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.

Eventually, I moved to Minnesota where there are probably between five and ten thousand lakes that a) are about the right size to walk around in several minutes to an hour or so and b) have a path to do so. That number could be way off, but in any event, it is a very large number.

So after being here for a couple of years, I started to become acquainted with the process as a form of geographical perambulation, socialization, and even, yes it is true, mating. My first real exposure to the charms of Minneapolis involved a visit to the rose garden along side one of these little round lakes. Later, my then significant other an I would meet daily at a certain lake that was between our places of work and walk around it. Some days, when we had the extra time we’d walk extra fast so we could get in two rotations. For our first date, my wife and I walked around a lake then went to get a beer.

I should not mislead you. Walking around the lake is not a Minnesota thing so much as a Twin Cities thing, and then, it is probably more of a Minneapolis Thing than a Saint Paul thing. Saint Paul has it’s lakes, but Minneapolis is “The City of Lakes” (thus, the name of our basketball team is The Lakers, or at least it was until they moved somewhere else), and there are several round lakes of just the right size with the path all around them. But really, when I think about it even further, I’d say that the walking around the lake thing is more of a South Minneapolis thing … because that is where almost all the lakes are in the city, and that is where the cultural behavior is most strongly manifest.

If you put my previous post on lakes together with this one, to put a longer term time perspective on it, it is not hard to imagine all these Minnesotans spinning around the rim of the lake which is really just a large mass of water ultimately flushing into the ocean.

Well, anyway, I’m pretty sure that the average person who walks around these lakes has very few thoughts of the geology, geomorphology, physical geography, and paleoclimatology that they are experiencing. For instance, with respect to lake physical form: Imagine standing along side a lake that is small enough to see the other side but big enough that you can’t quite make out the people on the shoreline across the way unless they are wearing blaze orange and jumping up and down (which is not uncommon in these parts). Now, somebody sidles up to you and says “This is a deep lake, according to this fishing map I just bought at the Mule Lake Store.”

So you look across the lake, and you think about it being deep. Imagine that. Imagine the slope, the contours, of the bottom of the deep lake, and imagine those contours being realized in your mind’s eye as the person continues, “As a matter of fact, out there, between here and that shore over there, is the deepest part of this particular lake” .. Now, the contours in your mind’s eyes deepen and steepen.

Now, ask yourself, are you even close to imagining something accurately here? And chances are, you are not.

Here’s a simple fact: In Minnesota, for the vast majority of lakes, no matter how deep they are, you can pick up a stone and with a good heft toss that stone horizontally out into the lake a distance that is close to the maximum vertical depth of the lake. Most of the lake will be less deep than the width of the average city street. The deepest part of a pretty deep lake will be about 60 feet, or slightly deeper than a city lot is wide, slightly less deep than a suburban lot is wide. Maybe the stone you throw will have to bounce a couple of times to get to that distance (depends on your arm) but I think you get the point. If the far shore of the lake is as I described above …. just that far away that you can barely make out a person … and the lake is about 30 feet deep, then it probably true that if the lake were empty and covered with mixed grassland/woodland vegetation and you were standing in the same place, you’d call it flat. Only an expert eye would recognize the stranded shoreline ringing the somewhat low spot at exactly the same elevation.

The lake is given its psychological depth, of course, by the water. Even in a clear lake it is hard to see below six to ten feet on a good day, and when one is looking through water at depth of 10 feet or more, if you can see the bottom, it is hard to estimate the depth. Of course, if you are a boater and you have a fair amount of experience, and work with soundings and maps, you can get good at this, but uninitiated, you’d probably miss-estimate. Then, if you are told “this is the deepest lake in the township” and you are out in the middle, and you see nothing but murky depth below you as you stare into the water along side the boat, one imagines a depth that is deeper than what is there. It is hard to perceive that most likely the average telephone pole would stick way up above the lake’s surface. If there was a telephone pole right in that spot.

The average person walking around the average lake in Minneapolis is ALSO walking around within a channel of an ancient, giant river. They may not have noticed driving down the bluff of the ancient river valley when they approached the lake, or the fact that they have parked in what must be the top of a sediment deposit several tens of feet thick within which huge chunks of ice were once trapped, subsequently melting and forming the lake about which they are about to perambulate. Those extinct rivers are why those lakes are there, and the whole process is linked to ancient glaciers and glacial cycles. That is probably worthy of further discussion.

