Dames & Moore, 1999 - USDA Forest Service

without scrapers and organisms requiring a clean upper stone surface and without
organisms requiring large interstitial spaces for hiding. The organisms found within these
affected communities are those that feed by collecting detrital materials, burrow in the
substrate and require small interstitial space. The numbers of these organisms are
generally reduced downstream from RC-9, in comparison with the Railroad Creek
reference stations. The prevalence of the iron oxyhydroxide precipitate on and in the
substrate has influenced the substrate downstream from RC-9 by infilling the interstitial
spaces and coating the surface of the substrate which generally limits the establishment of
periphyton. The benthic macroinvertebrates inhabiting the stations downstream from
RC-9 will expend more energy in burrowing in the affected substrate because of its finer
and more compact nature. In addition, these organisms will have to ingest a larger
quantity of sediment, because the sediments contain a quantity of metal hydroxides that
do not occur in native sediment, to obtain an adequate amount of fine organic matter.
The fine organic detritus is the food source for these organisms and will be more dilute in
the sediments than would otherwise occur because of the addition of the metal
hydroxides. Therefore, the basic principles of bioenergetics would indicate that these
organisms expend more energy to live in the substrate and to ingest and pass this added
amount of material through their digestive tract than the same organisms in unaffected
areas of the stream.
It is noted that at sampling stations RC-7 and RC-9 a total of three new genera are found
that do not occur at any other site sampled. These genera are the Plecopteran Leuctra sp.
found at RC-7 and the Plecopteran Kathroperla sp. and the Dipteran Oreogeton sp. found
at RC-9. The organisms are detrital feeding organisms that generally live the substrate.
The new Plecopteran genera, as members of the Ephemeroptera, Plecoptera, and
Trichoptera group of pollution sensitive organisms, are generally considered pollution
sensitive (EPA, 1989), and are so likely represented because of the alteration in habitat.
It is also interesting to note that the filter feeders are variously present throughout Railroad
Creek. ~ilter feeding insects are generally considered to be sensitive to compounds of
concern in the water column because of their necessary greater exposure to water
containing compounds of concern. That is, they must position themselves in the flow of the
stream for their food capturing nets to work efficiently.
Sampling station RC-3 demonstrates a level of recovery from habitat effects because the
benthic community is largely restored in composition.
Com~arison With Recent Data Collected by Others
The review of the ;uly 1997 report by Washington State Department of Ecology (Ecology), Eflects of the
Holden Mine on Water, Sediments and Benthic Invertebrates of Railroad Creek (Lake Chelan), Publication
No. 97-330 disclosed the following:
The report describes work conducted in June and September 1996. The June effort was a
reconnaissance and'water sampling event. The September sampling included the sampling
of water, sediment and benthic invertebrates.
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17693-005-019Uuly 19.1999:4:5 1 PM;DRAFT FINAL RI REPORT