# Water as a critical zone currency: linking water storage and age to root uptake and biogeochemical transport

Sylvain Kuppel, Isabelle Braud, Yves Godderis, Sekhar Muddu, Jean Riotte, Laurent Ruiz

► To cite this version:

Sylvain Kuppel, Isabelle Braud, Yves Godderis, Sekhar Muddu, Jean Riotte, et al.. Water as a critical zone currency: linking water storage and age to root uptake and biogeochemical transport. EGU General Assembly 2020, May 2020, Vienna, Austria. 10.5194/egusphere-egu2020-15958 . hal-03126261

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Submitted on 30 Jan 2021

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# Water as a critical zone currency: linking water storage and age to root uptake and biogeochemical transport

Sylvain Kuppel <fnref n="1" />,<fnref n="2" />, Isabelle Braud <fnref n="1" />, Yves Goddéris <fnref n="3" />, Sekhar Muddu <fnref n="4" />,<fnref n="5" />, Jean Riotte <fnref n="3" />,<fnref n="5" />, and Laurent Ruiz <fnref n="5" />,<fnref n="6" />

<figure><img src="image_2.png" /></figure>

sylvain.kuppel@inrae.fr

<figure><img src="image_3.png" /></figure>

## Background

Analyzing responses of water ages to changes in hydrological status (e.g., storage) gives insights into water-mediated CZ functions.

**Prospect.** Anticipating sensitivity of ecosystem health and biogeochemical balance to changing climatic and land-water use conditions.

## Questions

How do water flow paths control

1. the age of root uptake

2. the variability of water chemistry within and across the critical zone?

## Method

Coupling spatially-distributed ecohydrological and geochemical modeling approaches in data-rich critical zone observatories

## Study site

**Mule Hole**, a 4 km<fnref n="2" /> sub-humid intermittent catchment in SW India, with a deep weathered profile on a granitogneissic basement, covered by a dry deciduous forest [1].

### Data availability

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

## Tracking water in the critical zone

**EcH₂O-iso**, a process-based and spatially-distributed ecohydrological model, tracking water signature (age and conservative tracers) across grid cells and CZ compartments [2].

<figure><img src="image_6.png" /></figure>

### Preliminary configuration

Daily simulations at 90m resolution.
2005-2017 (+90-year spinup)
35m-deep hydrological domain.

Uniform vegetation cover (deeply-rooted trees 90%). Manual parameters calibration to discharge and piezometric levels.

Root uptake accesses deep, old waters, consistent with previous studies [3]. Hysteretic relationship with CZ storage reflect cross-season carry-over. Large inter annual variability from hydroclimate.

### Model-data time series

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

### Catchment-scale age-storage simulations

<figure><img src="image_9.png" /></figure>

## Biogeochemical budget

**WITCH**, a modular chemical weathering model – simulating dissolution/precipitation rates of mineral phases based on kinetics laws [4] (spatialized version).

### Preliminary simulations

Monthly simulations forced with EcH₂O-iso water fluxes and contents. No spinup. Laterally-uniform mineralogy, 9 vertical layers.

Example with Ca<fnref n="2" />⁺: strong signature of varying water fluxes and storage

### Variability of calcium concentration

<figure><img src="image_10.png" /></figure>

**Effect to root uptake depth:** alteration of control configuration (roots >25m) towards shallow roots (<1m).

## Summary

**Proof-of-concept:** even when simplifying the Critical Zone structure, space- and time-changing water flow paths create complex patterns of rock - root - water interactions *within* and *across* the landscape

Multi-scale datasets are required for model evaluation

### Ca<fnref n="2" />⁺ profile difference

<figure><img src="image_11.png" /></figure>

## References

[1] Riotte et al. (2014), *Geochimica et Cosmochimica Acta*, 145, 116-138 [link].

[2] Kuppel et al. (2018), *Geosci. Model Dev.* 11(7), 3045-3069 [link].

[3] Chitra-Tarak et al. (2018), *Journal of Ecology*, 106(4), 1495-1507 [link].

<footnote n="1">¹ IPGP, CNRS - University of Paris, Paris, France</footnote>

<footnote n="2">² INRAE, Villeurbanne, France</footnote>

<footnote n="3">³ Géosciences Environnement Toulouse, France</footnote>

<footnote n="4">⁴ Indian Institute of Science, Bangalore, India</footnote>

<footnote n="5">⁵ Indo-French Cell for Water Sciences, Bangalore, India</footnote>

<footnote n="6">⁶ INRAE, Rennes, France</footnote>