(Read all the “Lakes” posts here.)

But despite the importance of lakes in our recreational regime, lakes were actually fairly uncommon in Upstate New York and New England. A surprising number of lakes in the US Northeast are actually rivers or streams that have been dammed. Much of the landscape was glaciated and much of that was blanketed with glacial drift, in which ponds and lakes often form, but since the landscape is hilly (often mountainous), rivers and streams have joined low spots together into a dendritic network of flowing water. Many of the lakes that may have been there right after the glaciers retreated had been swallowed up by this network.

For example, this is the region of upstate New York where I spent much of my childhood and teenage years:

There are lakes, but most of the terrain is uplifted and drained by streams and rivers. Indeed, many of the lakes you see on this map are formed by dams and are not natural. One of the main walleye fishing lakes in New York State is the Great Sacandaga, a reservoir.

Where I now live,in Minnesota, there is not that much change in elevation, so there are lots and lots of lakes, to the extend that this is called “The Land of Lakes.” If you’ve ever seen “Land o’ Lakes” butter or other dairy products … well, that’s from here. Land o’ Lakes is one of our local businesses.

For example, this is where I spend much of my time during the summer here in Minnesota:

The same glacier covered this area and upstate New York, but here there are more lakes, owing mainly to the flatter terrain. Also, very few of these lakes are regulated by dams (though more were in the past during logging days, the dams now in disuse) and I’m 99 percent certain that not one of the lakes shown on this map are human-made. (This map and the one above of New York show roughly the same land area.)

It is worth noting that people who live in Upstate New York can typically tell you where various rivers and streams are, and can tell you what river or stream feeds into what other rivers and streams. In contrast, I’ve found that Minnesotans often have no idea what the nearest stream or river is, or where it goes . In the region depicted here, if you ask someone which way the Mississippi River is (all the water you see here drains into it) people will simply not know or will point in a random direction.

A lake is the landscape thumbing its nose at time. All elevated regions … all places on Earth where you can stand in one place all day and NOT have the briny sea lapping at your ankles (or knees) at least a couple of times a day … are subject to being eroded down to sea level, someday. Wind, rain, phytochemical activity, and running water will eventually flatten any and every continent to the level of the ocean’s tides.

Or at least, that is what the forces of erosion would do were it not for forces of uplift and deposition happening at the same time. And as mountains or uplands rise above the theoretical tide line, rivers cut down into the emerging hills, and seas grind away at the edges, every here and there forms a low spot that does not drain gravity-ward, and that can hold water for a time. Sometimes that time is days, after a rain. Other times, it is tens of thousands of years, until the low spot is breached by erosion and let out to the sea. Eventually, every lake may give up its basin to a stream, and thus its water to the ocean directly, by surface flow (it had already been feeding the sea indirectly via groundwater movement and evaporation).

(There is another way to think of lakes that views them as windows into an underground system of rivers and reservoirs. That perspective works better in a different kind of discussion, so we’ll set it aside for now.)

There is no reason to believe, by the way, that the forces of uplift and deposition on continents is in balance with the forces of erosion. There is no reason to expect that there have not been times in the past when most of the continental regions of the Earth was inundated by shallow seas, with few rises and almost no mountains above them. Conversely, there may be times where much of the world’s water is trapped in ice, so the ocean rests much lower than the continental margins, and much of the land is high and dry. I sometimes wonder how one would characterize the present day in this regard, relative to other time periods. There are major “inland seas” (the Caribbean, for instance) but it seems some major seas and low areas have been elevated in recent millions of years (the Tethys Sea, which once ran from Gibraltar to the Black and Caspian seas, cutting off Africa from Eurasia; The Miocene seas and lowlands of South Asia now known as Pakistan and Afghanistan; the sea that was an arm of the Pacific, where the Amazon now stands; etc.)

