NUTRIENTS IN THE CANADIAN ENVIRONMENT
Highlights

Reporting on the State of Canada's Environment

Nutrients are elements or compounds that are essential to the growth and survival of organisms. The supply of nutrients within an ecosystem has a substantial influence on both the abundance of plant and animal life and the types and variety of species that can inhabit the ecosystem.

Expanding human populations and various human activities have greatly increased the biologically available supply of two key nutrients, nitrogen and phosphorus, in the environment. These nutrients, when present in excessive amounts, can overstimulate the production of plants, to the detriment of other species, and are associated with a variety of direct and indirect toxic effects on organisms, including humans.

The state of the environment (SOE) report on nutrients looks at how the Canadian environment is being affected by nitrogen and phosphorus compounds that are released as a result of human activities. The report describes the mechanisms by which nutrients affect the environment, assesses their impact on the environment, especially through enrichment, and their potential for future damage, and outlines the major sources of these compounds. It also looks at what has been done and what can be done to alleviate these problems.

At present, environmental problems caused by excessive nutrients are less severe in Canada than in many countries with a longer history of settlement and agricultural production. This is in part due to protective measures implemented by governments in the last 30 years. Nonetheless, while successes have been realized, environmental and human health problems related to nutrients are evident across Canada.

Highlights from the SOE report follow.

What are the impacts of nutrient additions?

The impacts of nitrogen and phosphorus loadings in the Canadian environment include both effects associated with nutrient enrichment and the direct toxic effects of nitrogen compounds on aquatic and terrestrial organisms as well as humans.

Enrichment effects

• In fresh waters, algal growth is often limited by the amount of phosphorus available, whereas the supply of nitrogen is generally the determining factor in ocean waters.
• Phosphorus loadings have accelerated the eutrophication, or overfertilization, of certain rivers, lakes, and wetlands, resulting in the loss or degradation of habitat and changes in biodiversity (e.g., changes in the types of bottom-dwelling organisms in lakes).
• Nitrogen loadings have caused local eutrophication in some coastal waters, including estuaries, which has led to a decrease in dissolved oxygen, a loss of habitat, and changes in biodiversity (e.g., an increase in nuisance algae).
• Some forest ecosystems have become saturated with nitrogen, which can leach to surface waters or groundwater and cause changes in soil chemistry, including nutrient imbalances.
• Nitrogen loadings have contributed to the acidification of soils and lakes in southern Ontario and Quebec.
• The aesthetic enjoyment of water may be impaired by turbidity, discoloration, foaming, and odour, and algae can restrict swimming, foul fishing gear, damage boat motors, and impede navigation.

Toxic effects

• A number of fish kills related to nitrogen-containing discharges, particularly those associated with agricultural activities, have occurred in recent years.
• Nitrate is believed to be at least partly to blame for declines in amphibian populations in Canada. Adverse effects include poor larval growth, reduced body size, and impaired swimming ability.
• Nutrient additions have led to higher risks to human health from the recreational use of waters contaminated with toxic algal blooms and from the consumption of tainted shellfish.
• Concerns about water quality have increased because of taste and odour problems and the contamination of some water supplies with nitrate and algal toxins. The frequency and spatial extent to which the drinking water guideline for nitrate has been exceeded in groundwater across Canada have both increased.
• The economic burden to Canadians has increased as a result of the closure of shellfish fisheries, the need for treatment of contaminated water, and the need to transport household water from off-site sources.

What are the principal sources of nutrients?

