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Criterion 4 Indicator 23
Rationale
Bodies of Water With Significant Variance of Biological Diversity From the Historic Range of Variability
 
Aquatic organisms, from trout to caddisfly larvae, depend on good water quality and habitat conditions. If these conditions start to deteriorate in streams, rivers, and lakes, some species may decline or disappear, and other species may increase. There may be a loss of biodiversity, with fewer species in a body of water. Often, however, what occurs is a subtle change in biodiversity. For example, if stream temperatures are warmer than they were historically, native trout may be replaced by fish species more tolerant of warmer water. Subtle changes in the stream macro-invertebrate community, such as stonefly or caddisfly larvae, may indicate a decline in water quality.
 
Since streams are dynamic, some variability in biodiversity is natural. But if biological diversity changes significantly in bodies of water from its historic range of variability, these changes can be an important indicator of possible problems such as toxic contamination, extreme temperature changes due to clearcutting, increased sediment due to erosion, and other effects. This information could be a useful tool in making policy decisions regarding forest management.

Can This Indicator Be Quantified
 
Data is not currently available to quantify this indicator. However, methodologies have been developed in the U.S. Environmental Protection Agency’s paper "Revision to Rapid Bioassessment Protocols for Use in Streams and Rivers, Periphyton, Benthic Macroinvertebrates and Fish." This paper provides information and methodologies for assessing the health and biodiversity of streams through biological surveys. These methods are best used for monitoring and detecting aquatic life impairments and their severity. Once a problem is detected, further chemical and habitat assessment may be necessary to determine the source.
 
There are many advantages to using biosurveys for monitoring. Biological communities reflect the overall ecological integrity of a system. Living organisms are sensitive to the effects of different stressors, including ones that may not be obvious at the time of the survey, and so provide a good measure of the cumulative impacts. Communities integrate the stresses over time and provide an ecological measure of fluctuating environmental conditions. Routine monitoring of biological communities can be relatively inexpensive, particularly when compared to the cost of assessing toxic pollutants.
 
The three assemblages commonly used as indicators of water body health are periphyton (algae), benthic macro-invertebrates (an example is stonefly larvae), and fish, each of which has some particular advantages. Algae have rapid reproduction rates, short life cycles, and are most directly affected by physical and chemical factors, making them valuable indicators of short-term impacts. Sampling is relatively easy and inexpensive, and standard methods exist for evaluation. Most importantly, algal assemblages are sensitive to some pollutants that may not visibly affect other aquatic assemblages, or may only affect them at higher concentrations.
 
Many benthic macro-invertebrates have limited migration patterns or attach themselves to the stream bed in one place. This group includes species that fill a broad range of trophic levels and have varying pollution tolerances, making them good indicators of site-specific and cumulative impacts.
 
Fish are good indicators of long-term effects and broad habitat conditions because they are relatively long-lived and mobile. Fish also include a range of species at various trophic levels and tend to show the cumulative effects of lower trophic levels. For example, toxic contaminants are increasingly concentrated as they travel up the food chain. Thus, fish community structure is reflective of integrated environmental health.
 
Habitat assessment is also an important part of the monitoring process. Both the quality and quantity of available habitat affect the structure and composition of resident biological communities. Habitat characterization is important for proper interpretation of biosurvey results.
 

Trends
   
Data not available.

Data Source and Availability
 
Data is available for various site-specific studies across the country. Generally, more information is available for marine environments than streams and lakes. Comprehensive surveys have not been done in Oregon.

Reliability of Data
  NA.

Scale
  Data not available.

Recommended Action for Data Collection
   
Data should be collected using the protocols cited in the reference below (EPA, 1997).

Definitions
  Trophic levels — hierarchy of energy transfers (i.e., nutrition levels within a food web).
producers – photosynthesizers
consumers (herbivores, carnivores, omnivores)
primary - herbivores, grazers
secondary - feed on primary consumers
tertiary - feed on secondary consumers
quaternary - feed on tertiary consumers
decomposers

Selected References
   
U.S. Environmental Protection Agency. 1997. Revision to rapid bioassessment protocols for use in streams and rivers, periphyton, benthic macroinvertebrates and fish. July 1997.