Best Management Practices for Agricultural Non-Point Sources of Pollution	Report Contents Report in Word Format
	Caribbean Environment Programme Technical Report #41 1998	All CEP Technical Reports

SECTION 3. AGRICULTURAL NONPOINT SOURCE POLLUTION

3.1 Introduction

Point source pollution is any pollution from a confined and discrete conveyance such as a pipe, ditch, channel, tunnel, well, fissure, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft (UNEP, 1996). Examples of point source discharges in the WCR include sewage effluent, industrial discharge (e.g., discharges from refineries and petrochemical plants, sugar factories and rum distilleries, banana washing and packing activities, and canneries), and municipal storm water outfalls.

Nonpoint source pollution, on the other hand, is more difficult to recognize than point source pollution. Nonpoint source pollution emanates from unconfined or unchannelled sources, including, agricultural runoff, drainage or seepage, and atmospheric deposition (UNEP, 1996). The pollutants are carried off the land by surface water or through ground water flows.

Nonpoint sources of pollution arise from a broad group of human activities. The main characteristics of nonpoint source pollution include the following (Ongley, 1996):

• They respond to hydrological conditions.

• They are not easily measured or controlled directly (and therefore are difficult to regulate).

• They focus on land and related management practices.

The effects of nonpoint source pollution can be just as detrimental as the effects of point source pollution on the coastal and marine environment due to the often perpetual nature of the runoff and the initial imperceptibility of some of the pollutants.

A major source of nonpoint source pollution is runoff from agricultural areas. Rainfall or irrigation that results in overland flow to surface waters, commonly referred to as runoff, can carry pollutants from agricultural land uses into receiving, waters. Environmental problems related to agricultural nonpoint source pollution include the following:

• Decreased biodiversity
• Loss of coral reefs, fisheries, and seagrass beds
• Bacterial contamination
• Increased turbidity
• Alcral blooms
• Siltation
• Increased cost of remediation

Agricultural pollutants that can affect ground and surface waters include sediment, nutrients, pesticides, pathogens, and solid waste. These pollutants are washed off and transported during rainfall events or during irrigation into streams, rivers, and coastal wetlands. In addition, agricultural cultivation practices and livestock production can accelerate soil erosion on land, leading to increased sedimentation and turbidity in water bodies and decreased soil productivity. These pollutants are discussed in Section 3.3.

Problems related to the physical alteration of the environment (e.g., ditching, draining, clearing) to promote agricultural practices also pose a threat to the coastal environment of the WCR. Forests are often considered an expendable resource that can be sacrificed to make way for agricultural development. Pressures to increase cultivation areas have necessitated the clearing of more and more land, which in turn has resulted in the establishment of agricultural plots on steep slopes that are highly susceptible to erosion (CCA and IRF, 1991). Deforestation is occurring throughout the WCR to obtain more land for agricultural purposes (Table 3-1). This can have serious implications, including the reduction of agricultural productivity through soil loss and degradation. More than 2 million hectares of Caribbean tropical forests are cleared annually, but only 70,000 hectares are replanted (UNEP, 1991). Important factors that tend to accelerate the process of deforestation are poverty, lack of access to other sources of income, inadequate land management, weak tenure rights, lack of access to technologies that are appropriate for cultivation under fragile ecological conditions, and a biased price incentive structure that promotes land-intensive monoculture crops (Government of Belize, 1996). Additional environmental problems resulting from the unregulated clearing of lands for cultivation and uncontrolled livestock grazing include the following:

• Soil depletion
• Loss of mangroves
• Reduction in river base flows
• Increase in flash flood occurrence

3.2 Sources of Agricultural Nonpoint Pollution

The following sections provide an overview of cultivation and livestock production in the WCR and nonpoint sources of pollution that may be attributed to the practices associated with each.

