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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...
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:
"...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, 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. 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
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 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, or it may not, 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
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
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
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,
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
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.