High‐resolution in situ stable isotope measurements reveal contrasting atmospheric vapour dynamics above different urban vegetation

<title xmlns:mml="http://www.w3.org/1998/Math/MathML">Abstract</title><p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en">We monitored stable water isotopes in liquid precipitation and atmospheric water vapour (δ_v) using in situ cavity ring‐down spectroscopy (CRDS) over a 2 month period in an urban green space area in Berlin, Germany. Our aim was to better understand the origins of atmospheric moisture and its link to water partitioning under contrasting urban vegetation. δ_v was monitored at multiple heights (0.15, 2 and 10 m) in grassland and forest plots. The isotopic composition of δ_v above both land uses was highly dynamic and positively correlated with that of rainfall indicating the changing sources of atmospheric moisture. Further, the isotopic composition of δ_v was similar across most heights of the 10 m profiles and between the two plots indicating high aerodynamic mixing. Only at the surface at ~0.15 m height above the grassland δ_v showed significant differences, with more enrichment in heavy isotopes indicative of evaporative fractionation especially after rainfall events. Further, disequilibrium between δ_v and precipitation composition was evident during and right after rainfall events with more positive values (i.e., values of vapour higher than precipitation) in summer and negative values in winter, which probably results from higher evapotranspiration and more convective precipitation events in summer. Our work showed that it is technically feasible to produce continuous, longer‐term data on δ_v isotope composition in urban areas from in situ monitoring using CRDS, providing new insights into water cycling and partitioning across the critical zone of an urban green space in Central Europe. Such data have the potential to better constrain the isotopic interface between the atmosphere and the land surface and to thus, improve ecohydrological models that can resolve evapotranspiration fluxes.</p>

<p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en">In situ measurements of urban atmospheric water isotopes (δ_v) at different heights produce reliable and stable high‐resolution data. Urban atmospheric vapour is influenced by varying drivers depending on the type of green space. δ_v above grassland and tree stands was similar at 10 m height, but near‐surface δ_v indicated higher evaporation and vapour enrichment over grass. We detected occasional dis‐equilibrium between vapour and precipitation isotopes.<boxed-text position="anchor" content-type="graphic" id="hyp14989-blkfxd-0001" xml:lang="en"> <graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:08856087:media:hyp14989:hyp14989-toc-0001"> </graphic> </boxed-text></p>

Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347

Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Einstein Stiftung Berlin http://dx.doi.org/10.13039/501100006188

Leverhulme Trust http://dx.doi.org/10.13039/501100000275

German Research Foundation http://dx.doi.org/10.13039/501100001659

Einstein Research Unit

Einstein Foundation Berlin and Berlin University Alliance

BiNatur

BMBF http://dx.doi.org/10.13039/501100002347

Leverhulme Trust through the ISO‐LAND project