Benthic Info

Benthic data published info from U.S.G.S. Open File Report 81-901

Benthic Invertebrate Populations Indicate a Wide
Range of Water Quality

An index computed for four sites in Area 19 showed that the
quality of water varied from excellent to poor.

Benthic invertebrates are useful indicators of water quality. Like all organisms, invertebrates have ranges of tolerance to environmental changes. When water quality is altered by increases in sediment and other pollutants, the population structure of benthic organisms responds with changes in species number and diversity. As sensitive species are eliminated, competition for food and shelter is reduced allowing those organisms more tolerant of pollution to flourish. Clean water is usually associated with a high community diversity while varying degrees of pollution produce lower diversities associated with lower or higher numbers in the total population.

Benthic invertebrates were collected at four sites in Area 19 during May and June of 1980 (fig. 5. 1 0- 1). Sampling methods included artificial substrates, square-foot bottom samplers, and kick sampling with dip nets. Individual organisms were identified to the lowest practical taxonomic level, usually to genus level.

A biotic index (Gore, Tennessee Technological University, written comm., 1980, modified from Hilsenhoff, 1977) computed for each site indicated a wide range of water quality within the area.

Biotic Index Sn_ia_i / N

where:

n_i is the number of individuals of a given taxon;

N is the total number of organisms collected;

a_i is computed by assigning a value of zero to organisms known to be found only in the cleanest streams and a value of five to organisms found in extremely polluted waters. Intermediate values are assigned as appropriate.

In the Biotic Index, water quality is rated on a scale of zero to five with lower values indicating better water quality. The categories defined are:

Biotic index                      Water-quality rating
< 1.75                                 excellent
1.75-2.25                              good
2.25-3.00                              fair
3.00-3.75                              poor
>3.75                                very poor

This index is presently based on data from streams known to be polluted by organic materials. Additional information concerning benthic invertebrate populations in streams draining coal-bearing rocks must be collected before the impact of mining practices can be defined.

Water quality for the sites in Area 19 as rated by the Biotic Index ranged from excellent (1.58) at Poplar Creek near Oak Ridge, Tenn., to poor (3.28) at Coal Creek at Lake City, Tenn. Water quality at the other sites in the area was rated fair.

Click here for partial view of Figure 5.10-1

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