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Evaluation of Primary Production and Trophic State in Lake Erie

We determined the concentration and isotopic composition of dissolved O2 at 4 stations during 3 cruises in Lake Erie in 2  2 to evaluate variation in trophic state and primary production.  In the western basin in July, low isotope values near ?6.  ?, and O2 saturation of 12 % were strongly indicative of a period of high primary production.  High isotope values, > 7.  ?, at depths greater than 35 m in the eastern basin were consistent with a strong predominance of respiration.  Ratios of respiration to photosynthesis (R:P) were calculated from O2 concentration and isotope values.  R:P provides a measure of trophic state and is an indication of the flux of CO2 between the lake and atmosphere.  R:P values varied from as low as  .45, consistent with eutrophic conditions, to values as high as 3.49, indicating regions and times of strong heterotrophy.  These results indicate that the trophic state of Lake Erie fluctuates markedly on seasonal and spatial scales and has a strong tendency for eutrophic conditions to predominate.

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Surveillance and Monitoring
Annex 17
Physical and transformational processes affecting delivery of pollutants

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