3.2.1 Cultivation

During the past 15 to 25 years, major changes have taken place in Caribbean agriculture (DeGeorges, 1990). Poor land use management is prevalent when considering agriculture and development. In the last two decades, prime, highly productive agricultural land in many WCR countries has been replaced by uses that tend to produce a greater economic return. At the same time, agriculture has been pushed to areas less suitable for cultivation, requiring, additional inputs such as fertilizer and pesticides to increase overall productivity. Table 3-2 provides a summary of total land in agricultural production in the WCR and the amount of inputs applied to those lands.

Crops are typically' cultivated to suit the soil, topography, or technical capabilities of the country in which they are grown, leading to a wide range of environmental problems that must be faced. For instance, on some islands banana production predominates, and pollution from pesticides, herbicides, detergents, and other pollutants reaches the sea via rivers and streams (Archer, 1987). Sugarcane production produces wastes with high biological oxygen demand (BOD) concentrations. High BOD concentrations are known to stress fish nurseries occurring within coastal mangrove systems.

Table 3-1. Percent deforestation in WCR countries and territories

NA = information not available.
() = indicates a loss.
_ = reported as zero or nonexistent.
Source: Hoagland et al., 1995.

The following sections describe some of the cultivation practices used in the WCR. As an example of issues typically associated with crop cultivation, bananas are discussed in detail. Following the discussion of banana cultivation, other crops are discussed in less detail.

3.2.1.1 Bananas

The cultivation of bananas in tropical America and the Caribbean has special importance, not only because of bananas' critical contribution to the local diet, but also in view of the economic benefits derived from commercial production activities. Commercial production contributes to the gross national product, the establishment of employment sources, and the generation of foreign currency and fiscal earnings (Jaramillo, 1986).

Cultivation practices on commercial plantations typically consist of disc ploughing followed by harrowing,. This method is also used by some small farms with access to machinery. Nonmechanized smaller farms generally plant suckers in holes prepared with hand tools on flat land. Manual preparation is the most common practice on steep slopes for both small and large farms (Gumbs, 1993).

Bananas are grown as low-input subsistence crops and high-productivity income generators. Because of this, they can be found on the richest soils as well as in the most marginal areas, with high impacts on both. Erosion can be significant since the roots do little to stabilize the soil (CCA and IRF, 1991). When rain events occur, erosion from banana plantations can be severe and soil is often washed into the coastal zone (DeGeorges, 1990). Bananas grown in a monocrop system for commercial production deplete soil nutrients at such a high rate that nutrients cannot be replaced by mineralization of the parent soil or natural fertilization through decomposition (Hernández and Witter, 1996).

Table 3.2. Agricultural land use in the WCR

NA = information not available.
- = reported as zero or noneexistent.
Source: Hoagland et al., 1995.

Depending on the irrigation and erosion-control practices employed, banana production can be a ma nonpoint source of marine pollution (Hoagland et al., 1995). Although the types of chemicals us in banana production are often regulated by the individual governments, the transnational companies have traditionally determined the volume and kinds of chemicals applied and the frequency of chemical use (Hernández and Witter, 1996). Nonpoint source pollutants associated with a production are generated through the improper use of commercial and natural fertilizers, nematocides, fungicides, and herbicides (Hernández and Witter, 1996). (See Figure 3-1.) The field losses of these compounds depend on the amount and frequency of application, agronomical practices, type of chemical, soil type, precipitation, temperature, wind velocity, location, and method of application (Hernández and Witter, 1996). There is considerable waste, however, when chemical fertilizers are applied heavily and infrequently because the plants cannot benefit from the application before m of it is washed away or dissipated (Hernández, 1997).

Pesticides are applied in a variety of ways depending on the target species. In Costa Rica, the insecticide widely used is impregnated in the plastic bags used to cover the raceme. Fungicides, on the other hand, are sprayed aerial, representing 12 to 16 percent of the cost of banana production (Herndndez, 1997). On many of the eastern Caribbean islands, tremendous amounts of pesticides used primarily for banana production (DeGeorges, 1990). (see Table 3-3). On the commercial plantations of Costa Rica, the chemicals most often used include (brand name) Karrax, Ranger Roundup, Counter, Dipole, Farad, Mobcap, Ruby, Bravo, Dothan, and Mertak. The principal fungicides are triazoles, benimidazoles, mancozeb, clorothalonill, morfolinas, and agricultural (Hernández, 1997).

