Dynamics of organic and black carbon in high-altitude soils: Insights from morphological, chemometric, and...

Black carbon (BC), an emerging contaminant and significant climate forcer, enters soil through deposition after residing in the atmosphere. Despite its role in long-term carbon storage and cycling, BC remains understudied in soil due to limited knowledge of its complex physical and chemical characteristics, variability, and fate. This knowledge gap is particularly prominent in India, a global BC emission hotspot, especially in its fragile mountainous ecosystems. To address this, a three-year (2020-2023) study investigated BC and soil organic carbon (SOC) dynamics across various land-use types in Kodaikanal, a high-altitude region in the Western Ghats of southern India. BC and SOC variations were assessed over time using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) and Fourier transform infrared spectroscopy (FTIR) to analyse morphological, structural, and chemical characteristics. Results revealed strong seasonal and inter-annual variability in BC concentrations across land-use types. The BC/SOC ratio was highest in fire-prone forests, suggesting wildfire-induced BC accumulation, while urban BC was linked to tourism and vehicular emissions. SEM-EDX and FTIR confirmed the presence of condensed aromatic BC structures, with lignin and cellulose dominating forest and agricultural soils. Environmental factors such as temperature, precipitation, and soil mineral composition significantly influenced BC and SOC distribution. These findings challenge the assumption of BC's high recalcitrance, highlighting its dynamic nature and emphasizing the need for detailed seasonal-scale studies to better understand the stability and sequestration potential of BC that can enable devising better environmental management strategies.