Environmental Engineering Reference
In-Depth Information
Nitrogen in water in the form of nitrate (NO
3
) indicates that the water may
be contaminated with sewage. Nitrates can also enter the groundwater from
chemical fertilizers used in agricultural areas. Excessive nitrate concentra-
tions in drinking water pose an immediate health threat to infants, both
human and animal, and can cause death. The bacteria commonly found in
the intestinal tract of infants can convert nitrate to highly toxic nitrites (NO
2
),
which can replace oxygen in the bloodstream and result in oxygen starva-
tion, causing a bluish discoloration of the infant (“blue baby” syndrome).
Note:
Lakes and reservoirs usually have less than 2 mg/L of nitrate
measured as nitrogen. Higher nitrate levels are found in groundwater
ranging up to 20 mg/L, but much higher values are detected in shallow
aquifers polluted by sewage or excessive use of fertilizers.
Phosphorus is an essential nutrient that contributes to the growth of algae
and eutrophication of lakes, although its presence in drinking water has little
effect on health. In aquatic environments, phosphorus is found in the form of
phosphate and is a limiting nutrient. If all phosphorus is used up, plant growth
ceases, no matter the amount of nitrogen available. Many bodies of freshwa-
ter currently experience influxes of nitrogen and phosphorus from outside
sources. The increasing concentration of available phosphorus allows plants to
assimilate more nitrogen before the phosphorus is depleted. If sufficient phos-
phorus is available, high concentrations of nitrates will lead to phytoplankton
(algae) and macrophyte (aquatic plant) production. Major sources of phos-
phorus include phosphates in detergents, fertilizer and feedlot runoff, and
municipal wastewater discharges. The USEPA 1976 Water Quality Standards
recommended a phosphorus criterion of 0.10 µg/L (elemental) phosphorus for
marine and estuarine waters but established no freshwater criterion.
Summary
The biological, physical, and chemical condition of our water is of enormous
concern to us all, because we must live in such intimate contact with water.
When these parameters shift and change, these changes affect us, often in
ways science cannot yet define for us. Water pollution is an external element
that can and does significantly affect our water, but what exactly
is
water
pollution? We quickly learn that the sources of water pollution do not always
travel a direct path to water. Controlling what enters our water is difficult,
because the hydrologic cycle carries water (and whatever it picks up along
the way) through all of our environment's media, thus affecting the biologi-
cal, physical, and chemical condition of the water we must drink to live. We
discuss water pollution further in
Chapter 9
.
