Temporal dynamics of tree xylem water isotopes: In-situ monitoring and modelling

Mapping Intimacies ◽

10.5194/bg-2021-35 ◽

2021 ◽

Author(s):

Stefan Seeger ◽

Markus Weiler

Keyword(s):

Soil Water ◽

Temporal Dynamics ◽

Length Distribution ◽

In Situ Monitoring ◽

Water Isotopes ◽

Stable Water Isotopes ◽

Root Tips ◽

Water Age ◽

Isotopic Signatures

Abstract. We developed a setup for a fully automated, high frequency in-situ monitoring system of the stable water isotopes Deuterium and 18O in soil water and tree xylem. The setup was tested for 12 weeks within an isotopic labelling experiment during a large artificial sprinkling experiment including three mature European beech (Fagus sylvatica) trees. Our setup allowed for one measurement every 12–20 minutes, enabling us to obtain about seven measurements per day for each of our 15 in-situ probes in the soil and tree xylem. While the labelling induced an abrupt step pulse in the soil water isotopic signature, it took seven to ten days until the isotopic signatures at the trees' stem bases reached their peak label concentrations and it took about 14 days until the isotopic signatures at 8 m stem height levelled off around the same values. During the experiment, we observed the effects of several rain events and dry periods on the xylem water isotopic signatures, which fluctuated between the measured isotopic signatures observed in the upper and lower soil horizons. In order to explain our observations, we combined an already existing root water uptake (RWU) model with a newly developed approach to simulate the propagation of isotopic signatures from the root tips to the stem base and further up along the stem. The key to a proper simulation of the observed short term dynamics of xylem water isotopes, was accounting for sap flow velocities and the flow path length distribution within the root and stem xylem. Our modelling framework allowed us to identify parameter values that relate to root depth, horizontal root distribution and wilting point. The insights gained from this study can help to improve the representation of stable water isotopes in trees within ecohydrological models and the prediction of transit time distribution and water age of transpiration fluxes.

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Temporal dynamics of tree xylem water isotopes: in situ monitoring and modeling

Biogeosciences ◽

10.5194/bg-18-4603-2021 ◽

2021 ◽

Vol 18 (15) ◽

pp. 4603-4627

Author(s):

Stefan Seeger ◽

Markus Weiler

Keyword(s):

Soil Water ◽

Temporal Dynamics ◽

Length Distribution ◽

In Situ Monitoring ◽

Water Isotopes ◽

Root Tips ◽

Water Age ◽

Modeling Framework ◽

Isotopic Signatures

Abstract. We developed a setup for a fully automated, high-frequency in situ monitoring system of the stable water isotope deuterium and 18O in soil water and tree xylem. The setup was tested for 12 weeks within an isotopic labeling experiment during a large artificial sprinkling experiment including three mature European beech (Fagus sylvatica) trees. Our setup allowed for one measurement every 12–20 min, enabling us to obtain about seven measurements per day for each of our 15 in situ probes in the soil and tree xylem. While the labeling induced an abrupt step pulse in the soil water isotopic signature, it took 7 to 10 d until the isotopic signatures at the trees' stem bases reached their peak label concentrations and it took about 14 d until the isotopic signatures at 8 m stem height leveled off around the same values. During the experiment, we observed the effects of several rain events and dry periods on the xylem water isotopic signatures, which fluctuated between the measured isotopic signatures observed in the upper and lower soil horizons. In order to explain our observations, we combined an already existing root water uptake (RWU) model with a newly developed approach to simulate the propagation of isotopic signatures from the root tips to the stem base and further up along the stem. The key to a proper simulation of the observed short-term dynamics of xylem water isotopes was accounting for sap flow velocities and the flow path length distribution within the root and stem xylem. Our modeling framework allowed us to identify parameter values that relate to root depth, horizontal root distribution and wilting point. The insights gained from this study can help to improve the representation of stable water isotopes in trees within ecohydrological models and the prediction of transit time distribution and water age of transpiration fluxes.

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Xylem water in riparian Willow trees (Salix alba) reveals shallow sources of root water uptake by in situ monitoring of stable water isotopes

10.5194/hess-2021-456 ◽

2021 ◽

Author(s):

Jessica Landgraf ◽

Dörthe Tetzlaff ◽

Maren Dubbert ◽

David Dubbert ◽

Aaron Smith ◽

...

Keyword(s):

