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Gammer
11-08-2016, 01:34 AM
Hey all,

I'm wondering just what would happen to fresh water source like a river and a lake when you dump a great deal salt into it. Would the salt clear out eventually or would it linger? If it lingered how long would it stay in the water?

In my work in progress a king, facing an inevitable overthrow by a rebellion, decides to to have the last laugh. He dumps all the salt he has gained from trade into all the nearby lakes and rivers in the kingdom. He also dumps the salt into the soil so nothing can grow.

Fast forward a few generations and when the MC travels to this old kingdom he finds the land dead since very few plants can grow and water so filled with salt it can't be consumed.

How plausible is that outcome?

Thanks in advance.

dinky_dau
11-08-2016, 01:58 AM
Off the top of my head:
Salt in a fresh water system would quickly dissipate due to the principle of diffusion. Then, just like other sediments,
the briny water is carried away. No real long term worry.

But salting a plot of land is a different matter. That will prevent vegetation growth for quite a while. It would have to be laboriously removed and then the ground (and the water table below) would need time to recover.

GeorgeK
11-08-2016, 02:17 AM
Salt in a river would wash away down stream pretty quickly although might poison the nearby fish temporarily. In a lake it would depend on the amount of salt and the amount of water. You'd have to know the volume of the lake and the mass of salt. Now a pond he could poison the fish. Salting the land realistically would affect things for a couple years until the rain washed it away. It would take really, really massive amounts of salt to do much more than that. When the Romans salted the fields of Carthage it didn't devastate the land for that long or turn it into a wasteland but did ruin the crops for a couple years and in a subsistence level society the people either starve or leave in that time. Now if you had poor quality soil already near a desert, then yeah it could spread the desert, but good quality land with decent rainfall, it will recover. Salt is not like agent orange.

King Neptune
11-08-2016, 03:25 AM
As has been pointed out, at most the fish would die, but it would take a really huge amount of salt to harm the fish in nearby lakes, rivers, etc. For brine to be toxic it would take something like a three tenths of a pound of salt to a gallon of water to get it to the salinity of the ocean. How much salt had been accumulated?

Salting the earth is more symbolic than anything else. Carthage was reoppupied and the land farmed within a few years after the Romans salted the area; the location was too good to abandon.

Gammer
11-08-2016, 05:16 AM
Well the kingdom in this instance is based off of medieval West Africa where salt was transported by pretty large blocks. Caravans of camels carried over 400 pounds of salt on each trip according to my research. There was so much of these salt blocks around that buildings were actually made from them. Kings controlled pretty much every aspect of the salt trade and a few actually hoarded a great deal of it. Some castles even had salt mines beneath their castles. So with so much salt on hand, I figured it would be no problem for the king in the story to douse the waters and soil with it. <br>
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In terms of the conditions of the land, the area of the kingdom is a fairly arid savanna with a significant bouts of dry season every few years.

Roxxsmom
11-08-2016, 05:39 AM
You'd have to calculate the volume of the lake and the total weight of the salt to get an idea of the change.

Seawater has an average salt concentration of around 3.5% (35 grams of salt per liter of water), which is a molarity of around 0.6. Brackish water (such as you might find in an estuary or salt marsh) ranges from 0.5 to 30g of salt per liter. Fresh water is less than 0.5 g of salt per liter, generally a lot less than that. Of course the fish, plants and other organisms living in a fresh water pond aren't able to tolerate high salt concentrations.

How many liters is the lake in your story? Here's a lake or pond volume calculator (http://www.vertexwaterfeatures.com/aeration/pond-or-lake-surface-area-volume-calculator) that will give you an approximate idea of the amount of water based on the surface area and depth. For instance, if your pond is 200 feet across and an average of 20 feet deep, it would contain 7,038,382 gallons (26,643,174 liters). To get this amount of fresh water as salty as the ocean, you'd need appx 932,511 kg (2,051,524 pounds) of salt. Of each camel carries 200 pounds, you'd need more than 10,000 camels (check my math, as I just dashed this all off). Of course, you could turn a lake this size middling brackish with considerably less, and if the point is to poison it to kill all the life and make it useless as drinking water, making it brackish would work. Still, that's a lot of salt.

Long term, if the lake has a good outlet (and if it didn't, it would likely be saline already, like the Great Salt Lake etc.), the salt would wash out over time, though it would cause fish kills and so on downstream.

King Neptune
11-08-2016, 05:53 AM
Well the kingdom in this instance is based off of medieval West Africa where salt was transported by pretty large blocks. Caravans of camels carried over 400 pounds of salt on each trip according to my research. There was so much of these salt blocks around that buildings were actually made from them. Kings controlled pretty much every aspect of the salt trade and a few actually hoarded a great deal of it. Some castles even had salt mines beneath their castles. So with so much salt on hand, I figured it would be no problem for the king in the story to douse the waters and soil with it. <br>
<br>
In terms of the conditions of the land, the area of the kingdom is a fairly arid savanna with a significant bouts of dry season every few years.

How much water is there? As I noted above, one would add about a third (call 0.30 pounds to the gallon) of a pound of salt to a gallon of water to reach the salinity of ocean water. There are 7.48 gallons in a cubic foot of water. Let's say that there is a lake with an average depth of ten feet, and it covers twenty acres, which is smallish. That's 8,712,000 cubic feet, and that would require 19,549,728 pounds of salt to turn it into brine. Even with buildings made of blocks of salt, that's a lot of salt, and that's just for one lake. How much water is there to be treated? I admit that when one owns a salt mine a few million pounds of salt bwcaome a small thing.