Monday, October 31, 2016
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