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1989 - 1994




Under the Great Lakes Water Quality Agreement, the governments of Canada and the United States are committed to addressing water quality issues in the Great Lakes basin.
Through a federal initiative called the Great Lakes Action Plan, Agriculture and Agri-Food Canada funded research to:

  • increase our understanding of how agricultural chemicals interact with the environment, and the Great Lakes in particular,

  • improve water quality in the Great Lakes basin,

  • develop and fine-tune farm practices that help farmers conserve soil, water, and air quality in the short and long term for all Ontarians.

The 5-year, $5-million project is now complete, although multi-disciplinary research continues in these important issues.

Here is a summary of results, which sheds light on the subject of pesticide, nitrogen, and bacteria movement in the environment, and provides food for thought to help us all advance farm management practices. If you would like more information, please refer to the list of Program Studies and Scientists on the flipside of this brochure.



The Great Lakes are sensitive to pollution for two main reasons:

  • the long retention time (less than 1% of the water flows out annually) allows some persistent contaminants to accumulate in sediments - in some cases, these may be released back into water.

  • the large surface area leaves them vulnerable to direct deposits of wet and dry atmospheric contaminants.

Agriculture and the agri-food sector contribute significantly to the Ontario economy. The annual farmgate value of crop and animal production is more than $5-billion. Its economic worth can also be counted in employment: about 150,000 Ontarians have production and processing jobs in the agri-food sector.

The Great Lakes basin is home to 80% of Ontario's cropland. Now more than ever, farmers face significant challenges in their efforts to produce low cost, high quality food products in an environmentally sustainable way.

The annual farmgate value of crop and animal production in Ontario exceeds $ 5 billion. PHOTO: OSCIA

Contaminants in the Great Lakes originate from all kinds of human activities. The chemicals and bacteria discussed here are those that are derived from agricultural sources. The most commonly used crop-protection chemicals (atrazine and metolachlor), manure and fertilizer nitrogen, and manure bacteria are the focus of the study.



Today's crop-protection chemicals are less persistent and less toxic to non-target species than their predecessors. Application rates are declining and crop-protection products are being used more efficiently. They are not accumulated in the food chain, and are effective at low application rates.

Nonetheless, because of their important role in food production, significant amounts of pesticides are applied each year in the Great Lakes basin. The combined Canada/USA use is about 25-million kilograms. Ontario farmers apply about 6-million kilograms.

Usage looks like this:

  • account for 75% of pesticide use
  • generally applied once a year to control weeds and optimize yield in field crops

   fungicides and insecticides:

  • account for 25% of pesticide use
  • applied up to 8 times a year to control diseases and insects on fruits and vegetables.
Field crops are usually sprayed once annually with herbicides.       PHOTO: OSCIA

When crop-protection chemicals are applied according to recommendations:

  • is there a potential for contamination of surface and subsurface water?

  • how much of applied pesticide is lost into the air?

  • what are the effects of agricultural pesticides on stream and wetland ecology?


How Herbicides Can Move From Fields

Rolling Landscapes
  • surface runoff is the main pathway:

  • runoff losses are maximized when rain storms closely follow application - field plot studies revealed high intensity storms caused up to 10% loss of atrazine and metolachlor

  • losses measured at edge of fields and from entire watersheds amount to less than 5% and 1% respectively

  • in small test plots in farm fields, chemicals in runoff waters exceeded water quality guidelines for up to 1 month after application.

Level Landscapes with Cracking Soils (e.g. Essex County)
  • large cracks and pores are the main pathways for herbicide transport to tile drains

  • groundwater sampled at 5-metre depth met water quality guidelines for herbicides under conventional and conservation corn cropping systems.

In General
  • while surface runoff is a dominant pathway for herbicide losses, some chemical is also lost in tile drains .

  • in the runoff water collected in the field shortly after application, the majority of atrazine and metolachlor is dissolved in the water and not attached to the sediment - this was true for conventional and conservation tillage cropping systems.

  • flow through large soil cracks and pores is an important transportation route that can lead to water contamination .

  • risk of transport through large pores is greatest shortly after application especially in cases of heavy rains:

  • when herbicides adsorb to soil particles, or herbicides break down naturally, the risk of transport through soil cracks and pores is largely reduced.


How Herbicides Move Between The Land And Atmosphere

  • crop-protection chemical lost to the atmosphere is a small percentage of applied material

  • three new measurement systems have been developed to more accurately quantify the exchange of agrichemicals between soil and air.


What Happens To Herbicides in the Soil

Some Herbicide Residues Bind with Soil and Organic Material

  • herbicides that bind with soil particles are held in the field where they are active - they are also retained in place for biological breakdown

  • bound herbicides in soil increase with time after application

  • if soil is eroding, bound herbicides can move with suspended soil particles in runoff.


Herbicide Breakdown And Movement in Soil

  • researchers have made detailed physical and chemical measurements: they can now better forecast the conditions under which crop-protection products will move in soils.


