THE IMPACT OF ACID TREATMENT ON SOILWATER CHEMISTRY AT THE HUMEX SITE

The effects of acid treatment on soilwater dissolved organic carbon (D OC) and inorganic chemistry are being monitored at the Humic Lake Acid ification Experiment (HUMEX) in western Norway. The HUMEX project invo lves artificial acidification of half of a dystrophic lake and the cor responding drainage basin. Soil water chemistry data were collected fr om 30 monitoring lysimeters and 130 grid lysimeters. The samples from the monitoring lysimeters were collected before and, for a period of t wo years, after the onset of acid treatment. Operationally-defined fun ctional fractions of DOC showed that hydrophilic (HPI) and hydrophobic (HPO) acids account for 60% to 90% of the DOC. In soils rich in DOC, the HPO acids were dominant, whereas in mineral soil horizons low in D OC, the HPI acid fractions were highest. The amount of DOC relative to labile aluminum and iron may determine the HPO/HPI acid ratio. The su lphate concentration has increased more in the treated than in the ref erence side. Coincident decreases in DOC and organically complexed alu minum (Al(o)) concentrations were observed for surface histosol locati ons. The temporal and spatial variations in c(Al(o)) were mainly expla ined by variation in c(DOC).