractions Be Used as Functional Indicators of Wetlands?

This work aimed to determine whether the organic carbon in wetland soils correlated with physico-chemical characteristics of wetlands (e.g. nutrient content, pH) and differentiated wetlands according to their plant community composition definied by the CORINE Biotope nomenclature. 96 wetlands were sampled in southeastern France, belonging to 14 CORINE habitats grouped into 3 CORINE hydrological categories: wet meadows, peatlands and aquatic wetlands. The total organic carbon content, the carbon content of humic fractions (humic acid (C-HA), fulvic acid (C-FA) and C-humin), and water extractable organic carbon were measured in samples collected in the upper 20 cm soil layer. These soil organic carbon fractions correlated with pH and soil nutrient content but differed slightly among the 14 CORINE habitats. In contrast, soil organic carbon fractions greatly differed among the 3 CORINE hydrological categories. The C-FA/C-HA ratio was significantly lower for wet meadows and peatlands and the proportion of C-Humin was significantly higher for peatlands and aquatic wetlands. These soil organic carbon fractions inform on the hydrological status of wetlands and may consequently be used as functional indicator in addition to a plant-based classification as the CORINE Biotope nomenclature.