The Influence of Hydrologic Conditions and Successional State on Dissolved Organic Carbon Export from Forested Watersheds

Concentration and export of dissolved organic carbon (DOC) were compared in streams draining four southern Appalachian watersheds with different treatment histories in 1969—1970 and again in 1979—1980. In 1969—1970 the watersheds were: old field (1 yr old), hardwood coppice (7 yr old), white pine (13 yr old), and mature hardwood (undisturbed for at least 45 yr). DOC concentrations in 1969—1970 were three to four times greater than in 1979—1980 on all watersheds, and the differences among watersheds were consistent both years: old field > hardwood > pine > coppice. Concentrations were always greater during the growing season. Annual runoff was 50% greater in 1979—1980, and annual DOC export in 1979—1980 was half the 1969—1970 value in all watersheds. Annual export was greatest from the hardwood and old—field watersheds and least from pine and coppice watersheds during both years. Although there appears to be a trend toward decreasing DOC concentration and export over the first two decades of secondary succession, differences caused by periodic variations in runoff are far more significant than any successional changes observed.