Threats to Sources of Drinking Water and Aquatic Ecosystem Health in Canada
- Executive Summary
- 1. Waterborne Pathogens
- 2. Algal Toxins and Taste and Odour
- 3. Pesticides
- 4. Persistent Organic Pollutants and Mercury
- 5. Endocrine Disrupting Substances
- 6. Nutrients—Nitrogen and Phosphorus
- 7. Aquatic Acidification
- 8. Ecosystem Effects of Genetically Modified Organisms
- 9. Municipal Wastewater Effluents
- 10. Industrial Point Source Discharges
- 11. Urban Runoff
- 12. Landfills and Waste Disposal
- 13. Agricultural and Forestry Land Use Impacts
- 14. Natural Sources of Trace Element Contaminants
- 15. Impacts of Dams/Diversions and Climate Change
13. Agricultural and Forestry Land Use Impacts
P. Chambers,1 C. DeKimpe,2 N. Foster,3 M. Goss,4 J. Miller5 and E. Prepas6
1Environment Canada, National Water Research Institute, Burlington, ON
2Agriculture and Agri-Food Canada, Research Branch, Ottawa, ON
3Natural Resources Canada, Canadian Forestry Service, Sault Ste. Marie, ON
4University of Guelph, Department of Land Resource Science, Guelph, ON
5Agriculture and Agri-Food Canada, Lethbridge Research Station, Lethbridge, AB
6University of Alberta, Department of Biological Sciences, Edmonton, AB
Land use and land management practices affect the quantity and quality of runoff water and, in turn, the water budget, water chemistry and biodiversity of aquatic organisms in receiving waters. In Canada, approximately 12% (119 million ha) of the total land base is currently managed for timber harvest, another 7% (68 million ha) is used for farming and an additional 1% (7 million ha) is in urban and industrial development.
Canada's forests, which represent 10% of the world's forests, cover nearly half of the Canadian landscape--some 418 million ha. Forests are a dominant feature of Canada's economy, culture, traditions and history. They represent an integral part of our natural environment and life-support systems. Forests also contribute 10% of Canada's gross domestic product in the primary production sector. In addition to their socioeconomic value, forests purify water, moderate climate, regulate water flow, provide habitat for wildlife and stabilize soil. Canada is one of the world's largest suppliers of wood products. Some 245 million ha (or 59%) of Canada's forestland are capable of producing commercially valuable timber, of which 119 million ha are actively managed for timber harvest (CCFM 2000). Changes in forest soil characteristics and forest hydrology following timber harvest have raised concerns about the quantity and quality of water supplied to nearby lakes, streams and wetlands and the effects of these water quality and quantity changes on aquatic organisms.
Agricultural production is the transformation of solar energy and nutrients into crops, much of which is then fed to livestock to yield meat, dairy and poultry products. Agriculture represents 29% of Canada's gross domestic product in the primary production sector, second after mining and energy (29%). Of the total agricultural land base, 83% is in the Prairies and about 13% is in Ontario and Quebec. Approximately 46 million hectares are improved land (i.e., cropland and summerfallow) while the remainder (22 million ha) is unimproved land, essentially pastures. The last century saw great development in many agricultural technologies such as high-yielding crop varieties, chemical fertilizers, pesticides, irrigation and mechanization. These developments have resulted in agricultural operations becoming increasingly specialized such that the emphasis is either on livestock or intensive cash cropping (DeKimpe et al. 2000). Whereas mixed farms were able to efficiently recycle animal manure by applying it to agricultural fields, geographic separation between intensive livestock operations and cash-crop farms has resulted in manure being regarded in some locales as a waste requiring disposal rather than as a fertilizer and soil amendment. In contrast, cash crop farms need to apply large amounts of manufactured fertilizers to meet crop requirements. This inequitable distribution of resources, along with the cultivation of marginal land caused by loss of prime agricultural land to urbanization, has raised concerns about the effect of nutrients and pathogens from manure and chemical fertilizers on air and water quality.
Two key science questions underlie concerns about sustainability of healthy waters in agricultural and forested landscapes: (1) has human activity affected the availability of the quantity and quality of water and the aquatic life supported by this water, and (2) how will new or additional stresses affect existing conditions?
