E coli and oxygen levels

[Robin Leech]

Hi fellow taxacomers,

I am assisting a student who is studying the E. coli levels in relation to water birds (geese, ducks, gulls, etc.) in an urban setting in Edmonton, Alberta.

The site was used for a triathalon event a couple of weeks ago, and will be used again next year for the same purpose during a major sporting event.  The E. coli count, for health safety reasons, has to be below 200, and should preferably be much lower than that.  Up to the last sampling before chlorine was added, there were several sites with counts between 220-340/mL

My student found a negative correlation between oxygen level decreases and E. coli count increases.  That is, as the oxygen levels decreased, the E. coli counts increased.

Is this result to be expected?  

Mean water temps during the course of the experiment were from 9.14C on May 16,  to 22C on July 10.  DO in ppm went from a mean of 8.43 on May 16,  to 7.77 on July 10.

Mean E. coli counts went from 81.43 on May 16, to 288.29 on July 10.

He also found in the areas where, because of wind activity (turn over cells?) or human activity (pedal boats, paddling), there was an increase when there was a mixing of surface and bottom waters.  Does this mean that ordinarily E. coli is found in lower counts at/near the water surface, and at higher counts on the bottom (water from 1-1.4 metres deep)?

We did not think to take synchronous bottom samples when we were taking our surface samples.  Because of the cost of analysis per sample, we tried to minimize the number of samples taken, and discussion about bottom samples did not enter the discussion.

Any comments much appreciated.

Robin Leech