Digital Signal Processing Reference
In-Depth Information
evaporation. To maintain the productivity of irrigated lands, accumulated salts must be leached below
the root zone. For this reason, irrigation is always scheduled to exceed the anticipated crop
consumption.
Trace Elements
Unlike nutrients and salts, trace elements typically do not originate from agricultural chemical
applications. Rather, irrigation mobilizes naturally present trace elements. Trace elements are found at
very low concentrations in all waters. Many trace elements are
at a low concentration
essential for
human, animal, and plant health. At higher concentrations, however, they may become toxic to
organisms. Trace elements may be mobilized in high concentrations along with other salts from
marine sediments or soils with a naturally high salt content. They dissolve in percolating drainage
water or groundwater and are discharged into wells or drainages, or in seepage into streams and lakes.
The principal impact of trace element pollution is its adverse impact on animal life through
biomagnification (the concentration of an element as it moves up the food chain) and on the
degradation of water quality when used for human consumption. Trace elements of concern to
irrigated agriculture include selenium, molybdenum, arsenic, vanadium, and boron. The water quality
control requirements for trace elements are stringent and water quality objectives are usually
prescribed in parts per billion. Because of its ability to impact beneficial uses of water at very low
levels, the control of trace elements is complex and difficult. Trace element pollution must be
examined on a case-by-case basis.
Pathogens
Pathogens are microorganisms and parasites that can cause illness in humans and in animals. A small
subset of all pathogens, the
zoonotic pathogens,
are shed in the faeces of livestock and many wildlife
species and can infect other animals as well as humans. These include
Salmonella, Giardia,
and
Cryptosporidium parvum,
and are the pathogens that cause concern with regard to food safety and
water quality. The potential for pollution of surface waters increases when flows resulting from
irrigation or rainfall come from land that has received untreated human or animal waste or when
irrigation water contains animal manure. Localized contamination of surface water, groundwater, and
the soil itself can result from animals in feedlots, corrals, exercise yards, pastures, and rangelands.
Other non-point sources of pathogens include septic tanks. The extent and concentration of pathogens
in surface water depends largely on livestock density, timing and frequency of grazing, and access to
streams and lakes. Pollution can occur when the daily rate of faecal deposition exceeds the ability of
vegetated buffers, soil, and solar radiation (sunshine) to either filter out or inactivate the pathogenic
microorganisms. Fecal coliform levels tend to increase as the intensity of livestock use increases.
Maintaining the health of livestock is critical, as is proper management of the herd, its byproducts, and
exposed land areas.
Temperature
Thermal pollution of surface waters has three basic sources that relate to irrig\ated agriculture:
streamside vegetation that shades streams and helps to maintain the cool water temperatures required
by many cold water fishes, especially trout, salmon, and steelhead.
a cold-water stream.
stream flows.
Water Quality Main Parameters
Water quality is generally described according to biological, chemical and physical properties.
Physical variables of water pollution include; color, temperature odor, total dissolved solids,
suspended solids and turbidity. Biological pollutants include; bacteria (Faecal coliforms Total
coliforms), viruses, parasites, algae. Chemical water quality variables include; nitrogen (e.g. nitrate,
nitrite, ammonia), phosphorus dissolved oxygen (DO), pH (acidity, alkalinity), major ions (e.g. Ca++,
Na+, Cl-), pesticides (e.g. herbicides, insecticides, fungicides), heavy metals and toxic constituents,
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