The greatest threats to forest ecosystems today are conversion to other forms of land use and fragmentation by agriculture, logging, and road construction. Logging and road construction, in turn, open intact forest to settlement and increases in hunting, poaching, fires, and exposure of flora and fauna to pest outbreaks and invasive species. In 1999, about 119 million ha (or 28%) of Canada's forestland were actively managed to produce timber. About 1 million ha (or 0.8% of this commercial forest area) was harvested, removing approximately 174.5 million m3 of wood. About 60% of the area harvested was left to regenerate naturally, usually after some form of preparatory site treatment; the remaining area was planted with seedlings or seeded. Areas affected by fire (1.7 million ha in 1999), insects (5.1 million ha in 1999), and disease were also left to regenerate naturally.
Undisturbed forests efficiently cycle water as well as large quantities of nitrogen and other nutrients with very small losses to surface and ground waters. Streams draining undisturbed forest generally have high water quality with low concentrations of dissolved nutrients and suspended sediments. Forest management practices that disrupt the cycle of nutrients between the soil and trees may increase runoff and concentrations of dissolved nitrogen, base cations and, to a lesser extent, phosphorus in adjacent streams and lakes. Timber harvest, when conducted near stream banks, results in an increase in water temperature due to removal of the forest canopy. In addition, removal of forest vegetation can increase soil erosion, resulting in increased sedimentation and detrital input to streams and lakes. Nutrient, cation and sediment inputs to streams and lakes as a result of forest management practices have been defined for relatively few sites in Canada. The effect of forest management practices on water quantity and quality is difficult to assess, therefore, and confounded by climatic, topographic and vegetation diversity across the country.
Over the past 40 years, the number of farms in Canada have declined, but those that remain have become larger and more productive. This transformation was made possible by greater mechanization, the use of mineral fertilizers and pesticides, new and better crop varieties, and innovative farming practices. Over time, some of these advances have clearly compromised environmental health, including water quality. Agricultural impacts on water resources are caused by:
- The need for additional water (semi-arid landscapes) or to route excess water off fields (humid landscapes). These practices have had positive effects on water quality (e.g., proper drainage reduces surface runoff and erosion, and loss of nitrogen by denitrification) but also detrimental effects (e.g., increased leaching or runoff of agrochemicals [nutrients and pesticides] and bacteria to surface and ground waters).
- The use of additional nutrients (in the form of mineral fertilizer, manure, compost, sewage sludge) to increase crop productivity. This practice has led in certain parts of Canada to a nutrient surplus in the soils with the potential loss of nutrients to surface and ground waters.
- The use of pesticides (fungicides, herbicides and insecticides) for disease, weed and insect control. Although the use of pesticides has increased the efficiency of fertilizer use, this practice has resulted in pesticide losses to the atmosphere and subsequent deposition from the atmosphere to surface water and non-agricultural lands, as well as runoff and leaching to surface and ground waters.
- Alterations to soil conditions caused by tillage and cropping patterns. Certain of these practices may cause soil degradation, which can lead to less infiltration of water into soil and, thus, increased runoff and movement of nutrients and pesticides to surface waters. Over the past 40 years, tillage practices have moved toward greater use of conservation practices, including no-till. These tend to encourage infiltration rather than runoff.
- Drainage of wetlands and canalling of streams has increased the area of agriculturally productive soils, but modified local ecosystems and changed the pattern of water partitioning between evaporation, streamflow and infiltration.
In 1995, about 995 thousand hectares of forest were harvested, representing 0.4% of Canada's total timber-productive forest area and 0.8% of the accessible timber-productive forest area (CCFM 2000). Softwood species (e.g., pine, spruce) accounted for more than 86% of Canada's total commercial timber harvest in 1995. Although total harvest levels for softwood in 1995 were below the allowable annual cut (AAC) on a national basis, the harvest reached the AAC in some regions while in other regions, timber supply shortages were reported. The hardwood component (e.g., poplar, maple) of the annual harvest increased between 1990 and 1995 by over 6%--representing an annual increase of 1.3%. This trend is expected to continue in order to meet market demand.
Timber harvesting methods include clear-cutting, selection cutting, shelterwood cutting and seed-tree cutting. Clear-cutting was the most widely used method in 1995. Because of environmental impacts associated with large cutblocks (e.g., forest fragmentation, increased potential for changes in runoff and water quality), forest management practices in Canada are shifting toward smaller cutblocks with irregular boundaries interspersed with uncut forest to create greater spatial and age diversity in the landscape. Clear-cutting, because it does not mimic the ecological effects of fire, sometimes results in fundamental ecological shifts in fire-dominated ecosystems (Carleton and MacLellan 1994).
