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WATER QUALITY
Introduction
The purpose of water quality monitoring is to determine the physical
and chemical properties of natural waters. Two important aspects can
be determined through water quality monitoring. These aspects
include 1) the actual physical and chemical characteristic of water
for a time period and 2) changes in the properties of water over
time for multiple monitoring events.
Properties of water such as temperature, pH, dissolved oxygen, and
the concentration of nitrates and phosphates are important
indicators of water quality. These properties can change as a result
of natural and human related processes. These properties can be used
to determine the effects of groundwater and stream water on aquatic
ecosystem health and can sometimes be used to identify sources of
pollution in water.
Changes in these parameters may be detrimental to the organisms in
and around the water source. Many factors can affect the quality of
the water in an ecosystem including discharges of industrial or
agricultural wastes. Field observations and measurements allow us to
look for links between land use and its effects on water quality. By
collecting and analyzing data from a local source we can approach a
community situation in a way very similar to the approach used by
practicing scientists
Water Temperature
Water temperature is an important property that determines water
suitability for human use, industrial applications and aquatic
ecosystem functioning. Water temperature can affect the dissolved
oxygen content, an important water characteristic that strongly
affects many aquatic organisms. The temperature of water is
controlled pimarily by climate. Water is generally warmer in the
summer and colder in the winter, ranging from about 30° C to near
freezing. Aquatic organisms depend on a narrow temperature range for
optimal growth and survival. Since growth and survival of aquatic
organisms is seasonal, they are adapted to specific temperature
ranges. If temperatures are outside the optimal range for prolonged
periods of time, aquatic organisms become stressed and can die.
Long-term shifts in temperature can also result in a change in the
composition of organisms that make a stream their home.
Thermal pollution occurs in surface water (lakes and streams) when
the temperature of the water is made unusually warmer or colder for
the appropriate season. Possible causes of thermal pollution of
surface water include removal of streamside vegetation that provides
shading, impoundments such as dams, discharge of hot water from
industrial cooling operations, urban storm water, and warm and cold
groundwater flows to the streams.
pH
pH is a measure of how acidic or basic water is. pH is important
because it controls many chemical and biological processes that
occur in the water. pH is measured on a scale that ranges from 0 to
14, with 7 considered neutral. Values of pH less than 7 are acidic,
while values higher than 7 are basic. pH can be used as a proxy of
water quality conditions since water pH is easily changed by
chemical pollution.
The figure above shows the pH range of stream
water as well as other common items for comparison. The pH scale is
reported in "logarithmic units," with each number representing a
10-fold change in the acid or basic content of water. On this scale,
a decrease in the pH by 1.0 unit is equivalent to a 10-fold increase
in acidity. A water sample with a pH of 5.0 is 10 times as acidic as
one with a pH of 6.0, and water with a pH 4.0 is 100 times as acidic
as one with a pH of 6.0.
The pH state of surface water is especially important since aquatic
organism have a tolerance for very narrow pH ranges. A pH value
higher or lower than the 6 to 8 range for stream water can decrease
the survival of aquatic organisms and lead to loss of stream
ecosystem diversity. High pH levels can occur when algae and aquatic
vegetation use CO2 for photosynthesis. Low pH can also be cause by
aquatic vegetation when they respire or from bacterial decay of
organic matter in the water producing high levels of CO2. Low pH in
water can allow toxic chemicals to become mobile and "available" for
uptake by aquatic plants and animals, producing conditions that are
toxic to aquatic life, especially sensitive species like rainbow
trout. Water with high pH can corrode household plumbing and their
associated systems.
Important examples of pH for natural waters:
· 6.5 to 8.5 is optimal for streams and ground water
· natural water 5.0 to 8.5
· fresh rain water 5.5 to 6.0
· alkaline soils 8.0 to 8.5
· seawater ~8.0
· Average pH for water in Indiana ~ 7.5
Guide for Water Quality Ranges
Dissolved Oxygen(% Saturation) Total
Phosphates(mg/L)
> 110 Good < 0.10 Excellent
90 - 110 Excellent 0.11 - 0.16 Good
70 - 90 Good 0.17 - 0.58 Fair
50 - 70 Fair 0.58 - 2.99 Poor
< 50 Poor > 3.00 Very Poor
Fecal Coliform (E. coli)(colonies per 100 mL)
Nitrate Nitrogen * (N)(mg/L)
< 50 Excellent < 0.3 Excellent
51 - 200 Good 0.3 - 0.8 Good
200 - 1000 Fair 0.9 - 2.0 Fair
> 1000 Poor > 2.0 Poor
Biological Oxygen Demand Turbidity
(mg/L or ppm) (JTUs) (ft or in)
< 2.0 Excellent 1 - 10 > 3' Excellent
2.0 - 4.0 Good 10 - 40 1' - 3' Good
4.0 - 10.0 Fair 40 - 150 2" - 1' Fair
> 10.0 Poor > 150 < 2" Poor
pH (units) Total Solids (mg/L)
< 5.5 Poor < 100 Excellent
5.5 - 6.0 Fair 100 - 250 Good
6.0 - 6.5 Good 250 - 400 Fair
6.5 - 7.5 Excellent > 400 Poor
7.5 - 8.0 Good
8.0 - 8.5 Fair Temperature Change (°C)
> 8.5 Poor 0.0 - 2.0 Excellent
2.0 - 5.0 Good
5.0 - 10.0 Fair
> 10.0 Poor
* Nitrogen value is not multiplied by
conversion factor of 4.4
Information provided by the Wood-Land-Lakes RC&D.
