EGU General Assembly 2020
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Do spatial patterns of water and matter fluxes below the main rooting zone depend on canopy processes?

Anke Hildebrandt1,2, Stephan Bock2, Christine Fischer2, Johanna Metzger, Joseph Weckmueller2, and Goekben Demir
Anke Hildebrandt et al.
  • 1Computational Hydrosystems, Helmholtz Centre for Environmental Research - UFZ, Leipzig, Germany
  • 2Institute of Geoscience, Friedrich-Schiller-University Jena, Jena, Germany

Besides precipitation also atmospheric deposition is modified by canopy processes. By passing the canopy, precipitation water washes out those deposited compounds and creates substantial heterogeneity of input of dissolved matter at the forest floor. At the same time, both dry atmospheric deposition of aerosols and net precipitation are affected by canopy heterogeneity, like variation in canopy density. In consequence, spatial patterns of both dry and wet deposition are expected to vary strongly in space and to depend on canopy structure, which may lead to hotspots of input and deep drainage. However, few studies so far have investigated the spatial patterns of deposition of e.g. nitrogen compounds. In this research we investigated the spatial and temporal patterns of nitrogen deposition and export from the main rooting zone in a beech dominated forest in the Hainich National Park.


We find that below canopy spatial patterns of both canopy drainage and nitrogen deposition show some temporal stability. Spatial variation in canopy drainage also affected soil water percolation in 30 cm depth, with higher canopy drainage leading to higher soil water fluxes. Nitrogen deposition at the forest floor however, seemed rather driven by canopy exchange than by drainage patterns or dry deposition. On the other hand, at 30 cm soil depth nitrogen export in seepage water was driven by the soil water flow, indicating that spatial patterns of transport capacity, and not nitrogen availability in the soil, determined the export of nitrogen from the main rooting zone. Interestingly, spatial variation of soil water fluxes was not dampened, but rather increased by passage of the rooting zone. In other words, the origin of spatial patterns of water flow and nitrogen export below the main rooting zone lay already within the canopy, but was further enhanced in the soil. The next steps will be to understand why the heterogeneity of water fluxes propagates and increases during rooting zone transit and whether there is an interaction with soil development.

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Display material version 1 – uploaded on 02 May 2020
  • CC1: Comment on EGU2020-9845, Jesse Radolinski, 08 May 2020

    Very cool work. Do you think the likelihood of preferential flow increases or decreases with distance from the stem?

    It also would be exciting if these patterns of throughflow and mass transport persist over long periods of time, which has basically been shown for soil mositure (Thinking something like this:Zimmerman et al., 2009   doi:10.1029/2008WR007470).

    • AC1: Reply to CC1, Anke Hildebrandt, 13 May 2020

      Thanks for those interesting questions!

      Yes, we expected a tendency of enhanced preferential flow near stems. Not only because of stemflow hotspots (these are beech with high stem flow yield), but also since we had observed that macro-porosity was increased near stems (Metzger et al., 2017, doi: 10.1002/hyp.11274). This is why we installed according to a factorial design for stem distance and throughfall. However, in the lysimeter data presented here, we did not observe increased vertical percolation near stems. Instead we did see the effect of throughfall gradients. But stemflow effects may be very localized and we may simply have missed the right spot. Areas receiving high and low throughfall are of larger extent and capturing that gradient is much easier.

      Indeed, the throughfall gradient was temporally stable over the two years (as in Zimmermann et al, 2009), and so were the qradients in soil water percolation. The ranking plot was not shown, but we did observe distinct high and low percolation spots.