These solids may come from soil erosion or
channelization from dredging. Increased water
flow rates erode stream banks and allow the
water to carry a heavier load of particles.Indicator Species
Indicator species are organisms whose presence, absence, or abundance reflect a
specific environmental condition. Indicator species can signal a change in the
biological condition of a particular ecosystem, and thus they may be used to
diagnose the health of an ecosystem. Examples of indicator species include:
■ Stoneflies (which indicate high oxygen water)
■ Mosses (which indicate acidic soil)
■ Lichens (some species of which indicate air pollution)
■ Mollusks (which indicate the water pollution status)
■ Tubifex (sludge) worms (which indicate undrinkable, stagnant, oxygen-
poor water)MAINTAINING WATER QUALITY—WATER PURIFICATION
Water quality refers to the chemical, physical, biological, and radiological
characteristics of water. The most common standards used to assess water
quality relate to the health of ecosystems, the safety of human contact, and the
purity of drinking water.
Drinking Water Treatment Methods
■ ABSORPTION—when one substance enters completely into another (e.g.,
think of people walking into and sitting down on a bus). An example is
using paper towels to soak up spilled oil.
■ ADSORPTION—when one substance just hangs onto the outside of another
(e.g., think of people holding onto a streetcar with one hand and leaning
off the side—they’re along for the ride, but not inside). An example is
contaminants that stick to the surface of granular or powdered charcoal.
■ DISINFECTION—using chemicals and/or cleansing techniques that destroy
or prevent the growth of organisms that are capable of infection.
Examples include chloramines, chlorine, chlorine dioxide, ozone, and UV
radiation.