Isotopic Composition ◽

Soil Water ◽

Water Uptake ◽

Sap Flow ◽

Root Water Uptake ◽

In Situ Monitoring ◽

Water Isotopes ◽

Stable Water Isotopes ◽

Salix Alba

Abstract. Root water uptake is an important critical zone process, as plants can tap various water sources and transpire these back into the atmosphere. However, knowledge about the spatial and temporal dynamics of root water uptake and associated water sources at both high temporal resolution (e.g. daily) and over longer time periods (e.g. seasonal) is still limited. We used cavity ring-down spectroscopy (CRDS) for continuous in situ monitoring of stable water isotopes in soil and xylem water for two riparian willow (Salix alba) trees over the growing season (May to October) of 2020. This was complemented by isotopic sampling of local precipitation, groundwater and stream water in order to help constrain the potential sources of root water uptake. A local flux tower, together with sap flow monitoring, soil moisture measurements and dendrometry were also used to provide the hydroclimatic and ecohydrological contexts for in situ isotope monitoring. In addition, bulk samples of soil water and xylem water were collected to corroborate the continuous in situ data. The monitoring period was characterised by frequent inputs of precipitation, interspersed by warm dry periods which resulted in variable moisture storage in the upper 20 cm of the soil profile and dynamic isotope signatures. This variability was greatly damped in 40 cm and the isotopic composition of the sub-soil and groundwater was relatively stable. The isotopic composition and dynamics of xylem water was very similar to that of the upper soil and analysis using a Bayesian mixing model inferred that overall ~90 % of root water uptake was derived from the upper soil profile. Sap flow and dendrometry data indicated that soil water availability did not seriously limit transpiration during the study period, though there was a suggestion that deeper (> 40 cm) soil water might provide a higher proportion of root water uptake (~30 %) in a drier period in the late summer. The study demonstrates the utility of prolonged real time monitoring of natural stable isotope abundance in soil-vegetation systems, which has great potential for further understanding of ecohydrological partitioning under changing hydroclimatic conditions.

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Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape in Germany

Hydrology and Earth System Sciences ◽

10.5194/hess-20-3873-2016 ◽

2016 ◽

Vol 20 (9) ◽

pp. 3873-3894 ◽

Cited By ~ 16

Author(s):

Natalie Orlowski ◽

Philipp Kraft ◽

Jakob Pferdmenges ◽

Lutz Breuer

Keyword(s):

Land Use ◽

Soil Water ◽

Hydrological Model ◽

Water Cycle ◽

Water Isotopes ◽

Stable Water Isotopes ◽

Age Dynamics ◽

Isotopic Signatures ◽

Spatially Distributed ◽

Water Isotope

Abstract. A dual stable water isotope (δ2H and δ18O) study was conducted in the developed (managed) landscape of the Schwingbach catchment (Germany). The 2-year weekly to biweekly measurements of precipitation, stream, and groundwater isotopes revealed that surface and groundwater are isotopically disconnected from the annual precipitation cycle but showed bidirectional interactions between each other. Apparently, snowmelt played a fundamental role for groundwater recharge explaining the observed differences to precipitation δ values. A spatially distributed snapshot sampling of soil water isotopes at two soil depths at 52 sampling points across different land uses (arable land, forest, and grassland) revealed that topsoil isotopic signatures were similar to the precipitation input signal. Preferential water flow paths occurred under forested soils, explaining the isotopic similarities between top- and subsoil isotopic signatures. Due to human-impacted agricultural land use (tilling and compression) of arable and grassland soils, water delivery to the deeper soil layers was reduced, resulting in significant different isotopic signatures. However, the land use influence became less pronounced with depth and soil water approached groundwater δ values. Seasonally tracing stable water isotopes through soil profiles showed that the influence of new percolating soil water decreased with depth as no remarkable seasonality in soil isotopic signatures was obvious at depths > 0.9 m and constant values were observed through space and time. Since classic isotope evaluation methods such as transfer-function-based mean transit time calculations did not provide a good fit between the observed and calculated data, we established a hydrological model to estimate spatially distributed groundwater ages and flow directions within the Vollnkirchener Bach subcatchment. Our model revealed that complex age dynamics exist within the subcatchment and that much of the runoff must has been stored for much longer than event water (average water age is 16 years). Tracing stable water isotopes through the water cycle in combination with our hydrological model was valuable for determining interactions between different water cycle components and unravelling age dynamics within the study area. This knowledge can further improve catchment-specific process understanding of developed, human-impacted landscapes.

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Exploring water cycle dynamics through sampling multitude stable water isotope pools in a small developed landscape of Germany

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-12-1809-2015 ◽

2015 ◽

Vol 12 (2) ◽

pp. 1809-1853 ◽

Cited By ~ 7

Author(s):

N. Orlowski ◽

P. Kraft ◽

L. Breuer

Keyword(s):