Municipal and rural wastewater

• Municipal wastewater - largely human waste - is the largest point source of nitrogen and phosphorus releases to the Canadian environment. In 1999, about 82 750 tonnes of total nitrogen and 4 950 tonnes of total phosphorus were released to lakes, rivers, and coastal waters from municipal sewage.
• Nitrogen loadings to Canadian fresh waters from municipal wastewater treatment plants in 1999 were 24% higher than in 1983 as a result of population increases.
• Phosphorus discharges to fresh waters were 44% lower in 1999 than in 1983 due to the implementation of advanced phosphorus removal at many municipal wastewater treatment plants.
• The level of sewage treatment across Canada is generally improving, as more municipalities upgrade their wastewater treatment facilities. An exception is municipal wastewater discharged to coastal waters. Many communities are still served by primary treatment or none at all.
• About 8 million Canadians, slightly more than one-quarter of the population, are served by septic systems, which released an estimated 15 400 tonnes of nitrogen and 1 900 tonnes of phosphorus in 1996. If these nutrients cannot be assimilated by the receiving land, they can move into groundwater and, from there, to surface waters.

Agriculture

• Nutrients in the form of chemical fertilizers and manure are applied to agricultural land to increase crop yields. In 1996, 1 57 6000 tonnes of nitrogen and 297 000 tonnes of phosphorus as fertilizer were applied to cropland in Canada. In addition, 384 000 tonnes of nitrogen and 139 000 tonnes of phosphorus were applied as manure.
• Total nutrient additions (fertilizer, manure, nitrogen fixation by legumes, atmospheric deposition, application of sewage sludges, etc.) to agricultural land are substantially offset by crop uptake. For all agricultural land in Canada, annual nitrogen inputs for 1996 (2.8 million tonnes) exceeded outputs (2.5 million tonnes) by 10.7%.
• In 1995, the storage and handling of manure and fertilizer added 570 000 tonnes of nitrogen in the form of ammonia to the atmosphere.

Industrial discharges

• An estimated 11 800 tonnes of nitrogen (as nitrate and ammonia) and 2 000 tonnes of total phosphorus are discharged annually to Canadian surface waters from industries with operating permits.
• Most light industries discharge their wastewater into municipal sewage systems for treatment at municipal wastewater treatment plants.
• Industrial emissions to the atmosphere in 1995 included 27 000 tonnes of nitrogen from ammonia, about one-third from industries manufacturing nitrogen fertilizers.

Aquaculture operations

• Aquaculture operations release nutrients through the excretion of dissolved or solid waste by fish and from unconsumed feed. Cage finfish aquaculture in open water is of most concern, as wastes are released entirely to the surrounding water.
• The total Canadian finfish industry is estimated to contribute 2 276 tonnes of nitrogen and 486 tonnes of phosphorus to inland and coastal waters annually.

Forestry

• Forests are the source of much of the water that enters streams and lakes. Forest management practices may increase concentrations of nutrients in streamwater. There is insufficient information at present to generalize about the impacts of forestry practices on dissolved nutrients in streams.

Atmospheric emissions and deposition

• In 1995, 1 471 000 tonnes of various forms of nitrogen were emitted to the atmosphere, of which 608 000 tonnes (41.3%) were from the agricultural sector, 428 200 tonnes (29.1%) were attributable to fossil fuel combustion for transportation, and 329 400 tonnes (22.4%) were from industry (combustion-related emissions and industrial processes).
• Much of the nitrogen released into the atmosphere is redeposited on the ground or on water. In Canada, atmospheric deposition as a result of long-distance transport supplies approximately 2.5 kilograms per hectare per year in the form of nitrate and ammonium, the only two compounds of atmospheric nitrogen examined. Atmospheric deposition is considerably higher in eastern than in western Canada as a result of industrial activities in central Canada and the northeastern United States. Atmospheric deposition of nitrogen compounds contributes to both eutrophication and acidification of surface waters.
• Atmospheric phosphorus, much of it from fertilizer application and production, accounts for only 1-6% of the total phosphorus budget in Canadian lakes.

What measures are being used to manage nutrients?

A wide range of measures has been developed in Canada to help control nutrient inputs into the environment.

Municipal and rural wastewaters

• Some municipal wastewater treatment plants are required to employ advanced phosphorus removal before discharging their wastes to sensitive waters.
• Repair and replacement of sewage systems have reduced leakage and pollutant loadings.
• Conversion of combined sewer systems to separate systems or shunting of the most toxic first flush of stormwater into storage facilities/ponds for subsequent treatment prevents untreated sewage from entering surface waters.

