Algae Sampling in Wetlands

Site locations & rationale

The Biological Monitoring Program has sampled algae from sites in freshwater wetlands distributed throughout the State of Maine since 1998. Sampling occurs during June and July to provide a standard index period for comparing sample results from year to year.  Sampling is usually conducted in shallow, soft-bottom habitats with aquatic vegetation including slow-moving streams, marshes, ponds and lake littoral zones.

Sampling methods

Plant stem rubbings  Epiphytic algae that grow on plant stems are collected using garden shears to clip the plant stems below the water line. The plant stems are placed into a plastic whirlpak bag and tap water is added. The stems are then massaged through the bag to remove attached algae, rinsed with additional water and discarded. The surface area of each plant stem is calculated from field measurements to obtain a quantitative sample.

Water column grab samples  Phytoplankton samples are taken using a long-handled dipper that collects water samples just below the water surface. Water samples from multiple areas of the wetland are combined into a single sample. The samples are used for quantitative analysis of phytoplankton abundance and species composition.

Additional Data Collected  Physical and chemical water quality data collected through field measurements and analysis of water samples at each site typically include temperature, dissolved oxygen, specific conductance, pH, nutrients, true color and alkalinity, although water sample analytes may vary somewhat in a given year. Habitat characteristics are also recorded, including water depth, plant community type and/or wetland Cowardin class, substrate type, and a list of dominant plant species at the site.

Department biologists complete a Wetland Human Disturbance Assessment (WHDA) at each site sampled to document and characterize environmental stressors that could adversely affect biological communities.  The WHDA includes sections for hydrologic and vegetative modifications, evidence of chemical pollutants, and a watershed characterization identifying potential non-point source pollution impacts.

Data analysis

The algae in both plant stem rubbing and water column samples are identified to the lowest possible taxonomic level. Diatoms are typically identified to species or subspecies level while green algae, red algae, cyanobacteria, and other algae are usually identified to genus or species level.  The data are reported with cell densities (cells per unit area or volume sampled) and cell biovolumes (micrometers per unit area or volume sampled).  The Biological Monitoring Program uses two separate statistical models for epiphytic algae and phytoplankton based on algal metrics calculated from sample data to predict the probability of a waterbody attaining aquatic life criteria for Class AA/A, B, C or GPA, or of not attaining criteria for any class (NA, non-attainment).

For more information on how the Biological Monitoring Program samples algae from wetlands, please visit our Materials Page.