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What is in Our Water?

Background slides for the whole unit

• The water cycle• Nutrients• Eutrophication

The Water Cycle

• Continuous movement of water above, below, and on the surface of the Earth

• Water moves between its solid, liquid, and vapor phases• melting, freezing, evaporation,

condensation, precipitation, sublimation, desublimation

• Powered by the sun

Distribution of Water on Earth• 96.5% in the ocean

• 321,000,000 cubic miles

• 2.5% freshwater• 73.1% ice and snow• Only a small fraction available for use • 46,000 cubic miles

Nutrients• Chemical components necessary to sustain life

– Humans: carbohydrates, proteins, fats, vitamins, minerals– Marine organisms: nitrate, ammonia, phosphate, silicate,

iron, manganese

• Often broken down into two categories:– Macronutrients: nutrients needed in relatively large

quantities– Micronutrients: compounds that are essential to life, but only

needed in very small amounts

Macronutrients• Nitrogen

– Used to build essential proteins– Found in many forms in the environment: nitrate,

nitrite, ammonium, urea, etc.• Phosphorous

– Forms the backbone of DNA, is a component of cell walls, is critical in energy transport in cells via ATP

– Generally found in natural waters as phosphate• Silica

– Used by some organisms to form hard body parts or shells, often used for protection

NO3-

PO43-

SiO2

Micronutrients• Iron - Essential to chlorophyll production and

photosynthesis– Also necessary for binding oxygen in your

blood with hemoglobin

• Zinc - Utilized by a wide range of enzymes to do everything from brain signal transduction to gene expression

• Manganese - Needed for oxygen evolution during photosynthesis, antioxidant enzymes, etc.

• Vitamin B12 - Helps manage DNA and fatty acid synthesis and regulation, as well as energy production. Contains cobalt, making Co also an important micronutrient

Why do we care about nutrients?• They control the growth of

algae, which form the base of the aquatic food webs

• Additions of nutrients will often lead to algae blooms

• Nutrient pollution into natural waters is therefore a huge water quality problem– Eutrophication, dead zones,

harmful algal blooms

Cyanobacterial accumulation at Binder Lake,<http://toxics.usgs.gov/highlights/algal_toxins/>

Sources of Nutrients to Water Bodies• Natural sources:

- Rivers, runoff, groundwater, atmospheric deposition

• Human caused (‘anthropogenic’):- Agricultural fertilizers,

sewage wastewater, fossil fuel burning, land use changes

Left: example of a normal, clean lake

Right: eutrophic lake, where excess nutrients have caused a thick bloom of green algae

Dead fish that washed onto the shore of California. Fish kills such as this are caused by the formation of dead zones, where oxygen levels are too low to support most forms of lifehttp://www.lakescientist.com/wp-content/uploads/2010/04/clip_image001.jpg

http://beforeitsnews.com/environment/2012/01/massive-fish-deaths-result-from-an-ocean-short-of-oxygen-dead-zones-expanding-1632999.html

Slides to accompany Lesson 1

• Spectrophotometry

SpectrophotometryMeasuring nutrient levels in water• We use a technique called “spectrophotometry”

which means that we measure the amount of color in a sample (=absorbance)

To create color, we add a chemical reagent that binds to the nutrient we want to study and the combined compound has a color.

Today, we will measure phosphate!

Color and Concentration• Absorbance = amount of light that is absorbed by a

solution.• The more concentrated the solution, the more light

it absorbs.• That is because light has to pass through more

molecules in the solution.• Beer’s law describes the relationship between

absorbance and concentration• Absorbance = Constant x Concentration

• Standard curves

Slides to accompany Lesson 2

Standards

• We need to know what absorbance corresponds to which concentration.

• So we make solutions of known concentrations (standards) and measure their absorbance.

• Then we plot each concentration with its matching absorbance and get a “standard curve”.

The Standard Curve

Concentration = 34.23*Absorbance + 0.2306

• Measuring phosphate in water samples

Slides to accompany Lesson 3

Phosphate in water samples

• Work in groups• Determine the phosphate concentrations in 6

unknown samples (A-F)• Report your answers on your worksheet• Based on what you’ve learned today, make a

guess as to where your samples came from

Which sample is which?• Rainwater

• Agricultural pond

• Mississippi river

• Monterey Bay

• Pacific ocean (surface)

• Sewage effluent

Let’s Discuss our Results• Why is the phosphate content in rainwater so low?

Why is there any phosphate in there to begin with?• Why is there so much phosphate in the agricultural

pond water and in the sewage effluent?• Why is there a lot of phosphate in the Mississippi

river?• Why is there a difference between Monterey Bay

and the Pacific Ocean?

Additional Resources for Teachers

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What is in Our Water Kit

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Example of an Absorbance Spectrum

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Beer’s Law

• Having a standard curve, one can measure the absorbance of an unknown sample and then calculate it’s concentration from the standard curve.

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Water Samples to Test for Phosphorus

• Collect or make samples to use as your unknowns. Add the color reagents, then measure absorbance and determine concentration from the standard curve.

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The Phosphorus Cycle

The phosphorus cycle (data from Schlesinger 1991, after Richey 1983, Meybeck 1982, Graham and Duce 1979).

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The Phosphorus Cycle