Reading: Chapter 8.

Homework:  Due 4/30/2013

Consider a lake of infinite horizontal dimension, a depth of 20 meters, and a thermocline at 10 meters.  The epilimnetic temperature is 25 oC.    The hypolimnetic temperature is 6oC.   Both layers are well mixed vertically.  The alkalinity of the lake is 0.10 mM.   The hypolimnion volume is 10% of the epilimnetic volume. Draw a sketch of the lake and use it to answer the questions below.

1) Calculate the equilibrium concentration of oxygen at depths of 5 and 15 meters in units of ppm and moles/liter.

2) Lakes in Maine tend to bloom when the dissolved phosphorus in the springtime is above 12 ppb (as P).   Assume that all of 12 ppb P is converted to biomass in the epilimnion.  What fraction of the epilimnetic biomass is required to reduce the oxygen in the deep water to below 1 ppm?

3) If bacterial oxidation of the deep biomass is complete, what is the phosphourus concentration in the deep water just before the fall overturn?

4) Qualitatively, will the pH of the deep water increase or decrease over the course of the summer?

Resources:  CH217-Geochem2-2012Carbonate Constants 2012, Belgrade Lakes Project

Review for the second exam – CH217 Exam II 2010


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