Boulder Creek
begins in the Rocky Mountains west of Boulder. The creek, as it flows
through the mountains and canyons toward Boulder, picks up pollution
particulates from the air, travels past old mines, and through some
agricultural and residential areas. When it reaches Boulder, the creek
flows through the middle of town. Here it is subject to the strains
of the city: automobile oil, paint, fertilizers, treated wastewater
effluent, food wastes, trash, etc. The creek eventually meanders into
eastern Boulder County where it traverses farms and new rural subdivisions.
On its journey from the high mountains to its convergence with the St.
Vrain River, Boulder Creek is influenced by every type of urban and
rural impact.
The health of a stream can be monitored
with physical, chemical and biological parameters. The primary physical
and chemical parameters include turbidity and color, temperature, flow,
dissolved oxygen, pH, and chemical pollutants such as heavy metals,
nitrate, and phosphate.
Color
and Clarity
We can learn a lot about a stream
by its color and clarity. Rainwater, groundwater and snowmelt run clear
unless a stream’s banks are eroding. Glacial meltwater, on the
other hand, appears milky gray from glacial flour, tiny suspended particles
of rock crushed by the grinding force of moving glaciers. Brown water
might be a sign of a mudslide in the mountains, a heavy storm event,
or local erosion. Greenish water may represent blooms of algae nourished
by excess fertilizers from yards, golf courses, or farms. Suds might
point to detergents or to septic tank failure.
An iridescent sheen on the water
may have been released from rotting leaves; however it could mean that
used motor oil or oil-based pesticides leaked or were dumped into the
stream, or perhaps it was picked up in runoff from roads, driveways,
and parking lots. To test the clarity of a creek, turbidity measures
are taken. Turbidity is defined as the light scattering capability of
a particle. In natural waters, it may be caused by algae or by organic
acids, which stain the water a dark brown. But it usually indicates
suspended sediments, fine soil particles, held in suspension by the
turbulence of the current which scatter light passing through the water.
Excess sediment reduces the clarity of water and it can harm the gills
of fish and aquatic insects. It also makes it more difficult for aquatic
species to find food or escape predators.
Temperature
Water temperature is another easy
test that tells a lot about a waterway. Temperature determines where
aquatic organisms can live. Plants and animals that live in the creek
are completely surrounded by water, and so their climate depends on
water temperature rather than air temperature. In fact, since fish and
aquatic insects are cold-blooded, they become the temperature of the
water. Their metabolism, growth rate, and all internal chemical reactions
are regulated by the water temperature.
The amount of oxygen found in a
waterway is directly connected to the temperature. Cooler water holds
more dissolved oxygen than warmer water. Different aquatic species have
found their habitat in streams according to food availability, oxygen
needs and temperature. Trout like cold, oxygen-rich waters, whereas
bass and sunfish prefer to live in warmer water.
Current
and Flow
Current and flow are also easy characteristics
to monitor. Stream Gauging: A Study of Flow activity (coming in Fall
1999) provides directions for taking flow on your waterway. Current
is determined in part by the gradient, or slope, of the stream. Mountainous
headwaters have swift currents because they drop quickly over a short
reach. Current also varies with the flow, which is the amount of water
carried by the stream channel at any given time. Water levels fluctuate
throughout the year. During the spring, the creeks in the Front Range
rise quickly and have swift currents because of melting snow in the
mountains.
By midsummer, when most of the snow
has melted and the hot, dry weather sets in, creeks slow down and sometime
even dry up. Creeks may rise for a short time during the summer if a
heavy thunderstorm releases a lot of rain over the headwaters of a creek.
During fall and winter, watershed creeks maintain a fairly slow, constant
flow, as rain and snow contribute more consistent water to the creeks.
During normal flow, currents are controlled by instream structures,
both natural and human-made. Large boulders, fallen trees, and beaver
dams are examples of natural current checks. On a larger scale, hydroelectric,
irrigation and flood-control dams also check the current. Knowing the
flow and current of a stream helps us know how quickly something, such
as a pollutant, might travel down a creek. We can also determine the
types of animals that live in the creek depending on the site.
Dissolved Oxygen
(D.O.)
Some important stream measurements
are not as visible as the first ones mentioned. There are certain things
that need to be measured with sampling equipment, such as the levels
of dissolved oxygen in a stream.
