WATER QUALITY IN AGRICULTURE: Risks and risk mitigation Water quality in agriculture: Risks and risk mitigation Required citation: Drechsel, P., Marjani Zadeh, S. & Pedrero, F. (eds). 2023. Water quality in agriculture: Risks and risk mitigation. Rome, FAO & IWMI. https://doi.org/10.4060/cc7340en The designations employed and the presentation of material in this information product and the presented maps do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations (FAO) or The International Water Management Institute (IWMI) concerning the legal or development status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. Dashed lines on maps represent approximate border lines for which there may not yet be full agreement. 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Users wishing to reuse material from this work that is attributed to a third party, such as tables, figures or images, are responsible for determining whether permission is needed for that reuse and for obtaining permission from the copyright holder. The risk of claims resulting from infringement of any third- party-owned component in the work rests solely with the user. Sales, rights and licensing. FAO information products are available on the FAO website (www.fao.org/ publications) and can be purchased through publications-sales@fao.org. Requests for commercial use should be submitted via: www.fao.org/contact-us/licence-request. Queries regarding rights and licensing should be submitted to: copyright@fao.org. Cover illustration and Graphic design : Yildiz Eviren ii 7 Livestock and water quality Camillo De Camillis, Pay Drechsel and Eran Raizman Global population growth has provoked an increase in global water demand across all sectors, and the livestock sector is no exception. Agriculture accounts for approximately 70 percent of available freshwater supply of which global livestock production represents about 30 percent. This proportion includes rain and irrigation water used for the production of feed and withdrawals for livestock husbandry (Mekonnen & Hoekstra, 2012), with a large proportion allocated to beef production. The relationship between water quality and livestock is double-edged: livestock require quality water, but the waste they produce can deteriorate water quality. Nitrogen (N) is one of the key parameters for livestock drinking water quality, however livestock is also responsible for major nitrogen releases into nature. One-third of human-induced reactive nitrogen losses can be traced to livestock systems. Most nitrogen is emitted in two forms: Nitrate (NO – 3 , 45 percent), which degrades water quality in freshwater and coastal systems, and ammonia (NH3, 41 percent), which contributes to air pollution and causes eutrophication and acidification (Mueller & Lassaletta, 2020). N emissions are also precursor to the formation of fine particles which enter the respiratory tract affecting public health (Cohen et al., 2017). Figures 7.1 and 7.2 show the global distribution of nitrogen emissions from livestock supply chains taking into consideration the diversity of livestock species, systems, production intensity, and the origins and management of different animal feed (Uwizeye et al., 2020). The Livestock Environmental Assessment and Performance Partnership (FAO LEAP), a multi- stakeholder initiative designed to build consensus on how to assess the environmental impacts of livestock systems, has developed several FAO guidance documents that consider, among others, the water footprint of livestock based on the life cycle assessment methodology and data collection in accordance with ISO 14046:20141. The water footprint of large ruminants consists primarily (often by over 90 percent) of the water needed for (irrigated) feed production, in addition to the direct water footprint associated with drinking water and the consumption of service water (Chapagain & Hoekstra, 2003). The guidelines suggest discussion of the impact of livestock supply chains on water consumption and water quality in defined system boundaries (FAO, 2015). While livestock water use is associated with livestock watering, feedlots, dairy operations, servicing (including farm and slaughterhouse cleaning), and other on-farm needs, this chapter focuses (i) on the water needs and quality that impact animal health and production, and (ii) the possible burden of livestock waste on water resources. 1 ISO 14046:2014 specifies principles, requirements and guidelines related to water footprint assessment of products, processes and organizations based on life cycle assessment (LCA). 