Martini-Glass Energy Banks

Martini-Glass Energy Banks

All about it... 1

So what are the problems?

Considerations and approaches

Shapes and sizes

Martini glass?

Real estate and applications

So, what are we waiting for?  9

All about it...

Myself when young did eagerly frequent
Doctor and sage and heard great argument
About it and about, but evermore
Came out by the same door as in I went

Omar Khayyam
as interpreted by Edward Fitzgerald

As you will have guessed, this essay has precious little to do with Martini glasses and even less to do with Martinis. Sorry 'bout that — I suppose.

It does however have something to do with energy banking.

I was thinking about the storage of energy in ways that enable us to rely on renewable energy sources such as solar energy and wind energy without worrying about sunless days and windless nights: simply gather all the energy one can while there is a surplus, save it somehow, and draw on our savings whenever necessary. I already have discussed some alternatives in other essays, in particular:

http://fullduplexjonrichfield.blogspot.co.za/2017/04/heavier-duty-banking-appendix-supplement.html

http://fullduplexjonrichfield.blogspot.co.za/2017/02/heavy-duty-energy-banking.html

http://fullduplexjonrichfield.blogspot.co.za/2011/01/energy-storage-renewable-energy-sources_04.html

In some of these I disparaged the use of water as an energy storage medium such as in hydroelectric or pumped storage schemes. One needs to raise too much water to make it worth while, it takes too much water and too much space, and it tends to entail troublesome ecological penalties.

As I have pointed out elsewhere, one can store energy by raising masses and recover it by lowering them again; the more you raise, and the higher you raise it, the more energy you bank. Ten times as high, or ten times as much mass, and you store ten times as much energy. Ten times as much of both, and you get one hundred times as much energy, and so forth. And there are ways to store the water indefinitely with negligible loss and re-use the energy with good efficiency.

Marvellous, not so?

But I also pointed out that this requires dismaying masses of water. I here plagiarise some text I posted earlier:

The fundamental problem is that it takes a lot of mass suspended at a considerable height to store many megajoules.

Oh. What are megajoules?

A convenient measure of energy in any useful form.

Consider: 3.6 megajoules (MJ) = 1 kilowatt-hour (kWh).

You might consume more energy than 1 kWh just in roasting a joint of meat for a family meal, and yet, just 1 MJ is how much energy it takes to raise a 10 Tonne mass 10 metres. That sounds energy-cheap of course, but unfortunately, the other side of the coin is that from a ten tonne mass raised ten metres, you can barely get enough energy to prepare a meal.

So it is hard to imagine the billions of tonnes of water that power utilities need for schemes to store power in elevated storage dams.

One tonne of water occupies about 1 cubic metre, and a ten-metre column of water exerts a pressure roughly the same as atmospheric pressure, and not surprisingly, as already mentioned, if we work with molten lead instead of water, then it takes a column about 1 metre high to exert a pressure equal to one atmosphere.

If we insist on pumping fluids, it would be nicer to use say mercury or molten lead; they are much denser than water.

But they also are a lot more expensive, and have other unfortunate properties, such as toxicity, and in the case of molten lead, also temperature.

And one more time, don't forget that we also are not speaking of producing energy, only of storing and recovering it. We first have to get the energy from other sources; we still will need sun, wind, coal, oil, gas, nuclear or other generators to supply the energy in the first place.

Not encouraging?

No.

So what are the problems?

I hope climate science becomes the big thing.
And then what I want is electrical engineers to solve the world's energy problems, energy distribution problems.
I want mechanical engineers to make better transportation systems.
I want chemical engineers to develop better solar panels, and so on.

Bill Nye

Let us think harder about water. For one thing, in a lot of places, such as inland deserts, we simply do not have enough water to spend on energy storage at all. In other places we don't have the space; you can't plunk down a Boulder Dam just anywhere. Also, we don't want to use fresh water for energy storage where energy storage would interfere with the environment or compete with other needs.

As problems these aren't always and everywhere unacceptable, but more often than not they are serious. Using seawater is good where there is plenty of seawater, but historically we haven't used seawater for much of our power generation, because seawater seldom occurs high up where we can use it to drive generators. And it is more corrosive than fresh water. Granted, there are a few tidal schemes and so on, but they are limited in scope and scattered in location because the necessary conditions are rare.

On the other hand pumping seawater into high towers is a viable, environmentally friendly option almost anywhere on the coast. Often it even is advantageous to wildlife, such as by providing warm water with increased nutrient loads, or creating de facto nature reserves where people aren't permitted to hunt and fish; the real estate around the tower need not be wasted. The seawater simply could run back into the sea when exhausted, or go back into the pumping cycle if it had been necessary to filter it or otherwise treat it for whatever reasons might apply; that would reduce the need to repeat some of the treatment every time much of the water passes through.

But storing billions of tonnes of water and its potential energy takes space; a billion tonnes of water occupies a cubic kilometre, a terrifyingly huge volume.

And if we store the water in a cylindrical tower, the simplest and most obvious option, then the output from a full tower comes out at high pressure, yielding lots of power.

High pressure is good.

