The acid buffer capacity of some finnish forest soils: Results of acid addition laboratory experiments

Batch acid addition experiments were carried out to determine the acid buffer capacities (amount of acid required to lower soil pH by one unit) of forest soils. Samples of O, E, B (or BC), and C horizons taken from 29 podzolic profiles in southern Finland were used in the experiments. Subsamples of soil were equilibrated for 24 h with NaCl solution containing additions of HCl acid. Cation exchange, mineral dissolution (weathering), and the protonation of organic matter all appeared to have been involved in the buffering of the acid additions. For the O horizon samples, most of the cations released in response to the acid additions were base cations. For the mineral soil samples, most of the cations released were Al³⁺ ions. With the exception of a few samples, the added acid was not fully neutralised and pH was lowered even with the lowest addition treatment. However, the acid addition treatments corresponded to many times the regional annual acid deposition load (1.6–2.0 cmol(c) m^?2). Calculated acid buffer capacities (cmol(c) kg^?1 pH^?1) ranged from 9.8 to 40.8 for O horizon soil samples and from 0.1 (C horizon) to 5.2 (E horizon) for the mineral soil samples. Total acid buffer capacities for a profile (to a depth of 50 cm) ranged from 500 to 2349, with a mean value of 1091 cmol(c) m^?2 pH^?1. It is concluded that, in addition to CEC and base saturation, acid buffer capacity is a useful measure to describe the ecological effects of acid deposition on soil.