Illustration 3-1. Systčme de production des bananes
(Cliquez sur l'image)

The high production requirements of commercial banana cultivation necessitate the use of high levels of nutrients and pesticides (FAO, 1994). Banana cultivation is predominantly a monocrop system, which further increases the need for pesticides and fertilizers. Monocrop agriculture increases the concentration of food sources for pests (insects, bacteria, and fungi), making crops vulnerable to pest infestation and requiring more pesticide use to control disease and eliminate competing organisms (CCA and H?,F, 199 1). Furthermore, herbicides are often used to minimize the understory vegetation

Table 3-3. Pesticide use in banana production on the eastern Caribbean islands

Source: DeGeorges, 1990.

[Photo: Plastic bags treated with insecticide are placed over the banana raceme.]

around banana trees. It is thought that weeds are a problem in banana production because they compete for water, nutrients, and light, thereby reducing the height and girth of the trees, delaying maturity, and reducing yields in the crop. Additionally, weeds provide habitat for a variety of insects and viruses that harm crops.

Herbicides commonly used to enhance banana production are outlined in Table 3-4. Treatment times and weeds controlled vary, as do the environmental effects of each herbicide. Paraquat, for instance, can be very toxic to humans. Ametryn, diuron, and simazine persist in the soil to prevent the growth of many weeds. This persistence, coupled with soil erosion, leads to their entrance into surface waters.

3.2.1.2 Other Significant Crops

Sugarcane. Sugarcane is also a dominant crop within the WCR. Barbados, St. Kitts, and the Dominican Republic have traditionally depended on sugarcane as an economic base, although many other countries also produce sugarcane (see Table 2-5).

Sugarcane production has evolved over many centuries. Although sugarcane is mostly a high-input industrial crop (FAO, 1994), small family enterprises and sugar-processing factories that use simple extraction techniques still persist in many rural areas of the WCR. On islands such as Barbados and St. Kitts, traditional manual cutting of sugarcane has been replaced by large-scale mechanization. This has resulted in a change in how the land is managed. To accommodate large equipment, fields are enlarged and many traditional practices that would have minimized soil loss are abandoned (DeGeorges, 1990).

Table 3-4. Herbicides used in banana production

Source: FAO, 1994.

Production is affected by weather, disease, insects, soil quality, and type of cultivation. Due to high levels of weed competition in sugarcane fields, soil tillage is almost always used. Regardless of the soil type, tillage by disc plough and harrowing is used as a form of weed control. This soil disturbance can lead to problems with soil erosion in some areas.

Herbicides are commonly used to supplement tillage (Table 3-5). Treatments and weeds controlled vary, as do the environmental effects of each. The hormone-type weedkiller 2,4-D has been used in sugarcane fields for almost 40 years (FAO, 1994). 2,4-D spray and vapor have been known to injure neighboring broad-leaved crops such as cotton and tobacco.

[Photo: Sugarcane is a dominant crop in the WCR.]

Cotton has long been considered a major contributor to soil erosion on sloped lands. Cotton grows slowly during early summer and provides little crop protection from rain impact and soil erosion. Its roots are located close to the soil surface for the first 42 days of its cycle, with cultivation enhancing the potential for soil erosion. In addition, cotton provides little residue to return to the soil or to leave on the surface to protect from erosion (York et al., 1993).

Cotton accounts for most of the insecticide use in Latin America at an average level of about 6 kilograms of pesticide per hectare (Altieri, 1991). In cotton-growing areas of Central America, insecticide application rates have reached 80 kilograms per hectare (LACCDE, 1990).

Table 3-5. Herbicides used in sugarcane production

Source: FAO, 1994.

[Photo: Tillage can lead to erosion problems within a sugarcane production area.]

