Low molecular weight organic acid adsorption in forest soils: effects on soil solution concentrations and biodegradation rates

Low molecular weight (LMW) organic acids are believed to play a key role in many rhizosphere and pedogenic processes; However, their efficiency is likely to depend on their susceptibility to sorption and biodegradation. The sorption characteristics of three organic acids (citrate, oxalate and acetate) and phosphate were examined over the concentration range 0–1000 μM in three coniferous forest soil profiles. Sorption to the soil's solid phase could be adequately described by the Langmuir equation with sorption capacity following the horizon series: B>C>E>O. The strength of anion sorption followed the series: phosphate>oxalate≥citrate≫acetate. Calculations indicated that between 50 and 95% (O and E horizons) and >93% (B horizons) of these LMW organic acids entering the soil will become sorbed to the solid phase. The amount of organic acids predicted to be present on the solid phase at typical soil solution concentrations ranged from