Benthic monitoring involves collecting benthic macroinvertebrates (otherwise known as benthos), which are mostly aquatic insects or the aquatic stage of an insect. These insects live in, crawl upon, or attach themselves to the bottom of the waterbody.

Benthic monitoring can provide an understanding of a waterbody's condition because these organisms are sensitive to the smallest changes in chemical and biological factors. Their presence or absence provides valuable information about a waterbody's health over time. Benthic macroinvertebrates are relatively inactive, inexpensively sampled, and fairly easy to identify.

Reference Condition Approach (RCA)

The reference conditon approach (RCA) to bioassessment involves the use of a set of minimally impacted reference sites to evaluate the condition of subsequent test sites. Test site data is compared to reference sites and an assessment of the level of impairment is produced. There are seven steps involved in applying the RCA to bioassessment:

1. Minimally impacted reference sites spanning a range of physiographic conditions are selected (ideally, this is done randomly), and sampled.
2. Biological conditions of these sites are summarized and are then grouped according to the similarity of their biological features.
3. Niche variables are identified.
4. A model that predicts a test site's reference group membership is built using niche variables.
5. Biological, habitat and physiographic data associated with a test site are gathered.
6. The test site is matched with its predicted reference site group.
7. Statistical tests are applied to determine if the test site falls within the normal range of biological condition defined by its matched reference site group.

(Ontario Benthos Biomonitoring Network Protocol Manual, Version 1.0, May 2004)

Once reference site data from minimally impacted sites across the province are collected and entered into a database, test sites will then be able to input data and generate an impairment value for their lake, stream or wetland. The Ontario Benthos Biomonitoring Network is currently in the process of developing this database, and requires more baseline data from minimally impacted sites to improve the accuracy of the database-generated assessments of impairment values.

(** All info is from the OBBN Protocol Manual)