## Thursday, October 1, 2020

### WATZON seminar series - I

The Project WATZON  has almost finished the first year of work. It was a troubled year,  since the COVID-19 pandemic and we could not meet and do the field work required. However, we learn to use better the resources Internet brought to us. Upon the initiative of Paolo Nasta we started a series of on-line conferences on the tools and topics of the project. He is providing in these days seminars about the use of Hydrus-1D, a leading software for estimating infiltration by using Richards equation.  He accepted his material to be uploaded on my VIMEO WATZON Channel.

To interested people, Paolo suggest the following material

Lecture 1: Introduction to Hydrus-1D - First part

Lecture 2: Introduction to Hydrus-1D-Second part
Lecture 3: Treating tracers with Hydrus-1d
Lecture 4 - Going deeper isotope transport in Hydrus-1D
Paolo Nasta also wrote: "In the attached Excel file I extracted Fig.6 from the  Stumpp's paper. In this exercise we consider only delta18O transport. First of all, we all need to measure delta18O for each rainfall event. This is quite unfeasible. But...we need to sample rainfall as much as we can in order to make reliable interpolation of delta18O contents in ech daily rainfall episode! Stable isotopes of water are reported in the delta notation as the δ-content (‰), which is a relative deviation from the international standard V-SMOW (Vienna-Standard Mean Ocean Water). Mostly, the δ-content is negative. It is not possible to calculate with negative “concentrations” in HYDRUS-1D, and therefore, the user has to add an arbitrary value to all isotope data for the simulations (input and observation data). Do not take the absolute values though!
In the PRIN WATZON activities, we sample the isotope concentration in the rainfall (very frequently!), plant, soil (at different depths) and groundwater table sporadically (it means every two weeks hopefully). So we use rainfall-isotope conc. as input.
We use the other sporadic isotope concentrations (in soil, plant, groundwater) as observation data for inverse modeling in Hydrus-1D. In inverse modeling we optimize the unknown parameters related to water flow (vG parameters, Feddes parameters) and solute transport (dispersivity, solute root uptake etc.).
Once we get the optimized parameters, we can have fun and run long-term simulations with known precipitation, known rainfall-isotope and calculate soil residence time, or travel times from rainfall to transpired water or to groundwater in each site. Please, let me know. I think it is getting quite clear so far.
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