The pressure is what we apply to generate power, and the higher the pressure, within limits, the more power we can generate. However, by the same token, the last several percent of the output will yield hardly any power at all because it is under hardly any pressure. The maximal energy we can get is proportional to the mass of the water times the height through which it falls. So we want to store our power in the form of as much water as we can manage and held as high as we can store it.

This involves all sorts of engineering complications because of realities of pressures and leaks and foundations and structural design. Not being that kind of engineer, I avoid most of the practical details and leave them to the structural and power engineers. This is a refrain I repeat periodically and unapologetically throughout this essay, which deals with just enough engineering to urge the importance of certain principles.

Firstly, let us repeat, a ground-level cylindrical vessel, or in fact any broad-based vessel, is not satisfactory. As I have pointed out in another article, a large fraction of the water in such a vessel is wasted because when the vessel is nearly empty the water column is not high enough to give you workable pressure. All that the bottom few metres of your expensive water store are good for is to raise the rest of the water column high enough to give good pressure.

One can improve matters by mounting the vessel on a high place, or building it on a tall stem, with the power generation equipment at the bottom of the outlet, far below the reservoir. That amounts to narrowing the base of your energy store. Most big water towers use that trick, though not on the scale that we shall be discussing here, and not using their power for more than delivering the water.

I propose that we consider that trick too, but increase the stem height more than usual, so that the water still delivers a thoroughly usable pressure until the vessel (and even most of the stem) is empty. There should be no technical obstacle to mounting the vessel on a tower say 100-200 metres high. In a typical tall building each floor is roughly 3 metres high so such a stem height would be equivalent to some 30-60 stories; that certainly is high, even impressive, but nothing dramatic. A strong, attractive shape for such a tower would be a hyperboloid, though most towers in that height range currently seem to be cylindrical, because the constant diameter simplifies tower builders' jobs.

But again, such details are for the engineers to specify — get used to that refrain, because I repeat it fairly often.

But those engineering details need not amount to technological barriers.

If our proposal is to be defeated on technological grounds, it will be by the sheer volume of water we would need to suspend up in the sky, not the height of the tower.

Considerations and approaches

We cannot solve our problems with the same thinking we used when we created them.

Albert Einstein

A column of 10 metres of water exerts a pressure of about one atmosphere, so a column 100-200 metres high would give about 10-20 atmospheres of pressure. That would be well within practical engineering ranges, both for storage and for generating power. If we use seawater, which is slightly denser than freshwater, the figures will be roughly 3% better, but still not different enough to affect any of our assumptions seriously, whether for good or ill.

Unless you already know the answer, you should be wondering about why we should want to build the towers so high. Height is expensive and dangerous, surely? And extra water is cheap, especially seawater.

Well yes, but, within reasonable limits, to build the tower twice as high is less expensive than building two towers, and reduces the need for extra foundations, real estate, and duplicated equipment in an extra structure. Given the same mass of water, a higher tower stores more energy and delivers it at higher pressure, which permits more efficient power conversion. In fact, the same mass of water, twice as high, stores and delivers at least twice as much energy (in practice, significantly more than twice). Of course, there are practical considerations, but decisions about the best design compromises are the responsibility of the engineers. Figures and forms I assume in this discussion are no more than examples to illustrate principles.

Furthermore, it is important to maintain perspective; the first full-scale tower (ignoring smaller prototypes and trial designs etc) will not be the only tower; even if you did build one tower large enough to serve an entire country much larger than Liechtenstein, that simply would leave you with unacceptable problems of power generation, distribution, and maintenance. We may look forward to water-tower "farms", much as we have wind-turbine farms, though it might be better to put isolated towers near to where the water or power is wanted.

If it should prove economical (which I doubt, but again, ask the engineers) to build towers so much higher that the pressure in the effective column of water becomes difficult to control, generators partway up the column could draw power and reduce the working pressure on the lower turbines.

You might wonder whether there is any point to discussing such nonsensically high structures at all, but the topic is not something to dismiss without serious engineering assessment. Consider: the Millau Viaduct is a bridge mounted on masts in southern France. Its tallest mast measures 343 metres high, which supports a very heavy road and heavy traffic.

At the time of writing no one is has yet begun to complain about the durability of the viaduct.

 

Shapes and sizes

Experts get their expert fun
Ex cathedra telling one
Just how nothing can be done
          Piet Hein

Now, the water vessel itself could most obviously be cylindrical, open at the top and half as high as wide, because that is the most economical shape for an open-topped, floored cylinder of a given radius (after all, why not open-top? Open-top works for hydroelectric dams, doesn't it? And it is cheaper than adding a roof. And at that height above ground, not many birds or bats will be a problem, and no one in a helicopter is likely to drop in to steal our seawater).  

Well, let us examine that idea. We won't want to build a 200 metre tower just to perch a bucket of water; the idea is to store enough water high enough to power a city for long enough to be worth while. We might want to do so to tide over a period in which there is no sunshine, wind or wave power, nuclear or fossil fuel power, or whatever forms of power generation might be locally important. The stored water also might be useful in smoothing out power demand so that we could run on base load power supply. When our power demand is too low to consume the base-load power level, we can use the excess power production for adding to our stores of masses of water as high as might be practical. When our demand is too high for economical use of  power from the base-load generators, so that power production becomes very expensive, we can meet excess demand by running accumulated water through the output power turbines.

