Using a periphyton sampler to collect material for algal biomass assessment

Superior Streams Algal Assessment

Duluth’s high-quality trout streams are sensitive to urbanization and rural development. These streams are subject to increasing water temperatures, decreasing aquifer recharge, and increasing water, sediment and nutrient runoff. Climate change predictions for the Great Lakes region indicate the potential for these impacts to be exacerbated via an increase in the frequency of intense storm events and decreased precipitation in the summer. Understanding how these changes affect stream health is key in developing protection and restoration activities. Stream health is evaluated using physical, chemical, and biological measures. The aquatic biological community, primarily aquatic macroinvertebrates and fish, is most often used to determine stream health, but algae (aka periphyton) are also used.  Periphyton, the algae that grow on surfaces such as rocks, wood and plants, are useful indicators of stream health because they are sensitive to many environmental stressors and respond rapidly to changes in nutrient concentration.  The ability of periphyton to grow rapidly in response to nutrient inputs offers the potential to use this community as a relatively low-cost, sensitive early-indicator of localized differences in nutrient loading.

2018 Field Sampling

Our 2018 project will measure periphyton in several Duluth trout streams using two methods.  The first uses traditional quantitative methods that involve scraping algae off rocks and measuring the chlorophyll and organic content of the material.

The second method will use a visual assessment (VA) technique to estimate percent coverage of algae along the stream bottom as well as the thickness or length of the algal film or mat. The VA method is much quicker and cheaper and has been used successfully in many areas (California and New Zealand to name a few.) to measure algal biomass. We will be working on comparing the two techniques in June and July. We will then perform statistical tests to determine if the VA method can be useful in estimating algal biomass for Duluth-area trout streams.

Volunteer Involvement

We are also interested in locating areas within the streams experiencing dense algal growth.  This is where our volunteers can help us.  We do not have the resources to walk all the streams throughout the Duluth-area.  What we would like volunteers to do is walk sections of their favorite (or assigned) stream, and record images and locations where they observe dense algal growth as seen in the image below. This image was taken in Amity Creek on June 14, 2018.

Amity Algae

Filamentous algal growth in Amity Creek


We would also like them to record some basic habitat observations including water temperature, recent and current weather, substrate type, approximate stream width and depth, primary riparian vegetation, and percent canopy cover. Nutrient availability, substrate type and available sunlight are probably the most important habitat components controlling algal biomass in streams.   Also any other pertinent observations including fish, aquatic vegetation or insects/hatches observed.  It is also helpful to note any stormwater outlets in the area or any other potential runoff issues.   We will provide maps of the entire watershed, data sheets, and thermometers, as well as bottles for algal samples.
The best time to look for these areas of dense algal growth is late July through mid-August, barring any rip-roaring rain events.


Learn more about primary producers - algae - and periphyton, click here.

Contact Elaine Ruzycki for more information and to sign up as a volunteer.


This page was prepared by NRRI using Federal funds under award NA17NOS4190062 from the Coastal Zone Management Act of 1972, as amended, administered by the Office for Coastal Management, National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce provided to the Minnesota Department of Natural Resources (DNR) for Minnesota’s Lake Superior Coastal Program. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the views of NOAA’s Office of Coastal Management, the U.S. Department of Commerce, or the Minnesota DNR.