Water quality as a global issue
Non-point source pollution defined
Scope of the problem
Agricultural impacts on water quality
Types of decisions in agriculture for non-point source pollution control
The data problem
Second only to availability of drinking water, access to food supply is the greatest priority. Hence, agriculture is a dominant component of the global economy. While mechanization of farming in many countries has resulted in a dramatic fall in the proportion of population working in agriculture, the pressure to produce enough food has had a worldwide impact on agricultural practices. In many countries, this pressure has resulted in expansion into marginal lands and is usually associated with subsistence farming. In other countries, food requirements have required expansion of irrigation and steadily increasing use of fertilizers and pesticides to achieve and sustain higher yields. FAO (1990a), in its Strategy on Water for Sustainable Agricultural Development, and the United Nations Conference on Environment and Development (UNCED) in Agenda 21, Chapters 10, 14 and 18 (UNCED, 1992) have highlighted the challenge of securing food supply into the 21st century.
Sustainable agriculture is one of the greatest challenges. Sustainability implies that agriculture not only secure a sustained food supply, but that its environmental, socio-economic and human health impacts are recognized and accounted for within national development plans. FAO's definition of Sustainable agricultural development appears in Box 1.
|
BOX 1: FAO's DEFINITION OF SUSTAINABLE AGRICULTURAL DEVELOPMENT Sustainable development is the management and conservation of the natural resource base and the orientation of technological and institutional change in such a manner as to ensure the attainment and continued satisfaction of human needs for the present and future generations. Such Sustainable development (in the agriculture, forestry and fisheries sectors) conserves land, water, plant and animal genetic resources, is environmentally non-degrading, technically appropriate, economically viable and socially acceptable. |
It is well known that agriculture is the single largest user of freshwater resources, using a global average of 70% of all surface water supplies. Except for water lost through evapotranspiration, agricultural water is recycled back to surface water and/or groundwater. However, agriculture is both cause and victim of water pollution. It is a cause through its discharge of pollutants and sediment to surface and/or groundwater, through net loss of soil by poor agricultural practices, and through salinization and waterlogging of irrigated land. It is a victim through use of wastewater and polluted surface and groundwater which contaminate crops and transmit disease to consumers and farm workers. Agriculture exists within a symbiosis of land and water and, as FAO (1990a) makes quite clear, "... appropriate steps must be taken to ensure that agricultural activities do not adversely affect water quality so that subsequent uses of water for different purposes are not impaired."
Sagardoy (FAO, 1993a) summarized the action items for agriculture in the field of water quality as:
· establishment and operation of cost-effective water quality monitoring systems for agricultural water uses.· prevention of adverse effects of agricultural activities on water quality for other social and economic activities and on wetlands, inter alia through optimal use of on-farm inputs and the minimization of the use of external inputs in agricultural activities.
· establishment of biological, physical and chemical water quality criteria for agricultural water users and for marine and riverine ecosystems.
· prevention of soil runoff and sedimentation.
· proper disposal of sewage from human settlements and of manure produced by intensive livestock breeding.
· minimization of adverse effects from agricultural chemicals by use of integrated pest management.
· education of communities about the pollution impacts of the use of fertilizers and chemicals on water quality and food safety.
This publication deals specifically with the role of agriculture in the field of freshwater quality. Categories of non-point source impacts - specifically sediment, pesticides, nutrients, and pathogens - are identified together with their ecological, public health and, as appropriate, legal consequences. Recommendations are made on evaluation techniques and control measures. Much of the scientific literature on agricultural impacts on surface and groundwater quality is from developed countries, reflecting broad scientific concern and, in some cases, regulatory attention since the 1970s. The scientific findings and management principles are, however, generally applicable worldwide. This publication does not deal with water quality impacts caused by food processing industries insofar as these are considered to be point sources and are usually subject to control through effluent regulation and enforcement.
Agriculture, as the single largest user of freshwater on a global basis and as a major cause of degradation of surface and groundwater resources through erosion and chemical runoff, has cause to be concerned about the global implications of water quality. The associated agrofood-processing industry is also a significant source of organic pollution in most countries. Aquaculture is now recognised as a major problem in freshwater, estuarine and coastal environments, leading to eutrophication and ecosystem damage. The principal environmental and public health dimensions of the global freshwater quality problem are highlighted below:
· Five million people die annually from water-borne diseases.
· Ecosystem dysfunction and loss of biodiversity.
· Contamination of marine ecosystems from land-based activities.