So, let's think 200 metres high. Ten tonnes falling through ten metres gives one kilowatt hour. Falling through 200 metres the same amount of water gives twenty kilowatt hours, enough to power a typical first-world household for a day or two. A million tonnes would should do for about 100000 families, say a small city. Similarly, a billion tonnes could supply a large country (ignoring problems of distribution etc). Or those billion tonnes could supply enough topping-up power to keep a modest sized country going for a month.

These figures are deliberately simplistic, intended to demonstrate principles, not to propose practical designs. At all times bear in mind that the idea is not to have one tower delivering full power for a whole country all year round. The towers are to accumulate energy when power sources are available at levels greater than consumption, and to generate power to supplement and smooth out the available supplies when the demand is greater than the available sources can realistically supply.

If we think of using a billion tonnes of fresh water, then in many countries we would have problems of supply and disposal, but they would hardly apply where we could use sea water, unless we also wished to desalinate our output, which would complicate matters, because we would need special arrangements to dispose of the salty discarded water. But that is not a complication we need consider here, though salt water at the appropriate pressures certainly should improve the economy of a modern desalination plant. It should in fact be adequate for desalination of brackish water.

For our purposes I shall assume that we are sited on the coast and that we take suitably strained and cleaned water from the sea. That is not as simple as it sounds, but it will do for purposes of our discussion.

But that big cylinder of water up there. Suppose it is 100 metres deep and 100 metres in radius. That would amount to  roughly 3 million tonnes of water at a mean height of 250 metres. However, when one speaks of millions of tonnes of water, one needs to be careful in designing the shape of the container. A flat-bottomed hollow cylinder with a wide base is not a suitable shape to suspend by the centre of its base; it would require massive reinforcing, which would add to the cost and reduce the stem's capacity to support the mass of water. Also, the water pressure inside the cylinder would be a lot greater near the bottom of the cylinder than near the top, and that would have to be taken into account as well. And the water near the top would be more profitable than near the bottom because it would be further from the ground, meaning that it would store more energy per tonne. In fact, in our example the water right at the top would be at a total altitude 100 metres higher, 300 metres. It accordingly would yield 50% more energy per tonne than water at the top of the stem (the bottom of the vessel) at an altitude of just 200 metres. 

Now, there are so many variables in calculating the best shape for the reservoir on top of the stem, that there is no simple optimum; the choice would depend on  the materials in use, the size of the structure, weather and earthquake proofing, difficulty of construction, the expected working life of the structure (nothing lasts forever) — all sorts of things. No single design would equally efficiently suit all climates and situations. So one thing I am sure of is that whatever shape I propose, some engineer who has had the patience to read so far will shoot it down in contempt. That doesn't bother me much, because if he were asked to suggest anything better, some other engineer would shoot down his alternatives as well. (Note that I speak here of male engineers, not so much because I am inclined to expect female engineers to be a bit more tolerant of my amateurish attempts to talk sense, as because of a personal distaste for clumsy PC circumlocution such as s/he.)

There are however several variables of interest.  For instance how high the bulk of the water can be held, how securely, safely and efficiently the shape and material can hold a full load, the sea, how costly the building process might be, how attractive the design might look, how efficiently and effectively the water can be extracted from the supply — you are welcome to add to the list.

The stem itself could be any of several shapes, of which the most obvious ideas would be cylindrical, conical or pyramidal, or hyperboloidal, possibly cable-stayed, and perhaps in some combination. Cylinders are simple and therefore cheap to build (up to a point), but for very tall structures they offer less strength than the same amount of material in the shape of a hyperboloid, and incidentally they also are less aesthetically attractive. This last point might seem frivolous, but seeing how many people complain about some very beautiful wind turbines, it could become important. And one thing that should apply to all classes of design of the stem, and very likely to the vessel on top, would be the addition of helical strakes to shed wind. See: https://en.wikipedia.org/wiki/Vortex_shedding

Think of the vessel on top of the stem: it must bear its own weight as a box that won't collapse when empty. It must bear the internal pressure of the water that tends to burst it open from within. And it must withstand the piercing stress of the stem supporting it from beneath like a spike.  Also, it must have capacity for a lot of water, and it must not in itself be heavier than we can help, or the stem would have to be too big, dangerous, and expensive. In meeting these requirements the shape of the vessel is very important, because it is one of the major factors determining its strength, the amount of material needed to build it, and how high it holds the water, which in turn is largely determined by the centre of mass of the full water load. 

It is tempting to think in terms of a spherical vessel, which would hold the most water for a given area of wall material, but both the localised stresses from the stem below, and the internal pressures from water within would complicate that. Besides, if we do not need a roof, we could do better with a hemisphere than a sphere; in fact, a hemisphere would work nearly twice as well, even allowing for giving it a stronger wall. In terms of the volume the hemisphere could hold, its capacity would be two thirds of the capacity of a cylinder of the same depth and radius, and it would be stronger. We also could improve the stresses in a hemispherical vessel at the point where it rests on the stem by narrowing the shell around the bottom to meet the stem top in an inverted teardrop shape. That would provide a stronger base, both for holding up the structure, and resisting the internal water pressure.

