ABSTRACT

Nutrients, such as nitrogen and phosphorus, are applied by agricultural producers to enhance plant growth. However, costs in terms of on-farm productivity reduction (Briggs and Bos, 1990) and off-farm water pollution (Pearce et al., 1985; PLUARG, 1978) can result if soil and/or the applied nutrients are lost through erosion and water infiltration. Nutrient water pollution can cause a number of health problems, upset ecosystem integrity and reduce recreational values. The health effects from excess nitrates include infantile methaemoglobinaemia, or ‘blue baby syndrome’, and stomach cancer in adults (Health and Welfare Canada, 1980; Hanley, 1990). In addition, excess nutrients can cause the growth of blue-green algae that produce toxins that are harmful to humans if ingested (Fuller and Flemming, 1990). A nutrient imbalance can affect the food web dynamic by upsetting the photoplankton community and cause excess algae growth that depletes the dissolved oxygen as it decays (Environment Canada, 1987). These ecosystem impacts may also influence the recreational enjoyment of the environment. A reduction in oxygen from eutrophication can decrease the stock of valued fish species such as trout and increase the stock of other species that require little oxygen such as sludge worms and carp (Environment Canada 1987).