Holm Voigt

Research themes
  • Water resources (management)
  • Land use and food security
  • Sustainable use of natural resources
  • Environmental Impact Analysis
  • Agriculture, land use, climate change
Research countries
  • Uzbekistan
  • Iran
Research projects
Water is a critical resource in the lower reaches of the Amu Darya due to climate aridity and high demands of irrigated agriculture and hydropower in the river basin. In the study region of Khorezm the decades of intensive irrigation led to elevated groundwater tables, resulting in ubiquitous soil salinization and adverse impact on crop production. The afforestation of degraded cropland patches with salt-tolerant trees that draw on groundwater, showed to be effective in increasing the land’s productive and carbon sink potential while contributing to rural income. This study addresses the impact of tree planting on the water and salt balance at the field scale, considering temporal and spatial variations. To this end, the dynamics of groundwater, soil water and solutes as well as the (ground) water use in three tree species are monitored and analyzed. An experimental tree plantation established in 2003 (Yangibazar) was used for estimating tree water use in the 10th and 11th year since afforestation (2012). The study site is characterized by moderate to strong rootzone soil salinity (2-15 dS m-1) as well as saline groundwater (1.4-3.3 dS m-1). Further afforestation sites have been developed and integrated into the monitoring to account for site specific factors. Main research objectives are How much water is transported at tree and stand level on different temporal scales? What are the species-specific variations of water transport? What are the governing factors controlling water fluxes in the local agroecological Atmosphere-Vegetation-Soil Continuum
Teaching

WS 2012-2013 ARTS-A3 Production systems

SoSe 2013 Geography-B2 Basic field methods

WS 2013-2014 ARTS-A3 Production systems

SoSe 2014 Geography-B2 Basic field methods

Additional Information:
Additional information

German Uzbek Agroforestry Project

Professional experience
2009-2011 GWSP - Research Assistant 2015-2016 Future Earth Research Associate
Degrees

Geography (Diplom)

Funding institutions

Robert Bosch Foundation

Thesis title

Hydrological dimensions of mixed species tree plantations in Khorezm, Uzbekistan

Thesis abstract

Water is a critical resource in the lower reaches of the Amu Darya due to climate aridity and high demands of irrigated agriculture and hydropower in the river basin. In the study region of Khorezm the decades of intensive irrigation led to elevated groundwater tables, resulting in ubiquitous soil salinization and adverse impact on crop production. The afforestation of degraded cropland patches with salt-tolerant trees that draw on groundwater, showed to be effective in increasing the land’s productive and carbon sink potential while contributing to rural income.

This study addresses the impact of tree planting on the water and salt balance at the field scale, considering temporal and spatial variations. To this end, the dynamics of groundwater, soil water and solutes as well as the (ground) water use in three tree species are monitored and analyzed. An experimental tree plantation established in 2003 (Yangibazar) was used for estimating tree water use in the 10th and 11th year since afforestation (2012). The study site is characterized by moderate to strong rootzone soil salinity (2-15 dS m-1) as well as saline groundwater (1.4-3.3 dS m-1). Further afforestation sites have been developed and integrated into the monitoring to account for site specific factors.

Main research objectives are

How much water is transported at tree and stand level on different temporal scales?

What are the species-specific variations of water transport?

What are the governing factors controlling water fluxes in the local agroecological Atmosphere-Vegetation-Soil Continuum

 

