How many lakes are there? We don't actually know. Lakes are often undercounted, or small lakes ignored, in larger scale geophysical surveys. It is hard to count the small lakes, or in some cases, even to define them. A recent study (published in Geophysical Research Letters) examines this question. We want to know how many lakes there are, and how much surface area they take up, in order to understand better the global Carbon cycle (and for other reasons). From the Abstract of this study:
An accurate description of the abundance and size distribution of lakes is critical to quantifying limnetic contributions to the global carbon cycle. However, estimates of global lake abundance are poorly constrained. We used high-resolution satellite imagery to produce a GLObal WAter BOdies database (GLOWABO), comprising all lakes greater than 0.002 km2. GLOWABO contains geographic and morphometric information for ~117 million lakes with a combined surface area of about 5 × 106 km2, which is 3.7% of the Earth’s nonglaciated land area. Large and intermediate-sized lakes dominate the total lake surface area. Overall, lakes are less abundant but cover a greater total surface area relative to previous estimates based on statistical extrapolations. The GLOWABO allows for the global-scale evaluation of fundamental limnological problems, providing a foundation for improved quantification of limnetic contributions to the biogeochemical processes at large scales.
So, there are fewer than thought but they take up more space than thought. Who would have thought?
Interestingly, there are more lakes at higher latitudes. Because of the uneven distribution of land surface in the Northern vs. Southern Hemispheres (more land in the north) this means more lakes in boreal regions, and more specifically, more lakes in previously glaciated regions. This makes sense because glaciation (and deglaciation, melting of the glaciers) produces lakes. The immature terrain produced by a glacier eventually matures with erosion joining streams and rivers to those lakes, making them disappear. If no glaciers return to a previously glaciated region, eventually all the lakes (or most of them) will disappear.
Look at the Congo, Amazon and Nile basins for examples of large inland regions in the tropics. There are very few lakes. Now look at North America north of the maximum extent of the recent (Wisconsin) glacier. Lots and lots of lakes.
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At very high latitudes there is also a permafrost layer which can be conducive to the formation of (numerous) thermokarst lakes. Permafrost also affects - prevents - surface drainage and thus promotes ponding of surface water. Look at Google Earth imagery of Alaska north of 68 degrees latitude. There are countless lakes.
To simplify counting, there's only one natural lake in Scotland, the Lake of Menteith. Of course there are [probably uncountable] lochs and lochans, which might have to be included.
I get a "403 forbidden" error when I click on the link so can't see the paper. Is there a simple (general?) guideline to distinguish between what qualifies as a lake and what we (here in Michigan) call a pond? Is that distinction not important?
In Australia we have the added complication that a lot of our lakes are temporary -very temporary!
Are we counting salt lakes such as Lake Eyre, Lake Torrens, and Lake Cadibarrawirracanna.
No, really I didn't make that one up -see :
http://en.wikipedia.org/wiki/Lake_Cadibarrawirracanna
Our inland rivers tend to be awfully variable as the early European explorers often found to their cost and the salt pans / lakes fill only for a very short time at irregular intervals maybe only once or thrice every third decade or so.
Maps of Australia that have these lakes painted a lovely shade of blue are highly misleading and the counting of these is, well, rather problematic.
See also :
https://www.youtube.com/watch?v=qwK-nNzOasQ
Apparently also a setting for Mad Max - which is something new I've just learnt about, oh, two minutes ago now!.
Plus there's some good pictures of Lake Eyre also now known as Kati Thanda from space and otherwise on its wiki page here :
http://en.wikipedia.org/wiki/Lake_Eyre
Plus there's the awesome starkness of scenery and photographic enduro of Salt on lake Eyre / Kati Thanda to get a quick taste of here :
https://www.youtube.com/watch?v=YyXGwB9B6bQ
One spectacular if slow doco - & a challenge to tell the salt from snow in some scenes.
PS. I gather Greg Laden there are similar(~ish?) salt pans in Africa incl. / alternatively of natron and extreme alkalinity? Turkana? With flamingos and awful caustic mud? Did you see anything like that there?
Astrostevo:
I was at a seminar, years ago, on freshwater lake coring and paleoclimatology, the speaker was Australian. He kept showing slides of the lakes he cored. One lake after another after another.
Finally someone in the seminar stopped him. "You keep using this word, 'lake', I don't think it means what you think it means. Those are all dry fields of dust!"
Southern Africa is full of lakes that are not full of water!
They be "virtual lakes", mate!
Yes indeed! Hard to say if that makes them playas here or not isn't it! ;-)
Interesting! Makes me think several thoughts:
1. On other planets, could quantity of lakes be used as a proxy for past but "recent" glaciation?
2. Glaciers produce or supply the necessary ingredients for lakes: they erode and/or deposit earth materials to form enclosed basins; they expose bedrock or deposit silts and clays, both impermeable earth materials, to line the bottoms of the basins; and then they melt and leave fluid to fill the basins. All of those ingredients (basins, impermeable bottoms, and fluid) can be supplied by other processes, of course.
3. How are the the alkane lakes on Titan formed? I know the fluid seasonally rains from the atmosphere, and I think the impermeable lake bottoms are "bedrock" of water ice, but how are the basins formed? Bolide impacts?
Many questions. Nice post!