Organic Carbon and Oxygen Demand Relationships in Stormflow from Southern Pine Watersheds1

Abstract

Total organic carbon (TOC) and chemical oxygen demand (COD) of stormflow from five undisturbed pine watersheds (1.5 to 2.8 ha) in northern Mississippi were determined during the 1976, 1977, and 1978 water years on both the solution and suspended sediment phases. Stormflow was measured in 0.9-m H-flumes and sampled with a Coshocton wheel. For the five watersheds, discharge-weighted solution TOC concentrations ranged from 6 to 16 mg/liter and solution COD concentrations ranged from 20 to 45 mg/liter. Watersheds with higher soil organic matter contents had higher solution and sediment TOC and COD concentrations in stormflow. Suspended sediment TOC concentrations indicated enrichment ratios (TOC sediment ÷ TOC soil) of 3.5 to 10.1 relative to their respective watershed soils. Presumably this TOC enrichment is related to an organo-clay enrichment of the suspended sediments. The discharge-weighted five-day biochemical oxygen demand in stormflow was low, ranging from 6 to 11 mg O2/liter. Mean solution plus sediment TOC yields ranged from 7.8 to 28.4 kg ha-1 year-1 of which 60 to 77% was transported vi the solution phase; the rest, in association with the sediment. Thus, the solution phase dominated the transport of TOC and COD from these watersheds. Rainfall input of TOC to the watersheds ranged from 38 to 49 kg ha-1 year-1 which exceeded solution plus sediment TOC yields.