Question

Organic tissue containing 0.2 moles of C is added to a 1000-liter sample of deep water from the North Pacific. The bacteria in the sample respond and consume the organic matter drawing on the oxygen in the sample (100 x 10^-6 moles/l). If we assume Redfield ratios:

A) Which will run out first C or O2?

B) How much CO2 will be produced?

C) How much NO3 and PO4 will be produced? Redfield ratio of C: N : P is given as, 106:16:1

D) After measuring the final concentration of NO3, you find these are lower than your estimates of how much NO3 was produced. What process may account for that difference?

Answer 1

(a) According to the Redfield Ratios,

Thus, Oxygen Demand= 0.2 x 1.35 = 0.27 moles

And, Oxygen Available= 1000 x 100 x 10^-6 = 0.1 moles

Hence, O₂ will run out before organic Carbon.

(b) Amount of CO₂ produced = = 74 x 10^-6 moles L^-1