Solution Parameters Influencing Dissolved Organic Carbon Levels in Three Forest Soils

A column study was conducted using selected horizons from three soils that were leached with pH 4.8 solutions containing either SO 2− 4 (0–0.208 mmol L −1 ) or NO − 3 (0–0.16 mmol L −1 ) at various ionic strengths (0.2–2.53 mmol L −1 ). The quantity of dissolved organic C (DOC) release into the soil solution decreased with increasing ionic strength, with DOC levels remaining constant for ionic strengths > 1.10 mmol L −1 . The addition of SO 2− 4 (0–0.208 mmol L −1 ) to the leaching solution resulted in elevated DOC levels over a wider range of ionic strengths, while DOC levels increased substantially for NO − 3 additions only at conditions of low ionic strength <0.5 mmol L −1 and higher NO − 3 concentrations > 0.048 mmol L −1 . The portion of total measurable DOC attributed to anion source, compared to that of ionic strength, was observed to increase under conditions of low ionic strength and high anion concentration. Results suggest that anion composition and ionic strength may regulate DOC levels in solution.