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Water Quality (Advanced)

Teacher Tips Overview & The Basics 
In order to have a understand what is contained in water, we can study its chemical signature through a variety of measurements which give us a "snapshot" of water's health.  These measurements include alkalinity, hardness, dissolved oxygen (DO), temperature, pH, nitrates, and phosphates. Before we explain how such tests are conducted, examine what each measurement refers to.

Alkalinity is a measure of the buffering capacity of water. Specifically, alkalinity is the amount of HCO3 - (bicarbonate) and CO3 2- (carbonate) ions dissolved in the water. The higher the alkalinity, the more carbonate and bicarbonate ions, and the easier it is for the water to assimilate or buffer acid insults (acid rain, acid mine drainage, etc.). Additionally, carbonate will remove toxic metals (lead, arsenic, cadmium, etc.) by precipitating and/or absorbing these toxic metals out of solution. Stream alkalinity is effected by the geology of the watershed. Watersheds with limestone (CaCO3 ) and sedimentary deposits will have a higher alkalinity (>100 mg/L) whereas watersheds where granite is predominate (such as found in the Indian Peaks) will have low alkalinity values (<50 mg/L). Boulder Creek alkalinity values increase as it flows from the upper alpine reaches down to where it meets the St. Vrain River. 

Hardness - Most people have heard of hard and/or soft water. Hard water leaves rings around the toilet bowl and sink and requires you to use more detergent in your washing machine - but what does it really mean when you have hard or soft water? Hardness generally refers to the amount of calcium and magnesium dissolved in the water. These metals bind with detergents and leave behind a white skum in your bathtub. They also reduce detergent effectiveness at removing dirt from your clothes. 

However, with respect to aquatic life Ca 2+ and Mg 2+ are considered "good metals". These "good metals" help keep trout and other aquatic life from absorbing "bad metals" (lead, arsenic, cadmium, etc.) into their bloodstream through their gills. The more Ca 2+ and Mg 2+ dissolved in the water the harder it is for toxic metals to absorb onto the gills. 

Therefore, hardness (positive ions or cations) and alkalinity (the negative ions HCO3 - , and CO3 2-) work together to make a stream a viable environment for aquatic life - in other words, they help make it a more productive stream. 

hardness - the measure of polyvalent cations in water. Generally refers to Ca 2+ , Mg 2+ , and Fe 2+ 
Dissolved Oxygen - Just as we need oxygen to survive, so do most other organisms. Dissolved oxygen is the amount of oxygen dissolved in the water, and this amount depends primarily upon two factors; (1) temperature - the colder the water the MORE oxygen that can be dissolved (this is why trout like cold streams), and (2) the amount of organisms utilizing oxygen in solution for respiration. Respiration includes plant respiration at night (opposite the production of oxygen during photosynthesis when the sun is out), and the respiration of bacteria as they decompose organic waste. 

As an example, if a large quantity of butter was dumped in a river (this has happened!!) bacteria would go crazy eating the butter (respiration) and oxygen would be pulled out of the water. Fish would be killed, not because they hate butter, but because the corresponding loss in oxygen would suffocate them. 

Temperature - The temperature of the water effects the ecosystem in a variety of ways including the amount of oxygen that can be dissolved in water. A healthy canopy of vegetation over the riparian area is important to shade the water and keep it from getting too warm. 

pH - Potential Hydrogen is a measure of the amount of hydrogen ions in solution. Low pH’s (0-5) can leach toxic metals from the surrounding rocks, effect oxygen uptake in gills, and kill fish. High pH’s (9-14) are just as harmful in denaturing cellular membranes and effecting aquatic life. 

It is important to understand  that the pH scale is a logorithmic scale, pH 5 is 10 times more acidic than pH 6. 

Levels of Water Hardness (mg/L CaCO3) 

  • soft 0-75
  • moderate 75-150
  • hard 150-300
  • very hard 300+
There are no water quality standards for alkalinity or hardness - but heavy metal water quality standards are often dependent on alkalinity and hardness levels. 

Trout generally require dissolved oxygen levels to be between 9-12 mg/L for optimal development, but they can tolerate ranges from 3-25 mg/L. 

Nutrients - Nitrogen and Phosphorous 

Nitrogen, phosphorous, and carbon are all essential nutrients for plant and animal growth. Because there is generally plenty of carbon around (as carbon dioxide, bicarbonate, and carbonate) nitrogen and phosphorous are termed limiting nutrients. 

Nitrogen can be found in many forms, as a gas (70% of the earth’s atmosphere is N2), as ammonia (NH3), as nitrate (NO3 - ), etc. The burning of fossil fuels releases NOx compounds into the air that fall to the earth as acid rain (HNO3). Fertilizers, detergents, and sewage effluent are high in both nitrates and phosphates and can effect algal growth rates in streams and lakes (see Activity 3.3). Excessive nutrients in a waterbody (eutrophication) cause algal blooms which can then result in dissolved oxygen consumption when the algae respire or begins to decay. Consequently, fish and other aquatic organisms can be killed. 

Phosphorous is generally always found as phosphate (PO4 3-). Detergents, fertilizers, and natural mineral deposits are the primary sources of phosphates to surface waters. 


As discussed in Activity 3.1, water quality sampling is merely a snapshot in time. To get the most meaning out of this lab it is better to have students analyze samples over time, or from different sources. 

Step 1. Sample Collection 

Samples can be either collected prior to starting this lab, or as part of the lab. When collecting samples students should take detailed notes of the conditions at the time of sampling (weather conditions, temperature, condition of river, etc.) A map should be drawn to show the location of each sample site. (see activity 3.6) 

Properly label and document each sample bottle. Sample bottles should be thoroughly cleaned prior to sampling, and then rinsed three times with stream water prior to sample collection. You should wear gloves at all times during sample collection so you do not contaminate your samples. Use a special dissolved oxygen bottle if possible for the DO samples (included in the Hach kit). 

Step 2. Analytical Procedure 

Once samples have been collected it is important to analyze them as soon as feasibly possible. If samples can not be analyzed the same day they should be placed in a refrigerator. Dissolved oxygen samples are the most susceptible to changes over time, and should be analyzed with 8 hours of being preserved with sulfamic acid. 

Step 3. Evaluation of Results 

Keep track of your data! As the activity is replicated over time it gets more and more interesting. Just as you would only draw limited conclusions from one photograph - so do you need more water quality "snapshots" to evaluate your stream. 

It often makes sense for groups of students to evaluate different parameters, share their results with other groups, and then write a summary report of their findings. If old reports are available they too can be used in the summary report to evaluate changes over time. 

Data can also be shared with other schools through BASIN or contact the City of Boulder Water Resources Educator at 413-7365. 

Teacher Tips
These activities are most appropriate for high school age students, although motivated younger students can find water quality monitoring of interest and relevant to them.

The Colorado Division of Wildlife's Rivers of Colorado Water Watch Program has developed a series of protocols around water quality testing which emphasize quality assurance (QA) and quality control (QC) of the data collected. 

A chart with data collected by students  participating in the Water Watch Program is located on the BASIN Learning website that you can use to show students the range of data over time and at different locations. Several activities will be added to this section by the Spring of 1999. Please share your ideas with us on how best to use this information. 

Over time we intend to support schools and neighborhood groups in the community develop year-round "stream teams" that can add to this initial water quality database.

Call the DIMC to check out Pond Kit (447-5189) 

Call the City of Boulder's Water Resource Educator at 413-7365 to check out the Hach Kit. 

#4.3 Students know major sources of water, its uses, importance, and cyclic patterns of movement through the environment. 

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Last Page Update - Tuesday December 27, 2005