Sediment driven redistribution of manganese, copper, and cobalt in alluvial soils of a floodplain agricultural landscape

Floodplain agroecosystems receive periodic inputs of trace elements through sedimentation, influencing soil geochemistry and plant nutrition. This study quantified the long-term influx of manganese, copper, and cobalt via flood sediments into reclaimed arable lands in the Oka River floodplain (Ryazan region, Russia) from 2022 to 2025. Field investigations employed sediment traps across a 20-hectare experimental site. Mobile fractions of the three microelements in sediments and underlying alluvial soil were analyzed using atomic absorption spectrometry. Average annual sediment load during flood years was 10.8 t/ha, with considerable interannual variability. Manganese concentrations in sediments exceeded those in underlying soil by 3.2%, while copper and cobalt were reduced by 26.4% and 21.3%, respectively. Mean annual inputs were 764.4 g/ha for Mn, 143.9 g/ha for Cu, and 36.8 g/ha for Co, representing 0.50%, 0.35%, and 0.38% of the respective mobile pools in topsoil. Regression models (R² = 0.996–1.0) described nonlinear relationships between sediment load and microelement concentrations. The accumulation sequence in sediments (Mn > Co > Cu) reflects differences in geochemical mobility and sorption characteristics. Regular sediment-borne micronutrient inputs replenish plant-available pools, counteracting depletion from crop removal, particularly under monoculture systems.