1. Dissolved Oxygen –The distribution and dynamics of dissolved oxygen are important in aquatic systems because it controls the distribution, behavior, physiology, and growth of organisms. –sources of O 2 : atmosphere & photosynthesis –sinks: respiration & chemical oxidation

2. Properties of O 2 atmosphere ~ 21% O 2 ; ~ 79% N 2 oxygen is more soluble in water than nitrogen solubility increases as temperature decreases equilibrium concentration increases with pressure solubility declines exponentially with increased salinity

3. Dimixis in Mountain Lake, Virginia A.spring turnover B. spring stratification C. summer stratification D. fall turnover E. inverse stratification under winter ice

4. Distribution of O 2 in Lakes orthograde O 2 profile 1.oligotrophic lakes: low nutrients & productivity 2.O 2 regulated by physical means e.g. spring mixing 3.100% saturation with depth

5. clinograde O 2 profile 1.eutrophic lakes: high nutrients & productivity 2.loss of O 2 through biological oxidation of organic matter 3.hypolimnetic O 2 depleted after summer stratification

6. metalimnetic O 2 maxima & minima Phytoplankton Zooplankton