93 Chapter Figure 7.1. Global distribution of nitrate (N03) emissions from livestock supply chains Source: Reproduced with permission from Uwizeye, A., de Boer, I. J.M., Opio, C., Schulte, R., Falcucci, A., Tempio, G., Teillard, F., Casu, F., Rulli, M., Galloway, J.M., Leip, A., Erisman, J.W., Robinson, T.P., Steinfeld, H. & Gerber, P. 2020. Nitrogen emissions along global livestock supply chains. Nature Food, 1: 437–446. Notes: Final boundary between the Sudan and South Sudan has not yet been determined. Final status of the Abyei area is not yet determined. Dotted line represents approximately the Line of Control in Jammu and Kashmir agreed upon by India and Pakistan. The final status of Jammu and Kashmir has not yet been agreed upon by the parties. Figure 7.2. Global distribution of ammonia (NH3) emissions from livestock supply chains Source: Reproduced with permission from Uwizeye, A., de Boer, I. J.M., Opio, C., Schulte, R., Falcucci, A., Tempio, G., Teillard, F., Casu, F., Rulli, M., Galloway, J.M., Leip, A., Erisman, J.W., Robinson, T.P., Steinfeld, H. & Gerber, P. 2020. Nitrogen emissions along global livestock supply chains. Nature Food, 1: 437–446. Notes: Final boundary between the Sudan and South Sudan has not yet been determined. Final status of the Abyei area is not yet determined. Dotted line represents approximately the Line of Control in Jammu and Kashmir agreed upon by India and Pakistan. The final status of Jammu and Kashmir has not yet been agreed upon by the parties. 94 Water quality in agriculture: Risks and risk mitigation 7.1. Water quality specifications for selected parameters potentially affecting livestock health The water requirements of livestock depend on physiological and environmental conditions. Consumption may vary greatly depending on the species, size and age of the animal, the physical state, the level of activity, food intake, the quality and temperature of water, and the environmental temperature. Because water plays a critical role in animal health, it is essential to provide clean and sufficient water for livestock. The vast majority of actual water required by animals is obtained as drinking water, followed by the water content of the feed. It is estimated that livestock bodies contain between 60 percent and 70 percent water, which is necessary for maintaining body fluids and proper ion balance; as well as functions such as digestion, absorption and metabolizing nutrients; the elimination of waste material and excess heat from the body; the provision of a fluid environment for foetuses; and transporting nutrients to and from body tissues. Several parameters should be considered when assessing water quality for livestock. These are: • sensory (organoleptic) attributes such as odour and taste; • physiochemical properties (pH, salts/total dissolved solids, hardness); • chemical composition o toxic compounds (heavy metals, pesticides, herbicides, etc.); o excess minerals or compounds such as nitrates; o biological contaminants (bacteria, algae, etc.); o spills of petroleum, etc. Water quality monitoring and evaluation is an ongoing process that requires regular access to a laboratory. The adverse effects of water on animal health and production depend on the location and might be related to high concentrations of minerals (e.g. nitrates and nitrites, sulfate salts, Mg), high levels of pathogenic bacteria causing infections, heavy growth of blue-green algae, and water contamination with chemical substances associated with agriculture and industrial activity such as pesticides and herbicides. Some of the thresholds for water quality parameters are presented below. 7.1.1. Salinity-related toxicity Excessively saline water may cause salt poisoning in livestock or stop animals from drinking, leading to a loss of production. Tolerance levels of salts2 3 4 are commonly measured in terms of total dissolved solids (TDS), which have been assessed for a number of livestock/animal species (Table 7.1). 2 https://www.agric.wa.gov.au/livestock-biosecurity/water-quality-livestock?page=0%2C0#smartpaging_toc_p0_s5_h2 3 https://www.msdvetmanual.com/toxicology/salt-toxicosis/salt-toxicosis-in-animals 4 https://extension.missouri.edu/eq381#mineralized 95 Livestock and water quality Table 7.1. Approximate tolerances of livestock to dissolved salts (salinity) in drinking water (TDS in mg/L) Livestock A: No adverse effects B: Animals may initially C: Loss of production and on animals expected exhibit reluctance to decline in animal condition (mg/L) drink or there may be and health would be some scouring, but stock expected. Livestock may should adapt without loss tolerate these levels for of production (mg/L) short periods if introduced gradually (mg/L) Beef cattle (mature, on dry 0–4 000 4 000–5 000 5 000–10 000 pasture) Beef cattle (feedlots) 0–4 000 >4 000b Dairy cattle (mature, dry) 0–2 400 2 400–4 000 4 000–7 000 Dairy cattle (milking) 3 500 Sheep (mature, on dry pasture) 0–4 000 4 000–10 000 10 000–13 000a Sheep (mature, dry, feedlots) 0–4 000 >7 