Trong điều kiện của tính hữu dụng thực tế, khả năng đồng hóa chất thải của các dòng như là một nguồn tài nguyên nước có cơ sở của nó trong hiện tượng phức tạp được gọi là dòng tự thanh lọc. Đây là một hiện tượng năng động phản ánh thủy văn và biến đổi sinh học, và các mối tương quan này vẫn chưa được hiểu theo thuật ngữ chính xác. Tuy nhiên, điều này không loại trừ việc áp dụng những gì được biết. Đầy đủ kiến thức có sẵn để cho phép định nghĩa định lượng. | Part IV Math Concepts Water Quality 2005 by CRC Press LLC Chapter 11 Running Waters In terms of practical usefulness the waste assimilation capacity of streams as a water resource has its basis in the complex phenomenon termed stream self-purification. This is a dynamic phenomenon reflecting hydrologic and biologic variations and the interrelations are not yet fully understood in precise terms. However this does not preclude applying what is known. Sufficient knowledge is available to permit quantitative definition of resultant stream conditions under expected ranges of variation to serve as practical guides in decisions dealing with water resource use development and management. . Velz 1970 balancing the AQUARIUM An outdoor excursion to the local stream can be a relaxing and enjoyable undertaking. However when the wayfarer arrives at the local stream spreads a blanket on its bank and then looks out upon its flowing mass only to discover a parade of waste and discarded rubble bobbing along and cluttering the adjacent shoreline and downstream areas he quickly loses any feeling of relaxation or enjoyment. The sickening sensation the observer feels increases as he closely scrutinizes the putrid flow. He recognizes the rainbow-colored shimmer of an oil slick interrupted here and there by dead fish and floating refuse and the prevailing slimy fungal growth. At the same time the observer s sense of smell is alerted to the noxious conditions. Along with the fouled water and the stench of rot-filled air the observer notices the ultimate insult and tragedy signs warning DANGER NO SWIMMING or FISHING. The observer soon realizes that the stream before him is not a stream at all it has become little more than an unsightly drainage ditch. He has discovered what ecologists have known and warned about for years contrary to popular belief rivers and streams do not have an infinite capacity for pollution Spellman 1996 . Before the early 1970s occurrences such as the one .
