Call for contributions

Zero hunger

Processes at the soil-root interface shaping soil functions (Communication session)

EUROSOIL2020CONT-2007

WATER BALANCE ESTIMATIONS IN A NORWAY SPRUCE FOREST SOIL WITH DEEP GROUNDWATER: A MULTIDISCIPLINARY APPROACH

Ursula Noell^{* 1}, Christoph Neukum², Henning Meesenburg³, Paul Koeniger², Susanne Stadler²

¹Groundwater and Soil Science, BGR, Berlin, ²Groundwater and Soil Science, BGR, Hannover, ³Northwest German Forest Research Institute (NW-FVA), Göttingen, Germany

Content: In Lower Saxony, the mortality rate of the spruce trees increased 2019 from 0.3 % (1984 - 2018 average) to 6.1% [1]. Many trees suffer from the combination of water shortage, rising temperatures and various calamities. The water retention capacity of the forest soil plays an important role for the trees’ resilience against drought and affects groundwater recharge. Therefore, we combined monitoring methods applied in forestry, soil science, hydrology, hydrogeology and geophysics to investigate three Norway spruce trees and their soil in the Solling region, Germany. The plot is located in a pure Norway spruce stand with an exceptionally long monitoring history.

The long-term monitoring comprises – among others – the observation of meteorological drivers, stand precipitation, soil water potential, soil water content and continuous circumference measurements. In March 2019 we installed an electrical resistivity tomography (ERT) array (7 x 17 m, 300 electrodes) enclosing three Norway spruce trees including their rooting zones. We measure their xylem flux since April 2019 and in November 2019 installed TDR devices. In January 2020 additional  tensiometers  forming a transect that cuts through the edge of the ERT array at depths of 20 cm, 40 cm, 60 cm and 82 cm complemented the installation. Stable isotope composition (δ¹⁸O and δ²H) was analyzed in open field and stand precipitation as well as soil water samples.

The hydrological modelling reveals only minor intervals of water stress despite very dry conditions in 2019 and the xylem flux showes a prolongation of the growing season until early November. The electrical resistivity tomography inversion detects an area of reduced resistivity surrounding the central tree down to a depth of about 0.5 m. This area is tentatively interpreted as rooting area. We suspect that the detected resistivity differences between intensively and extensively rooted soil regions reveal the influence of soil water uptake on water percolation. To estimate this difference quantitatively we combine ERT results with the data of the TDR devices and the tensiometers.  

 [1] Niedersächsisches Ministerium für Ernährung, Landwirtschaft und Verbraucherschutz, Waldzustandsbericht Niedersachsen 2019 (www.nw-fva.de)

Disclosure of Interest: None Declared

Keywords: None