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I have an idea for a world where land prevails over water and what waters there are are largely relegated to scattered lakes of varying sizes. Some of these lakes would be mega lakes, the size of the Mediterranean. Maritime travel in ancient times was a lot more efficient than overland travel, and was the main artery for trade. With maritime regions being pocketed, trade would be largely regional, and the development of civilizations would be discrete and therefore divergent from one another. This is what attracts me to the setting.

But I'm wondering what the salinity of these pocket lakes would be? My understanding is that outflow to the oceans in our own world is what cleanses the various inland bodies of water of their salt content, so that their existence allows everywhere else to remain clean. In the world I'm imagining, would it be the case that some lakes would be salty and others not, depending on the contours of the landscape (how much inflow vs. outflow a given lake receives)?

Going beyond this, how would salt content be likely to influence the development of a civilization? My thoughts would be that a civilization bordering a freshwater lake would be better off due to its usefulness for irrigation and human consumption. But I also understand that salt was a valuable resource in the pre-modern age, due to its efficacy in preserving food, so that salt-water (and the option to dry it in the sun) could yield a supply of this important commodity. I like the idea of there being some 'dead' lakes, where civilization is either entirely absent or scarce due to the lake's inability to sustain human life. I'm not sure if water salinity could cause this, though.

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    $\begingroup$ The major problem is that rain comes mainly from the ocean; no ocean means very little rain. A lake becomes salty only if it has no outlet; a lake through which water flows won't become salty. I don't know about your world, but Earth has mountains of salt. Salt extraction from sea water was practiced in those few lands which (1) did not have convenient salt deposits, (2) were located in warm regions, (3) on the sea shore. Everybody else mined salt. (And still does; we use vast amounts of salt in the chemical industry.) $\endgroup$ – AlexP Oct 25 '18 at 23:26
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    $\begingroup$ Hi Red. These are both interesting questions re salinity of lakes in a world like this and the necessity of salt for civilization. It is one question per post, so how about you split these off into 2? Also good to have the title with a question mark, or put in bold what your specific question is. Otherwise it comes across as musings. $\endgroup$ – Willk Oct 26 '18 at 1:08
  • $\begingroup$ Most ancient civilizations emerged in rather temperate climes, in places with a reliable water supply for irrigation. Without oceans to regulate and moderate heat flow, most of the globe-spanning continent will be blisteringly hot in the summer, blisteringly frigid in the winter, and arid all the time. Fewer civilizations may take much longer to emerge in such an unforgiving climate. $\endgroup$ – user535733 Oct 26 '18 at 2:07
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Looking at the salt content question. It's complicated! There are multiple effects pushing in multiple directions.

(1) If rainfall remained constant, to a pretty good approximation the rate of salt entering the lakes (in kg/sec) would be the same as the rate of salt entering the oceans on Earth. But since the total volume of water in lakes and oceans would be less -- probably a lot less -- the lakes on Lake World would be decidedly more saline. Roughly in proportion to the ratio of Earth's water volume to Lake World's. This might be 10 times or even 100 times as salty.

(2) But as @AlexP pointed out in a comment, rainfall would likely be less on Lake World, so water flow (and thus salt transport) into the lakes would be smaller. This would mitigate some (but probably not all) of the increase from (1).

(3) A third effect is that deposition of salt in salt domes and the like occurs mostly in shallow water like the Great Salt Lake today. (This is the main way salt is removed from lakes and oceans.) On the face of it, it looks like this would be more efficient on Lake World than it is on Earth because smaller bodies of water are more likely to precipitate salt. This also mitigates some of the increase from (1), but as the effect is strongest in very salty water and weakest in less salty water, it can't mitigate all of it.

Bottom line: Assuming the geology is otherwise similar (i.e., the sources of salt on land are the same) Lake World's lakes would probably be significantly more salty than Earth's oceans are, but any estimate more accurate than that would need really detailed modelling.

Note also that oceans are caused by plate tectonics. If Earth had a lot less water (and assuming that the oceans are not an essential lubricant for plate tectonics) then it wouldn't be a flat world that is everywhere continent, but would be a world of lakes on the real Earth's sea bottoms with giant, dry, continental uplands.

Without plate tectonics, Earth would probably be more like Australia everywhere. Australia has not had a mountain range raised on it in a very long time and consequently is low relief as continents go. Without plate tectonics you get hot spot volcanism and consequent bulges, but nothing like mountain ranges. It would be quite a different world.

Regarding the effects on civilization, life on Lake World would doubtless have evolved to deal with the higher salt concentrations, so I doubt that there'd be a huge effect on whatever civilization grew there. It does seem likely that salt would rarely be a limiting factor for life (on Earth in many areas it is) and its place would necessarily be taken by something else.

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