Wednesday, January 21, 2015

Water Quality Assessment Using Diatoms with High School Students

We have all seen the world of water quality through all those fantastic aquatic insects but new organisms, or not so new are making its debut in Connecticut, and that is the “DIATOMS”.

In 2010 and thanks to a grant from the National Oceanic and Aeronautic Administration ( NOAA)  we at Education Connection, located in Litchfield, CT were able to involve 8 school district high school in doing water quality monitoring using Diatoms as indicator species. This is the fifth year of this project and we have been challenged teaching Diatom Biology to more than 12 teachers and 2.000 students. The program’s name is Project Periphyton.

Water Quality assessment using Diatoms as indicator species have been done worldwide for more than 20 years. Most state environmental protection agencies are involved in it.  The main difficulties of using them with high school students as opposed to using aquatic insects are that diatoms are small and it requires the use of good microscopes to be able to do the job (400X and 1000X with oil immersion). Identification is also a challenge as there are so many diatoms that look alike, but here in Connecticut we have use two major published papers, (Using algal metrics and biomass to evaluate multiple ways of defining concentration-based nutrient criteria in streams and their ecological relevance published by Nathan J. Smucker, Mary Becker, Naomi E. Detenbeck, Alisa C. Morrisona, Ecological Indicators 32 (2013) 51–61   in 2013 and The Diatom Pollution Tolerance Index: Assigning Tolerance Values by Cara Muscio Watershed Protection. Development News, City of Austin,  published in June 2002).


Collecting diatoms is much easier as all it takes is to gather some rocks from a stream and rub them with a tooth brush. Students go out into the field to an assigned stream two times a year, in the fall and once again in the spring. In the field they take physical and chemical measurements such as dissolved oxygen, alkalinity, stream flow, temperature, etc., and then they collect 5 fist size rocks. Using tooth brushes and wire brushes they rub the stones and collect all the periphyton attached to the rocks in distil water. They use Lugol’s solution to fix the diatoms which they take into the classroom to clean and prepare for viewing.

Cleaning of the sample is done using Clorox and a centrifuge. Clean samples are used to prepare several permanent microscope slides that will be used to identify the diatoms.(For diatom Identification we use “Diatoms of the United States” website). Here is Connecticut we have prepared a Genus level pollution tolerance level chart the students use to calculate a PTI (Pollution Tolerance Index) for the stream. For additional information on our methods send an email to Alberto Mimo at We have several schools that collect aquatic insects in addition to the diatoms. They use both methods to compare these two water quality assessment tools.


I was the developer and director of Project SEARCH in Connecticut that was done through the Connecticut Department of Environmental Protection from 1985 until 2000 and it is still used by many schools. Project SEARCH uses aquatic Insects, and I wanted to try a similar methodology using Diatoms now and for some time. Diatoms are more challenging because of their size and anatomy but at the same time teachers and students can complete collections with a much less effort, they are easier to keep and occupy less space. Many of the methods used compliment what schools are teaching to their students in Biology and still introduce students to the concepts of water quality, biodiversity, classification, trophy levels, geographical basins and ecological integrity.

As part of the program we also bring students to the shore to collect a sediment core and use a seine to catch some fish and study their stomach content, integrating many more ecological concepts such as sedimentation, the formation of the Long Island Sound, glaciation, food webs and differences between fresh and salt water environments.


As part of the program we use EDMODO (www., a web based communication system to exchange ideas and information between teachers and students. Students download on the web their excel sheets, their photographs of diatoms and pictures of their field trips and their experiences.


In addition to this educational experience school collect one additional sample for me. I take the sample and identify the diatoms, complete all the calculations and write a report that is sent to the schools, to NOAA, to the USGS and to the Connecticut Department of Environmental Protection. This way they can compare their results and identification of diatoms to my results.  I also compare the results to data obtained under the USGS SPARROW program to evaluate the phosphate load on the streams basins in Connecticut.


As part of the program all the schools are given a school campus copy of ARCGIS. The objective is to get the students to complete all their mapping work digitally. I visit the schools and provide GIS education for the teachers and the students.

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