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Willamette River
Columbia River
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Columbia River,  click link and see also lower  this page.

Willamette River, click  link and see also the following:

Willamette River, Benton County, Oregon                                                             

Above, Looking downstream

Left, Looking upstream, fallen log on right.

Left, clear water, broken rubble and stones, algal growth, and some debris cover stones.

    In July 2009, samples were taken in the Willamette River, Benton Co., Oregon, (above)  for comparison with July samples from the Saskatchewan River (Notes #3).   At Borden Bridge, Sask., 15 minutes of sampling yielded a diverse community including Odonata, Plecoptera, many kinds of Ephemeroptera, and some Trichoptera.  See pdf.

Borden Bridge july 2006 edited 09.pdf

The pdf shows detailed results from 2006, and the July 2009 samples were similar.
       In contrast,  very little was found in the Willamette River in July- -a total of about a dozen  individual specimens of Hydropsychidae, Baetidae, Heptageniidae, and Gammarids after 15 minutes of sampling.   The dozen or so specimens in the Willamette River contrast with the hundreds of individuals in samples from Saskatchewan in July. Sampling conditions were good in both places and the same methods were used.

     On a second sampling date in early August at Albany, Oregon, in the Willamette River, only two taxa  of mayflies and one caddis were collected, these being Tricorythodes, Heptagenia, and Brachycentrus, species names yet to be determined.
This individual of the genus Tricorythodes is only about two mm long.  The character that separates this genus from all others is the triangular abdominal gill, attached behind the hind leg.  See Ephemeroptera for comments and classification, and Keys for identification.

 The difference  in diversity between the Saskatchewan and Willamette Rivers in mid-summer is most certainly explained  by ecological conditions and climate- and not because of pollution or ecological disturbance.  My notebook graphs (below) from many years ago show that adults emerge in nearby Oak Creek in Benton County  from April to June, and there is almost no emergence in July.  This and other samples show that few or no immature stages are present in July. 
       More observations are needed, but it  seems that stream insects in Oregon avoid the hot weather  from July to Sept. and pass this period in the egg stage.   In  contrast in Saskatchewan, July to Sept. have the greatest diversity and abundance of larvae present in the river. In Saskatchewan  the pattern is to escape the cold months (October to March and April), and greatest activity is in the summer. 
      I commented on this adaptation to the very hot and dry summers with rainy winters in Oregon in an early paper:
Lehmkuhl D.M. 1973. Adaptations to a marine climate illustrated by Ephemeroptera.  In: Peters W.L. & Peters J.G. (eds). Proceedings of the 1st international conference on Ephemeroptera. E.J. Brill, Leiden: 33-38, 1 pl. See Oregon Winter  Ponds for related discussion.

marine climate.pdf

Mayfly emergence,  Benton County, Oregon, Oak Creek Tent Trap, all species
         March             April                     May                   June                  July 
       Few or no adults March     Many adults May, June                 Few or no adults July
Below, total emergence, all species
 Few or no adults March               Many adults May, June              Few or no adults July
  Water temperature minimum, 4 C February, High 19 late June.   
Columbia River
     We (with Rie Miyazaki) took samples in the Columba River in early  August 2009. The photos show the area and sampling conditions, and comments and results are given below.
Columbia River, view from Vista House, near (east of) Portland, Oregon
Boat ramp leading to Columbia RiverStones with algae
    We (Rie Miyazaki and I) have had lots of experience sampling in large rivers, and we collected for about half an hour at the site above, near Vista House.  Conditions were very good.  Substrates included rubble and broken stones, sand depositional areas, and branches and log wood substrates.  Current was not detectable as directional, but wave action created much turbulence over the substrates.

     In a half hour, no insects were found except Chironomid tubes.  Dozens of Gammarids could be collected in the rubble pictured above, and several leeches, not identified, were also collected.  Green filamenous algae was present in small quantities on the rocks.

Further information and comments to follow: