Importance of humic substances for carbon and nitrogen transport into southeastern United States estuaries

For the time period 1974–1993, fluxes were estimated of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) brought to the salt marshes of Georgia and South Carolina by eight rivers, which drain approximately 75% of the upland watersheds of these estuaries. During this period, concentrations of DOC and DON averaged 5–28 mg C l−1 and 0.35–0.75 mg N l−1, respectively. The DON represented 40–90% of the total dissolved nitrogen (TDN) in the rivers during that period. River inputs to the marsh estuaries averaged 32.4±8.8 thousand tonne yr−1 for DOC and 27.8±10.0 hundred tonne yr−1 for DON. These inputs represent approximately 0.6 and 0.15%, respectively, of the DOC and DON estimated to be produced in situ in the salt marshes.