Unit 3 (part 2): Water Chemistry and Nutrient Cycles
Concepts: Students will explore the water cycle, the nitrogen cycle, the
phosphorous cycle, and the solubility of oxygen in water.
Objective: The purpose of this lesson is to explore the nutrient cycles of
chemicals found in water that are important to algal growth.
Summary: Water is important to all life. Many species of algae are aquatic and
absorb nutrients from the water. It is valuable to understand the nutrients
contained in water and how they get there.
Useful Websites:
http://en.wikipedia.org/wiki/Nitrogen_cycle
http://en.wikipedia.org/wiki/Carbon_dioxide#Isolation_and_production
http://en.wikipedia.org/wiki/Phosphorous_cycle
http://en.wikipedia.org/wiki/Water_cycle
http://en.wikipedia.org/wiki/Oxygen_saturation
http://www.youtube.com/watch?v=og9cQKxlFnE
http://www.youtube.com/watch?v=_1oCoKj7b2o&feature=fvw
http://www.youtube.com/watch?v=okZBiy_IdBA&feature=related
http://www.youtube.com/watch?v=vYBjPE0wekw&feature=related
http://water.usgs.gov/owq/FieldManual/Chapter6/6.2.4.pdf
http://www.northwestky.com/news/documents/Algae.pdf
Materials:
Activity Sheets:
‘The Water Cycle’
© 2010, Ohio Northern University: Dr. Debra Gallagher, Dr. Robert Verb, Dr. Ken Reid and Ben McPheron
‘The Phosphorous Cycle’
‘The Nitrogen Cycle’
‘Solubility Chart’
Engage:
1. Explain: water is an extremely important component of our environment,
and is specifically important to algal growth. Because of the importance of
water, it is important to understand the water cycle, the nutrients present in
the chemistry of water, and the way that those nutrient become a part of that
chemistry.
2. Watch ‘The Water Cycle Song’ or ‘Cool Water Cycle Song’.
http://www.youtube.com/watch?v=_1oCoKj7b2o&feature=fvw
http://www.youtube.com/watch?v=okZBiy_IdBA&feature=related
3. Watch ‘The Earth’s Water Cycle – Environmental Science’
http://www.youtube.com/watch?v=vYBjPE0wekw&feature=related
4. Hand out ‘The Water Cycle’ sheet and ask students to describe each aspect
of the water cycle.
Explore:
1. Hand out ‘The Phosphorous Cycle’ sheet.
a. Use the information below and in the teacher background section to
describe the phosphorous cycle.
i. Main reserve on Earth is within rocks
ii. Phosphorous released when rocks are weathered or eroded
iii. Phosphorous is absorbed by photosynthetic organisms (preferred in
the form of phosphate [PO4-3])
iv. Phosphorous transferred to organisms through consumption
v. Returned to the environment via waste excretion and decomposition
of detritus
b. Many natural freshwater environments are inundated with extra
phosphorous.
© 2010, Ohio Northern University: Dr. Debra Gallagher, Dr. Robert Verb, Dr. Ken Reid and Ben McPheron
i. Wastewater (sewage)
ii. Fertilizer
iii. Pesticides
iv. Soil Erosion
c. Phosphorous is a valuable nutrient that plays a role in the formation of
nucleic acids, phospholipids, ATP and the process of photosynthesis.
2. Hand out ‘The Nitrogen Cycle’ sheet.
a. Use the information below and in the teacher background section to
describe the nitrogen cycle.
i. 80% of Earth’s nitrogen in located in the atmosphere, but this is
unusable to algae and plants
ii. Algae and plants require nitrogen in the form of nitrate (NO3-) and
ammonium (NH4+) ions
iii. Abiotic processes such as lightning and volcanic eruptions, along with
selected terrestrial bacteria and cyanobacteria (blue-green algae), can
alter (fix) atmospheric nitrogen (N2) into NH4+
iv. NH4+ can be further altered by nitrifying bacteria or dissolved oxygen
into NO3v. Both NH4+ and NO3- can be used by algae in metabolic processes
b. Human activities such as wastewater effluent and fertilizer application
have increased nitrogen content in freshwater environments
c. Nitrogen is an essential component in proteins, nucleic acids and
photosynthetic pigments used to absorb light
3. Eutrophication is the nutrient enhancement of waters by human activities
(sewage, fertilizers, pesticides, etc.)
4. Explain the relationship between carbon and pH using the teacher
background section.
