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Can Nutrients in Water Cause Harm?

Author(s): Nancy P. Moreno, PhD, Barbara Z. Tharp, MS, and Judith Dresden, MS.

Session 1

Ask the students if they remember what happened to Marigold Marsh in the story, Mystery of the Muddled Marsh. Allow everyone to share his or her ideas. Tell students they will investigate what happens when fertilizer is added to a water ecosystem, and that they will be able to see some of the tiny plants and animals that lived in the muddled marsh.

Have one or two students label the three containers “NF” (no fertilizer/control), “N” (natural fertilizer), and “C” (chemical fertilizer). In bilingual classrooms, also label the containers: “SF” (sin fertilizante), “N” (fertilizante natural), and Q (fertilizante químico).

Show the students the prepared hay infusion culture or natural pond water. If possible, have students observe a few drops of the water under a microscope. Explain that they will be growing similar living things in the bottles. Add about 250–500mL of the prepared or natural pond water, along with some hay or dried grass, to each container.

Place the containers in a bright window or under a bright fluorescent light for 1–2 days to allow the culture to develop. Bright light is important. In low-light conditions, hay infusions tend to develop mold and/or foul-smelling bacteria within 2–3 days.

Note: If you are using pond water that already has plenty of green algae and other growth, the cultures do not need time to develop or “rest.” In this case, proceed directly to the next step.


Funded by the following grant(s)

National Institute of Environmental Health Sciences, NIH

National Institute of Environmental Health Sciences, NIH


The Environment as a Context for Opportunities in Schools
Grant Number: 5R25ES010698


Houston Endowment Inc.

Houston Endowment Inc.

Foundations for the Future: Capitalizing on Technology to Promote Equity, Access and Quality in Elementary Science Education