000b Sheep (mature, dry 0–4 000 >7 000c confinement feeding) Sheep (weaners, lactating and 0–4 000 6 600 pregnant on pasture) Sheep (lambs, intensive 0–4 000 >4 000b feeding) Horses 0–4 000 4 000–6 000 6 000–7 000 Poultry 0–2 000 2 000–3 000 3 000–4 000 Pigs 0–4 000 4 000–6 000 6 000–8 000 a Sheep on lush green feed may tolerate up to 13 000 mg/L TDS without loss of condition or production. b Intensive feeding for growth. c Confinement feeding for maintenance. Source: DPIRD https://www.agric.wa.gov.au/livestock-biosecurity/water-quality-livestock Salinity caused by the presence of salts is strongly correlated with electrical conductivity (EC) of the water. It is therefore more common and practical to measure conductivity rather than TDS, and subsequently convert the EC value to TDS5. The EC units used are milliSiemens per metre (mS/m). Table 7.2 summarizes the guidance values of EC thresholds applicable to livestock. 5 See www.agric.wa.gov.au/livestock-biosecurity/water-quality-livestock. 96 Water quality in agriculture: Risks and risk mitigation Table 7.2. Electrical conductivity specifications for livestock and poultry. Water salinity (EC) Rating Remarks (dS/m) <1.5 Excellent Usable for all classes of livestock and poultry. 1.5–5.0 Very satisfactory Usable for all classes of livestock and poultry. May cause temporary diarrhoea in livestock not accustomed to such water; watery droppings in poultry. 5.0–8.0 Satisfactory for May cause temporary diarrhoea or be refused at first by livestock animals not accustomed to such water. Unfit for poultry Often causes watery faeces, increased mortality and decreased growth, especially in turkeys. 8.0–11.0 Limited use for livestock Usable with reasonable safety for dairy and beef cattle, sheep, swine and horses. Avoid use for pregnant or lactating animals. Unfit for poultry Not acceptable for poultry. 11.0 – 16.0 Very Limited Use Unfit for poultry and probably unfit for swine. Considerable risk in using for pregnant or lactating cows, horses or sheep, or for the young of these species. In general, use should be avoided, although older ruminants, horses, poultry and swine may subsist on waters such as these under certain conditions. >16.0 Not Recommended Risks with such highly saline water are so great that it cannot be recommended for use under any conditions. Source: Ayers, R.S. & Westcot, D.W. 1994. Water quality for agriculture. FAO Irrigation and Drainage Paper 29, Rev. 1. Rome Among salinity-causing salts, those containing sulphate can be particularly relevant for livestock, especially in location where the hot climate evaporates surface waters, increasing salt concentrations. Table 7.3 gives related guidelines (German, Thiex & Wright, 2008) in this regard. In general, the maximum concentration of sulphate (SO4) in drinking water for livestock, which is often set as 1 000 mg/l, depends significantly on the additional sulphate intake through feed (i.e. the dietary sources). Water consumption by cattle begins to decrease at sulphate (SO4) levels of 2 500 to 3 000 mg/L, which will lead eventually to dehydration and death6. 6 https://waterquality.montana.edu/well-ed/interpreting_results/fs_livestock_suitability.html and https://agriculture.canada.ca/en/ agriculture-and-environment/agriculture-and-water/livestock-watering/water-quality-impacts-livestock 97 Livestock and water quality Table 7.3. A guide to the use of water containing sulfates for livestock and poultry Sulfate (SO4) mg/L or Comments ppm Less than 250 Recommendations for poultry are variable. The more conservative guidelines indicate that (poultry) sulfate content above 50 mg/L may affect performance if magnesium and chloride levels are high. Higher sulfate levels have a laxative effect. Less than 1500 For livestock, no harmful effects- except some temporary, mild diarrhea near upper limit, and (livestock) animals may discriminate against the water due to taste at the upper limit. The calculations of total sulfur intake is recommended when using sulfur-containing feeds (e.g., molasses, distiller’s grains, corn gluten feed). 1500-2500 For livestock, no harmful effects- except some temporary diarrhea. In cattle this water may contribute significantly to the total dietary sulfur intake. May cause a reduction in copper availability in ruminants. Calculating total sulfur intake is recommended. 2500-3500 Poor water for poultry, especially turkeys. Very laxative, causing diarrhea in livestock that usually disappears after few weeks. Sporadic cases of sulfur- associated polioncephalomalacia (PEM) are possible. May cause substantial reduction in copper availability in ruminants. The calculation of total sulfur intake is recommended. 