Measurements of water stable isotopes (2H and 18O) allow to track water movement along ecohydrological pathways. An interdisciplinary collaboration project (“Ecohydro”) between the Chair of Hydrology and the Chair of Ecosystem Physiology is currently running a measurement setup for various isotopic, ecophysiological and hydrological parameters in the Black Forest (Ettenheim). Here, the isotopic composition in the soil compartment and tree xylem of mixed and pure stands of beech and spruce are 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 2022. 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. A new isotope method aims at taking discrete vapor samples through the in-situ isotope probes into airtight bags for a later analysis in the lab. The applicability of this lab-based method should be tested in the field (Ettenheim).

The aim of this thesis is to transfer a lab-based measurement approach to the field and compare it to the in-situ isotope data continuously monitored at the field site in Ettenheim. Natural abundance in trees as well as the isotopic distribution in forest soil and trees, following an artificial labelling event will be measured. The focus will be on I) further development of a lab-suitable approach for deployment in the field II) analyzing stable isotopes in the collected vapor III) estimating and comparing root water uptake depths and amounts of different tree species for the two different isotope methods (in-situ vs. bag method approach)

Figure 1: Schematic of vapor sampling via in-situ (a) soil- and (b) xylem-water isotope probes. The left part describes the field setting while the right part shows the laboratory setting. Vapor of interest is sampled via in-situ isotope probes with small pumps and dry air, filled into air-tight bags; bags are later analyzed in the lab on a Picarro isotope analyzer (CRDS).

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

Barbara Herbstritt, Natalie Orlowski

Dr. Barbara Herbstritt: barbara.herbstritt@hydrology.uni-freiburg.de; Tel. 0761 - 203 3539 Dr. Natalie Orlowski: natalie.orlowski@hydrology.uni-freiburg.de; Tel. 0761 – 203 9283

Deutsch/Englisch

Literature will be provided. Lab tests have been conducted and first data are available.