QUALITY OF WATER Water Source

It is necessary to conduct the physical and chemical analysis of the water before de-signing a drip irrigation system and choosing an appropriate filtration system [12].

For the chemical analysis, it is important to take a representative sample of the water.

If the water source is subsurface (e.g., deep well), the sample must be taken an hour and a half after the pump begins to work. When the water source is from a lake, river, pool, or open channel, the samples must be taken at the surface, at the center, and at the bottom of a water source.

It is important to analyze the sample for suspended solids, dissolved solids and the acidity (pH), macro organisms, and microorganisms [5]. The acidity of the water must be known, since it is a factor that affects the “chemigation directly” and therefore the chloration. For example, the chloration for the control of bacteria is ineffective for a pH > 7.5. Therefore, it is necessary to add acid to lower the pH of irrigation water and to optimize the biocide action of the chlorine compound. If a chemical analysis of the water is known, we can predict the obstruction problems and take suitable measures. In addition, a program of adequate service and maintenance can be developed. The physi-cal, chemiphysi-cal, and biological agents are classified in Table 9.1. The factors are classified in order of the risk: from low to severe. When the water contains amount of solids, salts, and bacteria within the acceptable limits, then the risk of clogging is reduced.

Also the particles of organic matter can combine with bacteria and produce a type of obstruction that cannot be controlled with filtration system. The fine particles of or-ganic matter are deposited within the emitters and are cemented with bacteria such as:

Pseudomonas and Enterobacter. This combined mass causes clogging of the emitters.

This problem can be controlled with super chloration at the rate of 1000 ppm (mg/L).

However, the chloration at these high rates can cause toxicity of a crop. The obstruc-tion caused by the biological agents constitutes a serious problem in the drip irrigaobstruc-tion system that contains organic sediments with iron or hydrogen sulfide. Generally, the obstruction is not a serious problem if the water does not have organic carbon, which is a power source for the bacteria [Promotes the bacterial growth]. There are several organisms that increase the probability of the obstructions when there are ions of iron (Fe⁺⁺) or sulfur (S^--).

Table 9.1. Water quality: Criteria that indicates risk of obstruction of the emitters.

Type of Problem Risk of Obstruction

Low Moderate Severe

**Maximum concentration of the representative sample of water. Given in ppm (mg/L).

*Maximum number of bacteria per milliliter. Obtained from field samples and laboratory analysis.

Algae in surface water can add carbon to the system. The slime can grow on the inner surface of the pipes. The combination of fertilizer and the heating of the poly-ethylene pipes (black) due to sunlight can promote the formation and development of these microorganisms. Many of the water sources contain carbonates and bicarbonates that serve like an inorganic power source to promote slime growth; also autotrophic bacteria (that synthesize their own food) are developed. The algae and the fungi are de-veloped in the surface waters. Besides obstructing the emitters, the filamentous algae form a gelatinous substance in the pipes and emitters, which serve as a base for the de-velopment of slime. Another type of obstruction can also happen when the filamentous bacteria precipitate the iron into the insoluble iron compounds (Fe⁺⁺⁺).

Growth of Slime in the Drip Irrigation System

The bacteria can grow within the system in absence of light and produce a mass of the slime or cause the precipitation of the iron or sulfur dissolved in water. The slime can act like an adhesive substance that agglutinates fine clay particles sufficiently large enough to cause clogging [2, 10, 11].

Growth of Algae in the Water Source or in the Irrigation System

One of the most frequent problems is the growth of algae and other aquatic plants in the surface water that can be used for drip irrigation. The algae grow well in the sur-face water. The problem becomes serious if the water source contains nitrogen, phos-phorus, or both. In many cases, the algae can cause obstructions in the filtration sys-tem. When the screen filters are used, the algae can be entangled in the sieves (screen) of the filter. In high concentration, these aquatic microorganisms can create problems in the sand filters. This requires a frequent flushing and cleaning of the filters.

Types of Algae

The main groups of organisms in surface water are classified like protists, plants, and animals. The protists include bacteria, fungi, protozoa, and algae. Algae are unicellular organisms or multicellular autotrophic and photosynthetic, and require organic com-pounds to reproduce. The major nutriments are carbon dioxide, nitrogen, and phos-phorus. The minor elements like iron, copper, and manganese are also important for the development of these organisms.

It is important to note that algae problems usually occur due to ponds being ne-glected. Often, people think you can simply “dig a hole” and then let the pond take care of itself. Unfortunately, this is not the case. Healthy ponds require proper aeration, bacterial treatments, and adequate pond weed management. The use of copper sulfate has NOT been recommended for algae control as research and field usages have shown a high potential for detrimental environmental effects. In certain waters, copper sulfate is quite toxic to fish and other organisms. Overuse of this product is common due to its short-term effectiveness. This can result in copper build-up in the sediments lead-ing to a sterile bottom, killlead-ing important beneficial bacteria, microorganisms, snails, and other beneficial “creatures.” Many large pond or lake owners are concerned about

“toxic algae.” Death and sickness to pets, livestock, wildlife, and even man have been attributed to the presence of certain algae, mostly blue–green forming species, in water supplies. Lethal substances produced by these algae are retained within the cells and released after death or are secreted from living cells. Many unattended farm ponds and other waters contain some of these toxic forms, posing a threat to human health and the environment. Medical case histories, biologist reports, and laboratory tests show some of the possible effects of toxic algae. A list complied by the U.S. Department of the Interior Federal Water Pollution Control Administration summarizes medical case histories of algal poisonings for a 120 year period. Exposure to and ingestion of algae caused a variety of “discomforts” including: skin rashes, headaches, nausea, vomiting, diarrhea, fever, muscular pains, and eye, nose, and throat irritation. California State Water Resources Control Board states in the Water Quality Criteria Handbook (Sec-ond Edition): “There have been reports of rapid deaths of a great variety of animals after drinking water containing high concentrations of blue–green algae such as Mi-crocystis, Aphanizomenon, Nostoc rivulare, Nodularia, Gleotrichia, Gomphosphaeria, and Anabaena. Fatal poisonings have occurred among cattle, pigs, sheep, dogs, horses, turkeys, ducks, geese, and chickens. It is believed that such algae may be toxic to all warm-blooded animals.” To find out how one can avoid algae problems in large bodies of water and create a healthier pond, please read an article from: http://www.pondsolu-tions.com/blue-green-algae.htm

Algae are primitive plants closely related to fungi (Figure 9.1). These exhibit no true leaves, stems, or root systems and reproduce by means of spores, cell division, or fragmentation. These “live” from excess nutrients in the water and sunlight for growth. Over 17,400 species of algae have been identified and thousands more prob-ably exist. The simplest algae are single cells (e.g., the diatoms); the more complex forms consist of many cells grouped in a spherical colony (e.g., Volvox), in a ribbon like filament (e.g., Spirogyra), or in a branching thallus form (e.g., Fucus). The cells

of the colonies are generally similar, but some are differentiated for reproduction and for other functions. Kelps, the largest algae, may attain a length of more than 200 ft (61 m). Euglena and similar genera are free-swimming one-celled forms that contain chlorophyll but that are also able, under certain conditions, to ingest food in an animal like manner. The green algae include most of the freshwater forms. The pond scum, a green slime found in stagnant water, is a green alga, as is the green film found on the bark of trees. The more complex brown algae and red algae are chiefly saltwater forms; the green color of the chlorophyll is masked by the presence of other pigments.

Blue–green algae have been grouped with other prokaryotes in the kingdom Monera and renamed cyanobacteria. There are four classes of algae for the irrigation system:

Figure 9.1. Types of algae.