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November 2004
Canada's federal government released the report "Nutrients and Their Impact on the Canadian Environment" in 2001. In response, the fertilizer industry has taken many steps to demonstrate stewardship of its products. One of these was to commission several scientists of the Soil Resource Group of Guelph, Ontario to review the report. It is hoped that this review will promote continued discussion of possibilities to improve the management of nutrients for agriculture, as well as contribute to an accurate understanding of the role of nutrients in sustainable agriculture and a healthy environment. Canada’s environment is comparatively healthy, 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. The executive summary follows, and the complete report is available to download as a PDF file.
Scientific Review of the 5NR Report
(Nutrients and Their Impacts on the Canadian Environment)
Authors: G.J. Wall, Ph.D., Principal Scientist, Soil Resources Group (SRG)
A.L. Huber, Ph.D., Environmental Microbiologist, SRG
D.J. King, M.Sc., Senior Agronomist, SRG
W.T. Dickinson, Ph.D
K.B. Macdonald, Ph.D.
Executive Summary
The 5NR Report “Nutrients and their impact on the Canadian environment” (Chambers et al., 2001) summarizes a large amount of valuable information and research, and provides a picture of the state of nutrients in the Canadian Environment at the time of writing. The task set before the authors of the 5NR report was extensive in both scope and depth, and most of the conclusions arrived at were significant. However, from the viewpoint of the Agricultural Industry, there are several important points that appear to be based on incomplete information, or are over-emphasized and appear to be unduly negative. This review of the 5NR report identifies some potential differences in perspective and balance based on information available, both at the time of the writing of the 5NR report and subsequent to it.
Most significantly, the assessments of Canadian agricultural industry’s contribution to nutrient loading to surface and ground waters (in particular P), and to the atmosphere (in particular NOx and long distance transport of NH3) appear disproportionate. As a consequence, the conclusions regarding effects of anthropogenic N and P loading to the environment, while generally valid, are more heavily weighted against the Agricultural Sector than seems appropriate.
As presented, the information in the summary Table 3.20 suggests that the agricultural sector is responsible for about 82% and 49% of the P and N loadings, respectively, even though the caption states that “data are not available as to the portion of this residual that moves to surface or ground waters”. Agriculture’s contribution has been calculated on the basis of the difference between nutrient inputs (fertilizer, manure, biosolids, N fixation, and atmospheric deposition) and crop removal or nutrient output (Table 3.22). No accounting is given for nutrient retention in the soil or losses to the atmosphere. However, data from studies such as the Pollution From Land Use Activities Reference Group study (PLUARG, 1982), from Ontario, indicate that for phosphorus in particular, losses are likely to be much less than given in Table 3.20. Inclusion of information from such studies would have enabled the construction of a more balanced picture of the relative contributions to surface water nutrient loadings, from the various sectors.
The 5NR calculation of overall nitrogen balance in agriculture, while more complex than for phosphorus, appears to be within the range of calculations by other authors, but again, the usefulness of using N balance calculations to estimate actual nutrient losses to surface waters has been questioned by a number of authors. Such calculations, however, are useful in pinpointing areas where there is potential for significant nutrient losses to surface and groundwaters. It should also be noted that, within the body of the 5NR report, it is pointed out that Canada’s nutrient surplus is among the lowest of the 28 OECD countries. However, this statement is not carried forward to the summaries or conclusions of the report.
It is also implied in the 5NR report (Table 3.22) that agriculture’s contribution to NOx is of a similar magnitude to that of industry. However, it can be estimated that Canadian agriculture’s contribution would be less than 2% of Canada’s total NOx emission. Photochemical smog, is primarily the result of fossil fuel burning and industry emissions, and agriculture’s contribution to NOx is in fact very small.
In general, agriculture is more efficient at recycling its nutrients than are the industrial and municipal sectors, which tend to operate on a once-through basis. Indeed, agriculture has been a target for analysis of status and trends for some time and is now moving along the path to more efficient and sustainable nutrient management. However, there is no alternative to some degree of unpredictability. Other sectors may not be as advanced in terms of assessment information or in terms of management techniques and BMPs to modify their nutrient impacts on the environment.
Nutrients are essential for the functioning of all ecosystems, and addition of nutrients to agricultural land is essential to maintain the level of production required to produce sufficient food for the world’s population. The 5NR report is primarily focused on the impacts of excess nitrogen and phosphorus on the Canadian environment. This excess nutrient loading has been caused by a combination of anthropogenic and non-anthropogenic inputs, both historical and present. Once nutrients enter the environment, their effect is independent of the source. Furthermore, due to internal recycling of nutrients, recovery from eutrophic status may be long term.