Climate change could have serious ecological and socioeconomic implications for Canada's forests. Climate warming will not only affect the frequency and severity of natural disturbances (e.g., wildfire and outbreaks of spruce budworm) but will also influence management practices such as harvest schedules, regeneration and afforestation, and forest protection. Climate warming may result in changes in the water table with resultant changes in storage and release of nutrients and metals from forest soils and wetlands.
The last century saw great development in agricultural technologies and production. Between 1950 and 1985, the success of the Green Revolution in reducing food shortages in several parts of the world was linked primarily to new crop varieties designed to maximize yields, facilitate multiple cropping, and resist diseases. To achieve the full potential yield of these improved varieties and to protect them against diseases and pest infestation, it was essential to provide crops with chemical nutrients, the consumption of which rose more than ninefold, and to employ pesticides, the use of which increased 32 times.
With little prospect for the development of significant areas of new farmland, yet continuing government policies encouraging more food production, agri-food production in Canada has increased in efficiency during the past two decades (DeKimpe et al. 2000). For example, grain production in Canada increased by 2.4-fold between 1961 and 1986 on a cropland base that increased by only 1.6 times (from 18 to 28 million ha). This production growth was achieved through improved crop strains and increased fertilizer use (from 2.0 million tonnes in 1967 to 4.2 million tonnes in 1987 of nitrogen, phosphorus and potassium fertilizers) and pesticide application. A 2.9% increase in milk production in Ontario between 1951 and 1991 (from 2.39 to 2.46 billion litres) was achieved using 849 thousand fewer animals and 573 thousand fewer hectares, and resulted in a 42% decrease in dairy cattle manure (from 21.4 to 12.5 million tonnes). Much of the grain used as feed was obtained from higher-yielding and more disease-resistant crops and employed farming practices that required less fossil fuel use (i.e., grain corn production increased from 3.3 to 5.3 million tonnes between 1975 and 1991 whereas litres of diesel fuel equivalents declined from 292 to 191 million over the same period). Although certain efficiencies in agri-food production have reduced threats to water quality, other efficiencies have increased the risks posed to water quality. For example, greater use of mineral fertilizers and pesticides and greater manure production can increase the risk of water contamination unless these substances are adequately managed. The situation is further exacerbated by the growing trend toward application of sewage sludge to cropland.
Demand for water is growing in Canada by the agricultural community (particularly to meet irrigation needs) as well as by other sectors. Competition for the finite supply of water, particularly in water-short areas such as the Prairies and the interior of British Columbia, or at times of drought in areas such as Ontario, has already given rise to conflict among users (Kienholz et al. 2000). This situation is likely to become worse in the future under possible climate change scenarios. Global warming scenarios indicate that drought will be more frequent and severe where precipitation does not make up for the increased water losses from evaporation. However, the uncertainty in climate models, particularly related to precipitation, makes it difficult to predict confidently where, when, and to what degree droughts will take place in the future. If the significant declines in streamflow, groundwater levels, and lake levels are realized, there will be greater potential for conflict over water allocation and for deterioration in water quality caused by reduced water availability for dilution of pollutants.
Physical Properties of Lakes and Streams
Timber harvest can increase water yield, suspended solids and temperature in streams. In general, total runoff increases with forest disturbance due to reduced interception and transpiration by the forest canopy. Annual peak discharge shows, however, a variable response with some studies reporting increases and others decreases, possibly due to differences in climate, geology, topography, vegetative cover, soils, and the timber harvesting method. For example, water yield and peak flow returned to preharvest conditions within three to six years for two northern hardwood streams (White Mountains, New Hampshire; Martin et al. 2000) whereas high runoff is predicted to persist for decades after forest clearance in the boreal forests of eastern Canada (Plamondon 1993). Increased stream discharge may be associated with higher sediment yields, although this may be controlled by employing best management practices (Martin et al. 2000).