3500-4500 Very laxative. Unacceptable for poultry. Not recommended for use for pregnant or lactating ruminants or horses, or for ruminants fed in confinement. Sporadic cases of sulfur-associated polioncephalomalacia (PEM) are likely. May cause substantial reduction in copper availability in ruminants. The calculation of total sulfur intake is recommended. Over 4500 Not recommended for use under any conditions. The calculation of total sulfur intake is highly recommended. Increased risk of mortality and morbidity. Source: German, D., Thiex, N. & Wright, C. 2008. Interpretation of water analysis for livestock suitability. Brookings, SD, South Dakota State University, South Dakota counties, and U.S. Department of Agriculture Sulphate containing salts are often sodium (Na2SO4) or magnesium (MgSO4) based. In general, sodium concentrations under 1 000 mg/l should be protective for livestock, unless sulphate levels are also high (Table 7.4). Sodium values above 5 000 mg/l can cause serious effects and death. Short-term exposure should not exceed 4 000 (MSU, 2021). Table 7.4. A guide to the use of water containing sodium for livestock and poultry Sodium (Na) mg/L or Comments ppm Less than 50 (poultry) Sodium levels pose little risk to poultry. 50 – 1000 (poultry) Recommendations are extremely variable and sodium itself poses little risk; however, water with sodium over 50 mg/L (ppm) may affect the performance of poultry if the sulfate or chloride is high. Sodium levels greater than 50 mg/L are detrimental to broiler performance if the sulfate level is also 50 mg/L or higher and the chloride level is 14 mg/L or higher. Excessive sodium has a diuretic effect for poultry. Less than 800 By itself, sodium poses little risk to livestock, but its association with sulfate is a concern. (livestock) Water with over 800 mg sodium /L can cause diarrhea and a drop in milk production in dairy cows. High levels of sodium, a major component of salt, may necessitate adjustments to rations. Care should be taken when removing or reducing salt from swine and diary rations to ensure a chlorine deficiency does not result. Salt may be reduced in swine diets if the sodium in the water exceeds 400 mg/L. Source: German, D., Thiex, N. & Wright, C. 2008. Interpretation of water analysis for livestock suitability. Brookings, SD, South Dakota State University, South Dakota counties, and U.S. Department of Agriculture Magnesium-based salts in cattle trigger a stronger sulfate response than sodium-based salts for which many animals have developed a recognized appetite (Grout et al., 2006). Table 7.5 shows the related drinking water guidelines for magnesium. 98 Water quality in agriculture: Risks and risk mitigation Table 7.5. Specifications for magnesium in drinking water for livestock Livestock Magnesium (mg/l) Horses 250 Beef cattle 400 Cows (lactating) 250 Adult sheep on dry feed 500 Ewes with lambs 250 Source: Ayers, R.S. & Westcot, D.W. 1994. Water quality for agriculture. FAO Irrigation and Drainage Paper 29, Rev. 1. Rome 7.1.2. Trace elements Trace elements can be important for livestock growth, but become a problem if they exceed certain thresholds. In particular, metals in drinking water can lead to toxic outcomes in animals. Some metals are geogenic in origin (i.e. inherited with location), while others are introduced due to anthropogenic activities. As trace metals can accumulate slowly, monitoring should therefore be performed periodically. Table 7.6 gives the upper limits for selected contaminants. Table 7.6. Specifications for limit values for trace metals in drinking water for livestock Constituent (symbol) Upper limit (mg/l) Aluminium (Al) 5 Arsenic (As) 0.2 Beryllium (Be)1 0.1 Boron (B) 5 Cadmium (Cd) 0.05 Chromium (Cr) 1 Cobalt (Co) 1 Copper (Cu) 0.5 Fluoride (F) 2 Iron (Fe) No reported toxicity Lead (Pb)2 0.05-0.1 Manganese (Mn)3 0.05 Mercury (Hg) 0.01 Nitrate + Nitrite (NO3-N + NO2-N) 1004 Nitrite (NO2-N) 10 Selenium (Se) 0.05-0.1 Vanadium (V) 0.1 Zinc (Zn) 24 1 Insufficient data for livestock. The value for marine aquatic life is used here. 2 Lead is accumulative and problems may begin at a threshold value of 0.05 mg/l. 3 Insufficient data for livestock. The value for human drinking water is used here. 4 These levels are rarely seen in surface water except in extremely contaminated water bodies, but can be found in groundwater. Source: Ayers, R.S. & Westcot, D.W. 1994. Water quality for agriculture. FAO Irrigation and Drainage Paper 29, Rev. 1. Rome 99 Livestock and water quality Nitrate is a particular common contaminant strongly influenced by human activities. Nitrate intake occurs mainly through feed and drinking water. Elevated levels may be found in forage due to heavy use of nitrogen fertilizer in fields or other types of water pollution. While acute nitrate poisoning is rare, elevated levels of nitrates in water for livestock or poultry may result in possible effects, which