(a) Assume that algae need carbon, nitrogen and phosphorous in the ratios 106:16
ID: 799093 • Letter: #
Question
(a) Assume that algae need carbon, nitrogen and phosphorous in the ratios 106:16:1.
What is the limiting nutrient in a lake that contains the following concentrations:
total C = 24mg/L, total N = 1.2 mg/L and total P = 0.15 mg/L?
(b) How can the use of detergents impact the nutrient availability in the lakes? Why is
phosphate used in detergents?
(c) If it is known that half the phosphorus in the lake (in part a) originates from the use
of phosphate detergents, will banning phosphate builders slow down eutrophication?
Explanation / Answer
C -> 24 mg/L => 24/12 = 2 m mole/L
As 'C' atomic weight is 12
N -> 1.2 mg/L => 1.2/14 = 0.086 m mole/L
As 'N' atomic weight is 14
P -> 0.15 mg/L => 0.15/31 = 0.0048 m mole/L
As 'P' atomic weight is 31
=> They are in ratio of 2:.086:0.0048 = 416.6 :17.9 :1 compared to 106:16:1
=>Both Carbon and Nitrogen are in excess to Phosphorus, So Phosphorus is the limiting nutrient.
It's like we have 20 batsmen,15 bowlers, 1 wicketkeeper. How many cricket teams can we form. Even though we have excess batsmen and bowlers we only have one keeper.So, we can only form one cricket team.
(A cricket team has 11 members)
b)
By adding Detergent we are increasing the concentration of Phosphorus which is deficient in the pond. So, we are increasing the nutrient availability in which Phosphorus in the form of Phosphate in the detergent is one of the nutrients.
With regard to cleaning uses, phosphates are used in automatic dish detergents and laundry detergents to help soften water and remove soil, oil, and grease.
c)
As phosphorus is the limiting nutrient, i.e., which is present in least amount comparatively. We already have excess nitrogen and Carbon. So by reducing Phosphorus we are reducing essential nutrients. So, yes reducing Phosphorus slows down eutrophication.
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