Urban Water Interfaces

Background

Urban green spaces are highly valuable in supporting the climate and infrastructure of cities through rainwater retention, evaporative cooling and shading (Gunawardena et al., 2017). Hence, understanding the complex interactions of water flux partitioning of incoming precipitation into “green” (i.e. evaporation and transpiration) and “blue” (surface runoff and groundwater recharge) water fluxes through urban vegetation is important to improve urban ecosystems functioning. There is still a lack of knowledge of spatial variability in evaporation and transpiration from urban areas and crucially, what influences this water flux partitioning (Gillefalk et al., 2021 & 2022; Marx et al., 2022).

The naturally occurring stable isotopes of water provide unique fingerprints of a water's origin, as the ratio of heavy to light isotopes is affected by various fractionating processes in the water cycle depicting the flow paths and age of the existing water. Previous research suggests that using stable isotope examinations in urban settings can reveal information about human influences on the hydrological cycle (Ehleringer, et al., 2016; Kuhlemann et al., 2021), as well as changing stream water ages and runoff generating processes (Kuhlemann et al., 2020 & 2021; Marx et al., 2021; Soulsby, et al., 2014). Especially valuable are long-term data sets, which are sampled along different streams throughout a city (Kuhlemann et al., 2022). Furthermore, hydrological models on urban rivers systems can be improved through tracer incorporation (Smith et al., 2023).

Isotopic signatures of atmospheric water vapour are indicators for the relevant evaporation and transpiration processes of green and blue spaces (Braden-Behrens, et al., 2020; Rothfuss et al., 2021) and are rarely studied within the urban surface boundary layer, e.g. within canopy elevation profiles. Those plant-atmosphere interfaces give insights on evapotranspiration partitioning and their impact on atmospheric vapour and consequently on the whole soil-plant-atmosphere continuum (Tetzlaff et al., 2021).

New technological developments allow now stable isotopes sampling and analysis at high temporal resolutions in-situ. The emergence of improved laser spectroscopy technology aids high-frequency capture of data (>1 second resolution) at lower analytical costs and advancing well-established destructive sampling methods (Herbstritt, et al., 2021). This increases our ability to fully unravel vegetation isotope dynamics in time (diurnal cycles) and scale (canopy profile evapotransipration) (Braden-Behrens et al., 2019; Smith et al., 2022). In-situ measurements of stable isotopes in atmospheric water vapour promote understanding the water cycle and helping to plan for climate change (Gao, et al., 2019), e.g. high frequency canopy scale isotope measurements demonstrate necessary insights on the behaviour of kinetic fractionation at the leaf versus canopy scales (Griffis, 2013).

Aim

This project aims to gain an improved understanding of the role of “green” and “blue” water flux partitioning at the urban surface boundary layer as well as isotopic dynamics in surface waters to fill the gap in understanding urban influences on water partitioning and isotopic fractionation, particularly evapotranspiration processes.

Methods

WP 1) 2021 proof of concept: High resolution in-situ atmospheric vapour dynamics under contrasting urban vegetation

  • in-situ real time sequential measurements of atmospheric water vapour elevation profile at different heights (0.15 m, 2 m, 10 m) from August-November 2021
  • at two types of urban vegetation: tree stand with Acer platanoides and grassland with flagmast (see fig. 1)
  • measurements of sapflow, stem dynamics (dendrometer), soil moisture (different depths), precipitation & groundwater isotopes (see fig. 2 of Isotope Lab) and general hydroclimate

WP 2) Entire Growing season 2022: High resolution in-situ atmospheric vapour dynamics under contrasting urban vegetation

  • extensions and add-ons to 2021 set-up:
  • automated laser calibration routine
  • high-resolution in-situ vegetation water dynamics (tree xylem) at two species (Acer platanoides and Betula pendula) within the tree stand at 1.5 m and 2.5 m height of the stems
  • monthly destructive samplings soil water isotopes
  • continuous eddy flux measurements at open field near in-situ site

WP 3) Surface water tracer dynamics in urban rivers

  • weekly river reference sampling in Berlin (see fig. 3) since 2018
  • at 4 major urban rivers Spree, Wuhle, Erpe and Panke
  • different tracers: stable water isotopes, major ions (DIC, IC, ICP), hydrochemistry (pH, EC, Temperature, O2)

WP 4) Seasonal and spatial dynamics in eDNA as tracers in major urban rivers

  • extension to WP 3 long-term weekly river samplings
  • detection of bacteria, algeae and diatoms
  • sample volume of (200-400 ml) filtered wit vacuum filter unit (45 mm plate) and membrane filter made from polycarbonate with mesh size of 0,2 µm, stored in 96% ethanol (nat.); then processed and analysed in DNA lab
  • results will be compared with dynamics of other tracers