There is another variable that could however increase the attractiveness of a spherical reservoir. If it were suitably designed to withstand internal pressure, it could contain a suitable amount of say, nitrogen or propane under pressure. The gas could float above the water, storing energy in about the same manner as a compressed spring, increasing the pressure by perhaps a factor of two or higher, which on the scale that we are discussing, would amount to storing a good deal of extra water in the tower. However, storing energy by compressing gas is tricky if you wish to avoid inefficiency, and the distribution of pressure as the vessel filled and emptied would be complicated, so here again evaluation of the options would be a job for the engineers.

However, in either a cylindrical or hemispherical container, the wall strength necessary to contain a fluid under pressure is roughly proportional to the diameter unless the whole wall is very thick, so in a deep container, if the wall is to be of consistent thickness, the internal diameter should decrease linearly from top to bottom, because the pressure increases linearly from top to bottom. Twice the depth gives twice the pressure. This most conveniently gives a right-angled funnel shape, which is a rough approach to the inverted teardrop.

Such a cone has half the capacity of a hemisphere of the same radius, but it also keeps the water's centre of mass higher and is easier to construct than a hemisphere. In an inverted ninety-degree cone roughly 85% of the water will be in the top half of the vessel's height, compared to 50% in the cylinder, and the conical shape is fairly strong. One could slightly increase the average height of the water mass still further by using an inverted hyperboloidal vessel shape, and possibly the strength of the vessel as well by constructing it in the form of a hyperboloid of one sheet.  (In case you are interested in that option, you might want to read some material at:
https://en.wikipedia.org/wiki/Hyperboloid )

I doubt that the advantage at this point of the exercise would be clear enough to pursue the matter here; the advantages of simply lengthening the stem slightly according to requirements would be more obvious at any rate. Let's leave the fine tuning to the engineers when they get involved; it is not a point to be settled without planning and detailed calculation.

Martini glass?

Be thankful for problems.
If they were less difficult, someone with less ability might have your job.

Jim Lovell

Subject to more work on the point, I would suggest a design in the shape of an open inverted ninety-degree cone on a hyperboloidal stalk, or some closely similar structure.

Notionally it would look rather like the diagram below (without showing any strakes for controlling wind resistance, nor stays for keeping the structure erect in earthquakes, nor details of wall thickness and other considerations):

Hence the Martini-glass appearance, minus swizzle sticks, cherries or pickles, but with lots of Martini.

Now let's think about the scale of Martini glass we might care to use. Let us suppose the stem to be the same height from ground to its tip, as the depth of the bowl from its narrow tip at the bottom, to the centre of its wide top. That is not necessarily the best in all cases, but it is a convenient assumption, though I suspect that a longer stem would be better. Let us consider some examples.

Suppose we have a tower 100 metres high, carrying a vessel 100 metres deep. It could hold over 1000000 tonnes of water at a mean height of roughly 175 metres above ground, yielding theoretically about 1.75 million kilowatt hours. By the time it has passed through the generators, it should have yielded say 600000 kilowatt hours of electricity at short notice (probably requiring less than a minute to get the turbines up to speed). A cylindrical vessel could store roughly thrice as much energy, but with the disadvantages I already have discussed. By increasing the stem height and vessel diameter and depth by about 32 metres, we could more than make up the difference in volume.

If we still maintain the proportions, doubling the height and diameter etc, we multiply the energy capacity by 16 (eight times the mass of water at twice the height at the head of the stem) yielding storage for somewhere near ten million kilowatt hours, enough to keep a sizable city going throughout a night in a temperate region, if all its other energy sources were to fail at once. If base load generators were kept running, such a Martini glass might be good for weeks.

And that is from just one Martini glass.

As for billion-tonne Martini glasses...

It might be worth splitting the interior of the vessel into say three to eight sectors, partly for reinforcement, and partly to permit balancing the load over the centre of the foundation under conditions of high wind or foundation settling. This would not be suitable for rapid response, such as for earthquakes, but could greatly increase the safety and lifespan of the structure in the long term. In quake-prone regions, say 1 or 3 or more metal or polymer vessels containing a few hundred tonnes of water or lead could be suspended above the vessel to be accelerated in suitable directions for rapid sway correction in earthquake-prone regions. There are alternative designs for quake- proofing, but some are not likely to be practical for controlling masses on the scale that we are contemplating.

As for scaling up the size of the martini glass, there obviously would be limits, but they would be surprisingly mild when one calculates them. A 100 metre high martini bowl would present only 10 atmospheres of pressure at the top of the stem, and if the stem also were 100 metres high, it would have to contain 20 atmospheres at the bottom when the bowl is full. That is a very modest figure; in fact barely interesting in power engineering terms. If we double the height of the stem, we roughly double the amount of energy for the same amount of stored water; we could quadruple it for four times the energy, and gain higher pressure  and higher efficiency at the same time. 

Quadrupling the stem height would nothing like quadruple the building costs, because most of the material would be in the bowl, which as yet we have not considered changing.