· Contamination of groundwater resources.
· Global contamination by persistent organic pollutants.
Experts predict that, because pollution can no longer be remedied by dilution (i.e. the flow regime is fully utilized) in many countries, freshwater quality will become the principal limitation for sustainable development in these countries early in the next century. This "crisis" is predicted to have the following global dimensions:
· Decline in sustainable food resources (e.g. freshwater and coastal fisheries) due to pollution.· Cumulative effect of poor water resource management decisions because of inadequate water quality data in many countries.
· Many countries can no longer manage pollution by dilution, leading to higher levels of aquatic pollution.
· Escalating cost of remediation and potential loss of "creditworthiness".
The real and potential loss of development opportunity because of diversion of funds for remediation of water pollution has been noted by many countries. At the 1994 Expert Meeting on Water Quantity and Quality Management convened by the Economic and Social Commission for Asia and the Pacific (ESCAP), Asian representatives approved a declaration which called for national and international action to assess loss of economic opportunity due to water pollution and to determine the potential economic impacts of the "looming water crisis". Interestingly, the concern of the delegates to the ESCAP meeting was to demonstrate the economic rather than simply the environmental impacts of water pollution on sustainable development. Creditworthiness (Matthews, 1993) is of concern insofar as lending institutions now look at the cost of remediation relative to the economic gains. There is concern that if the cost of remediation exceeds economic benefits, development projects may no longer be creditworthy. Sustainable agriculture will, inevitably, be required to factor into its water resource planning the larger issues of sustainable economic development across economic sectors. This comprehensive approach to management of water resources has been highlighted in the World Bank's (1993) policy on water resource development.
Older chlorinated agricultural pesticides have been implicated in a variety of human health issues and as causing significant and widespread ecosystem dysfunction through their toxic effects on organisms. Generally banned in the developed countries, there is now a concerted international effort to ban these worldwide as part of a protocol for Persistent Organic Pollutants (POPs). One example of such an effort was the Intergovernmental Conference on the Protection of the Marine Environment from Land-based Activities, convened in Washington DC in 1995 jointly with UNEP (more information is included in Chapter 5).
TABLE 1: Classes of non-point source pollution (highlighted categories refer to agricultural activities) (Source: International Joint Commission, 1974, and other sources)
|
Agriculture |
|
| |
|
|
Animal feedlots Irrigation Cultivation Pastures |
Runoff from all categories of agriculture leading to surface and groundwater pollution. In northern climates, runoff from frozen ground is a major problem, especially where manure is spread during the winter. Vegetable handling, especially washing in polluted surface waters in many developing countries, leads to contamination of food supplies. Growth of aquaculture is becoming a major polluting activity in many countries. Irrigation return flows carry salts, nutrients and pesticides. Tile drainage rapidly carries leachates such as nitrogen to surface waters. |
Phosphorus, nitrogen, metals, pathogens, sediment, pesticides, salt, BOD1, trace elements (e.g. selenium). |
|
Forestry |
Increased runoff from disturbed land. Most damaging is forest clearing for urbanization. |
Sediment, pesticides. | |
|
Liquid waste disposal |
Disposal of liquid wastes from municipal wastewater effluents, sewage sludge, industrial effluents and sludges, wastewater from home septic systems; especially disposal on agricultural land, and legal or illegal dumping in watercourses. |
Pathogens, metals, organic compounds. | |
|
Urban areas |
|
| |
|
|
Residential Commercial Industrial |
Urban runoff from roofs, streets, parking lots, etc. leading to overloading of sewage plants from combined sewers, or polluted runoff routed directly to receiving waters; local industries and businesses may discharge wastes to street gutters and storm drains; street cleaning; road salting contributes to surface and groundwater pollution. |
Fertilizers, greases and oils, faecal matter and pathogens, organic contaminants (e.g. PAHs2 and PCBs3), heavy metals, pesticides, nutrients, sediment, salts, BOD, COD4, etc. |
|
Rural sewage systems |
Overloading and malfunction of septic systems leading to surface runoff and/or direct infiltration to groundwater. |
Phosphorus, nitrogen, pathogens (faecal matter). | |
|
Transportation |
Roads, railways, pipelines, hydro-electric corridors, etc. |
Nutrients, sediment, metals, organic contaminants, pesticides (especially herbicides). | |
|
Mineral extraction |
Runoff from mines and mine wastes, quarries, well sites. |
Sediment, acids, metals, oils, organic contaminants, salts (brine). | |
|
Recreational land use |
Large variety of recreational land uses, including ski resorts, boating and marinas, campgrounds, parks; waste and "grey" water from recreational boats is a major pollutant, especially in small lakes and rivers. Hunting (lead pollution in waterfowl). |
Nutrients, pesticides, sediment, pathogens, heavy metals. | |
|
Solid waste disposal |
Contamination of surface and groundwater by leachates and gases. Hazardous wastes may be disposed of through underground disposal. |
