Macroinvertebrate Sampling in Wetlands

Site locations & rationale

The Biological Monitoring Program has sampled aquatic macroinvertebrates 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

Standard D-net Sweeps  Macroinvertebrate samples are taken from areas of emergent vegetation using a measured sweep with a standard D-frame dip net. A sample is collected by submerging the net and sweeping through the water for a distance of one meter. The net is bumped against the bottom substrate three times (at the beginning, middle, and end of the sweep) to dislodge and collect organisms from the sediment and water column. All material collected is placed in a sieve bucket. Large pieces of vegetation are washed and discarded, while finer plant material and detritus are retained. Three replicate samples are collected. These samples are preserved for later sorting and taxonomic analysis in the laboratory.

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

Macroinvertebrates collected in standard D-net samples are identified to the lowest practical taxonomic level, typically genus or species. The Biological Monitoring Program uses a statistical model based on macroinvertebrate 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 macroinvertebrates from wetlands, please visit our Materials Page.