Well, what if we double the height and radius of the bowl? 

Now things get a little more complicated. Other things being equal, that would double the pressure at the collar of the stem, and the thickness of the bowl would have to double, more or less, again yielding higher pressure and higher efficiency. However, and more importantly, the area of the bowl wall would quadruple and its mass would increase by a factor of eight. 

Not so good.  

However, the volume of the bowl would increase by a factor of eight as well, and with it the mass of the water and the energy stored, and the centre of mass would be higher.

Increase the size of the bowl by a factor of four, and the pressure still would rise only by a factor of four, very manageable and with a very beneficial effect on efficiency, but the mass and volume of the bowl would increase by a factor of sixty-four, which is sobering, but we could console ourselves with the thought that we also would increase the energy stored by a factor of sixty-four.

Not so bad.

And if we quadrupled the height of the stem as well, we could store 256 times as much at eight times the pressure and with still increased efficiency.

All this is very simplistic, but it certainly makes it clear that one would have great incentive to think very hard about the appropriate scale of our martini glass.

And the quality of our foundations and our building. 

   

Real estate and applications

Technology sometimes gets a bad rap because of certain 
consequences that it's had on the environment and 
unforeseen problems, but we shouldn't use it as an excuse 
to reject our tools; rather, we should decide that we need 
to make better tools to solve the problems caused by the 
initial tools in a progressive wave of innovation.

Jason Silva

The land that such structures would occupy need not be wasted. It could be used for agriculture, for recreation, for solar energy, as a nature reserve, for industry or as residential areas.

If the visual effect of the Martini glass shape were locally unpopular, it could be built invisibly into other structures such as office or residential buildings. Planting vines probably would not be adequate. At night the underside of the bowl should make a profitable surface for advertising, using laser projection. 

 

In theory, the design could be established offshore as a floating structure, using wave power to charge the glass, but I am fairly confident that underwater compressed-air tent farms would be a better option in every way. I discuss that proposal at:
https://fullduplexjonrichfield.blogspot.com/2011/01/energy-storage-renewable-energy-sources_04.html

Climatically, if the tower used brackish- or seawater, and began to produce enough ice in winter, the ice could be harvested as free desalination.

In hot climates, the inside of the cone could be black, heating the water to provide power via heat pumps, or water vapour to condense for consumption.

Electricity generation need not be the only possible application. Suitable freshwater designs could be used as a source of water for emergencies such as fires, for mechanical power in factories, and for storage of irrigation water and irrigation power.   

So, what are we waiting for?

Snow and adolescence are the only problems that disappear if you ignore them long enough.

Earl Wilson

A few million dollars for prototypes and a few stages of progressively larger installations, such as sized to suit light industry, should be worth the investment.

Sewage, Healthy and Not so Healthy

A man lived by a sewer
And by that sewer he died
So at the coroner's inquest
They called it sewer-side.

Chorus: Oooohhh, it aint gonna rain no more no more,
                      it aint...

Anonymous bard

Not long ago I linked to an URL in which the importance of dragonflies and damselflies (Odonata if you like) as indicators of healthy water bodies were discussed:

https://theconversation.com/dragonflies-as-sentinels-for-fr…

It was a good article with useful links, but afterwards a friend asked me to explain some points that had occurred to her. She said in part:

"...at the [local] human waste sewerage plant you cannot breathe without a mask, I have seen an abundance of dragons and damsels. How does that give any indication of the water quality? I cannot get close enough for photos, my system is not built for that smell."

That was a good, sensible question, and one that is no novelty to ecologists, though it gets asked too seldom in practice. Naturalists have known for years (centuries?) that sewage dams commonly are excellent beats for anosmic birdwatchers and for many other classes of wildlife students as well.

When people speak of an ecology as being healthy, they generally mean a clean, lean situation with nutrients in short supply, and vigorous, stably competing, elaborately cooperating,  populations of plenty of kinds of animals and plants. In this they are right as a rule, because when large numbers of species live together and depend on each other then it takes a very bad event to upset the system, and the ecology has a lot of flexibility in adjusting to changing conditions and cleaning up messes. The presence of such large numbers of species in reasonably stable ecological relationships is what we call high biodiversity.

Stable ecological relationships do not mean that nothing dies and rots, that nothing gets killed and becomes smelly, or that there is no manure to tread in, but it does mean that dead plants and animals soon get used up as food, shelter or other resources, by creatures that in turn become resources for others. In fact, for almost anything that dies or grows too plentifully, there will be other things that will clean it up by eating it up or using it up. Usually that happens in several ways at once.

And generally there is much storage of nutrients and other materials in the system. Living creatures accumulate material in their bodies or their homes or in the plants that shelter them, or in the material that surrounds them, such as soil humus that acts as a food store that supports worms on which moles and birds feed.

For example, in large regions of the Amazon jungle the soil is mainly sterile sand that cannot hold onto nutrient minerals. Sand tends to let nutrients wash out instead of holding onto them where they can act as a store of food in the soil. Nearly all soil contains some sand, but most soils also contain a fair amount of clay, and it is largely the clay that holds onto minerals and humus. That sounds marvellous, but not all clays release the nutrients well enough to suit all plants, and some hang onto trace minerals so tightly as to cause plants without mycorrhizae to suffer trace element deficiencies.