Weed competition also poses a serious threat to cotton production, with nearly 30 percent of world cotton production lost due to the adverse effects of weeds (FAO, 1994). If the crop is not weeded regularly, the losses can be up to 90 percent. To obtain high cotton yields, crops must be kept free of weeds from 14 to 60 days after crop emergence (FAO, 1994). This requires use of herbicides. Table 3-6 outlines some of the herbicides typically used in cotton production.

3.2.2 Livestock Production

Animal farming has become a major source of pollution and environmental degradation. Nonpoint pollution sources associated with livestock production include fields used for land application of manure and wastewater (as a fertilizer), manure accumulations around livestock watering, locations, and intermittently used stock pens (Sweeten, 1993). Livestock gazing can influence the water quality of streams, lakes, coastal systems, and aquifers. The nonpoint source pollution potential of pastured livestock depends in part on stocking density, length of grazing period, average manure loading rate, uniformity of manure spreading by grazing livestock-, and disappearance of manure with time (Sweeten, 1993).

Livestock production can result in adverse water quality impacts due to improper manure management. Manure production varies with breed, species, and feeding level (Graves, 1992). The primary constituents of livestock manure that can contaminate around water and surface waters include pathogenic organisms, nitrates, and ammonia (Sweeten. 1993). Animals on pasture distribute their manure during the grazing process. Manure includes the fecal and urinary wastes of livestock;

Table 3-6. Herbicides used in cotton production

Source: FAO, 1994.

process water (such as that from a milking parlor); and the feed, bedding, litter, and soil with which they become intermixed (USEPA, 1993). The following pollutants may be contained in manure and associated bedding materials and could be transported by runoff and process wastewater from confined animal facilities (USEPA, 1993):

• Oxygen-demanding substances.

• Nitrogen, phosphorus, and many other major and minor nutrients or other deleterious materials.

• Organic solids.

• Salts.

• Bacteria, viruses, and other microorganisms.

• Sediments.

Pathogens (bacteria, viruses, or any microorganisms that can transmit disease) can be transmitted to humans through contact with animal feces. Runoff from fields receiving manure as fertilizer will contain extremely high numbers of bacteria if the manure has not been mixed with other substances or the bacteria have not been subject to stress (USEPA, 1993). Although not the only source of pathogens, animal waste has been responsible for shellfish contamination in some coastal waters (USEPA, 1993).

Animals congregating in and along streams can affect stream integrity, plant biodiversity, and water wuality (Photography by Doug Norton, USEPA Office of Water).
(Click on image to view full photograph (232K))

Channel

Source: Adapted from Ongley, 1996.

Erosion. In the WCR, the most serious constraint to agricultural production is the inadequacy of the soil resources for agricultural purposes, a problem that can be compounded by mismanagement (Gajraj, 1981). Specific natural soil characteristics, type of vegetation cover, intensity of rainfall, winds, topography, and poor land use management affect the conservation of soil in the region. Approximately 25 percent of Latin America is composed of hillsides and plateaus susceptible to erosion and land degradation (Altieri, 1991). Some estimates of the long-term effects of soil erosion suggest losses of 30 percent of the potentially cultivatable unirrigated land in Central America. The areas most vulnerable to erosion are the Greater and Lesser Antilles, parts of Caribbean South America, and Trinidad and Tobago (Gajraj, 1981).

Figure 3-2. Pathways through which sediments, nutrients, pesticides, pathogens, and solid waste are transported from agricultural land to become water pollutants (USEPA, 1993).
(Click on image to see full figure.)

Soil erosion is a natural process characterized by the transport or displacement of particles (sediment) that are detached by rainfall, flowing water, or wind. Although it is a natural process, adverse impacts on receiving waters increase due to agricultural activities that alter the landscape and increase the rate of erosion. Soil erosion can be caused by the improper use of lands for cultivation or grazing and by deforestation (LACCDE, 1990). The types of soil erosion associated with agricultural activities are as follows (Figure 3-3):

• Splash erosion, which occurs when rain hits exposed soils.