Nutrients, metals, pathogens, organic contaminants. | |
|
Dredging |
Dispersion of contaminated sediments, leakage from containment areas. |
Metals, organic contaminants. | |
|
Deep well disposal |
Contamination of groundwater by deep well injection of liquid wastes, especially oilfield brines and liquid industrial wastes. |
Salts, heavy metals, organic contaminants. | |
|
Atmospheric deposition |
Long-range transport of atmospheric pollutants (LRTAP) and deposition of land and water surfaces. Regarded as a significant source of pesticides (from agriculture, etc.), nutrients, metals, etc., especially in pristine environments. |
Nutrients, metals, organic contaminants. | |
1 BOD =Biological Oxygen Demand
2 PAH = Polycyclic Aromatic Hydrocarbons
3 PCB = Polycyclic Chlorinated Bi-Phenyls
4 COD = Chemical Oxygen Demand
Non-point source water pollution, once known as "diffuse" source pollution, arises from a broad group of human activities for which the pollutants have no obvious point of entry into receiving watercourses. In contrast, point source pollution represents those activities where wastewater is routed directly into receiving water bodies by, for example, discharge pipes, where they can be easily measured and controlled. Obviously, non-point source pollution is much more difficult to identify, measure and control than point sources. The term "diffuse" source should be avoided as it has legal connotation in the United States that can now include certain types of point sources.
In the United States, the Environmental Protection Agency (US-EPA) has an extensive permitting system for point discharge of pollutants in water courses. Therefore, in that country, non-point sources are defined as any source which is not covered by the legal definition of "point source" as defined in the section 502 (14) of the United States Clean Water Act (Water Quality Act) of 1987:
"The term "point source" means any discernible, confined and discrete conveyance, including but not limited to any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft, form which pollutants are or may be discharged. This term does not include agricultural storm water discharges and return flows from irrigated agriculture."
The reference to "agricultural storm water discharges" is taken to mean that pollutant runoff from agriculture occurs primarily during storm flow conditions. However, even in the United States, the distinction between point and non-point sources can be unclear and, as Novotny and Olem (1994) point out, these terms tend to have assumed legal rather than technical meanings.
Conventionally, in most countries, all types of agricultural practices and land use, including animal feeding operations (feed lots), are treated as a non-point sources. The main characteristics of non-point sources are that they respond to hydrological conditions, are not easily measured or controlled directly (and therefore are difficult to regulate), and focus on land and related management practices. Control of point sources in those countries having effective control programmes is carried out by effluent treatment according to regulations, usually under a system of discharge permits. In comparison, control of non-point sources, especially in agriculture, has been by education, promotion of appropriate management practices and modification of land use.
Prevention and modification of land-use practices
Table 1 outlines the classes of non-point sources and their relative contributions to pollution loadings. Agriculture is only one of a variety of causes of non-point sources of pollution, however it is generally regarded as the largest contributor of pollutants of all the categories.
FIGURE 1 Hierarchical complexity of agriculturally-related water quality problems (Rickert, 1993)
Non-point source pollutants, irrespective of source, are transported overland and through the soil by rainwater and melting snow. These pollutants ultimately find their way into groundwater, wetlands, rivers and lakes and, finally, to oceans in the form of sediment and chemical loads carried by rivers. As discussed below, the ecological impact of these pollutants range from simple nuisance substances to severe ecological impacts involving fish, birds and mammals, and on human health. The range and relative complexity of agricultural non-point source pollution are illustrated in Figure 1.
In what is undoubtedly the earliest and still most extensive study of non-point source pollution, Canada and the United States undertook a major programme of point and non-point source identification and control in the 1970s for the entire Great Lakes basin. This was precipitated by public concern (e.g. press reports that "Lake Erie was dead!") over the deterioration in water quality, including the visible evidence of algal blooms and increase in aquatic weeds. Scientifically, the situation was one of hypertrophic1 conditions in Lake Erie and eutrophic1 conditions in Lake Ontario caused by excessive phosphorus entering the Lower Great Lakes from point and non-point sources. The two countries, under the bilateral International Joint Commission, established the "Pollution from Land Use Activities Reference Groups" (known as "PLUARG") which served as the scientific vehicle for a ten year study of pollution sources from the entire Great Lakes basin, and which culminated in major changes both to point and non-point source control. The study also resulted in an unprecedented increase in scientific understanding of the impacts of land use activities on water quality. This work, mainly done in the 1970s and early 1980s, still has great relevance to non-point source issues now of concern elsewhere in the world.
