Water Quality Measures
Alsea Falls, South Fork Alsea River
Using macroinvertebrates is a more accurate way of evaluating stream health than the riparian zone because the organisms are more affected by the stream; riparian zones more often affect the stream’s health and not as much the other way around. Macroinvertebrates are organisms that lack backbones, are very often microscopic, but can also be big enough to be seen by the naked eye. Many flying insects begin their life as aquatic nymphs and larva, living under logs, rocks and among the vegetation in the stream. It is in this life cycle that people can learn about the real quality of the water. Even though a stream looks healthy and clean, it doesn’t necessarily mean it is. Much of the time the water is contaminated with silt, pesticides, bacteria or other substances that make it nearly impossible for organisms to live. Each macroinvertebrate has a certain tolerance to various forms of pollution, making it easy to tell whether the stream is in good health or not (“Stream Water”).
Susan Sternadel performs a macroinvertebrate sampling
The best method for retrieving macroinvertebrates from their habitat is to
use a kick-net, which is a fine meshed net with a flat bottom one foot wide
and is
placed on the stream bed. One just disturbs a one square foot area upstream from
the kick-net making sure to do a thorough job so as to get all the organisms
off the rocks and into the net. What is caught is put in a tray with water to
make it easy to sort the organisms by species (Barnes 380).
Each macroinvertebrate can also be classified into a different functional feeding
group which provides an interesting look at what may be the most abundant food
source in the stream. These groups are shredders, collectors, predators, and
scrapers. The easiest way to tell the health of the water that the sample is
from is to look at the diversity of species and see if there is a high diversity
or a low diversity (Barnes 382). In general if there are a good number of species
in a sample then the water quality is good because it can support a wide range
of life. If there are only one or two different species of organisms in the sample,
then the water quality is probably in poor health (Dodds 183).
Some good water quality invertebrates include the “big three”:
stoneflies, caddisflies, and mayflies. If all three of these nymphs are found
in the stream
in abundance, then that is a sign of good water quality. On the other side of
the scale though, if leeches, bloodworms, and an abundance of snails and clams
are found, then that probably means the water quality is rather poor (“Stream
Water”). Invertebrate information can also be quantified into Pollution
Tolerance Index (PTI) and Diversity Index (D.I.) which both have classifications
for stream water quality. The Pollution Tolerance Index ranks macroinvertebrates
into a point system where good water quality species are awarded more points.
Each species is only counted once per sample and the higher the PTI number the
better indication of good water quality with low pollution levels. The diversity
index is slightly more complicated but results in the species diversity rating
for that stream. Higher the diversity ratings usually mean better stream water
quality.
There are many species or aquatic organisms that are becoming increasingly
rare or endangered. Among these is the fresh water mussel Margaritifera margaritifera
which indicates marvelous water quality. Margaritifera is extremely pollution
intolerant and is dying off because of the amount of pollution in rivers
and streams. According to Dodds in his book Freshwater Ecology, pristine environments
don’t exist anymore because pollution is everywhere in the air, water
and atmosphere and people are unable to just clean up an area and call it
good (270).
Invertebrates are extremely good indicators of change over time in a stream
and provide long-term data as opposed to instant one-time data provided by
digital
meters.
Invertebrates can give an idea of whether there is pollution or contaminants in the water, but it is harder to see more technical measurements such as dissolved oxygen, pH and turbidity, which are all just as important in stream health. If all the water chemistry tests are performed together, they can show relationships and explain why one test turned out a certain way.
Dissolved oxygen (D.O) is important because it is what the organisms require for cellular respiration; it also encourages more life in the stream to grow. Healthy populations of algae and bacteria keep the food web in working order but can also largely deplete D.O. supplies if the body of water is slow moving, warm, and murky, by respiring more than photosynthesizing and using oxygen when decomposing organic material in the stream (Murdoch)(Sternadel, “The Values”). Too low of a concentration of D.O. causes organisms to die from not being able to breathe and unfortunately if there is too high of a concentration of D.O. from conditions like an overabundance of photosynthesizing plants, then organisms will die from too much oxygen. Life in the streams can adapt, so there is no fine line on what is too low or too high, but it depends on the species at hand (Hamilton 5-22).
Temperature goes hand in hand with dissolved oxygen because it is inversely
related to it. Cold water tends to hold oxygen more easily than warm water
because the water and oxygen bonds are weaker with warm water and can be
broken more easily. With more dissolved oxygen in the water there is more
of an abundance of life. Low temperatures by themselves don’t indicate
good water quality but if compared with dissolved oxygen then more can be
seen. Aside from a few cases, as the temperature decreases there is an increase
in dissolved oxygen concentration, and as the temperature of the water increases
then the dissolved oxygen decreases.