are presented in Table 7.7. Table 7.7. Possible effects of nitrates in water for livestock or poultry (in mg/L or ppm) Nitrate level as NO3 a Nitrate level as NO3-N a Possible effects b 0 to 100 0 to 23 Unlikely for livestock or poultry 101 to 500 23 to 114 Possibility of reduced gains, increased infertility 501 to 1 000 115 to 227 The water should not harm livestock or poultry by itself, but in combination with normal nitrate intake through feed can result in distress symptoms (shortness of breath, rapid breathing) over 1 000 over 227 Suffocation signs, lack of coordination or staggering, ultimately death of cattle, sheep or horses a When a laboratory reports the concentration of nitrate, it might refer to the nitrate ion (NO3-) or to the nitrogen within the nitrate ion (NO3-N). b Assumes normal or close to average nitrate levels in forage and feed. Sources: Adams, R.S., McCarty, T.R. & Hutchinson, L.J. 2021. Prevention and control of nitrate toxicity in cattle. University Park, PN, Pennsylvania State University; German, D., Thiex, N. & Wright, C. 2008. Interpretation of water analysis for livestock suitability. Brookings, SD, South Dakota State University, South Dakota counties, and U.S. Department of Agriculture 7.1.3. Pesticides, herbicides and pharmaceutics The Canadian Environmental Quality Guidelines online database contains a large range of pesticides, herbicides, other organic contaminants and heavy metals that may be found in livestock drinking water (CCME, 2021). A comparison of the different regulations governing these substances is found in Valente-Campos et al. (2014). Although drinking water can contain pharmaceutical residues, related guidelines for livestock have emerged only slowly as concentrations remained very low for many years compared, for example, with those of purposely administered antibiotics (e.g. through feed or water). The use of antibiotics for growth promotion purposes was banned in the European Union in 2006, and the use of sub-therapeutic doses of medically important antibiotics in animal feed and water became illegal in the United States on 1 January 2017. More bans are expected as awareness increases of the risk of transmitting drug-resistant bacteria to humans, accompanied by calls for standards for total livestock and poultry intake (including via water). 7.1.4. Water-borne microbial infections Several microbes, some of them zoonotic in nature, have been associated with water transmission and disease outbreaks. The risk of contamination is greatest in surface waters (dams, lakes, dugouts, etc.) that are directly accessible by stock, or that receive runoff or drainage from intensive livestock operations or human waste. In comparison, groundwater is considered a low-risk source (Olkowski, 2009). Bacterial pathogens: The pathogens of greatest concern in water supplies for farm animals include enteric bacteria such as E. coli, Salmonella, Clostridium botulinum and Campylobacter jejuni. The presence and survival of bacteria in natural aquatic ecosystems depends upon a number of factors, 100 Water quality in agriculture: Risks and risk mitigation including nutrient content, exposure to direct sunlight and temperature, and competition with other microorganisms. Strict tolerance values for livestock have not been established. It is however often recommended that drinking water for livestock should contain less than 100 coliforms/100 ml. Botulism and salmonellosis are two bacterial livestock diseases that may result from contamination of water with organic matter: • Botulism is a rapid-onset, usually fatal disease caused by the botulinum toxin produced by the bacterium Clostridium botulinum. Typical signs include hindlimb weakness progressing to paralysis, collapse and death. Common sources of the toxin include animal carcasses, rotting organic material and poorly prepared silage. Treatment is rarely attempted but vaccines are available for disease prevention in cattle. For more information see www.agric.wa.gov.au/livestock-biosecurity/botulism-cattle. • Salmonellosis of sheep is an infectious bacterial disease causing illness and death. It results from proliferation of salmonella bacteria in the gastrointestinal tract and other organs. A possible source can be faecal contamination of feed or water. Profuse diarrhoea is commonly present and pregnant ewes may abort. For more information see www.agric.wa.gov.au/livestock-biosecurity/salmonellosis-sheep. Of particular importance are water sources such as reservoirs used by cattle and humans. Cattle are considered a primary source of E. coli O157, which is one of the Shiga toxin-producing E. coli (STEC) strains. These toxins usually do not cause disease in animals but may cause watery diarrhoea. Water contaminated with cattle faeces, as well as direct or indirect