Based upon values in the Field Manual for Water Quality Monitoring,
10th ed., by Mitchell and Stapp.
pH pollution in stream and groundwater can
arise from increased acidity from acid rain, acid groundwater
discharge to streams, acid mine drainage, and from industrial and
municipal discharges.
Dissolved oxygen
Dissolved oxygen (DO) is a measure of the amount of oxygen in water
that is available for chemical reactions and for use by aquatic
organisms. In the aquatic ecosystem, dissolved oxygen balance in
water is important for the survival of certain microorganisms and
higher organisms such as zooplankton and fish. Most of the oxygen in
water is derived from the atmosphere by mechanical mixing (churning
action of water as it flows). Rapidly moving water, such as in a
mountain stream or large river, tends to contain a lot of dissolved
oxygen, while stagnant water contains little. In Indiana, water
flowing over rocks and waterfalls help oxygenate stream water.
Changes in the dissolved oxygen levels in water can be caused by
aquatic vegetation. When aquatic vegetation photosynthesize,
dissolved oxygen levels in water increase, while levels can be
decreased when the same vegetation respire, which uses up oxygen and
produces CO2. Streams can also loose oxygen due to the decomposition
of organic matter by bacteria and from chemical reactions that
consume oxygen.
The temperature of water also controls the amount of dissolved
oxygen in water. Cold water can absorb more oxygen, producing higher
values, while warm water produces lower values (when measured as
mg/L).
Important examples of dissolved oxygen ranges for natural waters:
· typical range in natural waters 5.4 to 14.8 mg/L
· Optimal range for aquatic growth activity 5.0 to 6.0 mg/L
· low range in natural water 5.0 to 0.1 mg/L
o DO levels of lower than 3 mg/L is stressful to fish
o DO levels between 2 and 1 mg/L will not support fish
· Average dissolved oxygen for Indiana waters ~ 9.2 mg/L
High oxygen content of water is good while low levels cans stress
aquatic organisms resulting in death. Low oxygen can result from
pollution from discharge from industries, urban runoff, wastewater
and sewage treatment plants which often contain organic materials
that are decomposed by microorganisms using oxygen in the process.
Other sources of oxygen-consuming wastewater include animal feedlots
and failing septic systems. Thermal pollution raises the temperature
of water and lowers its oxygen content.
Nitrates
Nitrate is a form of nitrogen that is an essential plant nutrient,
but in excess amounts they can cause significant water quality
problems. Nitrogen can be found in other forms in terrestrial and
aquatic ecosystems. These additional forms of nitrogen include
ammonia (NH3) and nitrites (NO2). Together with phosphorus (see
section on phosphates), nitrates in excess amounts in streams and
other surface waters can accelerate aquatic plant growth causing
rapid oxygen depletion or eutrophication in the water. Nitrates at
high concentrations (10 mg/l or higher) in surface and groundwater
used for human consumption are especially toxic to young children.
Children can be afflicted with a syndrome called the blue-baby
syndrome that affects the ability of blood to carry oxygen. This
syndrome causes increased susceptibility to illness in children and
may even result in death.
Important examples of nitrate
(nitrate-nitrogen) ranges for natural waters:
· typical range in natural waters is between 0.9 to 3.15 mg/L
· unpolluted waters less than 4.0 mg/L
· levels higher than 40 mg/L in water renders it unsafe for drinking
· Average nitrate level in Indiana waters ~ 2.05 mg/L
Sources of nitrate pollution in groundwater and streams include
wastewater treatment plants, runoff from fertilized lawns and
farmland, failing septic systems, runoff from animal feedlots and
animal manure storage areas.
Phosphorus
Phosphorus is an essential nutrient for plants and animals. In
addition, phosphorus is a limiting nutrient (nutrient in short
supply) in most fresh waters. Excess phosphorus in streams and
surface waters can cause accelerated plant growth and algae blooms
which then cause rapid oxygen depletion or eutrophication in the
water. The end product is water with low dissolved oxygen which
cannot support aquatic life including certain fish, invertebrates,
and other aquatic animals.
The main source of phosphorus in the environment is from soil and
rock weathering. In nature, phosphorus usually exists as part of a
phosphate molecule (PO4). Phosphorus in aquatic systems occurs as
organic and inorganic phosphate. Organic phosphate consists of a
phosphate molecule associated with a carbon-based molecule, as in
plant or animal tissue. Phosphate that is not associated with
organic molecule is considered inorganic phosphorus. Inorganic
phosphorus is the form required by plants. Animals can use either
organic or inorganic phosphate. Both organic and inorganic
phosphorus can either be dissolved in the water or suspended
(attached to particles in the water column). The term
"orthophosphate" refers to the phosphate molecule all by itself.
"Reactive phosphorus" is a corresponding method-based term that
describes what you are actually measuring when you perform the test
for orthophosphate. Because the phosphorus analysis procedure isn't
quite perfect yet, you get mostly orthophosphate but you also get a
small fraction of some other forms.
Important examples of phosphate ranges for natural waters:
· typical range in natural waters 0.02 mg/L
· unpolluted waters less than mg/L
· levels higher than mg/L is unsafe for drinking
· Average phosphate level in Indiana waters ~ mg/L
Sources of phosphorus contamination in the environment include
industrial and municipal wastewater discharges, runoff from
fertilized lawns and farmland, failing septic systems and from
animal feed lots and animal manure storage areas. In addition,
phosphorus can be derived from disturbed land areas, drained
wetlands, water treatment, and commercial cleaning preparations.
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