2017

Holm Voigt, Asia Khamzina, Bernd Diekkrüger, Inken Rabbel.  2017.  Quantifying stand water use through sapflux and groundwater measurements at a multi-species afforestation site in Uzbekistan, Central Asia.  Irrigated agriculture is the main economic activity in the lower Amudarya Basin of Uzbekistan characterized by arid, continental climate. The sector is threatened by precarious irrigation water supply and increasing soil salinity. Afforestation trials on degraded cropland with a shallow water table showed the potential to provide alternative agro-ecosystem services and rural income from the degraded land while requiring only little irrigation. To assist in afforestation planning, we assessed the stand water-use of three tree species, Elaeagnus angustifolia, Populus euphratica, and Ulmus pumila, using heat dissipation sensors during the growing season (March-October), 9 and 10 years after planting (2012 and 2013). Furthermore, the stand water use was quantified from observations of diurnal groundwater observations (for more details please see the respective poster submission). Previous dryland studies on tree stand water use suggest that stand water use ranges from 0.2 to 4.0 times the reference crop evapotranspiration (ETref) according to Penman-Monteith. The seasonal ETref was 868 and 854 mm in 2012 and 2013, respectively. Water use values derived from measurements of the field-calibrated heat dissipation sensors ranged from 0.01 to 0.37 of ETref (or 10-170 mm). Applying the original Granier function resulted in higher seasonal stand water use ranging from 0.02 to 0.66* ETref (or 15-552 mm). Analysis of the groundwater oscillations resulted in seasonal stand water use of 1.12‒4.9* ETref (or 942-4279 mm). Peak water use recorded with the sapflux probes occurred during the early and late season, whereas the groundwater measurements suggested peak water-use in the mid-season. Populus euphratica showed the highest water use among the species with either method. While estimates derived by sapflux measurements tend to underestimate stand water use, results calculated from groundwater oscillations might be overestimations. However, due to its generally high water use P. euphratica should be recommended cautiously for the dryland afforestation efforts. Further Information
Holm Voigt, Bernd Diekkrüger, Asia Khamzina, Inken Rabbel.  2017.  Stand water use assessed by diurnal groundwater oscillations – an alternative approach to sapflux quantification.  Tree water use is a major component of hydrological balances in forested watersheds. The frequently used heat-based sapflow measuring techniques is challenged by the necessity of upscaling the sapwood area based measurements to whole tree and stand levels. In agro-ecological systems with a shallow groundwater table, water uptake of trees leads to distinct diurnal fluctuations of the groundwater table. We developed a method to directly evaluate stand-level water use based on these fluctuations. The measurements were conducted at a mixed-species (Elaeagnus angustifolia, Populus euphratica, and Ulmus pumila) afforestation site in irrigated croplands of the lower Amu Darya Basin. Groundwater depth was monitored during the growing season (March-October) of 2012 and 2013 in the 9-10-year-old plantation of about 2.5ha. The soil water retention curve was derived from soil properties using the description of van Genuchten (1980). Assuming equilibrium soil moisture characteristics, the water uptake by trees per day was computed as the integral over the water retention curve from completely saturation to the soil suction equivalent of the difference between daily minimum and maximum groundwater depth. To account for lateral groundwater fluxes, the daily trend of the groundwater table (〖tGW〗_d) was assumed to be reflected by the difference between the daily minimum, average and maximum groundwater depth compared to the day before. To reflect the assumption that tree water uptake is primarily active during daytime, 〖tGW〗_d was related to the actual duration of sunshine. During the measurement period, the groundwater table fluctuated between 0.3 and 2.8 m below the soil surface with small daily magnitude during early and late season and high daily magnitudes during summer months. The average daily oscillation was 10.2 cm. The estimated seasonal water use ranged between 1618 and 4279 mm in 2012 and between 942 and 2502 mm for 2013, peaking in plots of P. euphratica. Further Information
Holm Voigt, Maximilian Weigand, Andreas Kemna, Bernd Diekkrüger.  2017.  Sensing sap flow by electrical self-potential measurements.  Sapflow represents a key process for understanding transpiration rates and water relations of plants. It is widely investigated by employing thermometric methods, which have been developed during the 1980’s and since then have undergone various improvements. However, these methods comprise several theoretic pitfalls and practical issues which lead to a huge variability in resulting sapflow estimates, especially when quantification is needed. We propose electrical self-potential (SP) measurements as a possible addition, or alternative, to established methods to gain information on sapflow in trees. To that end we performed two experiments to investigate the feasibility of the SP measurement approach: on freshly cut stem segments (experiment I), and on a living specimen of Picea abies at the Wüstebach field site (experiment II). For experiment I, freshly cut tree segments were subjected to a pressure head of ca. 0.45 bar to emulate water flow through the xylem. “Flow” and “non-flow” conditions periodically alternated in approx. 60 minute intervals. SP measurements were conducted using two non-polarizable electrodes located at the top and the bottom of the stem segment. The measurements show consistent behaviour during the three relevant phases: initiation of water flow, water flow, termination of water flow. For experiment II, we installed five non-polarizing electrodes along a vertical transect and additional four electrodes in a circumferential transect at approx. 2 m above the ground. The tree under investigation was also equipped with thermal sapflux sensors. Electric potentials were measured with reference to an electrode located 4 m northwest of the tree in the soil. The recorded signals followed the climatic patterns. Our results suggest that electrical self-potential measurements can be used to non-, or minimally, invasively infer information on sapflow in trees. Future work will address the optimization of the measurement methodology as well as the quantitative interpretation of the results. Further Information