It is all a matter of structure. The best soil contains a lot of sand plus finer particles (sometimes called "silt") plus submicroscopic particles we call clay. When the mix is right, we call such a soil "loam". The chemistry of the clay is very important, and it is important that it should match the chemicals in the soil, that the plants need. (Actually, it also might be important to animals too; some animals and birds eat clays as antidotes to poisonous plants that they eat; the clays adsorb the poisons. But never mind that just now.)

Anyway, as a result of the shortage of clays and other suitable minerals in such sandy soils in parts of the South American jungles, the plants and the animals they support have had to adapt. They grab nutrients and water as soon as rotting releases resources from dead leaves or animals. The jungle then supports itself as a sort of inhabited living sponge of humus (or rain forest) on what otherwise would be an eroded sandy desert.

As long as it can go on collecting and juggling its riches without dropping too much, such a jungle is a very healthy ecology, though always hungry, but where you destroy such rain forest, say for agriculture, you soon are left with something that really does amount to a sandy desert. Turning that desert back to jungle does not happen easily or quickly; you have to build it up, and if the denuded region is large, that can take thousands of years. If you begin to destroy such a forest by clearing large areas to establish agriculture, you soon are left with nothing that supports anything stable (unless you call the desert stable, and even that erodes away in a one-way process through the ages).

And that is the general scheme in a healthy ecology. For any living species the rule is: waste not – want not. Even if what you can’t use becomes food for something that later may shelter or feed or serve you, that is better than nothing. The squirrel that buries more nuts than it can dig up again to eat, may thereby cause the growth of trees that can feed and shelter more generations of squirrels. This does not imply that the squirrel knows anything about that, but it conveys a clear message to the ecologist. Whatever is conserved might assist some other species to reproduce effectively; what goes around may come around, or it may not, but as a rule, what you destroy is gone.

Well, if that murderous, grabby, death-eating sort of ecology is how biodiversity tells us what is healthy, then what could be unhealthy?

For one example, whatever causes drastic reduction or extinction of any important part of the populations in the ecology generally reduces the viability and resilience of that ecology. Such reduction tends to create waste and mess.

If the destruction is bad enough, it can wreck the ecology for thousands or millions of years. We call that we call such a long-lasting event “permanent” destruction, especially if whatever finally replaces it in any healthy way, differs grossly from what had been there before, so that whatever had been good in the past is gone forever, even if good things replace it all millions of years later. If that is what happens, then we have a special type of destruction that is a kind of succession or replacement. Often however, lesser damage can be recovered in a few seasons or decades if things happen in just the right way.

What could cause such gross, lasting breakdown? In the long term it could be continental drift, astronomic events, or major climate change, such as in the Permian some 250 million years ago. On a shorter time scale one class of disaster could be poisons, either from human activity, or mineral accumulations of poisonous chemicals such as from copper- or arsenic-rich minerals.

Another form of major breakdown may result when harmfully invading species kill entire populations, causing waste and loss of the flexibility necessary for dealing with changes. Other examples include either bush encroachment or bush destruction, disastrous erosion, prolonged drought, and gross pollution. Many such things could result either from human activity or natural events; you name it. The results often turn out to be Badlands of various sorts.

One form that we are familiar with is pollution from human activities. Examples of such pollution include industrial wastes, mine tailings and the like, but some of the most obvious and most widely spread examples are domestic garbage and sewage. Garbage usually has fairly mild, local, but rather persistent, nasty effects, but where disposal builds up for too long, the results commonly are disastrous, making the rivers about you and the soil beneath you offensive, disease-ridden or simply poisonous. If you are curious, read: https://en.wikipedia.org/wiki/History_of_water_supply_and_sanitation plus associated articles.

But small quantities of some kinds of garbage, especially persistent garbage, such as empty food containers, though ugly, may actually be beneficial, in creating some kinds of valuable cover for many species of small animals. Much of that kind of potentially useful garbage however, can choke or otherwise harm cattle or wildlife or sea life.

The fact remains that in the last century or two the garbage or sewage problem has grown so much that it has become very hard to ignore it. Garbage often accumulates so persistently that it forms a sort of fairly stable local ecology of its own type, with scavengers such as rats, insects, gulls, crows, and so on, feeding on selected wastes and often on each other. And such animals tend to be unhealthy, dirty scavengers too.

Although they are temptingly rich in some resources, including food and shelter, such dumps are not really ecologically healthy, because wastes of such types are full of harmful things on which animals choke, or trace poisons that accumulate to cause ill health, short lives, and hormonal or reproductive problems. They also are not ecologically stable, because the things that go in will vary in time and place as the habits and circumstances of the humans that supply the garbage change, which they do all the tine. Still, where dumps of domestic garbage are isolated, they tend to form islands that are unlikely to disrupt major systems. Major disruptions usually occur where human communities spread and intensify to the extent that they swamp or fragment entire regions, causing extensive changes and local extinctions. We see some of that in slums, city dumps and landfills, though encroachment of the cities themselves is worse. 

