WI DNR Field Procedures Manual
Intranet Edition

Scope

Artificial substrates are useful for collecting macroinvertebrates associated with the water column and can be used to demonstrate water quality and effects of contaminated sediments on the overlying or downstream water column. They can be used in almost any stream or lake habitat, either suspended in the water column or anchored to the bottom. They are left in the water for relatively long time periods (2-8 weeks) to be colonized by drifting or swimming aquatic organisms.

The main advantage of artificial substrates is the minimization of the effects of physical variables between sites such as: substrate type, depth, and light penetration. Data comparisons between stations are, therefore, simplified.

Some disadvantages include: large effort and time to results (two separate field trips, 2-8 weeks to colonize), loss of sample because of weather or vandalism, and unquantifiable loss of invertebrates if samplers are accidentally disturbed.

For sediment assessments, the most significant attribute is the bias for aquatic rather than benthic invertebrates. Invertebrate colonies from artificial substrates generally reflect water quality rather than sediment quality unless the sediment is directly affecting the quality of the water above it. So, artificial substrates should be used to demonstrate a change in water quality near or downstream from a sediment and in conjunction with other sediment data, but should not be used as a direct measure of sediment quality alone. Discussions of both the advantages and disadvantages of artificial substrate samplers appear in, Klemm et al (1990), Rosenberg and Resh (1982), Weber (1973) and Chapter 5 of Downing (1984).

Equipment

Several different designs of artificial substrates are available, but only two common types will be described here. Other types are described in the scientific literature (Klemm et al, 1990; Rosenberg and Resh, 1982).

Collection Procedure

1. Setting the samplers

   Artificial substrates are anchored or suspended at the sample site to be colonized by drifting and swimming invertebrates. Placement within the water column depends upon the objectives of the study. For sediment assessments, the samplers should usually be placed close to the sediment, but samplers from all sites should be at similar depths. For water quality assessment, samplers are normally placed in the euphotic zone (1-3 feet from water surface) to collect the highest diversity and abundance of invertebrates possible (Mason et al. (1973) in: Klemm et al. (1990)).

   Care should be taken to prevent silt from building up and thus reducing the colonizable surface area of the substrate.

   To prevent vandalism, place samplers out of the view of passers by and away from boat traffic and heavily used fishing areas. If water levels at the site will fluctuate, place the sampler so it will be midway in the water column at low-flow or at least will not ever be exposed to the air.

   It is recommended to place at least three samplers at each site. There is no exact standard for exposure time, but six weeks is recommended by many authorities (Klemm et al, 1990, American Public Health Association, 1985, and Weber, 1973). Whatever the exposure time, data should not be compared between samplers exposed for different lengths of time.

   The best times for sampling invertebrates is spring/early summer, and fall. This is when there is the most activity and the highest abundance of invertebrates can be obtained. Remember that invertebrate assemblages will change through the seasons, so the time of year will affect the numbers and species of invertebrates obtained.

2. Retrieving Samplers

   The method used to retrieve an artificial substrate is critical to the resulting quality of data. Some invertebrates will abandon the substrate as soon as the sampler is disturbed. For this reason, samplers should be retrieved with great care to reduce the loss of invertebrates from the sample. Ideally, the sampler is approached from downstream and enclosed with a U.S. Standard #30 or finer mesh bag or dip net before it is moved and brought to the surface. SCUBA or a remote enclosure system can be used in deep water. But, if these are not viable options, samplers should be pulled up with the least amount of disturbance and netted before reaching the surface.

   The same procedures to deploy samplers should be used for all samples and sites that will be compared (e.g., depth, exposure period, current velocity, sunlight exposure, habitat type).

Sample Processing

After retrieval, multi-plate samplers can be placed directly into containers large enough to hold the sampler plates (one quart, large mouth jars or sturdy plastic bags) and preserved with 70-80% ethanol until processing; or they can be cleaned (organisms removed) in the field. Rock baskets are almost always cleaned in the field. The contracting laboratories will normally clean samplers if asked, but the work must be included in the contract, and will cost slightly more per sample.

Remember: If stored in preservative, substrates absorb the preservative and are considered unsuitable for reuse.

Alternatively, samplers can be stored in sieved, refrigerated water from the sampling site. Sorting and preservation should proceed within 24 hours of storage.

With all artificial substrate types, the enclosing net used during retrieval should be inspected for invertebrates and the recovered invertebrates included in the sample.

Always place a water resistant sample label inside the bag or jar as well as on the outside. Information should include: Site ID, location, habitat type, time, date and names of collectors.

1. Cleaning samplers

   1. Disassemble the sampler and place plates, spacers or rocks in a tub of water (sieved to prevent introducing non-sample organisms if site water is used) and gently scrub plates or rocks into the tub with a soft bristled brush to remove all invertebrates.
   2. Concentrate the resulting sample by pouring the tub of water through an appropriate sized sieve, and then place into sample containers with the appropriate preservative (10% formalin or 70-80% ethanol). With multiplate samplers, the sampler is disassembled and each plate and spacer is inspected with the aid of a low power magnifier. All target invertebrates are then removed for preserved storage in 70-80% ETOH. The ETOH remaining within the sample containers is then poured through a #30 or #60 mesh sieve and all retained macroinvertebrates are included in the sample. The inside of the emptied sample container should also be inspected for invertebrates to be included in the sample.
   3. For rock basket samplers, rocks stored in preservative are treated similarly to the plates in the above example. If only the organisms and associated materials from the rock surfaces were retained in ETOH, the ETOH/organism mixture is passed through a #30 or #60 mesh sieve. The retained organisms and debris are then transferred to a white pan for sorting, with the aid of a low power magnification device.

   For quantitative work, the surface area of the artificial substrate sampler must be determined to allow for calculation of organism density per unit surface area.

2. Sorting and Subsampling

   Refer to the sorting and subsampling parts of 702.1 Benthic Invertebrate Surveys - Benthic Samples.

3. Taxonomic Identification

   Refer to the taxonomic identification part of 702.1 Benthic Invertebrate Surveys - Benthic Samples above for procedures and a list of invertebrate taxonomy laboratories.

Documentation

Information about the sample site and collection procedures are recorded on Department Form 3200-81, Macroinvertebrate Field and Bench Sheet. It is very important to label the specimen container(s) from each site with the corresponding Sample ID number that appears on Form 3200-81 for that site. See 701.3 for additional information on documentation. See the download section for an electronic copy of form 3200-81.

Quality Assurance

To ensure quality data from artificial substrate samples, the investigator should be aware of the following:

1. Samplers should be retrieved very carefully to prevent the loss of organisms. Samplers should not be disturbed at all prior to retrieval (approach site from downstream) and should be enclosed during retrieval with a net having a mesh size at least as fine as U.S. Standard #30 or #60 or small enough to retain target organisms.
2. Multiplate samplers or others made from porous materials should not be reused after exposure to oils/toxins in water or storage in preservatives.
3. Samplers to be reused should be inspected carefully to remove all organisms to prevent carryover to successive sample sites or exposure periods.
4. Artificial substrates may not sample all organisms found on natural substrates with equal efficiency. Use caution when interpreting data from artificial substrate samples. Refer to Chapter 5 of Downing (1984) for a more complete discussion.
5. Sampler to sampler variability can be estimated from results for replicate samplers placed at each location. Samplers should be placed so that they do not interfere with each other by changing water flow, light, siltation, etc.