Land Use ◽

Soil Water ◽

Agricultural Land ◽

Water Cycle ◽

Mean Transit Time ◽

Arable Land ◽

Water Isotopes ◽

Stable Water Isotopes ◽

Isotopic Signatures ◽

Water Isotope

Abstract. Conducting a dual stable water isotope (δ2H and δ18O) study in the developed landscape of the Schwingbach catchment (Germany) helped to unravel connectivity and disconnectivity between the different water cycle components. The two-year weekly to biweekly measurements of precipitation, stream, and groundwater isotopes revealed that surface and groundwater are decoupled from the annual precipitation cycle but showed bidirectional interactions between each other. Seasonal variations based on temperature effects were observed in the precipitation signal but neither reflected in stream nor in groundwater isotopic signatures. Apparently, snowmelt played a fundamental role for groundwater recharge explaining the observed differences to precipitation δ-values. A spatially distributed snapshot sampling of soil water isotopes in two soil depths at 52 sampling points across different land uses (arable land, forest, and grassland) revealed that top soil isotopic signatures were similar to the precipitation input signal. Preferential water flow paths occurred under forested soils explaining the isotopic similarities between top and subsoil isotopic signatures. Due to human-impacted agricultural land use (tilling and compression) of arable and grassland soils, water delivery to the deeper soil layers was reduced, resulting in significant different isotopic signatures. However, the land use influence smoothed out with depth and soil water approached groundwater δ-values. Seasonally tracing stable water isotopes through soil profiles showed that the influence of new percolating soil water decreased with depth as no remarkable seasonality in soil isotopic signatures was obvious at depth > 0.9 m and constant values were observed through space and time. Little variation in individual isotope time series of stream and groundwater restricted the use of classical isotope hydrology techniques e.g. mean transit time estimation or hydrograph separation. Still, tracing stable water isotopes through the water cycle was valuable for determining interactions between different water cycle components and gaining catchment specific process understanding in a developed, human-impacted landscape.

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Supplementary material to "Xylem water in riparian Willow trees (Salix alba) reveals shallow sources of root water uptake by in situ monitoring of stable water isotopes"

10.5194/hess-2021-456-supplement ◽

2021 ◽

Author(s):

Jessica Landgraf ◽

Dörthe Tetzlaff ◽

Maren Dubbert ◽

David Dubbert ◽

Aaron Smith ◽

...

Keyword(s):

Water Uptake ◽

Root Water Uptake ◽

In Situ Monitoring ◽

Water Isotopes ◽

Stable Water Isotopes ◽

Salix Alba ◽

Supplementary Material ◽

Willow Trees

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Supplementary material to "Temporal dynamics of tree xylem water isotopes: In-situ monitoring and modelling"

10.5194/bg-2021-35-supplement ◽

2021 ◽

Author(s):

Stefan Seeger ◽

Markus Weiler

Keyword(s):

Temporal Dynamics ◽

In Situ Monitoring ◽

Water Isotopes ◽

Supplementary Material

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Technical note: Evaluation of a low-cost evaporation protection method for portable water samplers

Hydrology and Earth System Sciences ◽

10.5194/hess-24-5821-2020 ◽

2020 ◽

Vol 24 (12) ◽

pp. 5821-5834

Author(s):

Jana von Freyberg ◽

Julia L. A. Knapp ◽

Andrea Rücker ◽

Bjørn Studer ◽

James W. Kirchner

Keyword(s):

Water Samples ◽

Low Cost ◽

Field Tests ◽

Technical Note ◽

Water Isotopes ◽

Stable Water Isotopes ◽

Sample Collection ◽

Isotopic Signatures ◽

Protection Method ◽

Cost Efficient

Abstract. Automated field sampling of streamwater or precipitation for subsequent analysis of stable water isotopes (2H and 18O) is often conducted with off-the-shelf automated samplers. However, when water samples are stored in the field for days and weeks in open bottles inside autosamplers, their isotopic signatures can be altered by evaporative fractionation and vapor mixing. We therefore designed an evaporation protection method which modifies autosampler bottles using a syringe housing and silicone tube, and we tested whether this method reduces evaporative fractionation and vapor mixing in water samples stored for up to 24 d in 6712 full-size portable samplers (Teledyne ISCO, Lincoln, USA). Laboratory and field tests under different temperature and humidity conditions showed that water samples in bottles with evaporation protection were far less altered by evaporative fractionation and vapor mixing than samples in conventional open bottles. Our design is a cost-efficient approach to upgrade the 1 L sample bottles of the ISCO autosamplers, allowing secure water sample collection in warm and dry environments. Our design can be readily adapted (e.g., by using a different syringe size) to fit the bottles used by many other field autosamplers.

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In situ estimation of actual évapotranspiration. A case study in Argos plain

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.16976 ◽

2018 ◽

Vol 40 (3) ◽

pp. 1409

Author(s):

P. Giannoulopoulos ◽

A. Poulovassilis

Keyword(s):

Water Content ◽

Soil Water ◽

Soil Profile ◽

In Situ Monitoring ◽

Experimental Methodology ◽

Actual Evapotranspiration ◽

Winter Period ◽

Time Step ◽

Matrix Potential

The following work refers to an experimental methodology employed for in situ monitoring of specific soil water fluxes constituting water balance components. The test area is located in the plain of Argos - Greece, within an orange grove. A micrometeorological station was installed in the site, equipped with several sensors for real time monitoring of various atmospheric parameters as well as water content and temperature in the soil profile. The soil profile was made accessible for sampling through a rectangular pit which was excavated close to the station. The soil water content was monitored making use ofTDR sensors which were calibrated against the traditional neutron probe technique and also by soil sampling. Tensiometeres were also installed in four different depths for monitoring the matrix potential. A software programme was developed for the analysis and the evaluation of the data collected in a 10 - minute time step. The analysis of the data showed that the three - year average of Actual Evapotranspiration, in this irrigated field, was approximately 857 mm, out of which almost 600mm occur between April and September and 260 mm in the winter period. Those results show that there is no significant water surplus for deep infiltration and aquifer recharge in clayey and clay - loam soils in this region.

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