Water Quality Management - River Dynamics and Integrated River Management - page 548

9 Water Quality Management
Abstract
This chapter begins by describing some general water quality management problems and the definition
of pollution from environmental and economic perspectives. The chapter then focuses on four of the
major water pollution problems facing rivers throughout the world: dissolved oxygen (DO), nutrients,
waterborne and water contact diseases, and sediment contamination. The DO relations are described
through the simple Streeter-Phelps concept relating carbonaceous biochemical oxygen demand (BOD) to
DO and the extensions of this concept to nitrogeneous BOD, benthic processes, and photosynthesis and
respiration. Dispersion effects on BOD and DO are discussed and then the total, simplified DO balance is
presented. Dissolved oxygen standards and the linkage between these standards and habitat are presented.
Finally, remedial methods to improve low DO concentrations are discussed.
The discussion of nutrient problems includes eutrophication, methemoglobinemia, and ammonia toxicity
in addition to effects of nitrogen on DO previously discussed. Methods of nutrient control also are discussed.
The types of waterborne and water contact diseases are discussed. Because it is impractical to sample for
all the pathogens that causes these diseases the need for and types of indicator organisms then are discussed.
Simulation of indicator bacteria levels is presented, and microbial risk assessment is presented as an
alternative or complement to the use of indicator bacteria. Finally, disinfection methods are reviewed.
The discussion of sediment contamination focuses on the assessment of the sediment toxicity and the
remediation/cleanup methods applied to contaminated sediment. Throughout the chapter examples from
around the world are given to illustrate the fundamental problems.
Key Words
Water quality management, Dissolved oxygen, Nutrients, Waterborne diseases, Water contact diseases,
Sediment contamination
9.1 Water Quality and Pollution
The water quality problems of rivers throughout the world are extensive and complex, and it is difficult
to comprehensively describe all the problems in a single chapter. Nevertheless, this chapter strives to
provide a useful overview of key problems and management solutions. The discussion begins with the
definition of pollution and then focuses on the causes and solutions for low dissolved oxygen. The
chapter then discusses nutrient loads and related problems, such as eutrophication. Pathogens and public
health then are discussed. Finally, toxic pollutants and contaminated sediment are discussed. For more
information readers should consult the useful textbooks that comprehensively discuss water-quality
modeling and management, such as Thomann and Mueller (1987), Chapra (1997), or Novotny (2003).
9.1.1 Water Quality
High water quality in rivers is necessary for public health and ecosystems. Masters (1991) reports that
“Water dissolves more substances than any other common solvent. As a result, it serves as an effective
medium for both transporting dissolved nutrients to tissues and organs in living things as well as
eliminating their wastes. Water also transports dissolved substances throughout the biosphere.”
The ability of water to easily carry away wastes has been exploited by humans for many centuries as
the primary means of sanitation. However, as waste loads overwhelmed the ability of rivers and streams to
carry away and/or assimilate wastes, public health and ecosystem viability deteriorated. These problems