2016

Bhaduri A., J. Bogardi, A. Siddiqi, H. Voigt, C. Vörösmarty, C. Pahl-Wostl, S. E. Bunn, P. Shrivastava, R. Lawford, S. Foster, H. Kremer, F. G. Renaud, A. Bruns and V. R. Osuna.  2016.  Achieving sustainables development goals from a water perspective.  Frontiers in Environmental Science, doi: 10.3389/fenvs.2016.00064   . (Open Access)  
Rabebel I, Diekkrüger, B., Voigt H. and B. Neuwirth.  2016.  Comparing ∆Tmax Determination Approaches for Granier-Based Sapflow Estimations.  Sensors, 16 (12)   : 2042, DOI:10.3390/s16122042   .

2015

Voigt H..  2015.  Earth Observations and Education for the Sustainable Implementation of the Nexus Approach.  Change and Adaptation in Socioecological Systems, 2   : 119-121   . (Open Access)   Download [PDF | 78.87KB]

2013

Holm Voigt, Sujan Maharjan, Asia Khamzina.  2013.  Afforestation of degraded cropland as part of integrated agricultural water and land management in Khorezm, Uzbekistan.  Water is a critical resource in the lower reaches of the Amu Darya due to climate aridity and high demands of irrigated agriculture and hydropower in the river basin. In the study region of Khorezm the decades of intensive irrigation led to elevated groundwater tables, resulting in ubiquitous soil salinization and adverse impact on crop production. The afforestation of degraded cropland patches with salt-tolerant trees that draw on groundwater, showed to be effective in increasing the land’s productive and carbon sink potential while contributing to rural income. This study addresses the impact of tree planting on the water and salt balance at the field scale, considering temporal and spatial variations. To this end, the dynamics of groundwater, soil water and solutes as well as the (ground) water use in three tree species was monitored at two afforestation sites, about 2 ha each. Further Information

2011

Kistemann, Th., Ch. Höser and H. Voigt.  2011.  Mapping Water and Health: Current Applications and Future Developments.  From elementary, illustrative description, medical cartography developed into a tool for analytical research already 150 years ago. Water has always played an outstanding role for health mapping. Temporal aspects and the perception of the interaction of multidimensional drivers necessarily pushed mapping of water and health forward into the field of spatial statistics. In recent decades, both the availability of computer processing capacity and an abundance of data becoming available from different sensors triggered the development of powerful Geographic Information Systems (GIS). This is especially the case when a ubiquitous element like water, which affects health in manifold ways, is the focus of interest. This opens up challenging demands and exciting tasks for experts, but may also include obstacles for less developed countries, where people are suffering from water-related health problems on an everyday basis. This paper provides a short review of the current state of the art and illustrates the utilisation and perspectives of GIS for water-related health research. Further Information

Voigt, H..  Impacts of mixed species tree plantations on the hydrological regime in an arid catchment in Uzbekistan under the pressure of global change.  Faculty of mathematics and natural sciences of the University of Bonn. 

Additionals, Curriculum Vitae
and Downloads

Holm Voigt

Researcher Project Management

Department :
ZEF C: Department of Ecology and Natural Resources Management

E-Mail:
hvoigt(at)uni-bonn.de