For many lakes, their death precedes their capture by the growing network of rivers and streams, as they are filled in with sediment, converted to bog and eventually become a flat marshy spot. The cost you pay for being amenable to settling water is muck and other sediments filling you in. Lakes with outlets don’t have this problem to the same degree, but those outlets are essentially topographical hemorrhages, cutting down even if there are ephemeral human dams in the way, stranding the shorelines and making the lake into an ever growing valley or canyon.

So when you see a lake, take a good look. It might not be there tomorrow.

Well, OK, it probably will be there tomorrow, but at the medium to large temporal scale, all lakes are temporary features of the landscape, thumbing their metaphorical noses at the tide line, to which, eventually, they are bound to sink. Unless something else, much more severe, happens to them, like being ground up by a glacier or subducted into the fiery mantle of the earth. Or the sun exploding. Or it turning out that the Universe is only a simulation game being played in some other universe that does exixt.

The distribution of water on Earth in cubic kilometers

(Biological means like your spit and guts and all the juicy parts of worms and tree saps and water in bacteria and stuff.)

USGS

Wikipedia

What happens if all that glacial ice melts and ends up in the ocean?

Play with this for a while to get an idea. The maximum rise in sea level in that model is probably not the maximum if all the ice melted, but all the ice won’t melt.

Maybe .

The lake was ice cold … dangerously cold if you fell in, but the dad/daughter combo risked taking the canoe out just to the edge of a marshy area from which protruded countless brown stalks left over from last year’s lush growth. From here, if they did fall in, it would be a simple matter to walk the canoe back along a sandbar that ran out from near the field research station’s dock. They would have cold toes but they would not die of hypothermia. Getting fully dumped into the deep part of the lake would be death in a minute or two, and such a death would come to a half dozen Minnesotans that year, but this close to shore, they were safe enough.

This particular lake was extra cold that year, Dad/Daughter would later find out as they learned such things about their new home in the Upper Midwest. Great slabs of ice rested along the downwind shores in the funny shaped body of water designated as Itasca, the source of the Mississippi. This was not really a fishing trip, but rather, a trip up from the Twin Cities to a conference at the University’s research station, but Dad/Daughter had prepared for the possibility of tossing in a line, having heard that the fishing was pretty good in Minnesota.

And now, under the purposefully blank stare of the man so well camouflaged … so the fish would think he was a tree covered island? … Dad/Daughter threw their first casts in the general direction of the dead brown stems.

Bam!

This 28 inch northern pike must have been waiting since ice-out for something tasty to come along, and the yellow Number 4 Mepps spinner bait was the perfect enticement. Just as Dad was bringing that fish along side the boat and releasing it…

Bam!

A 32 inch Northern hit daughter’s yellow Aguilla spinner and nearly dragged her out of the canoe. But the fish was landed and released after a great deal of giggling and screaming. And then …

Bam! A 2-pound red-eyed rock bass …

Bam! A small Northern …

Bam! A really big Northern …

Bam! Something never quite seen but big enough to bend the pole in half and move the boat about two feet sideways, strengthening out the hook and swimming off to find something good to eat elsewhere.

That was probably a Muskie. And when the Muskie swims through, things tend to go quiet. Which was fine, because Dad/Daughter had had enough.

And when Dad/Daughter glanced up to see if there would be a reaction from Big Tree Island Man, he was gone. And for the rest of the day he in his boat and thirty or forty other boats with similar men, most in camo, some in pairs or triplets, fished these waters with their complex rigs, minnows, and live leeches, from their $30,000 boats. Back and forth and back and forth across the lake.

But no one seemed to catch a thing.

Later, Dad/Daughter would learn of their sacrilege. They had blundered out on the lake on The Opener. Fishing Opener is the first day walleye (and some other fish) can be angled from most lakes in Minnesota. It is usually on Mother’s Day weekend. It is the single biggest migration of the year, and more boats will be on the lakes than any other day with the possible exception of the Fourth of July. And most of the boats will be operated by big men in camo with complex rigs designed to catch the walleye.

And some years, the walleye are ready to feed and be caught. Some years they are not.

Dad has fished on The Opener almost every year for 12 years. He has yet to catch a walleye worth talking about. But the northerns … well, that’s another story.

Oh … and up in the Lake Region … always start out by throwing a yellow bait.