Sorption of dissolved organic carbon in soils: effects of soil sample storage, soil-to-solution ratio, and temperature

Experiments on the sorption of dissolved organic carbon (DOC) in soils were mainly conducted in batch approaches. Because varying setups were used in these studies, comparison of the results requires knowledge on the effects that different experimental conditions may have on the sorption of DOG. Thi s investigation evaluated the DOC sorption of soils using differently pretr eated soil samples (field-fresh (two sampling dates), air-dried, stored at 3 degreesC and -18 degreesC), at different soil-to-solution ratios (1:40, 1 :20, 1:10 and 1:5 w/v) and different temperatures (5 degreesC, 15 degreesC, 25 degreesC and 35 degreesC). The sorption of DOC was analyzed using the i nitial mass (IM) approach, which regressed the initial amount of sorbate (n ormalized to soil mass) against the sorbed amount (normalized to soil mass) . The DOC release - when a solution without DOC was added - strongly increa sed with temperature and soil-to-solution ratio. Among the different types of sample storage and preparation, air-drying resulted in the largest DOC r elease. The smallest release was from the field-fresh samples. Freezing and storage at 3 degreesC resulted in intermediate DOC release with freezing h aving the greater effect. The release from air-dried samples exceeded that of field-fresh samples by a factor of four at maximum. In contrast, none of the experimental setups influenced the slope of the IM isotherms. Thus, it seems possible to compare directly the binding affinity of DOC to differen t soils as determined at Varying experimental conditions. (C) 2001 Elsevier Science B.V. All rights reserved.