Friday, March 9, 2018

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:
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:
" 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, stable 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. 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 a fair amount of 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 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 may shelter or feed or serve you later, 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, just that it presents a clear example to the ecologist. Whatever is conserved might assist some other species to reproduce effectively; what goes around may come around, but 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 flexibility 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. 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 result can 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: 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, 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 poison or smother whole living communities or choke 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.
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.

No comments:

Post a Comment