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Effects of Suction‐Dredge Gold Mining on Benthic Invertebrates in a Northern California Stream
Author(s) -
Somer William L.,
Hassler Thomas J.
Publication year - 1992
Publication title -
north american journal of fisheries management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.587
H-Index - 72
eISSN - 1548-8675
pISSN - 0275-5947
DOI - 10.1577/1548-8675(1992)012<0244:eosdgm>2.3.co;2
Subject(s) - dredging , benthic zone , canyon , invertebrate , hydrology (agriculture) , sediment , oceanography , cobble , environmental science , tributary , sedimentation , fishery , ecology , geology , habitat , geography , biology , paleontology , geotechnical engineering , cartography , geomorphology
The effects on benthic invertebrates of mining with two suction dredges were investigated in 1983 by using artificial‐substrate samplers in Big East Fork Creek, a tributary to Canyon Creek in northern California. The samplers were placed in Big East Fork Creek above and below the dredge site and in Canyon Creek above and below the confluence of Big East Fork Creek. The effects of dredging on invertebrates varied with taxa and were site‐specific at the level of dredging during the study. Total numbers of invertebrates that colonized samplers and their diversity indices did not differ significantly between Big East Fork and Canyon creeks or above and below dredges in either creek. Numbers of invertebrates peaked earlier in samplers below the dredges. In Big East Fork Creek, shredders were more abundant above than below dredges, whereas gatherers were more abundant below dredges. Filterers rapidly colonized samplers below dredges and were later displaced by siltation. Shredders were more abundant above dredges in Big East Fork Creek and less abundant above dredges in Canyon Creek. Sediment and organic matter fractions in samplers were higher below than above the dredges. Habitat variables (water depth and velocity, organic matter, sediment) accounted for 17–75% of the variation observed in abundance of common taxa. In drift samples, numbers of gatherers were higher below than above dredging sites; numbers of other functional feeding groups were similar. Sedimentation rates in Big East Fork Creek were higher below than above the dredging sites. Sedimentation rates in Canyon Creek were similar above and below Big East Fork Creek. High water flows and bed‐load movement in winter filled dredge holes and flushed sediment from the study site.