Influence of Land Use and Geochemical Landscape Position on the Vertical Distribution of Soil Organic Carbon in a Protected Regional Park

Soil organic carbon (SOC) is a key indicator of soil quality, ecosystem functioning, and climate regulation. However, the combined influence of land use and geochemical landscape position on the vertical distribution of SOC remains insufficiently understood, particularly in protected landscapes. This study evaluated SOC concentration in agricultural land, grasslands, and forests located within autonomous and superaqual geochemical landscapes of the Neris Regional Park (Lithuania). Composite soil samples were collected from three depth intervals (0–10, 10–20, and 20–30 cm) following the European Soil Sampling Protocol, and SOC concentration was determined using a Shimadzu SSM-5000A analyzer. SOC concentration generally decreased with increasing soil depth regardless of land use. Agricultural soils generally exhibited lower SOC concentrations (0.84–4.41%) than forest and grassland soils, although a comparatively high value of 4.41% was recorded at one agricultural plot. In forest ecosystems, SOC concentration ranged from 1.12–1.47% in autonomous landscapes and from 4.17–4.98% in superaqual landscapes, indicating approximately a threefold difference between geochemical positions. Grassland soils contained 1.33–2.54% SOC in autonomous landscapes and 2.16–3.28% in superaqual landscapes. These findings characterize observed patterns of SOC concentration variability associated with land use, geochemical landscape position, and soil depth within the investigated protected landscape. The reported findings contribute to understanding the observed vertical and spatial distribution of SOC concentration within protected landscapes and provide a basis for future investigations incorporating complementary soil physicochemical measurements and broader spatial sampling designs.