The measurement of water stable isotopes (2H and 18O) allows us to track water movement along the ecohydrological cycle. With this basic objective the Ecohydro project -an interdisciplinary collaboration project between the Chair of Hydrology and the Chair of Ecosystem Physiology- is currently running a measurement setup for various ecophysiological and –hydrological parameters in the Black Forest. Here, the isotopic composition in the soil compartment (4 different depths, 9 plots) and tree xylem (at the base of the tree stem, mixed and pure stands of beech and spruce) is measured through in-situ isotope probes with high temporal resolution. Measurements currently take place under natural isotopic abundance conditions. Artificial labelling campaigns with deuterated water are planned for this year. These measurements allow for estimating root water uptake depths and amounts and take temporal shifts in root water uptake patterns by the different tree species into account. While stem base xylem measurements can be considered as an integrated signal of water from different soil depths and lateral distances, soil measurements are naturally limited to the close surrounding of the measurement probe. To secure a correct interpretation of the in-situ soil isotope profile data, it is therefore necessary to examine the rooting zone as a whole and to account for spatial heterogeneity and water distribution patterns along soil-vegetation pathways.

The aim of this thesis is to investigate the isotopic distribution in forest soil following an artificial labelling event. The focus will be on I) assessing the spatial heterogeneity within the rooting zone of trees and II) identifying potential patterns in the soil isotopic distribution in dependence to tree stem distance. In combination with stem base xylem measurements, the integrated root water uptake signal can be reconstructed regarding temporal as well as potential spatial effects.

After a labelling campaign (probably in Apr/May) soil core samples will be taken along a transect with increasing distance to tree stems and afterwards measured in the lab regarding their isotopic composition and water content. Thus, vertical 2D distributions can be generated and compared for different points in time. Isotope data from the destructive samplings will further be compared to the in-situ isotope probe data.

Field work, lab work, statistics, interdisciplinary work, creativity

Natalie Orlowski, Judith Mach

Dr. Natalie Orlowski: natalie.orlowski@hydrology.uni-freiburg.de; Tel. 0761 – 203 9283; M.Sc. Judith Mach: judith.mach@hydrology.uni-freiburg.de; Tel. 0761 – 203 9290

English/Deutsch

Literature will be provided.