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Scientific Investigations Report 2012–5017


Geomorphic Setting, Aquatic Habitat, and Water-Quality Conditions of the Molalla River, Oregon, 2009–10


Table 13. Diatom indicator species (guilds) in the Molalla River, Oregon, July and August 2010.


[Percent relative abundance for each periphyton guild. Guild information from Porter (2008). Replicate samples from Goods Bridge in August were averaged. Bahls’ pollution tolerance from Bahls (1993)]


Date Site Abundance
expression
(percent)
Nutrients   Oxygen and pH   Lange-Bertalot
pollution tolerance
  Bahls’ pollution
tolerance
(Low)
Oligotrophic
(High)
Eutrophic
High
dissolved
oxygen
Low-
moderate
dissolved
oxygen
High
pH
Less
tolerant
Tolerant-
very tolerant
Pollution
sensitive
Pollution
tolerant
July 30, 2010 Molalla River at Glen Avon Bridge Biovolume 14 68   75 25 61   80 20   70 0.0
  Molalla River at Highway 211   9.1 78 76 24 89 77 23 70 0.0
  Molalla River at Highway 213   7.0 89 39 51 90 49 51 45 0.0
  Molalla River at Goods Bridge   8.4 88 80 0.3 74 99 0.3 88 0.0
  Molalla River downstream of Knights Bridge   7.4 64 43 56 62 49 50 42 0.0
  Molalla River at Glen Avon Bridge Density 41 38 94 6.3 18 98 2.2 85 0.0
  Molalla River at Highway 211   37 51 90 10 42 93 7.8 76 0.0
  Molalla River at Highway 213   31 62 78 21 38 78 20 68 0.0
  Molalla River at Goods Bridge   44 44 98 1.0 20 98 1.0 85 0.0
  Molalla River downstream of Knights Bridge   19 57 68 29 27 82 17 69 0.0
Aug. 15, 2010 Molalla River at Glen Avon Bridge Biovolume 14 62   76 24 59   94 6.3   60 0.3
  Molalla River at Highway 211   7.3 77 45 40 69 59 37 48 0.0
  Molalla River at Highway 213   11 57 79 20 63 75 20 68 0.0
  Molalla River at Goods Bridge   26 39 77 23 45 74 25 59 0.2
  Molalla R. downstream of Knights Bridge   13 49 89 11 40 83 17 65 0.5
  Molalla River at Glen Avon Bridge Density 27 55 76 23 37 91 8.6 65 0.8
  Molalla River at Highway 211   28 56 80 19 27 82 14 67 0.0
  Molalla River at Highway 213   22 59 82 16 21 76 13 74 0.0
  Molalla River at Goods Bridge   47 31 92 7.0 18 93 5.6 79 0.7
  Molalla River downstream of Knights Bridge   41 21 94 6.0 14 92 7.7 77 0.8
Averages July Biovolume 9 77   63 31 75   71 29   63 0.0
  August   14 57   73 24 55   77 21   60 0.2
  July Density 35 50   85 14 29   90 10   76 0.0
  August   33 44   85 14 23   87 10   72 0.5
Overall averages   23 57   76 21 46   81 17   68 0.2

First posted February 29, 2012

For additional information contact:
Director, Oregon Water Science Center
U.S. Geological Survey
2130 SW 5th Avenue
Portland, Oregon 97201
http://or.water.usgs.gov

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