Assessment of Phosphate Concentration in Local Water Bodies.
Targets and Assessment
WA Science Standards Addressed:
 9-12 INQA- Scientists generate and evaluate
questions to investigate the natural world.
 9-12 INQB - Scientific progress requires the use
of various methods appropriate for answering
different kinds of research questions, a thoughtful
plan for gathering data needed to answer the
question, and care in collecting, analyzing, and
displaying the data.
 9-12 INQC- Conclusions must be logical, based
on evidence, and consistent with prior established
knowledge.
Assessments:
 Phosphate testing is just one component of a
larger unit on water quality. A final lab report
will be written detailing various pollutants
levels, stream velocity, and aquatic invertebrate
abundance (for example see “Rubric for Peer
Review”).
 In the phosphate section in the final report
students will be graded on their:
 On line search of how phosphates gets into the
water, what levels are safe in drinking water,
and what phosphates do to the human body.
 Graphical representation of phosphate levels
throughout the body of water.
Lesson Parameters
Content Area: Biology, Chemistry, Geology
Overview: Investigating the phosphate levels
of water bodies to understand pollutant
accumulation and movement in watersheds.
Grade Level: 10th
Suggested Time: 1:45 minute period
Special Materials: Per group (~3-4 students)
 One phosphate HACH kit complete with
phosphate 5 reagents, a HACH DR/ 2000
spectrophotometer, and two test tubes
with stoppers.
 Various water samples (preferred within a
single stream gradient so students can see
accumulation of phosphates downstream).
Learning Outcomes:
Knowledge: Phosphate testing can be used to evaluate the effects of human impacts on a water body.
Students will be able to recognize how pollution accumulates and migrates within a
watershed if multiple water samples are taken from the same stream gradient.
Skill: In this lesson students gain exposure in:
o
Finding credible websites to access information
o
Following detailed instructions
o
Performing experiments
o
Handling and measuring chemicals
o
Graphing and Interpreting results
o
Sharing information with peers
o
Testing phosphate concentrations in local water
In writing the final report (next two lessons) students gain exposure in:
o
Compiling information into a formal lab report
o
o
o
Creating and analyzing graphs using real data
Peer evaluation
Disseminating information to interested parties
Science Concept Background:
Phosphate testing is part of a 6 day unit assessing pollution levels in
Cowiche Canyon watershed (http://www.cowichecanyon.org/). The canyon is
located six and a half miles northwest of Yakima, Washington. Water
samples were taken from four sites along Cowiche stream starting at the
base of the Cascades and ending just before Cowiche Stream joins the
Naches River.
Phosphates get into the water table via agricultural runoff from fertilizers, industrial waste, and human waste
from septic tanks. In high agricultural areas such as the Yakima Valley, phosphate levels may be high.
Phosphates can interfere with human digestion. The Washington state standard for phosphate levels in drinking
water cannot exceed 5 mg/l of water. Environmental effects include changing the composition and diversity of
organisms due to eutrophication and depletion of oxygen in the water. Regular testing of waterways for
phosphate pollution is necessary to preserve biodiversity, monitor general health of water body, and protect the
health of the general public.
http://extoxnet.orst.edu/faqs/safedrink/phos.htm
http://www.epa.gov/
http://www.water-research.net/Watershed/phosphates.htm
Materials:
– All supplies can be purchased from:
http://www.ohiopurewaterco.com/shop/customer/home.php?cat=342&gclid=CIyPye6slaUCFQoEbAodJEGIOQ
o Approximately 4 water samples collected from local water body throughout a gradient.
o 1 Phosphate Hatch Kit per group (3-4 students) containing:
 Sufficient phosphate 5 reagents for number of water samples tested.
 2 test tubes with rubber stoppers
 1 phosphate color wheel
Procedure:
Begin class by having the students anonymously write the answers to the following questions on a piece of
paper. They do not need any previous knowledge about pollutant just ask for common sense answers.
1. How they think phosphates enter the water table.
2. What effects do high levels of phosphates have on the human body?
3. Why would it be important to regularly test water?
Answers should be balled up and tossed around the room for one minute to thoroughly mix. Next, going around
the room students should read their answers to show their preconceived notions. Incorrect theories can be
addressed at this time, but don’t give the students the answers as they’ll learn more by finding it on their own.
Students should be given the following questions and asked to do an online search using credible web sites for
the answers (see “Field Trip Follow up Nitrates and Phosphates”).
1. How do Phosphates enter the water table? (hint: where do they come from?)
2. What is the maximum amount of Phosphates drinking water can have for the Environmental
Protection Agency to consider it is still safe? (hint: how many milligrams of nitrates in 1 liter of
water is safe to drink?)
3. What will high levels of Phosphates do to the human body? (hint: describe diseases or effects it
will have on our health - don’t just list them.)
Give a brief introduction to the HACH kits but allow the students to read the detailed instructions and decipher
their contents within their groups. A safety discussion should remind students not to eat or drink anything
around their work bench, to use care in handling glass instruments, and the proper disposal of broken glass.
Instruct the students on proper disposal of waste solutions (dumped down the drain) and all hands should be
washed after handling the chemicals.
Finally, students will graph their results for each of the water samples (see the following example from “Field
Trip Follow up Nitrates and Phosphates”).
Please make a bar graph of Phosphate Levels at each field site.
Water sample #1
Water sample #2
Water sample #3
Water sample #4
Conclusion:
In final 15 minutes of class students will discuss their web findings with class and each group will plot their
phosphate levels on a graph drawn on the front board to show variation among groups due to experimental
error. Discuss where errors could have occurred. Guide the discussion in the interpretation of the graph looking
for trends.
Extension(s):
The students are required to write a formal lab report compiling previous lessons testing for fecal coliform,
nitrates, water velocity, and aquatic invertebrate abundance in their water source. The students are responsible
for compiling an introduction, methods, results of each water quality test, discussion, and literature cited. Their
lab report will be reviewed by their peers using the “Peer Review Rubric” and then submitted to the local land
managers (in this case Cowiche Canyon Conservancy).
Teaching Tips:
Work through the HACH kit so you will be able to field questions regarding the procedure.
Safety: Solutions may not be consumed. Waste may be dumped down the drain. Hands should be washed after
experimentation. Broken test tubes may be a hazard and should be addressed prior to experiment.
Supplements:
See attached “Field Trip Follow up Nitrates and Phosphates”, “Rubric for Peer Review”, and “How to Write a
Field Report”.
Sources:
http://www.water-research.net/Waterlibrary/watermanual/wqfieldmanual.pdf
http://www.ohiopurewaterco.com/shop/customer/home.php?cat=342&gclid=CIyPye6slaUCFQoEbAodJEGIOQ
http://www.cowichecanyon.org/
http://extoxnet.orst.edu/faqs/safedrink/phos.htm
http://www.epa.gov/
http://www.water-research.net/Watershed/phosphates.htm
Author: Melissa Reitz, Yakima WATERS Project, CWU, Fall 2010