• Sheet and rill erosion, which mainly moves soil particles from the surface or plough layer of the soil. Surface sediments typically contain higher pollution potential due to richer nutrient content, the presence of chemicals from past fertilizer and pesticide applications, and natural biological activities.

• Rill and gully erosion, severe erosion in which trenches are cut to a depth greater than 1 foot. Generally, trenches too deep to be crossed by farm equipment are considered gullies (USEPA, 1994).

• Stream and channel erosion, which occurs due to increased rates and volumes of runoff from agricultural land uses flowing through a stream or channel.

Figure 3-3. Four types of soil erosion on an exposed slope (UNEP, 1994a).
(Click on image to see full figure.)

During the Pollution Control Measures for Agricultural Runoff Experts Meeting in St. Lucia (January 22 and 23, 1998), several causes of erosion and sedimentation were identified. They include the following:

• Planting on steep slopes

• Deforestation

• Clear-cutting

• Improper tillage methods

• Improper timing of site preparation

• Compaction by animals

• Improper irrigation methods and water management practices

• Channelization and artificial drainage

The primary factors affecting soil erosion rates include rainfall intensity and frequency, soil characteristics, vegetative and other surface cover, topography (slope), and climate (e.g., degree of exposure to trade winds) (USVI Conservation District, 1995). Soil characteristics play a key role; even low-intensity rainfall induces erosion in areas where soils are easily saturated (UNEP, 1994a). In addition, the topography, slope length, and slope steepness influence soil erosion. Steeper slopes are susceptible to erosion due to increased runoff velocity, greater downslope transport of rain-splashed soil, and greater susceptibility to landslides (UNEP, 1994a). Disruption of soil through earthmoving (tilling, ploughing, etc.) or livestock activity increases erosion potential regardless of the soil type. Generally, the more vegetative cover, the less potential there is for erosion.

Turbidity, Siltation, and Sedimentation. When soils are eroded from agricultural lands and carried to coastal waters in runoff, the result is usually increased turbidity, siltation, and sedimentation. Throughout the WCR, siltation and turbidity of coastal waters are on the rise due to the transport of eroded soils to the sea. Data on the distribution of sediments and the turbidity of coastal waters of the WCR are insufficient to assess the magnitude of the adverse effects of present-day land use practices (UNEP, 1994a). However, reefs near the Central American coast and areas of the eastern Caribbean are believed to be suffering from sediment stress related to agricultural practices, and some estimates of the long-term effects of soil erosion suggest losses of potentially 30 percent of arable unirrigated land in Central America (Hoagland et al., 1995).

The adverse impacts of accelerated erosion and sedimentation include the following:

• Loss of agricultural productivity. Erosion removes valuable topsoil and thus reduces the productivity and water-holding capacity of agricultural land.

• Lost reservoir capacity. Sedimentation reduces the water storage capacity of reservoirs and shortens their functional life span. In Puerto Rico, for example, some reservoirs have lost virtually all of their storage capacity and others are filling with thousands of cubic meters of sediment annually.

• Other downstream impacts. Sedimentation can fill culverts, ponds, and storm drainage systems. Navigation may be impeded by increased sediment loading to receiving waters, necessitating expensive dredging (UNEP, 1994a).

Erosion and sedimentation affect water quality in many ways:

• Suspended solids reduce the amount of sunlight available to aquatic plants, cover fish spawning areas and food supplies, smother benthic communities, clog the filtering capacity of filter feeders, and clog and harm the gills of fish. Turbidity interferes with the feeding habits of fish. These effects combine to reduce fish, shellfish, coral, and plant populations and decrease the overall productivity of coastal waters.

• Turbid waters reduce the recreational appeal of coastal areas, limiting sportfishing, diving, and swimming opportunities.

• Sediment can cause property damage and cost property owners money for removal (USVI Conservation District, 1995).

• Nutrients and pesticides are transported mixed with sediment, or chemically bound to the sediment, changing the aquatic environment through eutrophication and introduction of toxics.

