Water Quality Management - River Dynamics and Integrated River Management - page 552

and agricultural waste discharged into water.” Included also are drinking water contaminants regulated
under the Safe Drinking Water Act. Further, under the definition of human-made or human-induced
alteration of the integrity of water any human action or alteration of a receiving water body that impairs
its integrity could be considered pollution. Under this definition, cutting down trees along rivers, which
increases temperature and impairs the habitat, straightening of channels and channel linings, hydraulic
modifications, and reducing low flows below tolerable levels by excessive withdrawals would be
pollution (Novotny, 2003, p. 27). Despite this broad definition of “pollution” this chapter focuses on the
following pollutants of concern:
¾ Suspended solids and their organic (volatile) content
¾ Biochemical Oxygen Demand (BOD)
¾ Chemical Oxygen Demand (COD)
¾ Pathogenic Microorganisms
¾ Nutrients (nitrogen and phosphorus)
¾ Toxic Compounds (both organic—PAHs & PCBs—and inorganic—metals and salts)
¾ Algae
Section 10.4 discusses stream restoration strategies that can be applied to remediate some of the habitat
modification forms of “pollution.”
9.2 Dissolved Oxygen
9.2.1 The Basic Dissolved Oxygen Problem
Dissolved oxygen (DO) is the primary constituent needed for healthy aquatic ecosystems. In nature, clean
waters are saturated with dissolved oxygen, or nearly so (Fair et al., 1971, p. 642). As DO concentrations
drop, fish and other aquatic life are threatened and, in the extreme case, killed. In addition, as DO
concentrations fall, undesirable odors, tastes, and colors reduce the acceptability of the water as a domestic
supply and reduce its attractiveness for recreational uses (Masters, 1991, p. 107). Thus, maintenance of
adequate DO concentrations is the key to the CWA's “fishable” requirement for water bodies. However,
because water contains only about 0.8% oxygen by volume at normal temperatures (10ÛC) the aquatic
environment is inherently and critically sensitive to the oxygen demands of the organisms that populate it
(Fair et al., 1971, p. 643). Thus, maintenance of adequate DO concentrations is a challenging problem.
Fair et al. (1971) provide an excellent summary of the life cycle of a discharge of biodegradable organic
waste and its effect on receiving rivers that is reproduced as follows:
(1) When a single, heavy charge of biodegradable organic waste is poured into a clean body of water,
the water becomes turbid, sunlight is shut out of the depths, and green plants, which by photosynthesis
remove carbon dioxide from the water and release oxygen die off.
(2) Scavenging organisms increase in number until they match the food supply. The intensity of their
life is mirrored in the intensity of the biochemical oxygen demand (BOD).
(3) The oxygen resources of the water are drawn upon heavily. In overloaded receiving waters the
supply of oxygen may become exhausted. Further, Masters (1991, p. 127) noted in extreme cases, when
anaerobic (without oxygen) conditions exist, most higher forms of life are killed or driven off, and
noxious conditions including floating sludges, bubbling, odorous gases, black water, and slimy fungal
growths, prevail.
(4) Nitrogen, carbon, sulfur, phosphorus, and other important nutritional elements run through their natural
cycles, and sequences of microbic populations break down ķ the waste matters that have been added,
ĸ the natural polluting substances already within or otherwise entering the water, and Ĺ the food made
available by the destruction of green plants and other organisms intolerant to pollution.