Forest organic acid concentration

P. A. W. van Hees, S. I. Vinogradoff, A. C. Edwards, D. L. Godbold, and D. L. Jones, Low molecular weight organic acid adsorption in forest soils effects on soil solution concentrations and biodegradation rates, Soil Biol. Biochem. 35, 1015-1026 (2003). 

Concentrations of LMW organic acids are high enough in some soils that salts of the acids are precipitated. Weddellite and whewellite (hydrated calcium oxalate) have been observed as coatings on fungal hyphae in forest soils (67). Oxalate, often one of the more abundant of the identifiable LMW organic acids, significantly enhances oxide dissolution in laboratory studies (22, 23). 

Laboratory studies provide some insight into the possible role of DOM onstituents in metal mobilization in soils. These studies suggest that LMW organic ligands, specifically bidentate ligands, are more likely to promote min-rral dissolution than are humic substances. LMW organic acids have been identified in soil waters and in leachates of forest litter at concentrations sufficient to effect oxide dissolution. 

Because Pb has to be transferred from the solid phase to the aqueous phase before it can be taken up by plants and aquatic organisms, the concentration of Pb in natural waters can be a sensitive indicator of the potential for Pb to become biologically available . To estimate how much of this Pb might be transferred to the aqueous phase, solutions collected from ten Swiss forest soils were measured for concentrations of total dissolved Pb (Peter Blaser, unpublished data) and found to range from < 1 to >60 p-g/L. Five of the profiles were acidic (pH 4-5) and these contained 20-60 pg/L Pb in the aqueous phase of the surface layers. These layers, however, are the most critical ecologically, as they represent the biologically active zone of acidic forest soils this is also the zone which has been most impacted by anthropogenic Pb. 

The effects of five phenolic compounds, catechol, protocatechuic, p-coumaric, p-hydroxybenzoic, ferulic acids and their mixture were studied on pH, organic matter, organic-nitrogen, total phenolic content and certain inorganic ions of forest mineral soils (Ae and B horizons). The A- and B-horizon soils, were amended with 104 M concentration of each phenolic compound and their mixture. In general, soil properties were affected by phenolics amendement. However, soils amended with catechol did not influence any of the soil characteristics. Contents of organic matter, nitrogen and phosphate were lower in soils amended with different phenolic compounds compared to the unamended control soil (Inderjit and Mallik, 1997). 

---