A Collaborative Effort
Title: Phosphates, Nitrates, and Algal Blooms
Class: Environmental Science
Grade: 11-12
Timeframe: 1 day for setup, approximately a week
for results
Knowledge Gap Topic
How does human use of fertilizers and detergents affect watersheds?
Subject Matter/
Key Vocabulary
Phosphates, Nitrates, Algal Bloom, Oxygen deprivation, detergents,
fertilizers
Essential Question/
Over-Arching Concept/
Key Understanding
Curriculum Connections
 OGT standards
 Local standards
Essential Question 2: How human activities influence stream?
Essential Question 3: How does energy and /or nutrients flow in the
watershed?
Physical Science Standards 9-10: B Explain how atoms react with each
other to form other substances and how molecules react with each other
or other atoms to form even different substances.
Instructional Objectives
Materials
Additional Documents
Introduction
 focus event
 varies with teacher
Development
 major parts of unit/
lesson
Rigor/Relevance Quadrant(s)
 link to rigor/relevance
document
Earth Science Standards 9-10: D Describe the finite nature of Earth's
resources and those human activities that can conserve or deplete Earth's
resources.
O1) Students will explore natural flow of phosphates and nitrates in the
watershed by setting up control and experimental beakers of chlorella
algae and treat them with various concentrations of nitrates from fertilizers
and phosphates from detergents
O2) Students will conduct a qualitative observation of resulting algal
blooms due to treatments as compared to controls
O3) Students will determine human activities involving fertilizers,
detergents which cause environmental problems such as algal blooms that
upset natural balance and cause O2 deprivation in system
Nitrates from fertilizers, phosphate detergents, algal culture (we used
Chlorella), beakers, pond or stream water, light source. These can be
cheaply obtained in a kit for teachers first trying this out … Wards, Science
Kit, Carolina all have them.
Go over basic nitrogen and phosphate cycles so students see that these
are natural products and part of natural cycles, just like Carbon Cycle.
1) Students set up three situations … control solutions, phosphate treated
solutions and nitrate treated solutions of Chlorella in beakers. 2) Different
% can be given to teams if desired
3) Beakers are exposed to light for 5-7 days and student observes
changes.
If quantitative data is desired, a photometer or colorimeter may be used to
measure % of light transmitted. As populations grow, less light will be
transmitted.
A: Must use terms correctly
B: Setup simulates real world conditions in ponds and watersheds and
their interactions with fertilizers and detergents
C: Students think through the fact that overpopulation of algae will actually
cause more decomposer growth which causes oxygen deprivation rather
Designing Watershed-based Education and Extension Efforts through a Mental Models Research Approach
USDA-CSREES National Integrated Water Quality Program
Product/Artifacts/Student
Evidence of Understanding
Accommodations
 plan B
 differentiated instruction
Formative
Assessment/Feedback
 measure of progress
Final Evaluation
 project rubric
 oral or paper quiz/test
 portfolio
Teacher Reflection
 complete after lesson
than more oxygen.
D: Brainstorm ways to restrict fertilizer run off or change our way of
cleaning with detergents
If students use quantitative measurements, they can produce graphs of
algal growth over time with colorimeter or photometer data
Doing the quantitative part of measuring light transmittance is not
necessary for basic idea … student can readily see differences without
graphing data.
Use questions during lecture to assess understanding of basic phosphate
and nitrate cycles
Ask probing questions about student predictions while they are setting up
solutions and correct any misconceptions at that time
Qualitative: Students take digital photographs of results as evidence
supporting that excess phosphates and nitrates cause algal blooms
Quantitative: Student collect % transmittance data over several days and
graph results to show evidence that supports excess phosphates and
nitrates cause algal blooms
This is a very simple, yet effective lab for showing problems that occur
when using fertilizers or detergents.
Designers/Email: Fred Donelson (fdonelson@gjps.org)
Additional Comments: I will probably use colorimeters next time to add a quantitative piece to this lab, but
students certainly found this easy to understand.
Designing Watershed-based Education and Extension Efforts through a Mental Models Research Approach
USDA-CSREES National Integrated Water Quality Program