Water Quality Parameters: Northern Kentucky University, Greater Cincinnati Region

Dissolved Oxygen- Saturation(%)

Determines how much oxygen gas is dissolved in a water sample

Compares to the maximum amount of oxygen the sample could hold at its measured temperature. For example, a water sample that is 50% saturated at 60 degrees Celcius has half the amount of oxygen that it can potentially hold at that temperature. Percent Saturation values of 80-120% are considered healthy, while values less than 60% or over 120% are considered to be poor. Values over 120% can indicate supersaturation and can be a sign of an algal bloom or other condition.

Dissolved Oxygen- Saturation(%) chart

Excellent: 91 to 110

Good: 71 - 90, >110

Fair: 51 to 70

Poor: <50

Dissolved Oxygen - Concentration (mg/L)

Aquatic organisms require oxygen in the free elemental state as a dissolved gas. The amount of dissolved oxygen in the water is fundamental to the survival of most aquatic organisms. Lack of significant levels of dissolved oxygen required by most aquatic organisms for respiration can cause impairment or death. Some organisms have adapted to low oxygen in water or are able to ingest air directly.

Biochemical Oxygen Demand (BOD)(mg/L)

Biochemical Oxygen Demand is the amount of oxygen consumed by aerobic bacteria in water. BOD is calculated by measuring the amount of dissolved oxygen in a water sample when it is collected, then keeping the sample at 20°C for five days and measuring dissolved oxygen again.

The value of the five-day sample is then subtracted from that of the original to get a BOD result in mg/L. High BOD levels can be associated with organic pollution, such as sewage. High levels can also result when nutrient pollution causes excessive growth and decay of algae and aquatic plants.

Biochemical Oxygen Demand (BOD)(mg/L) chart

Excellent <2

Good 2.0 to 4.0

Fair 4.1 o 10

Poor >10

E. coli (CFU/100ml)

Escherichia coli, or E. coli, is bacteria found naturally in the intestines of warm-blooded animals. Therefore, it is used as an indicator of fecal contamination in waterways. Although most strains of E. coli are not pathogenic themselves, the presence of E. coli indicates the possible presence of other bacteria, viruses or protozoa found in fecal material that can cause disease.

E. coli (CFU/100ml) chart

E. coli

Purple, no halo
Purple with pink halo
Purple with purple halo
Blue or dark blue, no halo
Blue with purple or pink halo
Dark blue wth teal halo

NOT E. coli

White
Pink, no halo
Pink with pink halo
Teal green
Pinpoints
Teal with teal halo

Fecal Coliforms (CFU/100ml)

Fecal coliforms are bacteria found in the feces of warm-blooded animals. While most fecal coliforms themselves are not particularly harmful, their presence in large amounts can indicate more harmful bacteria and viruses such as those that cause typhoid, cholera, and Hepatitis A, as well as the presence of other pathogens like Cryptosporidium and Giardia.

pH (pH Units)

pH is a measure of hydrogen ions concentration in water. The concentrations of these ions determine if a substance is acidic or basic. Aquatic organisms are sensitive to pH, especially during reproduction. pH also affects the toxicity of many substances in water that can potentially affect humans and aquatic life.

pH (pH Units) chart

Excellent 6.5 to 7.5

Good 6.0 to 6.4, 7.6 to 8.0

Fair 5.5 to 5.9, 8.1 to 8.5

Poor <5.5, >8.6

Water Temperature (°C)

Temperature affects metabolic rates and reproductive function of many aquatic organisms. Temperature also affects other chemical parameters, such as the amount of dissolved oxygen in water.

To convert the Celcius temperature to Fahrenheit, use the following formula: °C * 9/5 + 32 = °F

Water temperature change is the difference in temperature between two sampling sites, with the same degree of shading and water velocity, approximately one mile away from each other. The temperature of the second site should be measured as soon as possible after measuring the first site. Changes in temperature should typically not exceed five degrees Celcius. Large changes in temperature can indicate thermal pollution or loss of riparian habitat or shading.

Water Temperature (°C) chart

Warm temperature conditions limit survival of many species.

The Ideal range for plant life and many fish diseases is 82° F (28°C) to 65°F (18°C).

The ideal range for warm-water species (most bass, crappie, bluegill, carp, catfish and mussels) is 80°F (27°C) to 65°F (18°C)

Ideal Range for cool-water species like smallmouth, rock bass, minnows, darters and mussels is 70°F (21°C) to 55°F (13°C)

Ideal range for cold-water species like trout, some minnows, darters, sculpins, and stoneflies is 60°F (16°C) to 45°F (7°C)

Overall range for many aquatic organisms including dragonflies, mayflies, coddsflies, crayfish, salamanders, terropins, and water beetles is between 78°F (25°C) and 35°F (2°C)

Phosphates (mg/L)

Phosphorus is an essential nutrient for plants and animals. Phosphorous can be found in several forms, including inorganic orthophosphate, which is readily taken up by aquatic plants and algae for growth. Other forms of phosphate can be converted into orthophosphate in a waterway. Excess phosphates in a waterway can result from sewage discharges, failing septic systems, and runoff of manure and industrial fertilizers. Excess phosphate can also be carried into waterways through soil erosion. Excess phosphate loadings can cause overgrowth of aquatic plants and algae, which in turn, use up dissolved oxygen in the process of decay.

