Pollution of Water Resources from Agricultural Fields and Its Control - Practices of Irrigation and On-farm Water Management - page 244

Nitrate contamination of groundwater is considered one of the most serious prob-
lems worldwide because of its diffuse type and the difficulties in its control and
management. There are several sources of nitrogen (N) in soil, including on-site
domestic waste disposal systems (e.g., septic tanks and cesspools), dairies, animal
feedlots, and irrigation with sewage effluent. The main source of nitrate contami-
nation is agriculture, especially the intensive application of nitrogen fertilizers. A
survey of wells constructed by the “U.S. Geological Survey” Department in 1985
found that more than 10% of the 2732 wells sampled in California were con-
taminated by nitrates at concentration of the Federal drinking water standard of
10 mg/l nitrate-nitrogen (nitrate-N) ( USGS, 1985 ) . Pollutants from municipal and
industrial waste water include chloride (Cl -1 ), lead (Pb), cadmium (Cd), zinc (Zn),
molybdenum (Mo), cobalt (Co), etc.
7.3.2 Some Relevant Terminologies
Contaminant/pollutant : The substance that makes pollution/contamination is
called contaminant/pollutant.
Contamination/pollution : Generally, the presence of any undesired
substance(s) in an environmental component makes that component
polluted/contaminated. Scientifically, the presence of any undesired
substance(s) in any environmental component in amount(s) more
than its recommended/permissible limit makes that component pol-
luted/contaminated. The process or activity that renders the environmental
component polluted/contaminated is called environmental pollution.
Environment : Environment of an individual is everything surrounding the same
individual and their inter- and intra-relationship. For example, a man's envi-
ronment is everything around the man. Among biotic components (i.e., all
living beings) are animals, plants, microbes etc.; and among abiotic com-
ponents (i.e., all physical entries) are air, water, food, weather, etc.; and the
relationship between /among the components.
Maximum permissible limit : “Maximum permissible limit” is the concentration
of a pollutant (normally expressed in mg/kg or ppm) in a substance or envi-
ronment (such as drinking water, air, food commodities, animal feed) to be
legally permitted by the national authority.
Persistent pollutants : The pollutants which persist or exist in the environment
for a long time. This type of pollutant degrades very slowly. They have long
half-life. Half-life is the time span within which the pollutant will degrade
by 50%.
7.3.3 Factors Affecting Solute Contamination
The initiation of irrigation may result in large quantities of water moving through
the soil profile. Concerns about subsurface water quality grow as more water moves