Water Pollution 77effects of certain pollutants, but lakes, bays, ponds, sluggish rivers, and oceans
have little resistance to the effects of water pollution. We have a long history of
introducing pollutants into aquatic environments, and have had only partial suc-
cess at repairing the damage that has already been done and curbing the activities
that result in environmental degradation. Nonpoint source pollution continues to
be a serious threat to receiving waters, as does the continued release of sewage
and industrial effluents throughout the world. As we have seen with mercury
contamination in fishes, environmental pollution can have widespread and lasting
consequences.
PROBLEMS4.1 Some researchers have suggested that the empirical analysis of some
algae gives it the chemical composition C106H181045N16P. Suppose that analysis
of lake water yields the following: C = 62 mfl, N = 1 .O mfl, P = 0.01 mfl.
Which element would be the limiting nutrient for the growth of algae in this
lake?
4.2 A stream feeding a lake has an average flow of 1 ft3/s and a phosphate con-
centration of 10 mgL. The water leaving the lake has a phosphate concentration of
5 mgL.
a. What weight of phosphate is deposited in the lake each year?
b. Where does this phosphorus go, since the outflow concentration is less than
c. Would the average phosphate concentration be higher near the surface of thed. Would you expect eutrophication of the lake to be accelerated? Why?
4.3 The following water quality data were collected at two stream sites. What canthe inflow concentration?lake or near the bottom?you say about the conditions at each site?
Dissolved oxygen Ammonia Phosphorus
(mgn) (mgn) ( mfl)Site (^1) 1.8 1.5 15
Site 2 12.5 tO.O1 tO.O1
4.4 Show how the compound thiodiazine - C21H26N2S2 - decomposes anaer-
obically and how these end products in turn decompose aerobically to stabilized sulfur
and nitrogen compounds.
4.5 If an industrial plant discharges an effluent with a solids concentration
of 5,OOOlb/day, and if each person contributes 0.21b/day, what is the population
equivalent of the waste?