What and Why?
Bioindicators are organisms used to assess the health of their environment which can then be used for:
  • setting protection or restoration goals;
  • determining what to monitor and how to interpret the results;
  • prioritizing stressors and choosing control measures and
  • assessing and reporting the effectiveness of management actions
Biomonitoring the bugs living at the bottom of lakes and streams is one of the most common and accurate ways of assessing the health of an aquatic ecosystem. These bugs referred to as macroinvertebrates are almost always present and are easy to sample and identify.  Done over time a credible collection of macroinvertebrate data can be gathered to aid in lake management decisions.

Benthic macroinvertebrates includes larval and nymph form of insects, while others are creatures that live in the water their entire lives such as crayfish, clams and leeches.

There are several advantages in using benthic macroinvertebrates as indicators of water quality:
  • they are present in almost all types of water bodies year round and in large quantities,
  • they are large enough to be seen with the naked eye with minimal training, and
  • different specimens are easily associated with water quality and ecosystem health because they have different levels of tolerance for poor living conditions and pollution.
  1. a standard D net with 500 micron mesh
  2. hip-waders

Site selection
If you are inexperienced in monitoring a convenient way to start is to:
  • select any body of water that's convenient and see what you can net,
  • RiverWatch has already compiled some baseline data for Neilan, Krugers and Hurds creeks, select one of these creeks and see what can be netted.  Check out your netting skills by comparing your results with Riverwatch's results.
  • once there's confidence in your skills select any body of water of personal interest and start by GPSing it for identification.
Sampling method
  • A common monitoring technique is the travelling kick and sweep method, which entails dragging the foot along the bottom to stir up the macroinvertebrates and then sweeping them up with a net as illustrated
  • get a representative sampling of benthos in a slow moving (pool) and fast moving (riffle) part of the stream,
  • after each sweep dump the contents into the same pail,
  • once the two transects have been completed select 100 specimens randomly from the pail with a spoon and place them into the cubicles of tray as illustrated,
  • transfer the cubicle contents to a dish with a pipette (or turkey baster) or suction flask etc. for identification,
  • identify and tally the benthos onto a data sheet.
Data Interpretation
RiverWatch recommends 2 indices that could be used for interpreting data:
  • EcoSpark
  • Ontario Benthos Biomonitoring Network (OBBN)
RiverWatch used OBBN so data could be more easily compared province wide.

Each parameter used to examine the benthic samples is an indicator of one or more of: water quality, habitat quality, presence of organic pollution/nutrient enrichment. By investigating each of the following 10 indices, a measure of overall stream health can be achieved. 

Each test can be rated as: unimpaired, potentially impaired, or impaired. Afterwards, ratings are compiled to give an indication of overall stream health; if 5 or more of these indices are unimpaired then the stream is classified as such.

% Worm:
Aquatic worms, flatworms and roundworms are included in this category.  High numbers of aquatic worms can indicate excessive organic inputs and a low oxygen level.  Less than 10% worms in a sample is preferred.
% Midge:
Midges have a relatively high tolerance for changes in water quality, and can survive in virtually any substrate type. Finding this animal in high numbers (>40%), could be an indicator of poor water quality. Inversely, it is highly unexpected to find none of these creatures at a site, so this may also be an indicator of negative stream impacts. Less than 10% in a given sample is best.
% Aquatic Sowbug
This animal is a scavenger, so is associated with organic decomposition and low oxygen levels. These benthos are fairly uncommon in healthy streams, so finding even one in a sample indicates the possibility of impairment. Five or more will give an impaired result for this index.      
% Snail
Aquatic snails feed by scraping algae from rocks, leaves, or anything else found in the
substrate (stream bottom). They have a relatively high tolerance to low levels of oxygen. Snails are quite common in stream environments, heavy enrichment and low water velocity can result in high numbers. It could reflect poor stream health if snails are either absent or found in large numbers. Snails in a given benthic sample are generally not of major concern unless there are other ‘red flags’ such as the presence of pollution tolerant benthos,
high midge or worm count, extremely low number of taxon, etc.

About Taxon (benthos that have natural relations)
High biodiversity is always a good indicator of ecosystem health, therefore, the higher the number of taxon, the better. If this value is low, it could indicate that habitat or water quality is degraded. If 11 or more taxon are found in a given sample, the site would be deemed unimpaired. This measure is inversely related to dominant taxon.

A high value for dominant taxon would be a concern because it indicates that one taxon is doing considerably better than the others, which creates an imbalance in the ecosystem. This can occur for different reasons such as poor water quality, limited range of habitat, or merely a recent hatch of a certain species. 

The type of benthos that is the most dominant in a sample can make a difference as well. For instance, it can be a concern if the dominant taxon is a highly tolerant species rather than a mid to low tolerant species. This measure is inversely related to the number of taxon.

 % EPT
Ephemeroptera (mayflies), Plecoptera (stoneflies) and Tricoptera (caddisflies) all require a rocky substrate with good concentrations of dissolved oxygen to thrive in  their nymph stage.  The presence of these species indicates good water quality and good habitat.  A sample with less than 10% of these creatures would be a concern, and less than 5% would be considered impaired.
 % Diptera
This group describes members of the fly family that spend their larval stage in the water.  This includes midges, mosquitoes, blackflies, horseflies, and craneflies.  Because dipterans are an important component to a healthy stream community, extremely low or extremely high values would indicate poor stream quality.  For a stream to be considered unimpaired, there have to be 20-45% dipterans in a given sample.   

 % insect
This parameter includes a large portion of the benthos, such as dipterans, beetles, dragonflies and EPT.  As with the previous index, extremely low or high values are of concern.  This is because insects tend to have a lower tolerance to poor conditions and degraded water quality.  An unimpaired site will have between 50-80% insects in its sample

Hilsenhoff Biotic Index
In this part of the study, each benthos is given a specific numerical value that indicates its pollution tolerance (PT). High numbers indicate more tolerance, whereas lower numbers indicate lower tolerance and therefore higher sensitivity. Weighted average calculations are carried out that consider the relative abundance of each benthic group, which is then summed into a single value. This reflects the relative nutrient status of a stream. If by the end a value of 6 or higher is attained, this could indicate excessive nutrient conditions, and would be of concern. See the ‘Hilsenhoff Tolerance Values Table’ in the appendix.

Summary of Indices
Though each of these indices depict important aspects of stream health, careful interpretation of the results combined with other factors such as site characteristics, history, and observations, are required. No single index can define the health of a stream. 

It's important to note that microhabitats in which benthos live are continuously changing. Changes can take place once every few decades or as often as several times a year. To overcome irregularities more than one assessment should occur initially to establish a credible baseline and then at periodic intervals of every few years thereafter.

assessment data entry