In the Caribbean, the most common marine pollution problems arise due to nutrient overenrichment resulting from sewage discharge and runoff from agricultural land uses. Sources of nutrient overenrichment include fertilizers, soil mineralization, and manure. During the Pollution Control Measures for Agricultural Runoff Experts Meeting, the causes of nutrient overenrichment in the WCR were identified as the following:

• Artificial drainage

• Overfertilization

• Poor crop siting (land use)

• Lack of natural buffers between agricultural and natural resources

• Timing of fertilization

• Erosion of absorbed nutrients in sediment

• Improper irrigation techniques

• Allowing open grazing of livestock

• Confined livestock facilities

• Volatilization of animal waste

Agricultural crops require nutrients for healthy growth. Some of these nutrients occur naturally, supplied to a plant through the air, water, and soil. To supplement the naturally occurring nutrients, organic and inorganic fertilizers are applied in a commercial dry or liquid form, as manure from animal production facilities, as crop residues, in irrigation water, and through aerial deposition. Table 3-8 presents data on the use of fertilizers in 17 countries of the WCR. When applied correctly, fertilizers promote plant growth; when used excessively or inappropriately, however, fertilizers can lead to nutrient overenrichment within water bodies, one of the most widespread coastal pollution problems today. As a result, surface water runoff from poorly managed agricultural lands may transport the following pollutants (USEPA, 1993):

• Particulate-bound nutrients, chemicals, and metals, such as phosphorus, organic nitrogen, and metals applied with some organic wastes.

• Soluble nutrients and chemicals, such as nitrogen, phosphorus, metals, and many other major and minor nutrients.

• Sediment, particulate organic solids, and oxygen-demanding material.

• Salts.

• Bacteria, viruses, and other microorganisms.

Excess nutrients also enter coastal waters through improper storage and handling of fertilizers and disposal of fertilizer containers. For example, if bags of fertilizer are stored in such a manner that the bags can break open and inadvertently release fertilizer into the environment, the fertilizer adds to the volume of nutrients that could flow to coastal waters in runoff.

Excess nitrogen and phosphorus, considered the nutrients that have the greatest effect on water quality, enter waters from agricultural fertilizers and manures. Nitrogen dissolves in water and is carried in runoff. Phosphorus is either dissolved or held tightly by soil clays and transported mainly through erosion (Lilly, 1995). Excess fertilizers in the form of liquid leachates, surface runoff, erosion, or gases leave the system and enter surface waters. Nutrients can increase the productivity and yield of a crop on land and may do the same to aquatic plants when they enter a water body. Excess levels of nutrients in runoff to coastal waters can result in an imbalance in the natural nutrient cycle, leading to unwanted and excessive plant growth, a process called eutrophication (USVI Conservation District, 1995). When nutrients are introduced into a stream, lake, or estuary at higher-than-natural rates, aquatic plant productivity can increase dramatically (USEPA, 1993). Increased productivity results in an increase of organic matter in the aquatic system. Organic matter dies and decays after a period of time. Since the decaying process requires oxygen, an excessive increase in plant productivity can ultimately result in a reduction in the oxygen supply. This can lead to anoxic conditions, resulting in an environment where few organisms can live.

Nutrient enrichment of coastal waters can lead to an increase in algal (planktonic) growth, which is harmful to coral reefs and other benthic communities. With increases in algal growth, turbidity increases, further inhibiting the growth of submerged aquatic vegetation (SAV). A loss in SAV equates to a loss of habitat. The accumulation of nutrients in deposited sediments can further compound problems associated with nutrient enrichment. Changes in the aquatic environment (e.g., temperature, salinity) allow the nutrients to be released from the sediment and serve as a long-term contributor to eutrophication.

The term pesticide includes any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest or for use as a plant regulator, defoliant, or desiccant (USEPA, 1993). For the purposes of this document, pesticides include insecticides, herbicides, fungicides, miticides, and similar substances. Within the WCR, regional experts have identified the following causes for pesticide contamination:

• Improper application (timing, method, amount, etc.)