1 These terms refer to the levels of nutrient enrichment in water; these are described in Chapter 3.
The PLUARG study, through analysis of monitoring data of rivers within the Great Lakes, from detailed studies of experimental and representative tributary catchments, and from research of agricultural practices at the field and plot level, found that non-point sources in general, and agriculture in particular, were a major source of pollution to the Great Lakes. By evaluation of the relative contributions of point and non-point sources to pollution loads to the Great Lakes, the PLUARG study proposed a combined programme of point source control and land use modification. The two federal governments and riparian state and provincial governments implemented these recommendations with the result that the two lower and most impacted Great Lakes (Erie and Ontario) have undergone major improvements in water quality and in associated ecosystems in the past decade. A significant factor in the agricultural sector was the high degree of public participation and education. Change in agricultural practices was, in many cases, achieved by demonstrating to farmers that there were economic gains to be realized by changing land management practices.
In most industrialized countries, the focus on water pollution control has traditionally been on point source management. In the United States, which is probably reasonably typical of other industrialized nations, the economics of further increases in point source regulation are being challenged, especially in view of the known impacts of non-point sources of which agriculture has the largest overall and pervasive impact. There is a growing opinion that, despite the billions of dollars spent on point source control measures, further point source control cannot achieve major additional benefits in water quality without significant control over non-point sources. In this context, it is relevant to note that agriculture is regarded as the main non-point source issue. Table 2 presents the outcome of a study by US-EPA (1994) on the ranking of sources of water quality deterioration in rivers, lakes and estuaries.
The United States is one of the few countries that systematically produces national statistics on water quality impairment by point and non-point sources. In its 1986 Report to Congress, the United States Environmental Protection Agency (US-EPA) reported that 65% of assessed river miles in the United States were impacted by non-point sources. Again, in its most recent study, the US-EPA (1994) identified agriculture as the leading cause of water quality impairment of rivers and lakes in the United States (Table 3) and third in importance for pollution of estuaries. Agriculture also figures prominently in the types of pollutants as noted in Table 3. Sediment, nutrients and pesticides occupy the first four categories and are significantly associated with agriculture. While these findings indicate the major importance of agriculture in water pollution in the United States, the ranking would change in countries with less control over point sources. However, a change in ranking only indicates that point source controls are less effective, not that agricultural sources of pollution are any less polluting.
TABLE 2: Leading sources of water quality impairment in the United States (US-EPA, 1994)
|
Rank |
Rivers |
Lakes |
Estuaries |
|
1 |
Agriculture |
Agriculture |
Municipal point sources |
|
2 |
Municipal point sources |
Urban runoff/storm sewers |
Urban runoff/storm sewers |
|
3 |
Urban runoff/storm |
Hydrologic/habitat modification |
Agriculture |
|
4 |
Resource extraction |
Municipal point sources |
Industrial point sources |
|
5 |
Industrial point sources |
On-site wastewater |
Resource extraction |
TABLE 3: Percent of assessed river length and lake area impacted (US-EPA, 1994)
|
Source of pollution |
Rivers (%) |
Lakes (%) |
Nature of pollutant |
Rivers (%) |
Lakes(%) |
|
Agriculture |
72 |
56 |
Siltation (sediment) |
45 |
22 |
|
Municipal point sources |
15 |
21 |
Nutrients |
37 |
40 |
|
Urban runoff/storm sewers |
11 |
24 |
Pathogens |
27 |
|
|
Resource extraction |
11 |
|
Pesticides |
26 |
|
|
Industrial point sources |
7 |
|
Organic enrichment DO |
24 |
24 |
|
Silviculture |
7 |
|
Metals |
19 |
47 |
|
Hydrologic/habitat modification |
7 |
23 |
Priority organic |
|
20 |
|
On-site wastewater disposal |
|
16 |
chemicals |
|
|
|
Flow modification |
|
13 |
|
|
|
TABLE 4: Number of States reporting groundwater contamination (maximum possible is 50) (US-EPA, 1994)
|
Pollutants |
No. of States |
Pollutants |
No. of States |
|
Nitrates |
49 |
Volatile organic substances |
48 |
|
Petroleum products |
46 |
Metals |
45 |
|
Pesticides |
43 |
Brine/salinity |
37 |
|
Synthetic organic substances |
36 |
Arsenic |
28 |
|
Other substances |
26 |
Other agricultural chemicals |
23 |
|
Radioactive material |
23 |
Fluoride |
20 |
|
Other inorganic substances |
15 |
|
|
The ranking of agriculture as a major polluter is highlighted by the statistics of Table 3. Fully 72% of assessed river length and 56% of assessed lakes are impacted by agriculture.
