ION-CHROMATOGRAPHIC ANALYSIS OF LOW-MOLECULAR-WEIGHT ORGANIC-ACIDS INSPODOSOL FOREST FLOOR SOLUTIONS

Low molecular weight organic acids (LMWOA) from root exudates, decompo sing organic matter, and other sources are important ligands involved in solution complexation reactions as well as ligand exchange reaction s at mineral surfaces. The purpose of this study was to (i) develop an ion chromatography method that could be used to determine LMWOA in so il solutions from Spodosols, (ii) assess methods for preserving LMWOA in soil solutions, and (iii) evaluate LMWOA concentrations in forest B oor solutions during a growing season. Solutions were collected weekly from zero-tension lysimeters installed within the forest floor (fores t floor leachate collectors). Limits of quantitation for acetic, formi c, malonic, oxalic, phthalic, and citric acids were 0.35, 0.14, 0.43, 0.41, 0.07, and 0.04 mu M, respectively, which in some cases are an or der of magnitude loa;er than reported in previous studies. Freezing so il solutions after filtering resulted in the best recoveries (between 90 and 100% for all LMWOA); other methods of preservation, such as fil tering alone and filtering and storing at 4 degrees C, resulted in low er recoveries. The average concentrations of LMWOA in the forest floor solutions were 10 mu M acetic acid, 0.7 mu M formic acid, and 3.3 mu M oxalic acid. Dissolved organic C from the forest floor contained a m aximum concentration of 2.0% acetic acid, 0.01% formic acid, and 0.15% oxalic acid. There were no apparent temporal patterns in LMWOA concen trations, except for a decrease in LMWOA concentrations from late Sept ember to a minimum in October.