Instream creatures depend on oxygen
that is dissolved in the stream water. Still or slow-moving water gets
some oxygen from the air above it. In a pond, for example, only the
upper layers receive much dissolved oxygen, while the bottom layers
are often depleted by the respiration of animals in the mud and by bacteria
decomposition.
Rushing water, as it churns over
rocks and plunges over hundreds of tiny falls, is aerated by the bubbles
of air that get caught by the water. Plants add oxygen to the water
during daylight as a byproduct of photosynthesis, but they also deplete
it as they respire a night. Water never contains large amounts of oxygen:
our atmosphere contains 23% oxygen, whereas even oxygen-saturated water
has less than 1%. Small losses or gains in D.O. levels can be critical
to instream species.
The amount of D.O. in a stream is
dependent on three things: water temperature, the amount of oxygen taken
out of the water by respiring and decaying organisms, and the amount
put back by physical aeration and photosynthesis. The cooler the water
is, the more dissolved oxygen it can hold. Large active fish like trout,
which need a lot of oxygen, are restricted to cool streams.
pH
pH is another invisible, yet very
important parameter to measure. pH is the amount of hydrogen ions in
the water (p stands for negative logarthim of; H for hydrogen ions).
The lower the number, the higher the acidity. The pH scale goes from
1-14. pH 7 is neutral (distilled water); pH 2 is acidic (vinegar); pH
13 is basic (ammonia). pH affects the solubility of many nutritive and
toxic chemicals in the water and thus their availability to stream creatures.
AlkalinityÑthe opposite of acidityÑis a measure or the
stream’s capacity to buffer, or neutralize, the effects of acidity.
Chemical
Pollutants
A final test to measure a stream’s
health is to monitor for chemical and heavy metal pollutants. Some pollutants,
not soluble in water, can be easily detected. Petroleum products spread
over the surface of water creating a rainbow sheen. Other chemicals
may have volatile gasses that can be detected by smell. And some, like
detergents, give a slippery feeling to the water or create suds on the
surface. Unfortunately, most chemicals dissolve in water and cannot
be detected except by expensive laboratory instruments. The only way
we see them is by noting their effects on stream lifeÑorganisms
sensitive to chemicals may die out while more tolerant ones thrive.
Major chemical spills will cause
dramatic plant and animal deaths throughout the impacted stream. However,
most waterways are slowly degraded over a period of months or years.
Certain chemicals and metals are tested regularly because of their effects
on the aquatic ecosystem and their potential danger to humans. Lead
is tested in our drinking water because its compounds are poisonous
and accumulate in the bone structure. Lead is seldom found in surface
waters because it is precipitated by a variety of substances. Nitrate
and phosphate are two chemicals tested for because they are nutrients.
High levels of nitrates and phosphates can lead to the excessive growth
of aquatic plants. High levels in natural water supplies may indicate
some nonpoint source pollution problems such as fertilizer runoff from
lawn or fields.
One other constituent often tested
for is the fecal coliform bacteria. It is important to find out if our
water sources are being polluted by septic tank or agricultural runoff.
If fecal coliform is detected in a waterway, it means that certain disease
causing pathogens are present. These pathogens can cause great harm
to both aquatic species and humans.
Stream
Insects
Benthic (creekbottom) mircoinvertebrates,
or stream insects are an important feature of the stream ecosystem.
Stream insects are monitored to check the overall health of the stream.
This bioassessment is conducted for a number of reasons:
1) macroinvertebrate communities
have limited migration patterns, thus they are good indicators of
localized conditions;
2) they integrate the effects
of different pollutants and other short-term environmental variations,
thus providing a holistic measure of the impact of various contaminants;
and
3) as a primary food source, they
are important to the overall health of the stream ecosystem.
As you can see, the creek ecosystem
is dependent on many things working together to maintain a healthy balance
of clarity, temperature, current and flow, dissolved oxygen, pH and
chemicals. To make sure our waterways are protected, these parameters
should be monitored regularly.
Source: Yates, Steve.
Adopting a Stream: A Northwest Handbook. Published by The Adopt-A- Stream
Foundation. 1988.
Go
to the Activity Section!
Return to
top of the page
