ABSTRACT
Water pollution results from a great variety of causes, includes complex changes in receiving waters, and affects subsequent water uses in numerous rather subtle, as well as obvious, ways. Conservative pollutants are not altered by the biological processes that occur in natural waters. Nonconservative pollutants are substances that are changed in form and/or reduced in quantity by the biological, chemical, and physical phenomena characteristic of natural waters. A measure of organic pollution load is Biochemical Oxygen Demand (BOD), which indicates the rate at which dissolved oxygen is drawn upon in a stream. The low, or critical, point on the oxygen sag is the focus of attention when sewage treatment plants are designed. Radiological pollution is somewhat in the same class as the "persistent" organics with respect to the conservative-nonconservative classification. Bacterial pollution, along with the degradable organics, has been the major focus of pollution control policy. Sediment pollution which is of major significance in some basins, results from land erosion.