Chemistry of Lakes and Streams
Loss of forest cover can disrupt biogeochemical cycles as a result of alterations of chemical sinks and sources, increases in soil temperature and humidity, changes in soil structure caused by logging equipment, and flushing of chemicals (e.g., nitrogen, phosphorus, dissolved organic carbon and major ions such as calcium, potassium and sulfate) from surficial soils. The impact of timber harvest on concentrations of dissolved solids depends on the intensity of harvest, forest cover, soil type, and slope steepness. Impacts will also vary with the level of protection afforded during disturbance, through the use of lakeshore or streamside reserves and buffer strips. Increases in water yield following timber harvest may further exacerbate nutrient and ion export. Our understanding of the effects of timber harvest on biogeochemical cycles is not sufficient to predict the magnitude and duration of environmental responses to logging. For example, clear-cutting around deep headwater lakes in northwestern Ontario caused only modest changes in nutrient and major ion concentrations (Steedman 2000) whereas concentrations of most dissolved substances were substantially higher in central Quebec lakes affected by wildfire or harvesting (Carignan et al. 2000). In aspen-dominated sites on the Boreal Plain, phosphorus but not nitrogen concentrations in lake water appear to be enhanced by winter harvesting practices (Prepas et al. 2001). Although the differing response between lakes in these three ecoregions may be due, in part, to differences in lake morphometry, drainage ratio and water renewal times, such variability is typical for the limited number of studies on timber harvest impacts on aquatic ecosystems in Canada.
Logging has also been found to cause increased concentrations of mercury in fish. Comparison of total mercury concentrations in northern pike (Exos lucius) from Boreal Shield lakes in Quebec showed that concentrations were significantly greater for lakes in logged watersheds than for lakes in reference or burned watersheds. Mercury concentrations in pike were above the World Health Organization safe consumption limit for all logged lakes (Garcia and Carignan 2000).
Timber harvesting can produce significant environmental impacts that may affect all trophic levels of stream or lake ecosystems. Studies on coastal streams have shown that the major impacts of timber harvesting operations result from increased stream discharge, sedimentation, detrital input (including logs) and water temperature. Increased production of fine sediments, in turn, reduces the availability of benthic habitats for attached algae, aquatic insects and fish. However, recent research on Boreal Shield and Boreal Plain lakes indicate that increased nutrient supply (notably phosphorus) can result in food web alterations. For example, total phosphorus and total organic nitrogen concentrations were significantly higher in Boreal Shield lakes in Quebec in the three years following timber harvest as compared with lakes in undisturbed watersheds (Carignan et al. 2000). In the lakes exposed to timber harvest, a significant increase in phytoplankton abundance was observed in the first year following harvest, an increase that likely would have been even greater if not for lower light penetration caused by inputs of dissolved organic carbon that coloured the water (Planas et al. 2000). On the Boreal Plain, only a small timber cut (15% of the watershed) resulted in a doubling in cyanobacteria abundance and a tenfold increase in an associated hepatotoxin, microcystin-LR; abundance of large zooplankton was also depressed (Prepas et al. 2001). An indirect consequence of timber harvest on aquatic biota arises as a result of road construction and improved access to previously remote regions. This improved access can, for example, lead to overexploitation of fish populations in small lakes.
On a national level, agriculture withdraws a relatively small amount of water (9%) compared to thermal power generation (63%) and manufacturing (19%). However, agriculture consumes a large portion of what it uses, returning less than 30% to its source (Kienholz et al. 2000). About 75% of all agricultural withdrawals of water occur in the semi-arid Prairies. The demand for water is growing for all sectors, increasing the potential for competition and conflict among water users. This situation becomes worse during the droughts that periodically occur in parts of Canada. At least 40 severe droughts have affected western Canada in the past 200 years. Droughts also occur in eastern Canada, but they are usually shorter in duration, smaller in area, and less frequent. The moisture deficit caused by drought places farmland soils at risk, poses a threat to both crop and livestock production, and may result in declines in the quantity and quality of surface and ground waters as more water is diverted to farm operations and less water is available for dilution of pollutants.
The introduction of soil into aquatic ecosystems can increase turbidity and thereby reduce plant photosynthesis, interfere with animal behaviours dependent upon sight (e.g., foraging, escaping from predators), impede respiration (by gill abrasion) and feeding, degrade spawning habitat and suffocate eggs. Although much of the sediment in rivers is derived from natural sources, agricultural practices such as tillage and allowing livestock access to streams, increase erosion and the movement of soil from farmland to adjacent waters. Between 1981 and 1996, the risk of soil erosion by water decreased in the Prairie provinces, Ontario and New Brunswick; remained the same in British Columbia and Prince Edward Island; and increased in Quebec and Nova Scotia (Shelton et al. 2000). Although these findings imply a decline in the sedimentation of water courses and water bodies by farm soil, sediment contamination continues to be a serious water quality problem at certain times of the year in many regions, for example in the Maritime provinces where wide-row crops are grown on rolling land with soils susceptible to erosion and in the south coastal region of British Columbia where intensive row cropping of vegetables and berries takes place. To reduce erosion, a number of measures have been implemented including winter cover crop and mulching for row crops, no-till crop production, and a reduction in the Prairies in the area under summerfallow.