Combined anthropogenic sources of nutrients have indeed accelerated eutrophication of certain rivers, lakes and wetlands in Canada, and in cases of severe eutrophication resulted in loss of habitat, changes in biodiversity and loss of recreational potential. However, it has also been shown that moderate loadings to certain systems may increase biodiversity, and indeed may benefit certain wildlife, e.g. waterfowl, by increasing food sources. Furthermore, instances have been cited in the body of the 5NR report where moderate enrichment of lakes has been desirable to maintain viable recreational or commercial fisheries operations.
The role of anthropogenic nutrient inputs in enabling undesirable increases in frequency and spatial extent of cyanobacterial and algal blooms, and aquatic weed growth in Canadian surface waters has been described in the 5NR report. It should be emphasized that other factors such as water depth, mixing, temperature, and flushing are also significant in the development, extent and toxicity of blooms. Nutrient inputs from both agricultural and municipal sectors, have been significant in the internal loading of water bodies which, in turn, will lengthen recovery times of these water bodies even if annual loadings have decreased.
The 5NR report emphasizes the frequency and spatial extent to which the drinking-water guideline for nitrate has been exceeded in ground waters in high intensity agricultural areas across Canada. However, the high concentrations described as “common” are firstly, incorrectly cited as nitrate-N rather than nitrate and therefore should be reduced by a factor of 4.4, and secondly, are specific to intensive farming on sandy soils over shallow aquifers. In general, the proportion of well waters that exceed the guideline has remained relatively constant, at less than 20%, over the past several decades. Furthermore, many of the claims relating to negative effects of nitrate in human health have been disputed over the last decade, and beneficial roles have been identified.
Emphasis has also been put on the possible contribution of high levels of nitrate to the decline in amphibians in southern Ontario; however, other factors such as habitat destruction and fragmentation, traffic mortality, roadway runoff, changes in water depth, pesticide use and pathogens appear to be considered more significant causes of decline. The main study cited in the 5NR report as demonstrating toxic effects of low levels of nitrate on amphibians, used ammonium nitrate as the nitrate source, thereby confounding the effect of the individual N sources. Other studies indicate that nitrate, added as potassium nitrate, is far less toxic than ammonium nitrate. Nitrate levels in surface waters are generally below the LD50 toxicity levels for amphibians described in most studies. The effects of nutrients on amphibians also appear to be species dependent, to the extent that reduced risk of deformity for some species correlates with higher environmental levels of P and/or N. Hence, the role of nutrients in the decline of amphibians in southern Ontario is not in any way clear.
The 5NR report describes a number of toxicity studies on the effect of ammonia on aquatic species, and ascribes fish kills due to ammonia toxicity primarily to the agricultural sector. Except in the event of a major, localized spill, the concentration of the toxic un-ionized form of ammonia will be too low in natural surface waters to cause fish mortalities. The agricultural sector has now put specific regulations in place that ban management practices with a poor record for spill prevention, and as further discouragement, general environmental protection laws make the producer of the spill liable. Furthermore, Environment Canada documentation points to municipal wastewater treatment plants as the most important source of entry of ammonia in the aquatic environment that must be targeted in risk management. Industrial spills that result in fish kills tend to be unrelated to nutrients, and thus are not commented on in the 5NR report.
The economic burden of water monitoring and treatment has been emphasized in the report. Firstly, most source water treatment is based on microbiological requirements, rather than the need for N or P removal. Municipal drinking water supplies rarely exceed the nitrate guidelines, and phosphorus removal is an issue for waste water treatment prior to release back into the environment. Secondly, to provide a balanced approach, the economic burden of water treatment or loss of recreational resources should be balanced with the economic gain resulting from increased agricultural production related to nutrient application for improved crop production.
Lastly, the 5NR report includes a discussion of the contribution of anthropogenic nutrient inputs to the acidification of soils and lakes in southern Ontario and Québec, through deposition of atmospheric nitrogen, with the result of incipient N saturation in some forested watersheds. The degree to which N saturation of Canadian forested watersheds is imminent is not clear, and no evidence of damage has been found by the Acid Rain National Early Warning Systems (ARNEWS). Furthermore, the geographical sources for this long distance transport are not discussed in the report, but it has been recognized that a significant portion is related to industrial emissions from non-Canadian sources.
The current review provides a somewhat different perspective on the issues dealt with in the 5NR report. However, its authors agree with the overall conclusions of the 5NR report that Canada’s environment is comparatively healthy, and that “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”.
Reference:
Chambers, P.A., M. Guy, E.S. Roberts, M.N. Charlton, R. Kent, C. Gagnon, G. Gore and N. Foster. 2001. Nutrients and Their Impact on the Canadian Environment. Agriculture and Agri-Food Canada, Environment Canada, Fisheries and Oceans Canada, Health Canada and Natural Resources Canada, 241p.
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