Ambient Diatom Community Monitoring Project

Since the 1970s, the DEEP Water Monitoring Group has routinely used benthic macroinvertebrates to assess water quality conditions in Connecticut.  In the early 2000s, the program expanded to include the use of fish community data as an indicator of water quality.   Most recently, the program expanded again to include the collection of annual diatom community samples from rivers and streams. Research is underway to evaluate these data and develop a third set of biologically-based tools for assessing water quality conditions in Connecticut. 

Indicators of Water Quality

Diatoms are a type of tiny, single-celled, algae found in waterbodies throughout the state as part of the periphyton community.  (Periphyton is a term used to describe the mix of aquatic organisms, including plants, algae, and bacteria, that live attached to underwater surfaces such as rocks on a riverbed.)  Diatoms are microscopic and therefore invisible to the naked eye, but play an important role in the ecology of rivers and streams.  In particular, diatoms serve as a critical food source for many other aquatic organisms. Diatoms have already proven useful elsewhere in the country as an indicator of water quality.  The structure of a diatom community is determined by water quality conditions over a period of time. Similar to fish and benthic macroinvertebrate communities, diatom communities are sensitive to changes in environmental conditions.  Diatoms are particularly sensitive to changes in nutrients, and are of great interest as a tool to identify and better understand phosphorus-related impairments.

Program Development Status

A pilot project to monitor diatoms was initiated between 2002-2004 during a statewide survey of wadeable streams. Analysis of these data as an indicator of water quality showed promising results.  

As a result, several follow-up projects were initiated to support development of diatom-related water quality metrics.  DEEP now annually collects phosphorus and diatom community data from rivers in Connecticut.  This data is being used to develop diatom tolerance metrics to assist in identifying phosphorus as a contributing cause of aquatic life impairment.  

Related Pages

For More Information Contact:

Mary Becker
Ambient Diatom Monitoring Project Lead /
Water Monitoring Unit Supervisor
CT DEEP Bureau of Water Protection and Land Reuse

Content last updated May 24, 2022.