Water Resources and Water Pollution

Chapter 9


Water issues

•Water quantity

–Too much

–Too little

•Water quality


–Water treatment

Supply of Water Resources


•A watershed describes the total area contributing drainage to a stream or river

•May be applied to many scales

–A large watershed is made up of many small watersheds



Use of Water Resources

Humans use over half of reliable runoff





Could be 70-90% by 2025

Water conflicts

Water conflicts: Global

Too Much Water:  Floods

•Natural phenomena

•Aggravated by human activities


Deforestation and flooding


Pollution Source terminology

•Point source = pollution comes from single, fixed, often large identifiable sources

–smoke stacks

–discharge drains

–tanker spills

•Non-point source = pollution comes from dispersed sources

–atmospheric deposition

–agricultural runoff

–street runoff


Types of Water Pollutants
from Table 9-1 p. 187

•Oxygen-demanding wastes

–human waste, storm sewers, runoff from agriculture, grazing and logging, many others

•Nutrient enrichment = Eutrophication

–N, P from fertilizers, detergents, atmospheric pollution

–leads to increased growth in aquatic systems, ultimately more non-living organic matter

•Elevated temperatures = Thermal Pollution

–water is used for cooling purposes, then heated water is returned to its original source

–any increase in temperature, even a few degrees, may significantly alter some aquatic ecosystems.

These three categories all contribute to BOD


•As micro-organisms decompose (through respiration) organic matter, they use up all the available oxygen.

•Biological Oxygen Demand (BOD) Amount of oxygen required to decay a certain amount of organic matter.

•If too much organic matter is added, the available oxygen supplies will be used up.



BOD and dissolved oxygen in a stream


•Eutrophic – well-fed, high nutrient levels present in a lake or river


•Oligotrophic – poorly-fed, low nutrient levels


•Water bodies can be naturally eutrophic or oligotrophic, but cultural eutrophication is human-caused



Dead Zone in the Gulf of Mexico

Types of Water Pollutants (con’t)
from Table 9-1 p. 187

•Infectious agents

–bacteria, viruses, protozoa

–from untreated sewage, runoff from feed lots

•Inorganic chemicals

–metals (lead, mercury, arsenic, selenium)



•Organic chemicals

–petroleum products, pesticides, fertilizers, industrial chemicals


–logging, roadbuilding, erosion

Oil Spills

•Exxon Valdez released 42 million liters of oil in Prince William Sound, contaminating 1500 km of Alaska coastline in 1989

•Was the cleanup effective?

•Most marine oil pollution comes from non-point sources:

–runoff from streets

–improper disposal of used oil

–discharge of oil-contaminated ballast water from tankers


Technological Approach:  Sewage Treatment

•Physical and biological treatment for organic wastes

•Disinfection by chlorine, ozone or UV radiation

•Physical and chemical processes to remove N & P

Septic Systems

•Septic tanks and various levels of sewage treatment can reduce point-source water pollution.

Storm-water treatment

•Storm-water runoff from streets is sometimes combined with wastewater systems.

–Combined in Olympia, Chehalis

–Untreated in Centralia

•Heavy rains lead to volumes too high to manage, discharged without treatment

•Storm-water may contain

–organic matter, chemical residues from streets, anything dumped accidentally or intentionally into storm sewers.


Drinking water treatment

•Add aluminum sulfate to cause suspended particles to settle out

•Filter through sand

•(Optional) pump through activated charcoal to remove organic compounds

•Disinfection - chlorine, UV radiation or ozone

–Link between chlorine and cancer caused Peru to stop chlorination in 1991.  Resulted in a cholera epidemic:

•300,000 people sick, 3500 dead.

–Milwaukee 1993 Crytosporidium outbreak

•370,000 people sick.

Is Bottled Water the Answer?

Is Bottled Water the Answer?

•Some bottled water is not as pure as tap water and costs much more.

•1.4 million metric tons of plastic bottles are thrown away.

•Fossil fuels are used to make plastic bottles.

–The oil used to produce plastic bottles in the U.S. each year would fuel 100,000 cars.