Studies were conducted in conjunction with the Integrated Lake-Watershed Acidification Study (ILWAS) to examine the chemistry and leaching patterns of soluble humic substances in forested watersheds of the Adirondack region. During the summer growing season, mean dissolved organic carbon (DOC) concentrations in the ILWAS watersheds ranged from 21–32 mg C l−1 in O/A horizon leachates, from 5–7 mg C l−1 in B horizon leachates, from 2–4 mg C l−1 in groundwater solutions, from 6–8 mg C l−1 in first order streams, from 3–8 mg C l−1 in lake inlets, and from 2–7 mg C l−1 in lake outlets. During the winter, mean DOC concentrations dropped significantly in the upper soil profile. Soil solutions from mixed and coniferous stands contained as much as twice the DOC concentration of lysimeter samples from hardwood stands. Results of DOC fractionation analysis showed that hydrophobia and hydrophilic acids dominate the organic solute composition of natural waters in these watersheds. Charge balance and titration results indicated that the general acid-base characteristics of the dissolved humic mixture in these natural waters can be accounted for by a model organic acid having an averagepKa of 3.85, an average charge density of 4–5 μeq mg−1 C at ambient pH, and a total of 6–7 meq COOH per gram carbon.
