Effects of Gypsum on Ca precipitation and EC

A discussion forum for Hydrus-1D users.
Post Reply
Posts: 4
Joined: Tue Feb 26, 2019 5:36 pm
Location: USA

Effects of Gypsum on Ca precipitation and EC

Post by ansleybrown1337 » Fri Jan 17, 2020 5:28 pm

Hello Hydrus Forums,

I’m trying to measure the effects of gypsum on EC in the UNSATCHEM model (particularly a subsect of that model, named “ExtractChem”).
The inputs I have to run the model are as follows:
input_table.png (14.53 KiB) Viewed 9754 times
imgur link as backup: https://imgur.com/9GctqdB

However, including Gypsum in the model from observed values results in inaccurate inflation of model predicted EC at lower salinity concentrations (see 1:1 graphs below):
EC_1to1.png (70.61 KiB) Viewed 9754 times
imgur link as backup: https://imgur.com/kcWUWgy

This is reflected by Ca concentrations in solution:
The attachment Ca_comparison.png is no longer available
imgur link as backup: https://imgur.com/SAdz3ll

My question is this: why might excluding gypsum from the UNSATCHEM model resulting in a more accurate representation of solution EC/Ion concentrations even though my gypsum values are from observed data?

I also have pore water solution data from soil suction lysimeters that correspond with each one of these saturated paste samples, with similar trends occurring in EC and Ca precipitation/dissolution if that is helpful for deduction purposes.<br/>

Thanks for the help,

Ca_comparison.png (61.82 KiB) Viewed 9754 times

Post Reply