Solute mass losses and mass balance

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Joined: Thu Jun 01, 2023 4:37 pm
Location: USA

Solute mass losses and mass balance

Post by jebenhack » Thu Jun 01, 2023 5:00 pm

Dear Jirka and others,
We are using HYDRUS 1D to simulate the transport of a solute through the vadose zone and we had a few questions come up when discussing putting our source term in.

Some background first:
Our flow model boundary conditions include, an Atmospheric BC with Surface Run Off as the upper boundary condition with input precipitation, PET, and LAI data. We will account for root uptake of water; however, we may or may not account for root uptake of solute depending on some of our initial runs. We assume Free Drainage as the bottom boundary condition. We assume that the solute is deposited in the model area through air deposition (both wet and dry) and we have an estimate of the combined deposition rate (ML-2T-1) which will be used to define our source term. This represents the mass of predicted solute that gets deposited per a given area in a year. In our model we are assuming all the air deposited solute will enter the model domain and we want to understand how the model treats this mass of solute.

Our questions are:
1. If we include this deposition rate as a Concentration Flux BC (ML-2T-1), does this automatically calculate a concentration in the precipitation entering the model, that will give us a concentration flux equal to the BC value we set?
2. Is mass of solute from the boundary condition lost to surface runoff when it occurs, or to Evaporation when it occurs?
3. And is mass lost to root uptake (Transpiration) only when solute root uptake is enabled?
4. Lastly, is there an easy way to check the overall mass balance (flow and solute) and the mass balance for each of the components that either put mass into the model (concentration in precipitation) or remove mass from the model (surface runoff and ET) as well as mass stored in the soil column?

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Location: Riverside, CA

Re: Solute mass losses and mass balance

Post by Jirka » Fri Jun 02, 2023 4:00 pm

HYDRUS-1D does not do any unexplained internal calculations with respect to the surface solute flux. The code multiplies the incoming actual water flux q [L/T] with a specified concentration value c [M/L3] to get the boundary solute flux qc [M/L2/T]. When there is no incoming water flux, the solute flux is zero as well. The mass which goes into the soil profile during the simulation is obtained by integrating this solute flux over time, i.e., qct [M/L2]. J.

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