Nutrient (nitrogen and phosphorus) addition to aquatic ecosystems promotes excessive growth of algae and rooted aquatic plants, a condition known as eutrophication. As well as increased plant growth resulting as a direct consequence of nutrient addition, indirect consequences include changes in the abundance and reduced diversity of higher trophic levels (e.g., benthic invertebrates and fish), increased abundance of toxic algae, and fish kills caused by loss of oxygen from the water. Eutrophication caused by nutrient loading from agricultural sources has been documented in the Lower Fraser Valley, British Columbia; lakes and rivers in the prairie ecozone; rivers and lakes in the mixedwood plains ecozone of southern Ontario and Quebec; agricultural watersheds throughout the Atlantic provinces and the estuaries and coastal waters into which these rivers flow (Chambers et al. 2001). Nitrogen addition can also stimulate the growth of toxic species of algae in both coastal and inland waters, resulting in contaminated marine shellfish or lake waters.
In addition to the enrichment effects caused by nutrient addition, nitrogen in the form of nitrite can be toxic to humans. Ingestion of high quantities of nitrate may result in methaemoglobinaemia ("Blue Baby Syndrome"), a condition resulting from conversion in the gut of ingested nitrate to nitrite which, in turn, causes oxidation of ferrous (Fe2+) to ferric (Fe3+) iron in haemoglobin, the oxygen carrier of mammalian blood. The resulting methaemoglobin has no oxygen-carrying capacity. The most sensitive subpopulation is infants less than three months of age and the usual source of nitrite is nitrate in drinking water use in formula preparation, with the ingested nitrate converted to nitrite by the microflora of the gut. Nitrate is present in nearly all groundwater underlying the main agricultural regions of Canada. In Canada, 26% of the population, approximately 8 million people, rely on groundwater for domestic water supply (Chambers et al. 2001). Risk of nitrate contamination is highest in areas where there is intensive cropping, high fertilizer inputs, intensive livestock operations, sandy soils, areas of high precipitation or irrigation, and where nitrogen in excess of crop requirements is applied.
Certain forms of nitrogen are also toxic to aquatic organisms and may affect aquatic biodiversity. For example, one factor contributing to the decline in population numbers for 17 of Canada's 45 frog, toad and salamander species is nitrate concentrations in agricultural streams and runoff water that exceed thresholds for chronic and acute toxicity of amphibians (Rouse et al. 1999). Ammonia is also acutely toxic to many aquatic organisms. Results from an assessment of ammonia conducted under the auspices of the Canadian Environmental Protection Act (CEPA) indicate that the acute critical toxicity value for freshwater organisms is 0.29 mg/L un-ionized ammonia and the chronic toxicity value for freshwater fish is 0.041 mg/L un-ionized ammonia. Ammonia is not routinely found in Canadian surface waters at high enough concentrations to pose a wide-scale toxic threat to invertebrates or fish. However, an examination of fish kills caused by agricultural activity in Ontario documented 53 fish kills between 1988 to 1998. Most mortalities were caused by spray irrigation of liquid manure to land from swine operations, and lethal effects were attributed to high ammonia or BOD concentrations (K. Tuininga, personal communication, DOE/Ontario).
To reduce inputs of nutrients from agricultural sources to surface and ground waters, efforts have been directed at better managing livestock manure. Many provinces have developed guidelines for manure application and advocate the use of nutrient management plans to ensure environmentally safe manure application. Precision farming will also help to improve the efficiency of fertilizer and manure use.
Pesticides (fungicides, herbicides and insecticides) are used to protect crops against pests and diseases. In 1995, herbicides were used on 67% of Canadian farms. Pesticides are often found in trace amounts in both surface and ground waters in Canada's agricultural regions. Depending upon the compound and concentrations involved, pesticides introduced into surface waters can kill fish and other aquatic organisms; cause sub-lethal effects on reproduction, respiration, growth and development; cause cancer, mutations and fetal deformities in aquatic organisms; inhibit photosynthesis of aquatic plants; and bioaccumulate in an organism's tissues and be biomagnified through the food chain. Although generally below the guidelines for Canadian drinking water quality, pesticide concentrations in surface waters sometimes exceed Canadian water quality guidelines for irrigation water or protection of aquatic life (see examples in Chambers et al. 2000). Most pesticides are applied to the soil. They are transported as aerosols, in surface runoff, and as seepage water. The quantity of pesticides lost from farmland and how it is lost is determined by the nature of the pesticide and the quantity used, weather conditions at the time of application, time elapsed between application and precipitation, slope of the field, and crop production practices.
