Stable carbon isotope analysis of fluvial sediment fluxes over two contrasting C4-C3 semi-arid vegetation transitions

RATIONALE Globally, many drylands are experiencing the encroachment of woody vegetation into grasslands. These changes in ecosystem structure and processes can result in increased sediment and nutrient fluxes due to fluvial erosion. As these changes are often accompanied by a shift from C4 to C3 vegetation with characteristic d13C values, stable isotope analysis provides a promising mechanism for tracing these fluxes. METHODS Input vegetation, surface sediment and fluvially eroded sediment samples were collected across two contrasting C4-C3 dryland vegetation transitions in New Mexico, USA. Isotope ratio mass spectrometric analyses were performed using a Carlo Erba NA2000 analyser interfaced to a SerCon 2022 isotope ratio mass spectrometer to determine bulk d13C values. RESULTS Stable isotope analyses of contemporary input vegetation and surface sediments over the monitored transitions showed significant differences (p