Sorption of dissolved organic carbon in soils: effects of soil sample storage, soil-to-solution ratio, and temperature
Introduction
Release and retention of dissolved organic carbon (DOC) affects the filter function and nutrient status of soils. It controls DOC-induced mobilization and translocation of metals and organic pollutants Berggren et al., 1990, Totsche et al., 1997 and the leaching of organic nutrient species (Donald et al., 1993). Binding of DOC also changes the properties of the sorbing soil material itself. Organic coatings on mineral particles improve their sorption capacity for metal cations and organic xenobiotics (Murphy and Zachara, 1995), reduce the further binding of organic matter (Kaiser and Zech, 1998) and anions (Sibanda and Young, 1986), affect the water retention Chittleborough et al., 1992, Jozèfaciuk et al., 1996, and increase the stability against acidic dissolution (Smeck and Novak, 1994). Finally, DOC release and retention are the driving forces of podzolization Dawson et al., 1978, McDowell and Wood, 1984.
These large environmental and pedological impacts induced an intensive research on the release and retention of DOM in soils. Besides some field studies Cronan and Aiken, 1985, McDowell and Likens, 1988, Guggenberger and Zech, 1993, the majority of experiments was carried out under controlled laboratory conditions. The objectives of these studies varied. Some of them aimed at the release of organic material from the forest floor Christ and David, 1996, Gödde et al., 1996, others tried to identify the parameters the DOM retention in mineral soil relates to. Investigated factors were soil constituents Jardine et al., 1989, Moore et al., 1992, Kaiser et al., 1996, solution composition Jardine et al., 1989, David and Zech, 1990, and DOM composition (Kaiser et al., 1997). Two principal approaches were used for the sorption studies: (i) batch experiments (e.g., Jardine et al., 1989) and (ii) column experiments (e.g., Qualls and Haines, 1992). Depending on the setup, both approaches may give similar (Qualls and Haines, 1992) or different findings (Totsche et al., 1997). Even within the batch studies, there were various differences in the experimental conditions such as differing soil-to-solution ratio, temperature, contact time, agitation mode, and preparation and storage of soil samples, making it difficult to compare the results.
In this study, batch sorption experiments were conducted at varying soil-to-solution ratios, temperatures, and soil sample storage methods. The objective was to evaluate how different experimental conditions may affect the sorption of DOM.
Section snippets
Soil samples
Subsoil samples (Bh, Bs1, and Bs2 horizons) were taken in October 1993 from the Hohe Matzen in the Fichtelgebirge, NE Bavaria, Germany. The soil was a Typic Haplorthod (Soil Survey Staff, 1994) derived from granitic solifluction material. The site had a forest cover mainly composed of 90-year old Norway spruce (Picea abies Karst. L.), and some few European larch (Larix europea Mill.) and European beech (Fagus sylvatica L.). Ground vegetation was dominated by blueberry (Vaccinium myrtillus L.)
Results and discussion
In all different experiments, the sorption was adequately described by the IM approach, regressing the sorbed amount of DOC against the initially added DOC amount. The coefficients of determination (r2) for the sorption of total and hydrophobic DOC ranged from 0.99 to 1.00. Somewhat smaller r2 values (0.84–1.00) appeared for the hydrophilic DOC. The reason for that was that for the Bh horizon, the relationship between sorbed and added hydrophilic DOC was slightly curved because of reduced
Conclusions
The results indicated that the affinity parameter (m) of the IM approach was slightly influenced by the type of soil sample storage, experimental temperature, and soil-to-solution ratio. It seems therefore possible to compare the IM affinity parameters (m) obtained for soils at differing experimental conditions directly. What might complicate such comparisons is the different nature of DOC used in the experiments (Moore and Matos, 1999). Dissolved organic matter fractions have different
Acknowledgements
The study was funded by the Deutsche Forschungsgemeinschaft (DFG) joint research program ROSIG.
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2022, GeodermaCitation Excerpt :The DOM composition in our Ca(NO3)2 soil extracts is dominated by the Hy fraction, which ranges from 38 to 69% with an average of 58%. The extracted amount of DOC from soil by water or dilute salt extracts after soil drying is known to increase, with a more pronounced drying effect for the Hy fraction (Kaiser et al., 2001; Koopmans et al., 2006; Koopmans and Groenenberg, 2011; Supriatin et al., 2015). The release of Hy upon soil drying has been attributed to osmotic shock and subsequent lysis of microbial and fungal cells (Kaiser et al., 2001; Zsolnay et al., 1999; Koopmans and Groenenberg, 2011).