New techniques for pest control are currently being developed. These include highly selective pesticides that are very specific and less persistent; determination of economic thresholds to support a pesticide application decision; improved application techniques that make pesticides more efficient through selective application to limited areas; genetic induction of pest resistance in plants; using a combination of chemical control and biological control (e.g., use of natural predators, use of pheromones or the release of sterile males); and promoting the growth of beneficial or neutral microoganisms that will help control the growth of detrimental microorganisms.
Heavy metals in agricultural soils may be derived from natural or anthropogenic sources. Soil amendments are a major anthropogenic source of heavy metals. The heavy metals in soil amendments of most concern are cadmium, cobalt, chromium, copper, nickel, lead and zinc. Most heavy metals are positively charged cations in soils, and are thus strongly adsorbed to clay particles. The solubility of heavy metal cations generally decreases with increasing clay content and pH. Therefore, fine-textured soils with high pH are less susceptible to runoff or leaching. However, soil loss from agricultural fields can be a major pathway for introducing heavy metals into surface water bodies when heavy metals are adsorbed to soil (Webber and Singh 1995). In addition, heavy metals that form chelated complexes with organic compounds are more susceptible to leaching than non-chelated forms. Heavy metals are of most concern for water quality in terms of protection of aquatic life, as many heavy metals are extremely toxic to aquatic life at low concentrations. For example, the recommended guideline for copper in water to protect aquatic life is between 2 to 4 µg/L.
Many prairie soils contain high concentrations of water-soluble salts, including the sulfates of calcium, magnesium and sodium. These salts originate from weathering of the soil parent material. In addition, soil amendments such as livestock manure can contain high concentrations of soluble salts, and long-term application of manure to agricultural land can cause an accumulation of soluble salts in the soil profile. The greatest concern about soluble salts is potential leaching into the groundwater. The risk of groundwater contamination by soluble salts will be higher for coarser-textured soils that have greater leaching because of high precipitation or irrigation. The main concern about soluble salts and groundwater quality is the potential harmful effect on crops irrigated with saline water, as well as the potential harmful impact on livestock that consume saline water.
Pathogenic organisms, including bacteria, protozoa, viruses and parasites, occur naturally in water and soil. Although pathogens occur naturally, pathogens from farm livestock can migrate into groundwater or be carried in runoff into surface waters. Pathogen contamination of irrigation waters, drinking waters or shellfish areas can pose risks to human food supplies. In addition, pathogens can also pose a threat to aquatic ecosystems and biodiversity.
Concerns about pathogenic organisms carried by water from farmland have increased as livestock operations have intensified. Regions of the country with high livestock densities are reporting fecal coliform counts that exceed Canadian water quality guidelines for both drinking and irrigation water (Fairchild et al. 2000). Agricultural runoff is also a major source for bacterial contamination of shellfish, particularly on the Atlantic coast, and has been directly implicated in some shellfish closures. In Ontario, the number of wells with E. coli counts exceeding the guideline has almost doubled over the past 45 years from 15% (of 484 wells) in 1950 to 1954, to 25% (of 1292 wells) in 1991 to 1992 (Fairchild et al. 2000).
Endocrine Disrupting Substances
Endocrine disrupting substances (EDSs) are natural and synthetic chemicals that can disrupt the endocrine system, the complex mechanism found in invertebrates, fish, birds and mammals that coordinates and regulates such functions as growth, embryonic development and reproduction. The agriculture sector has been identified as a potential source of endocrine disrupting substances to aquatic ecosystems as a result of runoff or leaching of land-applied manure (which contains natural hormones excreted by livestock), land-applied sewage sludge (which contains natural and synthetic EDSs of human origin), and certain pesticides (which are either directly estrogenic or break down to form estrogenic compounds). Concerns over the potential impacts of substances that disrupt endocrine function in biota in the Canadian environment lead to CEPA 1999 making research on "hormone disrupting substances" a Ministerial duty for both Environment Canada and Health Canada.
