Contribution of SO3 to the acid neutralizing capacity of Andosols exposed to strong volcanogenic acid and SO2 deposition

Abstract

SummarySoil response to acid and sulphur inputs is influenced largely by the soil's physico‐chemical properties. We studied the effects of such depositions in two types of Andosols exposed to volcanogenic emission (Masaya, Nicaragua), namely Eutric Andosols rich in allophanic constituents, and Vitric Andosols rich in volcanic glass. Small mineral reserves and large contents of secondary short‐range ordered minerals indicate a more advanced weathering of the Eutric than the Vitric Andosols. Strong correlations between soil specific surface and oxalate‐extractable Al, Si and Fe contents highlight the predominant contribution of short‐range ordered minerals to surface area.Both types of Andosols showed a decrease in pH upon acid input. Sulphur deposition increased the soil's S content to 5470 mg S kg−1. However, the acid neutralizing capacity of the soil solid phase (ANCs) was not significantly affected by the acid and S inputs. Non‐exchangeable (mineral reserve) and exchangeable cations and total contents of sulphur and phosphorus dictate most of the ANCs variation. In the Vitric Andosols, mineral reserves contributed up to 97% to these four additive pools, whereas the exchangeable cations accounted for 1–4%. In the Eutric Andosols, the contribution of mineral reserves was less (71–92%), but the exchangeable cation content was greater (1–20%), whereas the contribution of sulphur and phosphorus was significant at 1–15% and 2–7%, respectively. The main process involved in H+ consumption is mineral weathering in Vitric Andosols and ion exchange in Eutric Andosols.