The Microscopic World of Diatoms

Sultany, M. and Bixby, R.
Type Category
Instructional Materials
Lesson/Lesson Plan , Article , Activity
This resource, vetted by NSTA curators, is provided to teachers along with suggested modifications to make it more in line with the vision of the NGSS. While not considered to be "fully aligned," the resources and expert recommendations provide teachers with concrete examples and expert guidance using the EQuIP rubric to adapted existing resources. Read more here.



This article in NSTA’s November 2016 issue of The Science Teacher describes a set of activities that engage students in three-dimensional learning by using diatom bioassessments to assess water quality and biodiversity in a variety of local aquatic ecosystems. Student work is guided by the essential question, “How does living in the Anthropocene affect the integrity of aquatic ecosystems?” After completing two pre-assessment activities to become familiar with diatom bioassessments and anthropogenic sources of pollution in their own neighborhoods, students design and carry out their own local investigations. Students collect and analyze data, obtain information from primary sources, and finally, assess how human activity impacts local water quality. A variety of assessments are suggested and a generalized assessment rubric for student learning outcomes is provided. The activities are supported with a list of online materials, including a simulation (SimRiver - ) which is reviewed in a separate NGSS@NSTA Hub entry.

Intended Audience

Educational Level
  • High School
Access Restrictions

Available by subscription - The right to view and/or download material, often for a set period of time, by way of a financial agreement between rights holders and authorized users.

Performance Expectations

HS-LS2-2 Use mathematical representations to support and revise explanations based on evidence about factors affecting biodiversity and populations in ecosystems of different scales.

Clarification Statement: Examples of mathematical representations include finding the average, determining trends, and using graphical comparisons of multiple sets of data.

Assessment Boundary: Assessment is limited to provided data.

This resource is explicitly designed to build towards this performance expectation.

Comments about Including the Performance Expectation
The activities described in this article are designed to help students make sense of the impacts of human activities on aquatic ecosystems. Preliminary activities elicit prior knowledge and also provide background information and training so students may successfully complete their diatom bioassessments. The activities provide ample opportunities for students to develop and use various mathematical representations. In the SimRiver simulation, students complete a data table, perform a series of calculations to get an index of water quality for each water sample, and create and analyze graphs. After collecting diatom data from their own local investigations, students calculate a numeric value for stream health. (See Fig. 7) Teachers will want to monitor student groups and discussions to listen for evidence that students are accurately and appropriately using these representations to supply evidence for their explanations. Teachers may also want to prompt students to continually make connections from the work they are doing at the microscopic scale of diatoms to the implications for the whole aquatic ecosystem. They can also make connections to landscape scale and larger factors affecting stream health. Information from local agencies about potential factors that affect the water quality of their chosen field sites may also be very useful in evaluating their results.

Science and Engineering Practices

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
The authors suggest that planning and carrying out an investigation be a collaborative process. They suggest that one way students can refine their ideas is by connecting with scientists via an interactive video chat. They also suggest that teachers can email local universities or museums to find diatom specialists who will provide helpful feedback to students on their research questions. The focus should be on helping students to develop a testable, relevant research question. In the article, the authors describe how the researchers who interacted with their students asked questions starting with, “Why?”, “How?” and “What might happen if?” Insights from this preparation will help students to have greater success in their investigation. The authors also provide videos and other resources to help students learn how to collect diatoms and how to prepare slides. In addition, the article suggests connecting with local colleges, universities, or businesses that may have more specialized equipment to help students view diatoms. The authors describe their students using a “Phenom Pro” - a desktop scanning electron microscope - which they borrowed from a local STEM Center.

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
Mathematical representations are used throughout these activities to help students engage with the phenomenon of human impact on biodiversity and populations in ecosystems. In the pre-assessment activities, students encounter a variety of maps, charts, and tables as they learn about anthropogenic sources of water pollution in their local area. SimRiver, a simulation that uses diatoms to assess water quality, provides students with data in graphical and tabular formats, finalized in a worksheet. Teachers may want to implement a similar worksheet for students to use in their own investigations. Also in SimRiver and in the students’ own investigations, there is the opportunity to calculate a diatom saprobity value based on the diatom species data they collect. This saprobity value provides quantitative evidence to support an explanation of the water quality of an aquatic ecosystem. At the end of the article, there is a link to another version of the SimRiver data collection table (, which students may want to modify for their own investigations. The authors suggest a variety of resources that may add more information to students’ own data. Students should be encouraged to consider how to use such data to support and revise their explanations of how human activity is impacting the aquatic ecosystems they are studying.

Disciplinary Core Ideas

This resource is explicitly designed to build towards this disciplinary core idea.

Comments about Including the Disciplinary Core Idea
Teachers will want to be sure to encourage students to connect their data with real anthropogenic impacts in the same local area as their field site. The article encourages students to connect with environmental agencies, as well as with diatom specialists, who may be familiar with the local aquatic environments, anthropogenic impacts, and diatom species. Examining the diatom species and numerical data from different sites will help students to compare the impacts in different areas within the same geographic region. If students collect additional data, such as stream chemistry, at their field sites they may also be able to make more specific inferences about cause and effect.

Crosscutting Concepts

This resource is explicitly designed to build towards this crosscutting concept.

Comments about Including the Crosscutting Concept
Diatom populations and communities change in response to human activity, revealing information about ecosystem stability. The focus of these activities is that what happens at this microscopic scale - the scale of diatoms - impacts the health of an entire ecosystem at a much larger scale. To be more explicit about the concept of scale, teachers may want to use freely available Internet resources to help students understand orders of magnitude (e.g.,,

Resource Quality

  • Alignment to the Dimensions of the NGSS: This series of activities does an excellent job of incorporating three-dimensional learning into students’ explorations of the phenomenon of human impact on local aquatic ecosystems. Students make sense of this phenomenon by developing and using a variety of mathematical representations to provide evidence for their explanations.

  • Instructional Supports: The activities engage students in authentic questions that reflect real-world science practices. The pre-assessment activities explicitly identify prior knowledge and build on this knowledge to equip students to successfully complete the rest of the activities. The authors encourage students to obtain information from local agencies and environmental experts, as well as diatom specialists, to build relevancy and engagement into their projects. The materials provided are scientifically accurate, and primary sources are provided. The authors provide a table (see Fig.1 on p. 57) and an additional handout on differentiation strategies ( All of the activities provide extra support for students who need it, as well as extension activities for highly engaged students. Multiple additional resources for teachers are available at

  • Monitoring Student Progress: All of the activities elicit direct observable evidence of student learning. In addition, suggestions for pre-assessment, formative assessment, and summative assessments are provided. A rubric to assess generalized student learning across all the activities is included. Students may be assessed in a variety of informal ways, and all of the materials are easily accessible.

  • Quality of Technological Interactivity: The pre-assessment activity uses the simulation, SimRiver. This simulation allows students to manipulate several variables and work at three different challenge levels. Please see the NGSS@NSTA Hub for a more complete review of this simulation.