These finding caused the US-EPA to declare that: "AGRICULTURE is the leading source of impairment in the Nation's rivers and lakes ...".
Since the 1970s there has also been growing concern in Europe over the increases in nitrogen, phosphorus and pesticide residues in surface and groundwater. Intense cultivation and "factory" livestock operations led to the conclusion, already drawn by the French in 1980, that agriculture is a significant non-point source contributor to surface and groundwater pollution (Ignazi, 1993). In a recent comparison of domestic, industrial and agricultural sources of pollution from the coastal zone of Mediterranean countries, UNEP (1996) found that agriculture was the leading source of phosphorus compounds and sediment.
The European Community has responded with Directive (91/676/EEC) on "Protection of waters against pollution by nitrates from agricultural sources". The situation in France has resulted in the formation of an "Advisory Committee for the Reduction of Water Pollution by Nitrates and Phosphates of Agricultural Origin" under the authorities of the Ministry of Agriculture and the Ministry of the Environment (Ignazi, 1993).
Agriculture is also cited as a leading cause of groundwater pollution in the United States. In 1992, fully forty-nine of fifty states identified that nitrate was the principal groundwater contaminant, followed closely by the pesticide category (Table 4). The US-EPA (1994) concluded that: "more than 75% of the states reported that AGRICULTURAL ACTIVITIES posed a significant threat to GROUNDWATER quality."
In an analysis of wetlands, the US-EPA (1994) reported that: "AGRICULTURE is the most important land use causing WETLAND degradation".
Similar data are difficult to obtain or are not systematically collected and reported in other countries, however, numerous reports and studies indicate that similar concerns are expressed in many other developed and developing countries.
Types of impacts
Irrigation impacts on surface water quality
Public health impacts
Data on agricultural water pollution in developing countries
As indicated in Table 5 the impacts of agriculture on water quality are diverse. The major impacts will be discussed in greater detail in subsequent chapters.
United Nations' predictions of global population increase to the year 2025 require an expansion of food production of about 40-45%. Irrigation agriculture, which currently comprises 17% of all agricultural land yet produces 36% of the world's food, will be an essential component of any strategy to increase the global food supply. Currently 75% of irrigated land is located in developing countries; by the year 2000 it is estimated that 90% will be in developing countries.
In addition to problems of waterlogging, desertification, salinization, erosion, etc., that affect irrigated areas, the problem of downstream degradation of water quality by salts, agrochemicals and toxic leachates is a serious environmental problem. "It is of relatively recent recognition that salinization of water resources is a major and widespread phenomenon of possibly even greater concern to the sustainability of irrigation than is that of the salinization of soils, per se. Indeed, only in the past few years has it become apparent that trace toxic constituents, such as Se, Mo and As in agricultural drainage waters may cause pollution problems that threaten the continuation of irrigation in some projects" (Letey et al., cited in Rhoades, 1993).
