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Urban Water InterfacesW1 Ecohydrological controls on urban groundwater recharge: an isotope-based modelling approach

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W1 Ecohydrological controls on urban groundwater recharge: an isotope-based modelling approach

Doctoral student: Lena-Marie Kuhlemann

Supervisors: Prof. Dr. Dörthe Tetzlaff, Prof. Dr. Chris Soulsby, Prof. Dr. Birgit Kleinschmit

Introduction / Background

Large urban areas comprise a heterogeneous mosaic of land covers that can differentially partition precipitation into “green” and “blue” water flow paths. Stable isotopes, combined with climatic and hydrometric measurements, are invaluable in quantifying water sources, flow paths and ages of waters draining catchments affected by urbanization.  While isotope applications are an established method in many experimental catchments, surprisingly few studies have been conducted in urban environments to quantify water partitioning in areas of different urban land use, with contrasting mixes of impermeable and permeable urban surfaces.

Aims

This project comprises three work packages (WPs), which address this research gap through a multi-scale study in Berlin. Synoptic sampling of precipitation, surface water, soil water and groundwater across different spatial scales (ranging from 0.02 to 900km2, see Fig. 1) and in different seasons facilitates the quantification of the influence of groundwater, effluents, urban storm runoff and evaporation on the city’s major surface waters.

Fig. 1: Overview of the different spatial scales representing the different work packages.
Lupe

Specifically, we aim to answer the following research questions:

  • What are the effects of different urban soil-vegetation units on water partitioning at the plot-scale?
  • What are the seasonal water inputs and outputs in a single urban catchment?
  • What are Berlin’s seasonal isotope patterns and flow paths in surface and subsurface waters at a large spatial scale?

Methods

To investigate the hydrological system of Berlin under different wetness conditions, seasonal sampling campaigns of surface and groundwater are conducted at the catchment scale (river Erpe) and at the city scale (across Berlin).

Fig. 2: Surface water sampling (left) and groundwater sampling (right) during the seasonal field campaigns.
Lupe

Daily sampling of precipitation and weekly monitoring of the isotope signal at selected locations is performed to investigate annual variations.

During the summer of 2019, a plot-scale investigation in Berlin-Steglitz is performed, including soil moisture and sap flow measurements and the monthly sampling of soil water isotopes (Fig. 3), to investigate water fluxes under different urban soil-vegetation units.

 

 

Fig. 3: Soil moisture sensors (left), sap flow sensors (center) and soil water isotope sampling (right) at the Steglitz field site.
Lupe

Results

To investigate temporal and spatial patterns over the course of one year, seasonal maps of hydrochemical parameters and stable isotopic composition in surface and groundwater at the catchment and city scale are produced (Fig. 4-5).

Fig. 4: Electrical conductivity (left) and water temperature (right) in surface water (circle) and groundwater (asterisk) measured during the catchment-scale field campaign at the river Erpe in April 2019.
Lupe

 

While the variations at the catchment-scale occur to a lower extent (Fig. 4), the temporal and spatial variations at the city-scale are more pronounced (Fig. 5). Combined with hydrometric and climatic data, these datasets will provide a unique insight into the seasonal changes of water distribution and dynamics in the urban environment of Berlin.

Fig. 5: Electrical conductivity (left) and water temperature (right) in surface water (circle) and groundwater (asterisk) measured during the city-scale field campaign across Berlin in May 2019.
Lupe

Collaborations

Other UWI projects: W3, H1, W2

Common topics: interfaces in urban watersheds

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