Controls on dissolved organic carbon quantity and chemical character in temperate rivers of North America

Understanding the processes controlling the transfer and chemical composition of dissolved organic carbon (DOC) in freshwater systems is crucial to understanding the carbon cycle and the effects of DOC on water quality. Previous studies have identified watershed-scale controls on bulk DOC flux and concentration among small basins but fewer studies have explored controls among large basins or simultaneously considered the chemical composition of DOC. Because the chemical character of DOC drives riverine biogeochemical processes such as metabolism and photodegradation, accounting for chemical character in watershed-scale studies will improve the way bulk DOC variability in rivers is interpreted. We analyzed DOC quantity and chemical character near the mouths of 17 large North American rivers, primarily between 2008 and 2010, and identified watershed characteristics that controlled variability. We quantified DOC chemical character using both specific ultraviolet absorbance at 254 nm (SUVA₂₅₄) and XAD-resin fractionation. Mean DOC concentration ranged from 2.1 to 47 mg C L⁻¹ and mean SUVA₂₅₄ ranged from 1.3 to 4.7 L mg C⁻¹ m⁻¹. We found a significant positive correlation between basin wetland cover and both bulk DOC concentration (R² = 0.78; p