TABLE 5: Agricultural impacts on water quality
|
Agricultural activity |
Impacts |
|
|
Surface water |
Groundwater |
|
|
Tillage/ploughing |
Sediment/turbidity: sediments carry phosphorus and pesticides adsorbed to sediment particles; siltation of river beds and loss of habitat, spawning ground, etc. |
|
|
Fertilizing |
Runoff of nutrients, especially phosphorus, leading to eutrophication causing taste and odour in public water supply, excess algae growth leading to deoxygenation of water and fish kills. |
Leaching of nitrate to groundwater; excessive levels are a threat to public health. |
|
Manure spreading |
Carried out as a fertilizer activity; spreading on frozen ground results in high levels of contamination of receiving waters by pathogens, metals, phosphorus and nitrogen leading to eutrophication and potential contamination. |
Contamination of ground-water, especially by nitrogen |
|
Pesticides |
Runoff of pesticides leads to contamination of surface water and biota; dysfunction of ecological system in surface waters by loss of top predators due to growth inhibition and reproductive failure; public health impacts from eating contaminated fish. Pesticides are carried as dust by wind over very long distances and contaminate aquatic systems 1000s of miles away (e.g. tropical/subtropical pesticides found in Arctic mammals). |
Some pesticides may leach into groundwater causing human health problems from contaminated wells. |
|
Feedlots/animal corrals |
Contamination of surface water with many pathogens (bacteria, viruses, etc.) leading to chronic public health problems. Also contamination by metals contained in urine and faeces. |
Potential leaching of nitrogen, metals, etc. to groundwater. |
|
Irrigation |
Runoff of salts leading to salinization of surface waters; runoff of fertilizers and pesticides to surface waters with ecological damage, bioaccumulation in edible fish species, etc. High levels of trace elements such as selenium can occur with serious ecological damage and potential human health impacts. |
Enrichment of groundwater with salts, nutrients (especially nitrate). |
|
Clear cutting |
Erosion of land, leading to high levels of turbidity in rivers, siltation of bottom habitat, etc. Disruption and change of hydrologic regime, often with loss of perennial streams; causes public health problems due to loss of potable water. |
Disruption of hydrologic regime, often with increased surface runoff and decreased groundwater recharge; affects surface water by decreasing flow in dry periods and concentrating nutrients and contaminants in surface water. |
|
Silviculture |
Broad range of effects: pesticide runoff and contamination of surface water and fish; erosion and sedimentation problems. |
|
|
Aquaculture |
Release of pesticides (e.g. TBT1) and high levels of nutrients to surface water and groundwater through feed and faeces, leading to serious eutrophication. |
|
1 TBT .= Tributyltin
FIGURE 2: Turbid irrigation return flow from a large irrigated area of southern Alberta, Canada
FIGURE 3: Seasonal nitrate variations in shallow sand aquifers in Sri Lanka in areas under intensive fertilized irrigation
(Yala refers to the dry season; maha refers to the rainy season)
Polluted water is a major cause of human disease, misery and death. According to the World Health Organization (WHO), as many as 4 million children die every year as a result of diarrhoea caused by water-borne infection. The bacteria most commonly found in polluted water are coliforms excreted by humans. Surface runoff and consequently non-point source pollution contributes significantly to high level of pathogens in surface water bodies. Improperly designed rural sanitary facilities also contribute to contamination of groundwater.
Agricultural pollution is both a direct and indirect cause of human health impacts. The WHO reports that nitrogen levels in groundwater have grown in many parts of the world as a result of "intensification of farming practice" (WHO, 1993). This phenomenon is well known in parts of Europe. Nitrate levels have grown in some countries to the point where more than 10% of the population is exposed to nitrate levels in drinking water that are above the 10 mg/l guideline. Although WHO finds no significant links between nitrate and nitrite and human cancers, the drinking water guideline is established to prevent methaemoglobinaemia to which infants are particularly susceptible (WHO, 1993).
Although the problem is less well documented, nitrogen pollution of groundwater appears also to be a problem in developing countries.
Lawrence and Kumppnarachi (1986) reported nitrate concentrations approaching 40-45 mg N/l in irrigation wells that are located close to the intensively cultivated irrigated paddy fields. Figure 3 illustrates the variation in N03-N which shows a peak in the maha (main) cropping season when rice growing is most intensive in Sri Lanka.
Reiff (1987), in his discussion of irrigated agriculture, notes that water pollution is both a cause and an effect in linkages between agriculture and human health. The following health impacts (in descending order of health significance) which apply, in particular, to developing countries, were noted by Reiff:
· Adverse environmental modifications result in improved breeding ground for vectors of disease (e.g. mosquitos). There is a linkage between increase in malaria in several Latin American countries and reservoir construction. Schistosomiasis (Bilharziasis), a parasitic disease affecting more than 200 million people in 70 tropical and subtropical countries, has been demonstrated to have increased dramatically in the population following reservoir construction for irrigation and hydroelectric power production. Reiff indicates that the two groups at greatest risk of infection are farm workers dedicated to the production of rice, sugar cane and vegetables, and children that bathe in infested water.· Contamination of water supplies primarily by pesticides and fertilizers. Excessive levels of many pesticides have known health effects.