Actually, human waste dumps are not the only type of waste dump one gets. The precious guano deposits that people used to strip from islands, would have been green oases in the ocean if the birds had not destroyed them with their thousands of years of droppings. However, in doing so, the birds did eventually create ecologically stable guano-based communities that supplied nesting sites and enriched the surrounding water.

We cannot safely sneer at nature's own landfills.

Other kinds of human ecological damage arise where there is extensive forestry or agriculture of single crops over wide areas ("monoculture"). Similarly, urban or suburban regions with lawns, flower beds, or concrete, all lead to a lack of contiguous thickets, and a reduced biodiversity in the resulting patchwork of plants. After all, who wants the thousands of species weeds that grow wild here, when you can buy a dozen species of garden flowers any time you like? In South Africa, especially the fynbos in the far South West, the problem is especially severe, because many pollinators are dependent on particular plant species, which in turn depend on those pollinators. Examples are long-tongued flies (in particular, Acroceridae, Bombyliidae, Nemestrinidae, and Tabanidae) that pollinate many Lapeirousia and many species of Pelargonium. 

You simply cannot grow enough of the tiny, unspectacular, but exquisite, gems of the veld to support enough of the pollinators, because you also would need to supply enough of the prey that their larvae need as hosts. In particular, even if there were enough plants, but fragmented into patches, that commonly is fatal. It takes only the failure of a single link in the chain, either food plant, prey species, or pollinator, and your ecology has lost an entire complex of creatures, and no photographs, no pinned specimens, and no tears will bring them back. 

In comparison the loss of the Rijksmuseum in Amsterdam, or the Louvre in France, would be trivial.

And apart from the disastrous fragmentation that large, uniform monocultures, such as thousands of square kilometres of field crops, orchards, or timber plantations cause, they are recipes for disastrous explosions of pest populations. They also are some of the worst possible examples of how to breed resistance to pesticides.

One thing that tends to upset people a great deal more than such habitat fragmentation and destruction, is the accumulation of sewage. Even among biologists, it demands special study to understand the biodiversity and ecological structures and aesthetics of undomesticated species. Surprisingly few of them even understand the unpleasant smell, flies, and infections associated with sewage, but at least one can explain stenches fairly easily to the more intelligent specimens, especially if education starts young. They then can understand explanations of the smells and the perceptions of disease and of disease-spreading scavenger insects such as many kinds of beetles and flies.

But sewage contains more than just smells and pests. For one thing, sewage usually contains a great deal of material that in virgin healthy ecologies would be valuable. A bit of dung in the forest or desert seldom lasts more than a day or two in its original form, because too many animals compete for it. For example, go to Signal Hill in Cape Town and look down beyond the seashore — at the time of writing there is a region where the water is brown. A major sewage pipe broke below the sea surface, much nearer to the rocky shore than where the proper outlet led.

The pollution around the break in the pipe got so bad that many species of fishes and other organisms simply could not live in the surrounding water, but many other scavenger species did very well there, and multiplied explosively. After all, with few predators, and huge food supplies, what more could they ask? And only a few hundred metres beyond the break, where the sewage is harmlessly diluted, other species grow fat on the scavengers. Those other species include humans who have learnt that there is no better place to find big, fat crayfish; by eating such scavengers one is in effect feeding on the sewage at a remove of one level.

Whenever we can manage that, it is a far shorter, more efficient recycling pathway than eating the abalone that eat the kelp, that absorb the thinly dispersed and bacterially digested sewage, right?

I do not say that regions too full of nourishing material speak well of human pollution, in fact we have a nasty word for them. We say that they are eutrophied, or even hypertrophied. Eutrophication means something like "full of food" in Greek, and that sounds good, but really, to an ecologist it means something more like "harmfully overfed". A bit like "obese", if you can imagine an obese ecology. Hypertrophication is to eutrophication as pathological obesity is to obesity, or perhaps as sewage is to compost.

Food for one creature is poison for another, and where there is too much food for one species, the excess food probably is killing some other species. For one thing, many bacteria digesting the wastes need oxygen, and most of them do not produce their own oxygen, so we find that sewage tends to contain very, very little oxygen. We say that the medium becomes deoxygenated. In deoxygenated soil or water there may be harmful creatures feeding and growing rapidly. Think of fungi and bacteria such as various Clostridium species. They are analogous to the rats and cockroaches in human dumps. You won't find many songbirds or antelope in dumps or sewage.

In that way (and there are many such examples) human eutrophication of various environments may be benign to some creatures even if they are harmful in other ways. Sometimes they only are harmful in very local spots where the muck is concentrated. When that happens, they often are largely beneficial from most perspectives. Under a garden manure pile only some kinds of earthworms and a few scavengers like beetle larvae and other specialist insects can live. And around the pile there is a border of dead earth, but a little further away some tough kinds of plants grow well, and still further away everything is lush for a few metres. Mostly weeds of course, but the very concept of a weed is slippery...

We could do better with our waste than wasting it perhaps, but in places like around the broken sewage pipe, where waves and currents helpfully disperse wastes, it takes bad pollution to do much harm. Examples might be where harmful substances accumulate in the food chains, or take very long to rot and stop poisoning or smothering whole living communities or choking animals with plastic wastes.

