Running Waters - Mathematics and Statistics for the Environment - page 558

water cycle, we continually reuse that same water; in fact, we are using water that was used by
the ancient Romans and Greeks. Increased demand has put enormous stress on our water sup-
ply. Humans are the cause of this stress, as we upset the delicate balance between pollution and
the purification process. Anyone who has kept fish knows what happens when the aquarium or
pond water becomes too fouled. In a sense, we tend to unbalance the aquarium for our own water
supplies.
With the advent of industrialization, local rivers and streams became deplorable cesspools that
worsened with time. During the Industrial Revolution, the removal of horse manure and garbage
from city streets became a pressing concern. Moran and colleagues (1986) pointed out that, “None
too frequently, garbage collectors cleaned the streets and dumped the refuse into the nearest river.”
As late as 1887, river keepers were employed full time to remove a constant flow of dead animals
from a river in London. Moreover, the prevailing attitude of that day was “I don't want it anymore,
throw it into the river” (Halsam, 1990).
Once we came to understand the dangers of unclean waters, any threat to the quality of water
destined for use for drinking and recreation has quickly angered those affected. Fortunately, since the
1970s we have moved to correct the stream pollution problem. Through scientific study and incorpora-
tion of wastewater treatment technology, we have started to restore streams to their natural condition.
Fortunately, through the phenomenon of self-purification, the stream aids us in this effort to
restore a steam's natural water quality. A balance of biological organisms is normal for all streams.
Clean, healthy streams have certain characteristics in common; for example, as mentioned, one
property of streams is their ability to dispose of small amounts of pollution. However, if streams
receive unusually large amounts of waste, the stream life will change and attempt to stabilize such
pollutants; that is, the biota will attempt to balance the aquarium. If the stream biota are not capable
of self-purifying, then the stream may become a lifeless body. This self-purification process relates
to the purification of organic matter only. In this chapter, we briefly discuss only organic stream
pollution and self-purification.
19.1.1 s ourCes oF s tream p ollution
Sources of stream pollution are normally classified as point or nonpoint sources. A point source
(PS) is a source that discharges effluent, such as wastewater from sewage treatment and industrial
plants. Simply put, a point source is usually easily identified as “end of the pipe” pollution; that is,
it emanates from a concentrated source or sources. In addition to organic pollution received from
the effluents of sewage treatment plants, other sources of organic pollution include runoffs and
dissolution of minerals throughout an area and are not from one or more concentrated sources.
Non-concentrated sources are known as nonpoint sources . Nonpoint source (NPS) pollution, unlike
pollution from industrial and sewage treatment plants, comes from many diffuse sources. Rainfall
or snowmelt moving over and through the ground causes NPS pollution. As the runoff moves, it
picks up and carries away natural and manmade pollutants, finally depositing them into streams,
lakes, wetlands, rivers, coastal waters, and even our underground sources of drinking water. Some
of these pollutants are listed below:
• Excess fertilizers, herbicides, and insecticides from agricultural lands and residential areas
• Oil, grease, and toxic chemicals from urban runoff and energy production
• Sediment from improperly managed construction sites, crop and forest lands, and eroding
streambanks
• Salt from irrigation practices and acid drainage from abandoned mines
• Bacteria and nutrients from livestock, pet wastes, and faulty septic systems
Atmospheric deposition and hydromodification are also sources of nonpoint source pollution
(USEPA, 1994).