· Microbiological contamination of food crops stemming from use of water polluted by human wastes and runoff from grazing areas and stockyards. This applies both to use of polluted water for irrigation, and by direct contamination of foods by washing vegetables etc. in polluted water prior to sale. In many developing countries there is little or no treatment of municipal sewage, yet urban wastewater is increasingly being used directly or recycled from receiving waters, into irrigated agriculture. The most common diseases associated with contaminated irrigation waters are cholera, typhoid, ascariasis, amoebiasis, giardiasis, and enteroinvasive E. coli. Crops that are most implicated with spread of these diseases are ground crops that are eaten raw such as cabbage, lettuce, strawberries, etc.
· Contamination of food crops with toxic chemicals.
· Miscellaneous related health effects, including treatment of seed by organic mercury compounds, turbidity (which inhibits the effectiveness of disinfection of water for potable use), etc.
To this list can be added factors such as the potential for hormonal disruption (endocrine disruptors) in fish, animals and humans. Hormones are produced by the body's endocrine system. Because of the critical role of hormones during early development, toxicological effects on the endocrine system often have impacts on the reproductive system (Kamrin, 1995). While pesticides such as DDT have been implicated, the field of endocrine disruption is in its infancy and data which support cause and effect are not yet conclusive. It is probably safe to conclude, however, that high levels of agricultural contaminants in food and water as are found in many developing country situations have serious implications for reproduction and human health. Box 2 presents a survey of the agricultural impacts in the Aral Sea region.
BOX 2: AGRICULTURE AND THE ARAL SEA DISASTER
The social, economic and ecological disaster that has occurred in the Aral Sea and its drainage basin since the 1960s, is the world's largest example of how poorly planned and poorly executed agricultural practices have devastated a once productive region. Although there are many other impacts on water quality in the region, improper agricultural practice is the root cause of this disaster. Virtually all agriculture is irrigated in this arid area. The Aral Sea basin includes Southern Russia, Uzbekistan, Tadjikistan, and part of Kazakhstan, Kirghiztan, Turkmenistan, Afghanistan, and Iran.
Population: 1976 = 23.5 million; and 1990 = 34 million
Area: l.8 × 106 km2
% Irrigated = 65.6% (1985)
Water Balance of the Aral Sea Basin
|
Perennial (average) water supply: |
118.3 km3/yr (100%) |
|
Irrigation demand (current estimates): |
113.9 km3/yr (96.3%) |
|
Consumptive use in irrigation is |
75.2 km3/yr (63.4% of available water supply) |
Irrigation Expansion and Inflow to Aral Sea
|
Irrigation: |
Since 2000-3000 B.C. |
|
1950s + - major expansion |
|
|
1985 - 65.6% of total land area |
|
Inflow to Aral Sea: |
Historical: 56 km3/yr |
|
1966-1970: 47 km3/yr |
|
|
1981-1985: 2 km3/yr |
Salinization
Magnitude and acceleration of salinization is demonstrated in Uzbekistan
|
|
Salinized Area |
% of Total Irrigated Area |
|
1982 |
12 000 km2 |
36.3 |
|
1985 |
16 430 km2 |
42.8 |
Public Health Impacts (Over past 15 years)
|
Typhoid |
- 29-fold increase (morbidity index up 20%) |
|
Viral Hepatitis |
- 7-fold increase |
|
Paratyphoid |
- 4-fold increase |
|
Number of persons with hypertonia, heart disease, gastric and duodenal ulcers -up 100% | |
|
Increase in premature births - up 31% | |
Morbidity & Mortality in Karakalpakia, from 1981-1987
|
|
Liver cancers: |
up 200% |
|
|
Gullet cancers: |
up 25% |
|
|
Oesophageal cancers: |
up 100% |
|
|
Cancer occurrence in young persons: |
up 100% |
|
|
Infant mortality: |
up 20% (1980-1989) |
|
Ecological and water quality impacts Salt content of major rivers exceeds standard by factors of 2-3. Loss of soil fertility. MISMANAGEMENT OF AGRICULTURE IS THE ROOT CAUSE * Increase in irrigation area and water withdrawals. UNEP (1993) concludes that, "high mineral [salt] content in drinking waters affects the morbidity of digestive, cardiovascular and urine-secretion system organs, as well as the development of gynaecological and pregnancy-related pathology," and "... the effects of pesticides on the level of oncological [cancer], pulmonary, and haematological morbidity, as well as on inborn deformities and other genetic factors .... exposure to pesticides also has been linked to immune system deficiencies...". (Source: UNEP, 1993. The Aral Sea) |
Data on water pollution in developing countries are limited. Further, such data are mostly "aggregated", not distinguishing the relative proportion of "point" and "non-point" sources. In Thailand, the Ministry of Public Health reported the results of pollution monitoring of 32 rivers (Table 6).