Nitrates (mg/L)

Nitrogen makes up about 80% of the air we breathe, and it is found in all living things. Nitrate is a form of nitrogen that is readily taken up by aquatic plants and algae and used for growth. However, excess inputs of nitrate can cause overgrowth of aquatic plants and algae, which in turn, use up dissolved oxygen in the process of decay. Excess nitrates can also be toxic to humans and animals. Sources of excess nitrate in waterways include sewage discharges, failing septic systems, and runoff of manure and industrial fertilizers.

Nitrates (mg/L) chart

Excellent <1.32

Good 1.76 to 3.52

Fair 3.96 to 8.36

Poor >8.8

Turbidity Tube

Turbidity is a measure of the relative clarity of the water and is a significant indicator of overall water quality. High turbidity levels can be caused by suspended sediment (caused by erosion and runoff), bacteria, and algal blooms. Excessive turbidity levels can impair photosynthesis and suspended particles absorb heat, raising water temperature and lowering dissolved oxygen levels. Turbidity is measured in units of length (cm), representing the depth to which light penetrates, or in turbidity units (NTU’s). Graphic explanations for both types of measurements are provided.

Turbidity Conversion Chart with distance from bottom of tube compared to NTUs.

Distance from tube (cm) is inversely related to NTUs

<6 = >240

6-7 = 240

7-8 = 185

8-9 = 150

9-10 = 120

10-12 = 100

12-14 = 90

14-16 = 60

16-19 = 50

19-21 = 40

21-24 = 35

24-26 = 30

26-29 = 27

29-31 = 24

31-34 = 21

34-36 = 19

36-39 = 17

39-41 = 15

41-44 = 14

44-46 = 13

46-49 = 12

49-51 = 11

51-54 = 10

54-58 = 9

58-60 = 8

Over the top = 6

Turbidity (NTU)

Turbidity is a measure of the relative clarity of the water and is a significant indicator of overall water quality. High turbidity levels can be caused by suspended sediment (caused by erosion and runoff), bacteria, and algal blooms. Excessive turbidity levels can impair photosynthesis and suspended particles absorb heat, raising water temperature and lowering dissolved oxygen levels. Turbidity is measured in units of length (cm), representing the depth to which light penetrates, or in turbidity units (NTU’s). Graphic explanations for both types of measurements are provided.

Turbidity Conversion Chart with distance from bottom of tube compared to NTUs

Excellent levels are 1 to 10,

Good levels are from 10.0 to 40,

Fair conditions are from 40.1 to 150,

and poor conditions are anything greater than 150

Secchi Disc (M)

Turbidity is the relative clarity and is a significant indicator of overall water quality. Excessive turbidity levels can impair photosynthesis and suspended particles absorb heat, raising water temperature and lowering dissolved oxygen levels. High turbidity levels are caused from erosion, runoff, and algal blooms.

Conductivity (mS/cm)

Conductivity is a measure of the ionic content of water which affects the ability of water to conduct electricity. Therefore the alternating current resistance of the water between two electrodes placed one cm apart is measured.

The unit is micro Siemens per centimeter (or sometimes Siemens per meter).

Conductivity in aquatic ecosystems is linked directly to total dissolved solids (TDS) and to salinity. The higher the total dissolved solids or the salinity, the higher the conductivity.

Different aquatic species can tolerate different levels of salts in the water. High conductivity in a water body that normally has low salinity or TDS can indicate sewage contamination or urban runoff.

Conductivity (mS/cm) chart

Less conductive to more conductive:

Distilled Water 0.0000055 mS/cm

Top Water 0.05 - 0.5 mS/cm

Sea Water 0.5 mS/cm

Water Hardness (mg/L or ppm)

Water hardness is a measure of the mineral content of the water. Usually it is measured as carbonate hardness caused by the presence of carbonate (CO32-) and bicarbonate (HCO3-) anions. The units of measurement are parts per million (ppm) or mg/L of calcium carbonate since calcium carbonate is usually the most abundant source of carbonate ions. Soap does not produce much lather in hard water, instead it precipitates as soap scum. The presence of hard water is usually linked to geology. Water is "hard" in places rich in limestone. Hard water buffers pH, so places with hard water may not be affected as much by acid rain or pH changing pollutants.

Air Temperature (°C)

Air temperature influences aquatic organisms by affecting water temperature. It varies with season and changes faster than the temperature of the water.

The impact of air temperature is more significant in shallow bodies of water such as streams.

Air temperature can cause streams to dry out, or to freeze. Some organisms have adapted to hot temperatures by being drought tolerant.

To convert the Celcius temperature to Fahrenheit, use the following formula: °C * 9/5 + 32 = °F

Air Temperature (°C)

Fahrenheit to Celsius Conversion

38°C = 100°F

18.9°C = 66°F

0°C = 32°F

-17.8°C = 0°F

-40°C = -40°F

Water Quality Parameters

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