Limited carbon contents of centuries old soils forming in legacy sediment

Accelerated erosion from European agriculture overwhelmed transport capacities of relatively low-gradient Piedmont watersheds and triggered widespread and massive sediment deposition on floodplains, referred to as legacy sediments. While erosion-driven soil loss on the Southern Piedmont landscape has been widely studied, the resultant legacy sediments deposited on hillslopes, floodplains, and in channels appear remarkably understudied. In the interim between deposition and future remobilization, legacy sediments are undergoing soil formation in ways that impact carbon stocks, nutrient retention, and a number of other soil-sediment functions. Here, we use a pedological framework to understand the dynamics of these legacy sediments by constraining the time since deposition and redevelopment of vegetation and the soil profile. In this study, we characterized the properties of legacy sediment and buried, pre-legacy sediment alluvium, established the timing of legacy sediment deposition and its volume in a 600-ha watershed, and analyzed the impact of accelerated sedimentation on floodplain soil carbon (SOC) storage.