Influence of vegetation structure on isotope content of throughfall and soil water

• Published in: Hydrological processes 2000-06, Vol.14 (8), p.1439-1448
• Main Authors: Brodersen, Christine, Pohl, Stefan, Lindenlaub, Martin, Leibundgut, Christian, Wilpert, Klaus v
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; enrichment; Exact sciences and technology; forest heterogeneity; Germany, Black Forest; Hydrogeology; Hydrology. Hydrogeology; oxygen-18; soil water; Soils; Surficial geology; throughfall
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/1099-1085(20000615)14:8<1439::AID-HYP985>3.0.CO;2-3

The stable isotope oxygen‐18 is often used as a natural tracer in stream‐flow separation studies in forested catchments. Knowledge about the 18O content of throughfall and soil water is needed. The present study was conducted in order to assess the effect of vegetation structure on the stable isotope 18O composition of rainwater input during its passage through the canopy and into the unsaturated zone. The research area was a small (0\1 km2) forested catchment in the mountainous ‘Black Forest’ region of southern Germany. During the 3‐month periods (September to December 1995 and April to July 1996) several structural units were instrumented according to tree species (beech and spruce) and canopy density. Overall throughfall was enriched compared with open rainfall by +0\38‰ and +0\36‰ for spruce and beech, respectively. Considerable differences existed in the results of the crown centre and the crown periphery sites. Throughfall in the crown centre showed a higher degree of enrichment, with a mean value of +0\30‰ for beech and +0\37‰ for spruce. Enrichment and depletion were observed in the lower canopy density locations. Mean results of the crown periphery were similar to those of open precipitation (+0\15‰ for beech and −0\01‰ for spruce). Soil water was sampled at five different depths (0, 15, 60, 120 and 180 cm). The signals of individual rainfall events could be traced down to a depth of 60 cm. The soil water in the upper layers followed the seasonal trend in the precipitation input. At a depth of 180 cm, soil water had a very constant δ18O value. The 18O composition of the soil water at various depths at different locations showed a similar behaviour. No detectable differences could be found between the structural units in the different layers, except at 180 cm depth. This might be attributed to downslope directed flow at that depth. Copyright © 2000 John Wiley & Sons, Ltd.