Nitrate, Sulfate, and Biphosphate Retention in Acid Forest Soils Affected by Natural Dissolved Organic Carbon
- Klaus Kaiser * and
- Wolfgang Zech
Natural dissolved organic carbon (DOC) may restrict the sorption of inorganic anions in acid forest soils due to the competition for binding sites. Competitive effects of DOC on the sorption of H2PO−4, SO2−4, and NO−3 were tested in experiments with intact soil cores taken from different soil types. Solutions were applied containing the inorganic anions at concentrations of 0.06, 0.24, and 0.12 mmol L−1, respectively, and the concentrations of DOC of the initial solutions varied between 0 and 5.6 mmol L−1. Most soil horizons showed only a slight decrease of the H2PO−4 sorption as the DOC concentration increased, indicating a higher sorption affinity of H2PO−4 than of DOC. Increase of the DOC concentration resulted in a strong decrease of the binding of SO2−4 for all soils investigated. Thus, sorption of SO2−4 seems to be weaker than that of DOC. At the highest DOC concentrations, a net release of SO2−4 nearly equal to the approximate amount of sorbed carboxyls was noticed for most soils. Thus, DOC may inhibit the sorption of SO2−4 to soils completely or even remove SO2−4 stored in soils. Because NO−3 was found not to sorb on soils, no competitive effects of DOC were observed. The results indicate DOC to be a factor controlling the storage and the mobility especially of SO2−4 in acid forest soils, whereas its effect on the sorption of phosphate and NO−3 seems to be less important.
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