Effects of EDSs on development and reproduction have been observed in wildlife in Canada, including: deformities and embryo mortality in birds and fish exposed to industrial chemicals or organochlorine insecticides, impaired reproduction and development in fish exposed to pulp and paper mill effluents, abnormal development of molluscs exposed to antifouling substances applied to the hull of ships, depressed thyroid and immune functions in fish-eating birds in the Great Lakes, and feminization of fish exposed to municipal effluents. Comparatively little is known of the potential risk posed by EDSs from the agricultural sector, although there is evidence that surface water can be impacted by estrogens if runoff or tile drainage occurs shortly after liquid manure from dairy cattle or gestating pigs is applied to land.
Pharmaceuticals are used for disease prevention and management in livestock and to promote growth. A significant amount of the original substance will leave the organism unmetabolized via urine or feces. Application of manure on fields may result in the movement of pharmaceuticals or their residues to surface or ground waters. Although antibiotic residues in the environment are suspected to induce resistances in bacterial strains and thus cause a serious threat to public health, little is known of the potential risk posed by veterinary pharmaceuticals to environmental or human health.
Understanding the Processes
- New or improved mechanistic models are needed that link hydrology and chemical transport from agricultural and forested watersheds to in-stream and in-lake responses such as water yield (streams) or flushing rate (lakes), water chemistry and biotic responses.
- Monitoring networks need to be maintained and accessible to allow assessment of trends over time, evaluate efficacy of new land management practices, and conduct effective watershed management.
- Improved knowledge is required on the regional diversity in processes such as climate, surficial geology and soil characteristics that affect water yield and contaminant movement from agricultural and forest soils.
- Improved understanding is needed of the pathways of chemicals from surface to ground waters and on the discharge/recharge of aquifers most at risk from forestry or agricultural operations (particularly aquifers used as sources of drinking water).
- An improved understanding is required on the fate of pesticides, chemical fertilizer, and nutrients, pathogens, veterinary pharmaceuticals and endocrine disrupting substances in manure and the long-term effects of these substances (individually as well as complex mixtures) on humans, aquatic organisms and their populations and communities.
- A process-level understanding is required of interactions between changing hydrologic regimes and aquatic habitat quality (changing light regimes, thermal regimes, and chemical characteristics).
Risk Analysis and Management
- An improved understanding is needed of methods for assessment and risk analysis of the cumulative effects of agricultural, forestry and other land use activities (e.g., ore, oil and gas exploration) as well as point-source inputs (e.g., municipal and industrial discharges) on surface and ground waters.
- Additional knowledge is needed as to the potential impact on surface and ground waters of agricultural application of biosolids derived from sewage treatment plants.
- Additional knowledge of biogeochemical and hydrological cycles is needed to scale up the effects of perturbations applied over a small area (i.e., disturbances applied to a plot, field or small watershed) to allow prediction of impacts on a broad geographic scale.
- Knowledge is needed as to the impact of land use on nutrient cycling and budgets, and water quality in watersheds. Inputs and outputs of nutrients such as N and P need to be determined so these nutrients can be more effectively managed to prevent surpluses.
- Development of decision support and information systems is required to enable better land use management and protect water sources from the impacts of forestry and agricultural operations.
More intensive use of land already zoned for a particular activity will undoubtedly continue in Canada and will likely increase with population growth and increased demand for forestry and agricultural products. To deal effectively with existing and emerging issues in the management of waters affected by land use change, continued research is required to ensure that new knowledge and technologies are developed for management of lands used for timber harvest, farming or other land-based activities. The following actions are recommended to ensure the protection of water quality from the effects of land use change associated with timber harvest and farming:
- Invest in research on how agricultural and forestry practices affect biogeochemical and hydrological processes; how regional diversity in climate, soil and vegetation modifies the effect of land use practices on these processes; and how land management practices can be altered to minimize impacts.
- Invest in targeted monitoring to determine trends, assess hazards, conduct ecological impact assessments and when warranted, provide for regulatory review, of the effects of timber harvest and agricultural practices on water quality.
- Establish scientifically credible practices, standards, and codes for agriculture and forestry operations, together with appropriate enforcement mechanisms, to ensure protection of ground and surface waters and aquatic biota.
- Incorporate agriculture and forestry practices within integrated watershed management to account for the cumulative effects of numerous environmental stressors.
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