Explain:
1. Ask the students to explain:
a. How phosphorus enters the water supply
b. How nitrogen enters the water supply
c. How pH and carbon are related
© 2010, Ohio Northern University: Dr. Debra Gallagher, Dr. Robert Verb, Dr. Ken Reid and Ben McPheron
Extend:
1. Explain to the students the importance of oxygen in the water and give them
the chart from:
http://water.usgs.gov/owq/FieldManual/Chapter6/6.2.4.pdf
2. Ask the students to draw a conclusion about what water temperature
contains more oxygen. (Lower temperature=more oxygen)
3. Hand out a copy of the article ‘Algae Research Proposed For Area’
http://www.northwestky.com/news/documents/Algae.pdf
4. Have students read the article and discuss the relation between the article
and what they studied today.
Evaluate:
1. Ask the students to draw the hydrologic cycle (without the help of the
handout) and explain each facet in a few sentences. Give them the following
terms to work from:
a. Evaporation
b. Condensation
c. Precipitation
d. Infiltration
e. Transpiration
Teacher Background:
Phosphorous
Phosphorous is a valuable nutrient that plays a role in the formation of nucleic
acids, phospholipids, ATP, and photosynthesis. The main reserve on Earth for
phosphorous is within rocks. As rocks are exposed to the atmosphere they become
weathered and the phosphorous is released into the environment where it is often
absorbed by photosynthetic organisms such as plants and algae. The usable form
of phosphorous preferred by organisms is phosphate (PO4-3), which after
absorption can be converted into organic compounds. The phosphorous can then
be transferred to other organisms via consumption. Phosphates can be returned to
the environment via waste excretion and decomposition of detritus. Since the
weathering of rock is a relatively slow process, phosphorous is often a limiting
© 2010, Ohio Northern University: Dr. Debra Gallagher, Dr. Robert Verb, Dr. Ken Reid and Ben McPheron
nutrient in the growth of algae. However, many of our natural freshwater
environments have been inundated with extra phosphorous (phosphate) from waste
water (sewage), fertilizer, pesticides, and soil erosion. The extra phosophorous can
lead to tremendous increases in algal growth and algal blooms.
Nitrogen
Nitrogen serves as an essential component in proteins, nucleic acids, and many
photosynthetic pigments (absorb light). The atmosphere of Earth contains the
majority of nitrogen on the planet in the form of N2. N2 accounts for roughly 80%
of the atmosphere, but this form of nitrogen is unavailable for use in most
biological activities by most organisms. Algae (and plants) can only use nitrogen
in the form of nitrate (NO3-) and ammonium (NH4+) ions. Abiotic processes such
as lightning and volcanic eruptions, along with selected terrestrial bacteria and
cyanobacteria (blue-green algae), can alter (fix) atmospheric nitrogen (N2) into
NH4+ (Figure 3). The NH4+ can be further altered by nitrifying bacteria or
dissolved oxygen into NO3-. Both are forms of nitrogen that can be taken up by
algae and used in metabolic processes. As seen in the phosphorous cycle, human
activities (sewage, fertilizer application) have enhanced the amount of usable
inorganic nitrogen (e.g., NO3-) in aquatic environments which can contribute to
more algal production. The artificial nutrient (nitrogen and phosphorous)
enrichment of our natural waters by humans is termed eutrophication.
The Relationship Between pH and Carbon
Carbon is another important nutrient to algal and plant growth. CO2 is soluble in
water. Once the CO2 is in water, it will spontaneously convert between CO2 and
H2CO3 (carbonic acid) forms. Depending on the pH, the form that the available
carbon will take varies. Furthermore, the relative concentration of various forms
of carbon is dependent on the pH. These forms include: CO2, H2CO3 (carbonic
acid), HCO3- (bicarbonate), and CO32- (carbonate). In neutral to slightly alkaline
water, bicarbonate is prevalent, and in very alkaline water, carbonate is most
predominant.
© 2010, Ohio Northern University: Dr. Debra Gallagher, Dr. Robert Verb, Dr. Ken Reid and Ben McPheron
It is interesting to note that a type of algae called chara grows in slightly more
alkaline waters and therefore has a crunchy texture due to the use of bicarbonate
and carbonate in its cellular structure.
The Relationship Between Temperature and Oxygen Saturation
Algae and other organisms use oxygen for cellular respiration. As a
photoautotrophic organism, algae will produce more oxygen than they absorb
during daylight hours. However, it important to maintain oxygen levels to sustain
life. Temperature directly affects the amount of dissolved oxygen that can be
present in water. The amount of oxygen dissolved in water in mL/L can be found
on the chart located at this website:
http://water.usgs.gov/owq/FieldManual/Chapter6/6.2.4.pdf
© 2010, Ohio Northern University: Dr. Debra Gallagher, Dr. Robert Verb, Dr. Ken Reid and Ben McPheron