contact with live cattle, are considered major routes of human infection. Cattle that carry E. coli O157 can thus be asymptomatic, but in humans this pathogen creates severe zoonotic infections, and in many cases is the cause of death (Olkowski, 2009). Protozoan: Cryptosporidium spp. are protozoan parasites that affect livestock, some of which are of public health importance due to their ability to cross over to humans. Transmission occurs via water, therefore, water sources in production systems should be monitored carefully. Among the many species which can infect human, cattle, small ruminants and poultry, C. parvum and e.g. C. andersoni are some of the most prevalent, affecting young livestock, especially pre-weaned ruminants (Fayer, 2004). Algae: Livestock can be poisoned by drinking water contaminated with blue-green algae (Cyanobacteira) and associated natural toxins such as acute hepatotoxins, cytotoxins, neurotoxins and toxins causing gastrointestinal disturbance. Blue-green algae are a group of bacteria that include Nodularia spumigena, Microcystis aeruginosa and Anabaena circinalis. They can produce spectacular blooms which resemble iridescent green paint or curdled greenish milk on water surfaces. Algae multiply rapidly (“bloom”) in shallow, stagnant and warm water when the water is contaminated by plant nutrients, including organic and faecal matter and phosphorus. Identification of cyanobacteria and especially the Microcystis species (Table 7.8) is difficult. The various species can be identified by experts with a microscope, but in the field such determination is limited to whether the bloom is filamentous (stringy) or planktonic. Filamentous algae are easily removed from water by hand, whereas planktonic algae/cyanobacteria are single celled and will slip through fingers. No toxin-producing cyanobacteria is of the filamentous type. 101 Livestock and water quality Table 7.8. Guideline for calculated tolerance levels (No Observed Effect Level) of microcystin LR toxicity equivalents and number of cells of Microcystis aeruginosa. Livestock category Body weight (kg) Peak water intake Calculated total Equivalent cell (L/day) toxin level (µg/L) number (cells/mL) Cattle 800 85 4.2 21 000 Sheep 100 11.5 3.9 19 500 Pigs 110 15 16.3 81 500 Chicken 2.8 0.4 3.1 15 500 Horse 600 70 2.3 11 500 Source: Olkowski. 2009. Livestock water quality: a field guide for cattle, horses, poultry, and swine. Ottawa, Agriculture and Agri-Food Canada 7.1.5 Good management practices for water quality to keep livestock healthy The following recommendations should be considered as part of good practices for farm •management: Assess water quality and quantity for effective production planning. If water quality is poor, livestock may drink less than they need or may stop drinking altogether. When animals drink less, they will eat less resulting in deterioration of their physiological condition. If they are • lactating, milk production will reduce or cease. Learn from colleagues, veterinarians and water experts about water contaminants that are likely to negatively affect animal health in your area. Seek laboratory support to identify the key parameters of principal water sources (e.g. algae, salinity, pathogens, trace metals, chemicals organic materials, etc.) to determine which ones are likely to play a critical role. This assessment may have to be performed in both the rainy and dry seasons. In the rainy season, more pollutants will be washed into water bodies; in the dry season, salt concentration will increase due to evaporation and less dilution. Where water is scarce and expensive, storage • pond cover sheets could be help reduce costs (Martínez Alvarez et al., 2009). Develop a Risk Mitigation Plan to monitor critical water parameters on a regular basis and identify changes in water quality before they have an impact on animals. Monitoring livestock health is a particularly important component of risk mitigation due to potential difficulties in analysing possible contaminants. Establishing a working relationship with a veterinarian is essential to ensure that animal health and welfare and disease notification issues are • addressed. Seek veterinary assistance to immediately investigate any signs of serious disease. The presence of water contaminants in livestock should be identified as early as possible, before the manifestation of adverse health effects in animals. Both producers and water specialists should be trained to recognize subtle adverse effects on growth rate, feed conversion ratio, reproductive success, milk yield and product quality. Preventive hygiene measures and good management are currently the most important tools to control cryptosporidiosis as chemical disinfectants have shown mixed success. Ensure that animal manure does not enter