References

  • Braden-Behrens, J., Markwitz, C. & Knohl, A., 2019. Eddy covariance measurements of the dual-isotope composition of evapotranspiration. Agricultural and Forest Meteorology, Band 269-270, pp. 203-219.
  • Braden-Behrens, J., Siebicke, L. & Knohl, A., 2020. Drivers of the variability of the isotopic composition of water vapor in the surface boundary layer. Biogeosciences Discuss., p. [preprint].
  • Ehleringer, J. R. et al., 2016. Urban water – a new frontier in isotope hydrology. Isotopes in Environmental and Health Studies, pp. 477-486.
  • Gao, J. et al., 2019. Collapsing glaciers threaten Asia’s water supplies. Nature, Band 565, 19-21.
  • Gillefalk M et al.  (2022) Estimates of water partitioning in complex urban landscapes with isotope-aided ecohydrological modelling. Hydrological Processes. doi.org/10.1002/hyp.14532
  • Gillefalk M et al. (2021) Quantifying the effects of urban green space on water partitioning and ages using an isotope-based ecohydrological model. Hydrology and Earth System Sciences (HESS), doi.org/10.5194/hess-25-3635-2021
  • Griffis, T. J., 2013. Tracing the flow of carbon dioxide and water vapor between the biosphere and atmosphere: A review of optical isotope techniques and their application. Agricultural and Forest Meteorology, Issue 174-175, pp. 85-109.
  • Gunawardena, K. R., Wells, M. J., & Kershaw, T. (2017). Utilising green and bluespace to mitigate urban heat island intensity. Science of the Total Environment, 584-585, 1040–1055. doi.org/10.1016/j.scitotenv.2017.01.158
  • Herbstritt, B., Gralher, B. & Weiler, M., 2021. Continuous in situ measurements of stable isotopes in liquid water. Water Resour. Res., pp. 48, W03601.
  • Kuhlemann LM et al. (2020) Urban water systems under climate stress: an isotopic perspective from Berlin, Germany. Hydrological Processes, doi.org/10.1002/hyp.13850.
  • Kuhlemann LM et al. (2021) Using soil water isotopes to infer the influence of contrasting urban green space on ecohydrological partitioning. Hydrology and Earth System Sciences (HESS), https://doi.org/10.5194/hess-25-927-2021.
  • Kuhlemann LM et al. (2021) Spatio-temporal variations in stable isotopes in peri-urban catchments: A preliminary assessment of potential and challenges in assessing streamflow sources. Journal of Hydrology, https://doi.org/10.1016/j.jhydrol.2021.126685.
  • Kuhlemann LM et al. (2022) The imprint of hydroclimate, urbanization and catchment connectivity on the stable isotope dynamics of a large river in Berlin, Germany. Journal of Hydrology, https://doi.org/10.1016/j.jhydrol.2022.128335.
  • Marx C et al. (2021) Isotope hydrology and water sources in a heavily urbanised stream. Hydrological Processes. doi.org/10.1002/hyp.14377.
  • Marx C et al. (2022) Spatial variations in soil-plant interactions in contrasting urban green spaces: preliminary insights from water stable isotopes. Journal of Hydrology, doi.org/10.1016/j.jhydrol.2022.127998.
  • Rothfuss, Y. et al., 2021. Reviews and syntheses: Gaining insights into evapotranspiration. Biogeosciences, Issue 18, p. 3701–3732.
  • Smith AA et al. (2022) Modelling temporal variability of in-situ soil water and vegetation isotopes reveals ecohydrological couplings in a willow plot. Biogeosciences, https://bg.copernicus.org/articles/19/2465/2022/
  • Smith AA et al. (2023) Enhancing urban runoff modelling using water stable isotopes and ages in complex catchments. Hydrological Processes. In press.
  • Soulsby, C., Birkel, C. & Tetzlaff, D., 2014. Assessing urbanization impacts on catchmenttransit times. Geophys. Res. Lett, pp. 41,442–448.
  • Tetzlaff D, Buttle JM, Carey SK, Kohn M, Laudon H, McNamara JP, **Smith A, Sprenger M, Soulsby C. (2021) Stable isotopes of water reveal differences in plant – soil water relationships across northern environments.Hydrological Processes. DOI: https://doi.org/10.1002/hyp.14023
BearbeitungAnn-Marie Ring  
BetreuungProf. Dr. rer. nat. Dörthe Tetzlaff (IGB)Prof. Dr. Chris SoulsbyProf. Dr. rer. forest. Birgit Kleinschmit (TUB)
KollaborationenW5, W6