Agriculture

• The nutrient requirements of crops must be balanced by the supply of nutrients to the crops from the soil and from fertilizers. Most provinces have guidelines for manure application to soils, typically based on nitrogen application rates.
• Nutrient management strategies (e.g., transporting surplus manure from animal producers to crop farms) will improve farmers' abilities to manage nutrients more effectively, with the ultimate aim of reducing overfertilization.
• Livestock incorporate only 20-40% of the nitrogen and phosphorus originally present in feed. Technologies are now emerging for adding enzymes or other supplements to livestock diets to increase nutrient retention by livestock.
• In areas of intensive livestock production, treatment of animal waste could reduce the risk of contamination of surface water and groundwater by manure.

Aquaculture operations

• Between 70 and 80% of nutrients added in aquaculture operations are lost to the environment as metabolic waste, feces, and uneaten food fragments. The development of more nutritionally balanced and digestible feed will reduce waste discharges from feeding.
• Environmental impacts associated with nutrient loss in aquaculture operations could be reduced by placing cages away from sensitive waters and shorelines, collecting and treating wastewater, and implementing good management practices.

What information gaps need to be filled?

Data limitations constrain scientists' ability to assess changes in ecosystems due to excess nutrients. These are principally insufficient monitoring data on emissions and ambient conditions and insufficient knowledge as to the effects of nutrient additions on ecosystem and human health.

Insufficient monitoring data

In attempting to define the status of Canadian ecosystems with respect to nutrients, data on sources and impacts are progressively less available as one moves from lakes to rivers/streams to wetlands to groundwater to coastal waters to forests. Some topics requiring particular attention are the following:

• Few nitrogen and phosphorus data are available for industries not connected to municipal wastewater treatment plants.
• Available data on nitrogen and phosphorus loadings for certain municipal wastewater treatment plants in Canada are not consistent in the parameters measured.
• Regional or national estimates of agricultural nutrient loadings to surface water and groundwater are not available, nor can estimates be obtained.
• Although estimates of atmospheric deposition of nitrate- and ammonium-nitrogen are available through a network of provincial and federal monitoring sites, similar data are not available for phosphorus or for total nitrogen, nor are estimates available for release from various sectors.
• Well water survey programs are patchy across the country.
• Reporting on fish kills from accidental spills/discharges of nutrient-related compounds is currently on a voluntary basis only.
• The potential impacts of climate change on nutrient loadings are poorly understood, as are the related measures to manage loadings.

Effects of added nutrients on Canadian ecosystems

Additional research is required to understand the effects of added nutrients on Canadian ecosystems. Areas requiring particular attention are:

• the role of nutrients in inducing algal blooms and toxin production;
• the role of nutrients in causing taste and odour problems of drinking water supplies;
• transport and fate of nutrients within different ecosystems (wetlands, coastal waters, forests, rivers, and lakes) and effects on biota; and
• long-term and cumulative effects on the aquatic and terrestrial environment from the combination of several nutrient sources all operating within a region.

What does the future hold?

Maintaining the quality of air, water, and soil environments with respect to nutrients is an important component of sustainable development. Yet studies have already shown that an overabundance of nitrogen compounds is overwhelming ecosystems in parts of the world. This nitrogen, in part from synthetic nitrogen fertilizers, can no longer be absorbed by terrestrial ecosystems and is ending up in rivers, lakes, groundwater, estuaries, and oceans.

Canada is in the position of being able to deal with nutrient pollution before it is overwhelming. Science-based solutions are available and new technologies are emerging that can assist in further reducing undesirable nutrient additions to the environment. Monitoring and research continue to be needed to ensure that decision-making is based upon sound science, and the best and most advanced science should continue to be integrated into practical solutions to maintain or improve the quality of Canadian air, water, and soil environments.