Wastewater with a nitrogen/phosphorus (N/P) ratio of 8 by atoms is being dischar
ID: 236941 • Letter: W
Question
Wastewater with a nitrogen/phosphorus (N/P) ratio of 8 by atoms is being discharged into a lake. The N/P ratio of the algae in the lake is 16 by atoms. Assume that the wastewater is the only significant source of nitrogen and phosphorus for the lake and that either N or P limits algal biomass in the lake. What will happen to the algal biomass in the lake if 2.5 The N in the wastewater is reduced by a factor of 10? a) No change b) Reduced by a factor of 2 c) Reduced by a factor of 5 d) Reduced by a factor of 10
Explanation / Answer
The relative concentrations of N-P have been traditionally used to estimate the limiting agent for the growth of algae in aquatic systems. The eutrophication of aquatic bodies is usually the result of excessive supply of nutrient material on which the algae forms thrive on. In fresh waters, P is assumed as the nutrient that is least present, hence is considered as the limiting agent for the growth of algal biomass. Whereas in marine environment, the supply of N is considered as the limiting agent for the growth of algal biomass.
Coming to our question, it is discussed about a discharge into a lake. Lake is a fresh water body in which Nitrogen fixing cyanobacteria exist in large quantities, hence there is always an excess supply of Nitrogen into the aquatic system. Well in case of a marine environment like a sea, these bacteria are always washed away with waves or currents so there is low Nitrogen in marine waters.
Which brings to the conclusion that, the amount of algal biomass in a fresh water system like a lake is defined by the amount of Phosphorus influx into the lake. Hence, if the N in the waste water is reduced by a factor of 10, a) No change in the amount of the algal biomass.
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