Particulate organic carbon sources and delivery to river channels in the Somerset Levels ECSFDI priority catchment, southwest UK

Abstract

Soil erosion and sediment delivery represent an important transport pathway for particulate organic carbon (POC) in fluvial systems. Catchment management strategies designed to protect soil resources therefore require reliable information on the significance of key sediment sources for POC transfers. Within this context, a composite fingerprinting procedure, incorporating uncertainty and prior understanding of catchment processes, was used to investigate the significance of eroding pasture or cultivated topsoils, damaged road verges, channel banks/subsurface sources and point source discharges as POC sources and the associated net delivery to river channels across the Somerset Levels, southwest UK. Overall mean relative contributions of POC from the five individual sediment sources were estimated at 41 ± 2% (pasture topsoils), 18 ± 1% (STWs), 15 ± 2% (cultivated topsoils), 14 ± 1% (damaged road verges) and 12 ±2% (channel banks/subsurface sources). Respective estimates of net sediment‐associated POC delivery to watercourses, provided by integrating sediment source ascription 50th percentiles bounded by 95% confidence limits, organic carbon content, sediment yield ranges and sub‐catchment or land use areas, ranged between 2.4–48.5 kg ha⁻¹ yr⁻¹, 0–16.5 kg ha⁻¹ yr⁻¹, 1.7–119.2 kg ha⁻¹ yr⁻¹, 0–13.8 kg ha⁻¹ yr⁻¹ and 0–7.4 kg ha⁻¹ yr⁻¹.

Keywords:

• Particulate organic carbon
• sources
• uncertainty
• catchment management