DISSOLVED ORGANIC-CARBON FRACTIONS IN SOIL AND STREAM WATER DURING VARIABLE HYDROLOGICAL CONDITIONS AT BIRKENES, SOUTHERN NORWAY

Spatial and temporal variations in the composition of dissolved organic carbon (DOC) in stream and soil water of the acidified Birkenes catchment were studied during summer and autumn 1990, Hydrophobic and hydrophilic acids were the dominant fractions in the soils (dominated by podzols and peats) and brook, accounting for approximately 90% of total DOC. The podzol displayed a vertical gradation of DOC fractions, with hydrophobic acids dominating in the O horizon (approximately 65%) and hydrophilic acids dominating in the E and B horizons (approximately 60%). In the bogs, hydrophilic acids were the dominant fraction at all depths. Temporal variations in the relative contributions of the various DOC fractions were most pronounced in the podzol O horizon and the brook during successive autumn rainstorms, and small in the mineral soils and bogs. In the brook, DOC increases at peak discharge were dominated by hydrophilic acids. If stream water was assumed to be a conservative mixture of water from the podzol O and B horizons and from the deeper layers in the bog surrounding the stream, 92% of the variability in the concentration of hydrophobic and hydrophilic acids in the stream could be explained. This mixing analysis suggested that base flow largely originated in the deeper layers of the bogs, while peak flow was primarily made up of B horizon (approximately 50-65%) and O horizon (approximately 35-50%) water.