Question

4. A lake with a cross-sectional area of 1 km2 and a depth of 50 m has a euphotic zone that extends 15 m below the surface. What is the maximum amount of the biomass that can be decomposed by aerobic bacteria in the water column of the lake below the euphotic zone during the summer when there is no circulation with the upper layer? The bacterial decomposition reaction is: (CH2O)n + n 02 →n CO2 + n H2O The solubility of oxygen in pure water saturated with air at 20°C is 8.9 mg L-4; 1 m3 = 1000 L. (answer in mol; 2 significant digits)

Answer 1

Ansue Gwen-that IKno O Cross-Sectional avCa ol lake euphotic 3one Depth 15m 16K lo Volune af euphotic one in lale 15 xlo0L Solubility el onggen in pure ter Saturated 8-q ng/ 20 C Wirth ai at Hars af oxygen dissol&ed in Uater = 8.9 xI'5X 1ooma a 1335x lomg 1-23.5 Y lo'3 Moles of oxygen dissolved 1335 los 3 2 9/m = 4121 X1ooles The bactevicl de lompo Sition reactionis CH20nto2-nCo2t hH20 Since,1 mole biomass is delamposed by wole oxyere Moles of biomass decoposed by 1 lo6moles Oxy gen 17x1o moles

Aoie a al C 12 g/mole Mass at biass de lopuse d lih gvans of bon) s 121Xto12 5.005 X10