ENVIRONMENTAL QUALITY
Of the many environments on earth, freshwater streams
are one I have studied the most. We tend
to automatically judge an environment in terms of its expected natural state
before civilization arrived. But erosion
of sediments and their deposition are not always something we would include in
our ideal stream even though it has been part of stream development forever. The different sediments of a stream provide
homes for different organisms based on particle sizes from silt to bare rock,
reflecting water velocity, and other organisms; the assortment is affected by those
factors as well as temperature, light, water chemistry and perhaps other
interactions.
Just looking at a stream, pond, or lake and determining
the gross aspects like water clarity, plants, and animals present may give an
approximation of the water quality and its ability to sustain life. Measurement of chemical and physical features
of the water along with a more precise inventory of plants and animals present
can tell more about present and past conditions of the water.
Dissolved
oxygen is often the most significant indicator of water
quality in terms of ability to sustain a diversity of fish, invertebrate, and
plant life. Chemical testing to determine
dissolved oxygen can show the oxygen level present at the time of testing. But a shallow body of water with high density
of plants could show depressed oxygen levels or even no oxygen at dawn and
supersaturated oxygen levels in the early afternoon on a sunny day.
In a stream, presence of several species of
case-building caddisflies and/or stoneflies shows good oxygen levels are
maintained because they need it to survive because their “gills” are out of the
main flow of water passing the insect.
Conversely, an abundance of fly larvae, especially rat-tailed maggots,
generally indicates organic pollution depressing oxygen levels; they survive
because they may extend their “tail” to the surface and breathe air. Like insects in general, most aquatic insects
have air filled trachea that extend throughout the body, but during their immature
aquatic phase the trachea do not terminate at surface spiracles but do extend
into the “gills”.
If the organic food wastes in the water are not
excessive, oxygen used by fish and other aquatic life can be replaced by plants
releasing oxygen produced by photosynthesis, and by diffusion from air at the water
surface. The surface input can be a
major source in small turbulent mountain streams. When dissolved and/or particulate organic
material is excessive, bacteria are a major user of oxygen; anaerobic bacteria
can continue the breakdown of organic matter when oxygen is depleted and in the
process release methane and other even less desirable by-products of anaerobic
respiration.
When excessive organic pollution enters a stream at a
specific location, the downstream portion will rapidly decline in dissolved
oxygen and most higher organisms. If excessive pollution loads are not entering
downstream the stream will gradually recover if toxic residues are not part of
the load. Toxic materials, if part of
the pollution load, can accumulate in stream sediments and be gradually
released as they further complicate recovery of a polluted stream.
In a lake or pond, a one-time input of organic waste
will over time have a recovery time sequence much as is encountered in the
downstream sequence in a polluted stream; the recovery time may be slowed as
compared to a stream because of the lack of turbulence.
A
biotic index of water quality can be determined from a
survey of the organisms that are present.
Since we know the requirements of most organisms they can be used to
define the water quality in a general way.
Good water quality is
often associated with a variety of fish and other vertebrate life, aquatic
insects, crustaceans, shelled mollusks, flatworms, annelids, diatoms and green
algae, and vascular plants. Water
clarity may allow one to see the bottom in water up to several meters in depth.
Reduced water quality
will result in an absence or reduction of the variety of the above groups,
perhaps an excess number of some that are more tolerant and an increase in blue
green algae both in the water and attached to solid structures. Visibility of objects below the surface is
very limited.
Severely polluted water
will have no fish, mammals, reptiles, amphibians, and few of other groups. Some fly larvae and tubificid worms may be present
or abundant in shallow sediments, as well as a coating of “sewage fungus” on
submerged objects. Some emergent plants rooted
in shallow sediments may be present. Water
may be nearly opaque.
Toxic substances may
result in the death of all organisms and give little visible evidence of their
presence. Mine drainage in mountain
streams may acidify the water and prevent aquatic life without being very
obvious. PCB’s in paper mill effluents
from efforts to recycle certain types of paper resulted in loss of all visible
bottom life in a stream that previously had some when it was severely polluted
by normal paper mill wastes.
Toxic substances may have killed off some or all of
the organisms as they pass downstream so a test of the water may not identify
the toxic material. Residues may be in
the sediments and/or retained in dead or living aquatic organisms present. An upstream search may help localize a
pollutant source if the junction with normal stream inhabitants is reached. A localized source of a pollutant is
referred to as a point source, more
generalized sources include surface
water runoff, atmospheric fallout, and sometimes groundwater discharge from
seepage or springs may also include contaminants.
Surface water runoff containing excess phosphorus and
insecticides is often worse from city lawns than from agricultural fields. City dwellers often think if a little bit of
chemical fertilizer or insecticide is good, more is better. Farmers know better, it is a waste of money
to apply more than is needed to do the job.
Many communities now have hazardous waste disposal facilities to reduce
contaminants that cannot readily be removed by standard sewage treatment;
otherwise a greater variety of toxic on other noxious substances reach our
streams, lakes, groundwater, and oceans.
A polluted atmosphere, like the one resulting from the
asteroid that killed the dinosaurs, is unlikely to occur in our time. That is especially so since we now have an
awareness of the damage fossil fuels have done in smog creation; acid rain that
acidified many wilderness lakes and shortened the life of exposed limestone
buildings and statues, concrete structures and roads; as well as producing
toxic mercury increases in lakes. The
concern about carbon dioxide buildup in the atmosphere causing global warming
alarmed many scientists well before Al Gore popularized the problem. If we were in a global cooling cycle there
would not be much to worry about, but that is unlikely to occur without an
unexpected drop in solar output or something like a complete melting of Arctic
ice providing so much atmospheric moisture that a new cycle of continental
glaciation begins.