the drinking water sources of livestock or of farmers downstream. Where drinking water is polluted consider treatment. Several methods and technologies are available to reduce and even eliminate the amount of different contaminates in water. In selecting a method, consider the cost effectiveness of the identified risk factors. Possible options include the following methods: 102 Water quality in agriculture: Risks and risk mitigation • Activated carbon filters: This method is based on passing water through a filter containing activated carbon granules. The contaminants attach to the granules and are removed. This method is able to remove mercury, some pesticides and volatile organic compounds, among others. Poor filter maintenance will decrease effectiveness, however, and may result in bacterial growth on the filters, potentially contaminating the water with pathogens. It is therefore important to replace the filters often, which increases operational costs. • Chlorination: This is one of the most common methods applied in water treatment to reduce pathogens in drinking water for livestock as well as humans. The chlorination process is very effective when used in conjunction with a filtration system to remove large particles that can house bacteria. However, the chlorine content of the treated water should be closely monitored to avoid possible harm to animals (Olkowski, 2009). • Coagulation: This method is used in livestock operations to remove fine particles, iron, arsenic, manganese and organics. The removal of particles prior to chlorination makes disinfection much more effective. Coagulation is a standard treatment for surface water prior to chlorination. The chemicals used in the process, such as aluminium sulphate (alum), neutralize the charge on the particles and cause them to coalesce into floc that can be removed by filtration or settling (Olkowski, 2009). • Sulfate reduction: Present treatment technologies to reduce sulfates are costly. They include ion exchange and membranes, such as nanofiltration. Due to the high cost, the best option is usually to find another water source with a lower concentration of sulfates. Avoid water sources that show elevated levels of cyanobacteria (blue algae). The prevention of cyanobacterial blooms is a more cost effective means of reducing the risk of toxicity than the typical water treatment process. Reducing the growth potential of cyanobacteria by lowering nutrient availability, for example, should be the primary goal when seeking to reduce the risks associated with cyanobacterial blooms (Downing, Watson & McCauley, 2001). Other options for eliminating blooms include the use of storage tank covering sheets for light shading (Craig et al., 2005), or the application of chemical algaecides. There is evidence that copper sulfate added to pond water up to a concentration of 1 ppm (1 mg/l) will successfully kill algae blooms, but will also likely harm other types of aquatic life. The Canadian AAFC-PFRA recommends a lower dosage between 0.06 mg/l and 0.25 mg/l based on the surface area of the water body. Treatment at the beginning of the bloom at a low dosage is more effective than later treatment, as it allows the zooplankton to populate and assist in the control of algae and cyanobacteria. It is important to remember that a sudden release of toxins can occur when cyanobacterial blooms die. Hence, the use of chemical algaecides may not eliminate the risk of toxicity; in fact, the risk of toxin exposure may increase if the algaecide is introduced at the wrong time7. 7.2. Livestock impact on water quality The livestock sector is growing and intensifying faster than crop production in almost all countries, and the associated waste, including manure, has serious implications for water quality. Where livestock is concentrated, the associated production of wastes can surpass the buffering capacity of surrounding ecosystems, thereby polluting surface waters and groundwater (Mateo-Sagasta, Marjani Zadeh & Turral, 2017). Increased loss of nutrients in agricultural runoff has potentially 7 www.ag.ndsu.edu/waterquality/livestock/Livestock_Water_QualityFINALweb.pdf 103 Livestock and water quality serious ecological and public health implications. Nitrogen and phosphorus are of particular significance in this regard, as both can lead to aquatic eutrophication if stemming from diffuse pollution from pasture-based cattle and sheep systems, or point pollution from indoor systems, as it is common for pigs and poultry (Figure 7.3). Finally, feedlots are often located on the banks of watercourses where (nutrient-rich) animal waste (e.g. urine) is released directly into the water. Figure 7.3. Pathways of diffuse and point sources of nutrients and farm effluent inputs to catchment waters in livestock farming areas Source: Modified after Hooda, P.S., Edwards, A.C., Anderson, H.A. & Miller, A. 2000. A review of water quality concerns in livestock farming areas. Science of the Total Environment, 250(1–3): 143–167. The organic and nutrient load of manure (Table 7.9) can consume significant amounts of oxygen in the water body (Table 7.10). Pathogens from livestock waste that are detrimental to public health include bacteria such as Campylobacter spp., Escherichia coli O157 (see above), Salmonella spp. and Clostridium botulinum, and parasitic protozoa such as Giardia lamblia, Cryptosporidium parvum and Microsporidia spp., all of which cause hundreds of thousands of infections every year (Christou, 2011). Figure 7.4 shows the common pathways of microbial water contaminants (Hooda et al., 2000). Table 7.9. Major nutrients in typical livestock waste Source Total nutrients (available fraction in parentheses) N P K Solids (kg/t) Cattle FYM (25% DM) 6 (1.5) 3.1 (0.78) 5.80 (3.48) Pig FYM (25% DM) 6 (1.5) 2.62 (1.53) 3.31 (2.90) Broiler litter (60% DM) 29 (10.0) 9.60 (5.67) 13.27 (9.95) Slurry (kg/m3) Cattle Slurry (6% DM) 3 (1.0) 0.52 (0.26) 2.98 (2.49) Pig Slurry (6% DM) 5 (1.8) 1.31 (0.65) 1.99 (1.65) Note: DM: dry matter; FYM: farmyard manure. Source: Hooda, P.S., Edwards, A.C., Anderson, H.A. & Miller, A. 2000. A review of water quality concerns in livestock farming areas. Science of the Total Environment, 250(1–3): 143–167, after Webb, J. & Archer, J.R. 1994. Pollution of soils and watercourses by wastes from livestock production systems. In I. Ap Dewi, R.F.E. Axford, I.F.M Marai & H. Omed, eds. Pollution in livestock production systems, pp. 189–204. Wallingford, UK, CAB International 104 Water quality in agriculture: Risks and risk mitigation Table 7.10. Ranges of biological oxygen demand (BOD) concentrations for various waste types Source BOD (mg/L ) Silage effluents 30 000 - 80 000 Pig slurry 20 000 - 30 000 Cattle slurry 10 000 - 20 000 Liquid effluents draining from slurry stores 1000 - 12 000 Dilute diary parlour and yard washing (dirty water) 1000 - 5000 Milk 140 000 Untreated domestic sewage 300 - 00 Treated domestic sewage 20 – 60 Clean river water < 5 Source: Hooda, P.S., Edwards, A.C., Anderson, H.A. & Miller, A. 2000. A review of water quality concerns in livestock farming areas. Science of the Total Environment, 250(1–3): 143–167, after Webb, J. & Archer, J.R. 1994. Pollution of soils and watercourses by wastes from livestock production systems. In I. Ap Dewi, R.F.E. Axford, I.F.M Marai & H. Omed, eds. Pollution in livestock production systems, pp. 189–204. Wallingford, UK, CAB International. Figure 7.4. Pathways of catchment water contamination with microbial and protozoan micro-organisms Source: Hooda, P.S., Edwards, A.C., Anderson, H.A. & Miller, A. 2000. A review of water quality concerns in livestock farming areas. Science of the Total Environment, 250(1–3): 143–167. 7.2.1. Good management practices to prevent water quality impacts from livestock Given the high risks involved in compromised water quality, good management practices should be developed to safeguard the health of animals and their environment as well as downstream water sources. As part of good practices in farm management, it is essential to comply with regulations concerning restrictions on animal movements and stocking rates, and consider the following practices to minimize negative impacts from livestock farming on the environment, in particular the quality of water sources in direct farm proximity: Water quality in agriculture: Risks and risk mitigation 105 • Study the landscape and context of the livestock production system to ascertain all the resources needed, in particular the water quality upstream and downstream of the farm or grazing area, the depth of shallow groundwater, the soil texture and infiltration rate. The objective is for the water downstream of the farm to have at least the same quality as the water upstream (i.e. zero negative impact). • Determine the pollution pathways (see Figure 7.3 and Figure 7.4) of highest probability and the related critical control points for risk monitoring and mitigation. • Implement measures to reduce farm runoff and leaching (see Chapter 8; ecology), and treat runoff from point pollution sources (e.g. through constructed wetlands) before the waste stream enters off-farm water bodies. Selected best management practices for livestock safety are described by Hooda et al. (2000) and FAO & OIE (2009), among others. 7.3. Conclusion This chapter describes how poor water quality can affect livestock, and how poor livestock management can affect water quality. It shows how impacts from farming can extend beyond the farm and reasons that such impacts are the responsibility of the farmer. 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