• Erosion (absorbed chemicals)

• Cropping systems (e.g. monocultures)

• Improper equipment maintenance

• Mishandling, storage, and disposal

• Inappropriate selection

• Leaching

• Improper water management

• Artificial drainage

• Volatilization

The pesticides most commonly used in agriculture are the organochlorine and organophosphorus types, the more toxic but less persistent being the organophosphates. These pesticides are toxic to crustaceans such as shrimp, lobster, and crab and are similarly toxic to some fish species. They are known to bioaccumulate in some marine fauna (Archer, 1987).

The impacts of pesticides are not necessarily limited to the intended sites of application. There is considerable waste when chemicals are applied heavily and infrequently; the crop cannot benefit from the application before much of it is washed away or dissipated (Hernández and Witter, 1996). Depending on the application method used, dispersion of pesticides off site occurs by wind, runoff, high-flight-altitude drift of spray outside crop areas, accidental spills, improper storage and handling, and improper disposal of pesticide containers. Heavy use of pesticides for agriculture in watersheds some distance from the coast can be as destructive as direct industrial discharges of toxics, depending on such factors as persistence of the pesticide, quantities reaching the aquatic environment, potential for bioaccumulation, and toxicity (Coté, 1988). The dispersal of a pesticide from sites of intentional or accidental application is strongly affected by its persistence in the environment, its solubility in water, and its tendency to bind to organic matter or clays in soil (Rainey et al., 1987).

Unintended effects of pesticide use include elimination or reduction of populations of nontarget desirable organisms, including endangered species (USEPA, 1993). The amount of field-applied pesticide that leaves a field in the runoff and enters a stream, as depicted in Figure 3-4, primarily depends on the following factors (USEPA, 1993):

• Intensity and duration of rainfall or irrigation.

• Length of time between pesticide application and rainfall occurrence.

• Amount of pesticide applied and its soil/water partition coefficient.

• Length and degree of slope and soil composition.

• Extent of exposure to bare (vs. residue- or crop-covered) soil.

• Proximity to streams.

• Method of application and formulation.

• Extent to which runoff and erosion are controlled with agronomic and structural practices.

Figure 3-4. Factors affecting the transport and water quality impact of a pesticide (USEPA, 1993).
(Click on image to see full figure.)

Pesticides that bind to soil particles and show little tendency to leach into ground water may still disperse if the soil particles themselves are eroded downslope and carried into streams, settling for varying times in stream or estuarine sediments or coastal marine habitats (Rainey et al., 1987). Furthermore, many pesticides are soluble in water and may enter surface waters through runoff.

Pesticide losses are generally greatest when rainfall is intense and occurs shortly after pesticide application, a condition for which runoff and erosion losses are also greatest (USEPA, 1993). This loss of pesticide not only harms the environment but also leads to economic losses. The misuse of pesticides, through misapplication or overapplication, increases costs for pesticides.

The pesticides that are particularly harmful are those that are resistant to degradation and, as a consequence, accumulate in the environment. According to their chemical make-up, pesticides can be transported through sediment transport or by dissolution in water. Pesticides may inhibit the development or reproductive process of certain organisms. Herbicides may eliminate food sources of aquatic organisms. Pesticides that bioaccumulate in marine biota can be transmitted through fishery resources to humans, posing serious health and ecological hazards (Diamante et al., 1991). Excessive and careless use of agrochemicals, specifically pesticides, is one of the predominant causes of chemical poisoning in the WCR (Hoagland et al., 1995). Pesticide residues present at dangerous levels in the food chain and water supply pose immediate threats to public health.