MEASURING ENVIRONMENTAL QUALITY
Quality sounds like an objective assessment could
easily be made. But that is not readily
determined until the subjective part has been determined. If it is a plot of land, do you want to grow
orchids or cactuses? Usually the
subjective part is almost implicit in the location and typical use made
depending on local environmental conditions.
My early experience focused on freshwater biology, especially bottom
fauna of streams. The principles of
assessment of quality are much the same for other habitats as well.
The quality of an environment is most readily
determined by observing the living organisms present. From observations of organisms over their
range, along with associated observations of the physical properties correlated
with their distributions, we can understand more of the factors responsible for
the quality of their environment.
A
diversity index is a good way to measure quality without
having to be able to identify the organisms.
A sample (standardized if comparison with samples from other locations
is desired) is sorted in groups of like organisms, the groups and number in
each group is recorded. The diversity
index is calculated using a formula combining the number of groups versus the
numbers of individuals in each group.
Low diversity and poor quality of the location starts at no diversity
with all in only one group. High
diversity and good quality is indicated by many groups with none vastly
outnumbering the other groups. The
results are fairly unaffected by sample size if at least a few dozen groups are
included.
The variability of natural locations makes it
difficult to characterize the diversity with just a few samples. An alternative sampling procedure is to use
an artificial substrate. A graduate
student doing a research project of analyzing the water upstream and downstream
from the discharge of the Kalamazoo sewage treatment plant included artificial
substrates as part of his study. He used
small leaf packs anchored and left for a time sufficient for a fairly natural fauna
to become established. The packs could
be collected and disassembled so all the aquatic invertebrates could be
analyzed.
Many physical parameters typically have a range
acceptable for aquatic life. For example,
cooling water or other effluent, may have variable limits based on season, as
well as volume and temperature of both effluent and receiving water. Flow and/or mixing with the receiving water
are also considered. Sewage treatment
plant effluents also have limits on residual chlorine disinfectant that can be
discharged.
EVOLUTION AND ENVIRONMENT
Physical changes in the environment can occur more
rapidly than evolutionary changes in organisms.
An organism’s optimal adaptation to the environment will be in a range
from minimum tolerated to maximum tolerated.
The optimum may be near the median value or closer to one of the
extremes. Consequently, a change in the
environment can reduce survival or eliminate a species; a shift toward the
optimum may improve the specie’s survival chances. Evolutionary changes in a stable environment
will usually shift optimum requirements closer to the environmental
conditions. Such stability is not
typical so organisms may have a range shift adaptive to geographic shifts in
the environmental condition. A number of
organisms have shifted their range northward in North America in recent years.
A study published about the adaptation of Hawaiian
fruit flies changing the relative proportion toward an annual cycle of
environmental conditions showed a seasonal shift in the abundance of the
different variants of the genes involved.
Presumably most organisms have enough heterozygosity (variation in
genes) to speed some adaptive changes.
The concentration of salt in cell fluids and blood is
close to the concentration in sea water.
It is considered to be evidence of the origin of life occurring in the
ocean. Once animals and plants developed
ways of preventing excess water entry or loss and elimination of wastes from
their cells and blood they had the potential to migrate to freshwater and
terrestrial environment. Echinoderms are
an ancient group that may have converted their excretory organs to other use
and thus never were able to invade freshwater or terrestrial environments.
Vertebrates, arthropods, mollusks, annelids,
nematodes, and many smaller microscopic groups are commonly represented in most
aquatic and terrestrial environments. Bacteria,
algae, and fungi are also widely distributed in all environments. Vascular plants presumably originated on land
and very few have adapted to life in intertidal waters of the ocean.
IS THERE A SAFE LEVEL FOR A POLLUTANT CONTAMINATION?
Not really, but most things are not too much of a
worry. Too much water might increase the
danger of flushing out needed electrolytes in the blood. Too much air from hyperventilation might make
you dizzy. And both could be much worse
if they are loaded with pollutants.
Standards for
maximum concentration of an element or chemical compound acceptable in drinking
water are set by national, state, or local regulating bodies. Some things are unacceptable in any amount;
radioactive materials, mercury, and polychlorinated hydrocarbons are
examples. But our ability to measure
contaminants has increased so much that it often scares people to learn a tiny
amount is present. I would not be too
alarmed if anything was present at less than one part per billion; and one part
per million is unlikely to be of much concern for most pollutants. One problem could be that many different
related compounds could collectively produce a problem even though each was at
a permissible level. Fortunately,
regulators typically set levels at 1/100 or less below the limit at which a
small percentage of people are likely to be affected.
Some chemicals such as sodium chloride (table salt)
have increased greatly in many of our natural waters. Limits for drinking water may be due more to
possible taste concerns, although one might prefer to keep from adding to their
sodium load if they were sensitive to it affecting their blood pressure. But table use and discharge of salt in sewage
could almost be used as a proxy for population numbers before its intense use
for salting roads for ice control in northern climates. There, ground water near heavily salted
intersections can have salt levels beyond acceptable drinking water
standards. Salt has leached from
underground deposits ever since the early continents rose up with salt beds
from once shallow seas. The return of
some salt to the sea is not much of a problem, but other substances are not so
innocuous. Before DDT was widely banned
it reached the ocean and turned up in animals that were never near its source;
agricultural runoff and urban drains via rivers, and perhaps airborne transport
to some extent, may have been the delivery vehicles.
Reduce, reuse, repurpose, repair, recycle may be part
of the solution that will help technology minimize the refuse problem.
Joseph Engemann
Kalamazoo, Michigan October 31, 2016