Still, where there is modest eutrophication, pollution often amounts to recycling. Even when the harm does keep some things away from a given area, it thereby might form a nursery shelter for young fishes or other organisms that otherwise cannot breed safely in the open.

Incidentally, there also are subtler forms of pollution that turn out to be beneficial in the end. The Koeberg nuclear power station ejects waste heat in its coolant water into the sea, and the result is what? Wildlife growing enthusiastically in the warm water. Certainly some species can’t survive the warmth, and close to the outlets they die out, but a little further away they do well, each seeking its own preferred level of warmth, and for the most part the effect is stimulating to the community rather than harmful. There are many examples of where industrial areas form de facto nature reserves by excluding hunting, fishing, and other human interference.

Then think of a clear stream with a few dams or lakes along its length. Suppose some community or agricultural activity begins to spill waste nutrients into the water in a few places. A lot of real harm results, possibly because some of the standing water simply turns into sewage, or because some of the bacteria and waste chemicals are lethal to animals adapted to very pure water. Places where we used to swim or fish simply get wiped out. Sometimes whole species become extinct.

We are tempted to say the stream is dead. Certainly the local biodiversity may be seriously reduced, and it definitely has changed. Sometimes it never will change back; you cannot bring back extinct species and it can be very difficult to re-establish local populations once they have been wiped out or even seriously distorted. Most of the things that once had lived in the clean, oxygenated, but nutrient-poor water would be dead or sick or gone away. In a standing dam the dirty water often becomes so rich in nutrients that solid mats of green algae soon cover the surface and smother all photosynthetic species below.

Algal mats may be unsightly, but we might console ourselves with the thought of all the oxygen that the algae produce. However, though that certainly is true, things are not so simple. Some of the algae and cyanobacteria in such mats release dangerous poisons. What is worse, such mats prevent wind or convection from circulating water from the surface down to the depths. None of the oxygen from the air or that the algae themselves produce, can get more than a few centimetres down below the surface. Deeper down, plants die for lack of light and bacteria deoxygenate the water completely. No fish, in fact few organisms apart from microscopic anaerobic life forms such as some bacteria can survive. The dam bed soon is covered with dead material similar to sewage sludge, and most of the water is unproductive and has a low biodiversity.

It is an ecological disaster.

Really.

But some creatures are adapted to flourish in such water bodies. Some live on the huge populations of scavengers, midges, mites, worms and so on, that can deal with low oxygen levels. To some species oxygen actually is poisonous; others depend on lack of oxygen for protection from predators that need lots of oxygen to support the high levels of energy that they expend in hunting.

Some animals that can survive in the green, oxygen-rich layers of the water, feed happily on the algae. Others live on those animals in turn. Many of the species that inhabit the surface algae are larvae that emerge to fly as midges, and in the air above such water dragonflies and damselflies will congregate, because there are so many more midges to feed on than elsewhere. Some of the dragonfly species will lay their eggs here, where the larvae will live in the algae layer near the surface where there is enough oxygen. Many species of dragonflies however, need clean, oxygen-rich water in which they can breed. But even if no dragonfly can live in sewage water, dragonflies from neighbouring cleaner bodies of water sometimes will aggregate where there are enough flying insects over filthy water. And so do many birds, including swallows and swifts.

For breeding, the dragonflies seek out other water, if other water is available, which need not be the case; my friend was asking about a semi-arid region where the sewage dams were almost the only open water in the neighbourhood.

Are such foul waters healthy then, just because we have lots of dragonflies, swallows and other welcome creatures flourishing over them? Definitely not. Whole populations, sometimes whole species, get wiped out in some places, and the biodiversity tends to be low, or at least lacking, in clean-water species.

Productivity too, tends to be low compared to what would be possible from the same resources in a healthy environment, because there is little turnover of the accumulated muck that settles out, muck that could take centuries to recycle even after the pollution stops. In a healthy ecology we want balanced input and output, and a healthy rate of throughput. Sewage or a dunghill might be a buffer in which nutrients accumulate, but it commonly is a buffer that dominates the nutrient cycles, and usually we can achieve more things and healthier things with our resources than just piling them up to rot. Ideally materials should be stored mainly in living creatures, such as fishes, insects, tadpoles, water plants, trees, otters and so on. It is good too pass nutrients rapidly from each to the next, conserving the energy from the sun and the minerals from erosion. Simply accumulating material as oxygen-free sewage sludge may attract scavengers and dragonflies, but it does not guarantee ecological health.

Species associated with various classes of ecology, such as those based on nutrient rich or nutrient poor conditions, or on particular poisons or temperature regimes, we often call indicator species. Indicator species are important resources for the ecologist, but the messages they convey, one must treat with insight. This has been known for thousands of years; as Aesop said in effect, "one swallow does not make a summer". Nor does one aggregation of dragonflies make a healthy body of water, or one dead rat an unhealthy garbage dump. It all is part of the immensely confusing, demanding, rewarding and important subject of ecology. One shouldn't just want to know the name of a species but also what it does and how it fits in.

Stop and contemplate; stop and wonder; stop and think; stop and enjoy.