Turbidity is another important test that can be taken of a water sample. It measures the amount of suspended particles in the water. Cloudy water equals a high turbidity reading (Hamilton 25). Despite the fact that some people might say turbid water could be beneficial to help fish hide from predators, high levels of turbidity are not good. Low levels of turbidity are normal and occur naturally from sediment and phytoplankton colonies. Lower turbidity in a stream is better for everything living in it. When there are a lot of suspended particles in the water, it affects the respiration of organisms by clogging up gills, and it hinders fish’s ability to smell out their spawning grounds (Hamilton 21). In fact turbidity also ties into water temperature and dissolved oxygen. Turbid water absorbs heat because it is darker so it doesn’t reflect the UV rays. Clear water reflects the light and doesn’t warm up as quickly. Conclusion being: turbid water equals warmer water, which equals lower dissolved oxygen levels. This combination is rather unhealthy for organisms that require clear water, low temperatures, and high dissolved oxygen levels (Sternadel, interview).
The pH scale measures the concentration of hydrogen and hydroxyl ions in the water, or the acidity or alkalinity of the water. This is done on a scale from 1 to 14, seven being completely neutral water or distilled water. Numbers below seven indicate the water is acidic and numbers above seven indicate the alkalinity of the water sample (Murdoch).
Although pH doesn’t usually change much from day to day, if it does change, it may be a sign that something is wrong. It could be anything from fertilizer leaking into the stream, to extra rotting debris giving off carbonic acid into the water. Monitoring pH can sometimes lead to an interesting investigation of what’s happening in the stream. Organisms in the stream can only tolerate a small range of change with pH, because a little step on the scale can equal quite the difference in the water.
The numbers on the pH scale are logarithmic and a one-point change on the scale is equal to a ten-fold change in acidity and alkalinity. For example 7.5 on the pH scale is 10 times more acidic than 6.5 but is 100 times more acidic than 5.5 and so on (Murdoch)(Jeffries).
The last common water chemistry test is the test for E. coli in the water. E. coli is a fecal coliform present in bird, and mammal feces; it is a good indicator if other more dangerous coliforms are likely present as well. This test is probably the most important when it comes to people’s health in relation to the water. The biggest thing people want to know about freshwater is “can we drink it” and that is why E. coli tests are taken.
E. coli is very easy to culture and if it shows up as being in the water, then there is a very good chance that other pathogens such as Klebsiella and Enterobacter are also present. It has been found that places of greater human disturbance have higher counts of E. coli than undisturbed places; this may be because of people stirring up the bacterium that has settled on the bottom of a stream (Hendricks).
Riparian zones interact with the stream health more than just interpreting it. A riparian zone provides shade for the water, which reduces temperature, which, as stated before, increases dissolved oxygen. The riparian zone serves many other purposes such as filtering pollution, providing wildlife habitat, controlling erosion and flooding; all of these things contribute to the streams health (Sternadel, “The Values”). The leaves that drop into the stream from the overhanging trees provide food for the invertebrates of the functional feeding group shredders. A diverse population of invertebrates indicates good water quality. The rotting decay from the trees enriches the water with nutrients making it a better, cleaner habitat for things living in it (Jeffries 87).
A good riparian zone acts as a buffer for the stream from pollutants and chemicals. The uppermost layer of soil within the riparian zone is loose and organic in nature so when runoff runs through it pollutants are caught within the soil and filtered out by bacteria before it runs into the stream.
An effective riparian zone needs at least twenty to fifty feet of vegetation
to work properly depending on different variables such as bank slope, surrounding
land use and soil type (Sternadel, Interview). Not only does the soil filter
out harmful substances but the root system of the trees holds the soil together,
preventing erosion of the banks into the stream. By soaking up rain water into
the soil and roots instead of having run directly into the stream riparian
zones help reduce the risk of flooding during the rainy season (Sternadel, “The
Values”). A healthy riparian zone means a healthy stream because there
will be more shade, lower temperature, lower turbidity, more diverse life,
and less pollutants in the water.
When just taken by themselves these tests only give a limited amount of information about the water, but when all three tests and results are combined one gets an in depth perspective of the water quality of that stream. There are many ways to monitor stream health and many of them do not require the use of expensive instruments making it easy for the common person to evaluate stream water quality. Good water quality is vital to life and as fresh water supplies dry up people are starting to care about the quality of the remaining stores. With very little work streams can be monitored and kept healthy for every living thing to use.