Pesticide consumption has strongly increased in all developing countries. In India, consumption increased nearly 50-fold between 1958 and 1975. Yet the Indian consumption in 1973-74 was reported to be averaging a mere 330 g/ha, compared to 1483 g in USA and 1870 g in Europe (Avcievala, 1991).
According to various surveys in India and Africa, 20-50% of wells contain nitrate levels greater than 50 mg/1 and in some cases as high as several hundred milligrams per litre (Convey and Pretty, 1988). In the developing countries, it is usually wells in villages or close to towns that contain the highest levels, suggesting that domestic excreta are the main source, though livestock wastes are particularly important in semi-arid areas where drinking troughs are close to wells.
Table 6: Pollution of 32 rivers in Thailand (Ministry of Public Health, Thailand, 1986)
|
Types of pollution |
No. of rivers affected out of 32 monitored |
|
Organic waste |
13 |
|
Microbial waste |
20 |
|
Heavy metals |
8 |
Decisions by agriculturalists for control of agricultural non-point source pollution can be at various scales. At the field level, decisions are influenced by very local factors such as crop type and land use management techniques, including use of fertilizers and pesticides. These decisions are based on best management practices that are possible under the local circumstances and are meant to maximize economic return to the farmer while safeguarding the environment. Local decisions are made on the basis of known relationships between farm practice and environmental degradation but do NOT usually involve specific assessment of farm practices within the larger context of river basin impacts from other types of sources. Decisions regarding use of waste water, sludges, etc., for agricultural application are also made using general knowledge of known impacts and of measures to mitigate or minimize these impacts. Specific recommendations are made in each chapter of this publication. However, the challenge for agriculturists is to mobilize the knowledge base and to make it available to farmers.
At the river basin scale, the nature of decision making is quite different. At this scale, the typical decision-making problem for non-point source control in many developing countries is that illustrated in Box 3.
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BOX 3: A TYPICAL SCENARIO FOR DECISION MAKING 1. Environmental status: HIGHLY EUTROPHIC or CONTAMINATED LAKE OR RIVER NO POINT OR NONPOINT SOURCE CONTROLS Nutrients WHAT IS THE MOST COST-EFFECTIVE MEANS OF REHABILITATION OR REMEDIATION? Comprehensive Basin Management |
It is not possible in this publication to describe in detail the "tools" that are used to address this basin-scale management problem. Moreover, many of the tools are not yet systematized to the point where they are easily accessible to agricultural practitioners.
One area, however, that is well known, is the data problem. The water quality database that is available in many developing countries (and in some developed countries) is of little value in pollution management at the river basin scale nor is it useful for determining the impact of agriculture relative to other types of anthropogenic impacts.
A common observation amongst water quality professionals is that many water quality programmes, especially in the developing countries, collect the wrong parameters, from the wrong places, using the wrong substrates and at inappropriate sampling frequencies, and produce data that are often quite unreliable. Further, the data are not assessed or evaluated, and are not sufficiently connected to realistic and meaningful programme, legal or management objectives. This is not the fault of the developing countries; more often it results from inappropriate technology transfer from the developed countries and an incorrect assumption by recipients and donors that the data paradigm developed by the developed countries is appropriate in the developing countries (Ongley, 1994).
Additionally, water quality monitoring programmes, worldwide, are under severe stress as governments reduce budgets, downsize, and shift priorities. "Monitoring" has become a dirty word and governments are increasingly reluctant to pay for it. Paradoxically, the need for reliable water quality information has never been greater. Fortunately, new scientific research, together with budget realities, now makes it possible to rethink and redesign data programmes that are inherently more focused, more practical, more efficient, produce more information and less data, and which meet programme goals in measurable economic terms (see Chapter 5).
This publication is not the place to deal substantively with new monitoring (data collection) techniques; however, it is sufficient to note here that monitoring technology has changed dramatically in the past decade, to the point where significant economic and information gains can be achieved in most monitoring programmes (Chapter 5). Significant for agricultural programmes is that water quality data are rarely collected by ministries of agriculture. Nevertheless, sustainable agriculture within the framework of comprehensive basin management will require relevant and reliable data upon which to make management decisions. This will necessitate intervention by agriculturalists in existing water quality data programmes if relevant data are to be collected for agricultural management purposes.
