Most land based plants would die if fed saltwater.
The water would in most cases sink away below the surface too.
While that’s true, a large saltwater deposit somewhere arid would allow for water to evaporate into the air and create humidity and increase the probability of rain occurring in that area regularly.
Rainwater typically has a TDS of 20 mg/L or less. Fresh water from lakes, rivers, and groundwater is more variable, with TDS ranging from 20 mg/L to approximately 1,000 mg/L. Brackish water is, by definition, water with TDS exceeding 1,000 mg/L and ranging as high as that of seawater, at approximately 35,000 mg/L.
First off, the water would need to be desalinated or you would ensure the land would be unsuitable for farming (and really growing anything) for generations.
Also, sand doesn’t hold water. In fact, when planting trees and other bushes, if you want more drainage, you typically add rocks and sand.
Second, most plants need non-sandy soil to grow on (palm trees and other beach bushes and plants aside) though those grow in areas that have lots of rain already.
Thirdly, the soil will need bacteria to aid the plants in obtaining nutrients and breaking down waste (dead leaves, dead plantlife, etc).
The way to do it is to look at a couple of projects that are fighting against desertification in Africa:
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The Great Green Wall https://education.nationalgeographic.org/resource/great-green-wall/
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Using compostable waste to fertilize soil https://jstories.media/article/greening-the-desert-with-trash
You’ll notice that many of these projects start at the edges of deserts. Instead of relying on pumping water onto sandy soil (which would just suck up the water as sand doesn’t hold water that well) they focus on extending the non desert ecosystem onto the desert so that the new soil will absorb water better, the weather over the newly terraformed area will be less dry, and it will eventually be self sustaining.
Saltwater doesn’t revive soil, it kills it.
It’s been done before (though not intentionally at first), at the Salton Sea.
And the results weren’t that bad (granted possibly a smaller scale than some are imagining when they forecast doom).
https://www.ppic.org/blog/the-troubled-history-and-uncertain-future-of-the-salton-sea/
But the problem is any deserts are deserts for a reason: lack of rainfall and/or natural inflow from rainwater upstream. The result is that you have to keep pumping in tons of water and/or rely on agricultural runoff which is nutrient-depleted and usually full of chemicals.
Read the rest of the linked article for what’s going on with that one.
It is also important to note that most of the water that made the Salton Sea came from the Colorado River being rerouted back into California, then from irrigation water seepage.
Even then, the Salton Sea has a hard time supporting marine life. I can’t imagine making it a salt water lake would really help the local wildlife.
The sheer volume of water that moves through even a small creek is shockingly massive.
The amount of water held in an aquifer is astounding.
The soils required for agriculture and general growing plants (ones that hold water and nutriet) specifically are lacking or depleted in deserts.
So… it’s a literal pipe dream.
You’re wrong about the soil nutrient content in deserts. Or at least it’s not a blanket statement like that since some deserts are essential in providing soil nutrients to other parts of the world through wind.
Oh the nutrients are there, the composition of the soil is what is lacking so those nutrients don’t infiltrate into water well so plants can’t access them. It’s mostly sand and clay, lacking in silts for proper loams and organic matter.
Also there’s usually a ton of salt in desert sand that doesn’t help.