The extensive use of pesticides due to intensive agricultural activity within the WCR is well documented, and its impact on land and coastal marine ecosystems is reasonably evident (UNEP, 1994b). In Colombia alone, more than 600 different pesticides are used, which represent approximately 33,000 metric tons per year (Tinoco, 1994). Through runoff, erosion, and misapplication, significant quantities of pesticides are reaching the coastal and marine environment, where they may affect nontarget species and, through the contamination of seafood, may become a public health problem (UNEP, 1994b). Furthermore, many pesticides that are banned in developed countries are widely used in Latin America (Altieri, 1991). Approximately 75 percent of the pesticides used in Central America are either prohibited or restricted in the United States (LACCDE, 1990). The use of pesticides is further influenced by government subsidies in some countries, which lower the financial burden and thereby induce farmers to substitute chemical for nonchemical methods of pest management.

Overall, the use of pesticides within the WCR appears to be on the increase. A 1992 report from the World Resources Institute showed a general increase in the use of pesticide compounds during the 1974-1984 period (Table 3-9). Pesticide use is expected to increase in Latin America by 280 percent during the period from 1980 to 2000 (Altieri, 1991). Those countries showing a reduction in use attributed this to changes in agricultural practices to reduce the use of pesticides and use less persistent pesticides with lower application rates (UNEP, 1994b).

Wastes from livestock production are a significant component of agricultural nonpoint source pollution (Myers, 1985). Animal use of water sources, improper location of animals, and improper application of manure can cause serious water quality problems. As stated in Section 3.3.2, runoff from livestock production areas can lead to water quality problems related to nutrients. This runoff can have serious human health impacts as well. Animal diseases can be transmitted to humans through contact with animal feces (USEPA, 1993) and dead animals. A number of pathogenic bacteria can be found in untreated wastewater, including those which cause typhoid fever, hepatitis,

Source: World Resources Institute, 1992, cited in UNEP, 1994b.

and dysentery (Lilly, 1996). Runoff from fields receiving manure will contain extremely high numbers of bacteria if the manure has not been properly treated for bacterial content. In addition, the amount of animal waste or manure in runoff can be quite substantial. For example, a 100-cow dairy herd produces as much fecal matter as a community with a population of 15,000 (Myers, 1985). The bacteria most often mentioned in connection with water quality problems are the coliforms, since they are reliable indicators of fecal contamination (Lilly, 1996). Although not pathogenic themselves, coliform bacteria are easily detectable and usually indicate that animal or human waste is present and, by inference, that pathogens might be present as well (Lilly, 1996).

Shellfish closure and beach closure can result from high fecal coliform counts. Although not the only source of pathogens, animal waste has been known to be responsible for shellfish contamination (USEPA, 1993). Shellfish that ingest pathogenic bacteria can cause disease when eaten by humans (Lilly, 1996).

Another source of pathogens in surface and ground waters is dead livestock. If decaying animals are not properly disposed of, they introduce fecal coliforms and other bacteria. Mammals serve as a host for a variety of microorganisms that may be released once the animal is dead. Depending on the cause of death, lethal substances might also be released. Decaying animals, like decaying plants, are also a source of nutrients.

Debris resulting from banana production operations can be transported off site.
(Click on image to see full photograph (2MB))

The pollution caused by solid waste is largely disregarded (Silva, 1994). All plants produce significant quantities of general waste, including large quantities of peels, cores, seeds, or other unusable parts of the raw product that must be discarded. In addition, many facilities produce office waste, plastics, twine, unusable containers, waste packaging materials, and household waste (if housing is provided for workers). Improper handling and disposal of these items, coupled with a lack of disposal alternatives, can result in a significant source of nonpoint source pollution. Trash and debris from an agricultural facility can be washed off site and into a water body. These artificial materials can litter the ocean floor and can be detrimental to marine organisms. Furthermore, solid wastes cause not only impacts related to infectious diseases and organic matter but also adverse impacts related to high organic concentrations, toxic waste, hazardous waste, infectious waste, and radiological waste (Silva, 1994).

Tables, Figures, Acronyms | SECTION 1. | SECTION 2. | SECTION 3. | SECTION 4. | SECTION 5. | SECTION 6. | SECTION 7. | GLOSSARY | REFERENCES CITED | APPENDIX A | APPENDIX B | APPENDIX C | APPENDIX D