Methods of urban ecohydrology

• hydrological variables: precipitation, interception, evapotranspiration, grounwater level, …

• ecological variables: vegetation cover, biomass, leaf area index, …

• chemical and physical variables: soil properties (texture, porosity, …), pH, dissolved oxygen, nutrients and pollutants

• high heterogeneity: ecohydrological characterisitcs change dramatically over very small space and very quickly -> need for high spatial and temporal resolution

• vandalism: installed devices attract attention

• permission: device installation, soil/water sampling, drone flying all need permits

• curiosity: when working in field, curiosity ill make people ask questions

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• Tensiometer: measures soil water tension -> can be converted to soil moisture

• time-domain reflectometry: sends electrical signal through steel rods placed in soil and measures signal and wet soil returns signal

Eddy covariance technique/ Eddy flux tower:

• multiple instruments

• measurement of turbulent fluxes

• ultrasonic anemometer-thermometer obtains fast-response values of wind components

• infrared gas analyser measures fast-response water vapour density and CO2 density

-> combination of measurement: sensible, latent heat and ET can be estimated

heated sensors: measuring the temperature diffenrence between heated sensors at 1.5m height in cardinal direction

-> older larger trees need more sets of sensors

-> sensor values were averaged and converted to sap flux velocity in mm/h

Lysimeter

-> urban studies require higher resolution

-> very expensive

• conservative tracers in hydrological cycle

• mainly deuterium and oxygen eighteen

• “stable” as individual atoms do not change by chemical or other process

• process in catchments (mixing or fractioning) can lead to enrichment or depletion of isotopic signatures

• important concepts: GWML, LMWL, soil evaporation lines, dual-isotope plot

global meteoric water line

-> describes relationship between deuterium and oxygen eighteen -> can be illustrated with dual isotop plot

• oxygen eighteen enriches more easily than deuterium -> evaporation leads to negative D-excess

local meteoric waterline

-> describes relationship locally -> due to local energy balance and rainfall, LMWL is expected to deviate from GMWL

• other waterline are for example local soil evaporative line (LSEL) -> stable water isotope values of soil water

field study at TU Berlin:

• six soil water sensors at different depths under different vegetation covers

• results

  • soil water are more enriched than groundwater and local streams

  • soil water under grassland deviates from LMWL

  • soil water under trres most enriched along the LWML

• seasonal variation in soil-plant interactions in contrasting urban green spaces

• multiple parks in Berlin

• results:

  • measurement at 0-5cm, using handheld probe, showed much higher dynamic from installed sensors -> rewetting druing summer mainly in most upper part of soil cover

  • values from grassland showed higher variablility than from below trees