Environmental Microbiology of Aquatic and Waste Systems

6 1 Nature, Properties, and Distribution of Water

temperature, and if it becomes colder it will rise
instead. This reversal causes deep water to remain
warmer than shallower freezing water. Because of this,
ice in a body of water will form first at the surface and
progress downward, while the majority of the water
underneath will hold a constant 4°C. This effectively
insulates a lake floor from the cold in temperate climates
(see Table 1.2).

1.1.6 The Low Electrical Conductivity

of Pure Water

Pure water has a low electrical conductivity, but this

increases significantly upon solvation of a small

amount of ionic material water such as hydrogen

chloride. Thus the risks of electrocution are much

greater in water with impurities than in waters in which

Condensation

Condensation

Condensation

Sublimation

Snow

Snow &

Glaciers

Melt

Runoff

Rain

Rain

Lake

Soil Moisture

Soil Moisture

Groundwater

Groundwater

Groundwater Flow

Evaporation

Percolation

Vegetation

Stream Streamflow

Evapotranspiration

InfiltrationOverland Flow

Advection

Advection

Ocean

Fig. 1.4 The hydrologic cycle (Copyright Michael Pidwirny; http://www.our-planet-earth.net. Reproduced with permission (Pidwirny
2006 ))

Table 1.1 Some properties of liquid water and their consequences on the environment (Modified from Sigee 2005 )

S/no Property Comparison with other substances Importance to environment
1 Density Maximum density at 4°C, not at
freezing; expands at freezing
(both are unusual properties)

In lakes prevents freezing and causes seasonal

stratification

2 Melting and boiling
points

Abnormally high Permits water to exist as liquid at earth’s surface;
moderates temperatures by preventing extremes
3 Heat capacity Highest of any liquid, except ammonia Permits only gradual changes in climatic
temperatures
4 Heat of vaporization One of the highest known Important in heat transfer atmosphere and in
oceans; and moderates temperatures by
preventing extremes
5 Surface tension Very high Regulates drop formation in clouds and rain
6 Absorption of radiation Large in infra-red and ultra-violet
regions; little in visible light area

Important in control of photosynthesis in water
bodies, and in the control of atmospheric
temperature
7 Solvent properties Excellent solvent for ionic salts and
polar molecules because of bipolar nature

Important in transfer of dissolved materials in

hydrological systems and biological entities