Imogolite related to podzolization processes in Danish podzols

The possible presence of imogolite was investigated in three Danish podzols underneath heather, spruce, and in a glade in a coniferous forest with ferns and grasses. Only a small quantity of proto-imogolite allophane material was detected in the lower B horizons underneath heather and in the glade. No well-crystallized imogolite was detected in any of the ecosystems. The relation to present-day soil-forming processes was studied in parallel under heather and spruce. Soil water was collected monthly from December 1997 to May 1999. The soil water sampling depths correspond to levels below the A, E, Bh, and Bs horizons. Identification of imogolite was done by chemical extractions, infrared spectrometry (IR), and transmission electron microscopy (TEM). Soil water analysis showed high Al concentrations underneath the spruce system compared to the heather system and compared to what was found elsewhere in Scandinavia. The elevated concentration was not due to weathering of Al-containing primary material. Instead, the source was degradation of formerly deposited organically complexed metals and up-concentration due to a high interception loss. C/Al and C/Fe ratios have been used as indicators of immobilization of metal-organic complexes by saturation in the B horizon. Former investigations from northern Scandinavia showed that the saturation ratios achieved from laboratory investigations were never reached in the field. Contrary to this, ratios, clearly indicating saturation were found in this study. Therefore, immobilization of organo-metal complexes by saturation is possible in the investigated acid systems.