Wetland Micro-organisms Can Help

  • much of the agricultural pesticide that reaches the Great Lakes passes through and may be retained in wetlands or marshes

  • some bacteria in wetland sediments degrade atrazine rapidly.

Much of the agricultural crop-protection chemicals that reaches the Great Lakes passes through wetlands or marshes.


Some poultry, swine, dairy, and beef feedlot production is concentrated on farms with insufficient land for proper waste disposal. Furthermore, many farmers are changing their manure handling systems from solid to liquid - about 50% of manure is disposed of in liquid form. Both of these facts increase the potential for water pollution.

Manure, when not incorporated into the soil, can run off the soil surface. Liquid manure can flow rapidly through soil via large cracks or pores to subsurface water, or to tile drains. Since roughly 40% of Ontario's improved agricultural land has some form of tile drainage, there is a high potential for contamination of tile water by nitrogen and bacteria.


Nitrogen from manure and chemical fertilizers is required for crop production. Since nitrates are soluble in water, they can move rapidly in surface runoff or groundwater. The issue becomes:

  • how to manage manure and fertilizer application to minimize water contamination.


How Bacteria and Nitrogen Travel in Water

Tile Drains and Surface Water

  • risk of bacteria being carried through large soil pores is greatest immediately after surface application, especially when followed by heavy rains.

  • nitrogen losses often occur primarily during the non-growing season.

  • nitrogen losses are predominantly through the soil to the tile drains or subsurface water.

Liquid manure injection systems that disrupt large cracks and pores in the soil can reduce tile drain contamination.      PHOTO: OSCIA




  • practical decision-making tools based on soil and chemical properties are available:

  • these will help the pesticide applicator select pesticides that have a low potential to contaminate water.


controlling water table levels and using conservation practices will help lead to:

  • higher crop yields and improved nitrogen use, especially in dry conditions, by optimizing moisture availability

  • improved water quality by reducing atrazine loss up to 47% and nitrate losses by about 50% - nitrate concentrations are reduced to within acceptable limits

  • lower farm production costs by improving N fertilizer efficiency.



  • using banded application for herbicides with inter-row cultivation can reduce concentrations in surface water by 50% regardless of weather, because you apply less chemical.



  • since agricultural runoff may contain crop-protection products and nutrients, conservation practices (e.g. contour and strip cropping, terracing, and buffer strips) that keep soil and water in the field will improve surface water quality

  • farm wetlands have important value in improving water quality - wetland organisms recycle nutrients and act as a sink for bacteria and herbicides

  • if you're considering adopting (or already have) a reduced tillage system, here are some observations regarding reduced and conventional tillage cropping systems:

  • crops grown with reduced tillage do not require more herbicide than

  • those grown with conventional tillage

  • there are no net differences in herbicide losses

  • flow through large cracks and pores is greater under reduced tillage, but total water loss (surface & subsurface) was greater with conventional tillage

  • total nitrogen loss is lower from reduced tillage systems, but reduced tillage also shows higher nutrient loss in soluble forms than conventional systems.



  • choose an injection system that disturbs soil immediately around the injection point - this breaks up large cracks and pores and reduces direct movement of nutrients and bacteria to tile drains.


(* not from one location)


Field-scale models can evaluate the effect of farm management systems on surface and ground water quality. These can be used for detailed farm planning exercises to:

  • locate environmentally sensitive landscapes

  • evaluate alternative remedial solutions.


Streams that are in farming areas have very different insect populations from forested areas. These differences are greatest in localized areas where insecticide use on crops is greatest. Agricultural activities generally change insect populations, but how these changes relate to water quality has yet to be established.


Researchers were able to predict potential non-point source pollution of groundwater by atrazine. The downward movement of annually applied atrazine over 10 years was simulated on a computer. Based on computations:

  • maximum predicted movement out of the root zone in any one year is about 1%, and actual movement is likely less.


A provincial-scale study has developed methods to locate agricultural areas with high potential for non-point source pollution. These were based upon relationships among:

  • the type and location of farming systems

  • their potential for land and water contamination from herbicides, nitrates, and bacteria.

This study identified areas where the results of field studies can be applied.

Crops produced with reduced tillage systems do not require more herbicide than when grown under conventional tillage systems. PHOTO: OSCIA

The rapid movement of contaminants through soil cracks and pores to the tile drains contributes significant bacteria loads, but low total nitrogen loadings. PHOTO: OSCIA



Implementation of study findings will increase the environmental sustainability and maintain the competitiveness of the agricultural sector. Further work is required to:

  • implement findings at the farm level

  • apply technologies for solving agricultural water quality problems in areas where Great Lakes Remedial Action Plans are being implemented

  • develop and test ecosystem-based management systems that protect the environmental quality of rural areas

  • use the findings on chemical transport at the watershed and provincial level to locate environmentally sensitive areas.



The assistance of the Ontario Soil and Crop Improvement Association (OSCIA) in the production and distribution of the brochure (from which the information herein was obtained) is gratefully acknowledged.



GLWQ Summary of Achievements


Thursday, May 05, 2011 01:06:39 PM