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Biological Assemblages and Protocols

In addition to habitat and water quality information, integrated river and stream surveys also require data regarding the health of aquatic communities. These data are obtained through sampling one or more biological assemblages. Studying a group of organisms will, by their presence and relative abundance, provide useful information on the condition of their environment. The three assemblages used in the RPBs are periphyton, benthic macroinvertebrates, and fish. When selecting an assemblage for river and stream bioassessment, the objective is to choose one or more assemblages that:

• Are useful and logical for the water body under study,
• Can be sampled and interpreted in a cost-effective way,
• Are consistent with the current mix of expertise available, and
• Can be easily interpreted and their results conveyed to managers (using, for example, a multimetric index of the assemblage.)

Different assemblages will require varying amounts of time and effort for sampling. This will largely depend on the specific characteristics of the watershed and the expertise and resources available to the agencies involved.

PERIPHYTON
The periphyton assemblage is made up of primary producers that play a fundamental role in the stream ecosystem. Periphyton attaches to stream substrate and is directly affected by physical and chemical changes that occur in the stream over time. Algae have a rapid reproduction rate and short life span, so they serve as an effective indicator of short-term environmental conditions and impacts. Sampling is relatively easy for this assemblage and causes little disturbance to resident biota. Some algae are vulnerable to low levels of pollutants, which do not affect other organisms until they are present at higher concentrations. This makes algae an effective "early warning" indicator, particularly for nutrient enrichment of the water body.

There are numerous methods available for periphyton sampling. Each should be considered in terms of the objectives of the program, the available resources, the number of streams that need to be sampled, the suspected stressors, and the physical habitat of the streams.

Technique 1
The field-based (i.e., processing done in field) rapid periphyton survey is useful for providing a quick, rough assessment of benthic algal biomass and taxonomic composition over a rather large scale. Besides a data sheet and a pencil, the only equipment needed is a meter stick and a "viewing bucket" with a clear acrylic bottom marked with a 50-dot grid. Before the assessment, three transects are established in the site across areas with visible algal accumulation. Three locations are then selected along each of these transects. At each of these nine locations, the viewing bucket is submerged so that the algae is visible through the clear bottom of the bucket. Algal biomass is roughly characterized by counting the dots that occur over macroalgae and by measuring the length and thickness of algal accumulation. If several types of algae are present, each type is assessed separately. After the visual assessment is completed, some statistical characterization of the algae is useful. Mean density and the average percent cover by each type of algae is easily calculated, and these values make the assessment much more comprehensive.

Technique 2
The standard, laboratory-based (i.e., processing done in laboratory) approach for periphyton sampling is a bit more involved than the field-based survey, but it is not difficult. After the sampling area is established, a visual assessment is made to estimate the percent coverage for each substrate type and the relative abundance of the various types of periphyton present. After this is completed, it is time for sampling. Equipment needed may vary according to whether there will be sampling from natural substrates or artificial substrates.

Algae samples are collected from all available substrates and habitats (e.g., runs, riffles, shallow pools, nearshore areas) to form one composite sample. This composite should be proportionally representative of the periphyton assemblage in the sampling area. The periphyton can be removed from the substrate by scraping or brushing. The composite sampled is stored in a jar with the appropriate preservative until it can be analyzed. It is important to store the periphyton composite in a cool dark place until that time. The exact method chosen will depend on the substrate type and other factors.

Periphyton protocols are most useful when carried out with one or more of the other protocols, particularly with habitat and benthic macroinvertebrate assessments, because of the close association among these three elements. Two periphyton protocols are presented in the RBP document. Click on the box below to review these complete protocols now, or continue with the remainder of this module and visit the full document site later.

Link to Chapter 6 of RBPs document