Contaminants
Topics
5 min read
Various practices on dairy farms can lead to the contamination of waterways with nutrients, sediments, and bacteria. It underlines that improper management of stock, farm infrastructure, irrigation, fertilisers and offal pits could lead to harmful runoffs or leaching. These pollutants not only degrade water quality but also affect the farm's productivity and potentially the value of dairy products. To ensure waterway health and farm productivity, you need to observe and manage these potential pollution hotspots effectively. This includes being alert to signs of contamination and implementing appropriate corrective actions.
There are many options available to improve the health of our waterways. This page will help you understand the actions you can take.
Hotspots for contaminant losses on dairy farms
Stock – dung and urine
Contaminant: N, P, faecal bacteria and sediment
Pathway to water: Runoff, leaching and direct deposition.
Signs: Stock on paddocks during wet periods, ponding and overland overflow, collections of dung in areas of a paddock prone to overland flow/flooding, ruts from vehicle movements, slips or slumps, extensive pugging.
Bridges and culverts
Contaminant: N, P, faecal bacteria and sediment
Pathway to water: Runoff into water and direct deposition.
Signs: Effluent, or water containing effluent, running off to channels that lead to water or directly to water. Effluent accumulating in areas where cows congregate.
Races
Contaminant: N, P, faecal bacteria and sediment
Pathway to water: Runoff into water and direct deposition.
Signs: Races in bad repair, with potholes and boggy patches. Water channels scoured into the race, particularly on steep slopes. Effluent, or water containing effluent, running off to surface water. Effluent or material build up, poor drainage.
Irrigation water
Generally, irrigation water is not a source of nutrient loss. Like rain, too much irrigation increases drainage which increases the risk of N leaching. Like rain, irrigation water can increase drainage which increases the risk of N leaching. Oversaturation of soils can also lead to pooling and runoff.
Effluent irrigation
Contaminant: N, P, faecal bacteria and sediment
Pathway to water: Runoff or leaching. Saturation of soils can lead to pooling and runoff. This can occur for several reasons, for example: if infrastructure is not well maintained, if effluent is applied at a rate or depth that is too high.
Signs: Burst pipes, blocked nozzles, pumps failing, irrigation over or close to water, ponding, ponding of effluent in paddock.
Effluent ponds and related infrastructure
Contaminant: N, P and faecal bacteria
Pathway to water: Runoff due to poorly maintained infrastructure, leaching due to unsealed storage.
Signs: Overflow of sump or ponds, pond level lowering without discharge indicates it may be leaking, vegetation on the surface which may cause blockages and system failures. Yards with cracked concrete.
Stand-off areas
Contaminant: N, P and faecal bacteria
Pathway to water: Runoff or leaching if effluent is not effectively captured
Signs: Effluent running off pad, no effluent capture system
Crops
Contaminant: N, P, faecal bacteria and sediment, depending on if the crop is grazed or harvested. Winter crops are particularly risky for nutrient and sediment loss.
Pathway to water: Runoff, leaching and erosion from stock, fertiliser applications, cultivation and harvesting activities.
Signs: Effluent or sediment running off into water during grazing off crop. Heavy rain washing soil off cultivated areas. Build-up of dung or disturbed soil in areas with the potential to run off. Stock on paddocks during wet periods, ponding and overland flow, collections of dung in areas of a paddock prone to overland flow/flooding, ruts from vehicle movements, slips or slumps, extensive pugging.
Supplements feed storage
Contaminants: N and P
Pathway to water: Runoff from stack or leaching below the stack.
Signs: Dark liquid leaking from stack or bales
Fertiliser storage
Contaminants: Depending on the fertiliser, could be N and/or P
Pathway to water: Runoff or leaching if fertiliser is expose to elements.
Signs: Fertiliser getting wet, visible runoff from storage site.
Fertiliser application
Contaminants: Depending on the fertiliser, could be N and/or P
Pathway: Runoff or leaching if fertiliser applied in inappropriate amounts, locations, or times.
Signs: Applying fertiliser close to or in waterways, applying fertiliser to wet soils or very dry cracked soils.
Offal pits
Contaminants: N, P and bacteria
Pathway to water: Runoff if the pit is in a location where water can run in and out or leaching if the pit is located within the groundwater level or not adequately compacted.
Signs: Water in the bottom of the pit, water flowing in or out of the pit.
For further detail in how nutrients are lost to water bodies click here.
Impacts of losing excess nutrients phosphorus (P) and nitrogen (N) to waterways
| Sources on farm | Potential impacts on waterways | Potential impacts on your farm | |
| P |
• Dung from stock • Phosphate in fertiliser • Farm dairy effluent • P attached to soil sediment |
• Promotes nuisance aquatic plants and algae growth in waterways which degrades water quality, blocks water intakes and makes water unpleasant for recreational activities and drinking. |
• Loss of Income through |
| N |
• Urine and dung from stock • N in fertilizer • Farm dairy effluent |
• Promotes nuisance aquatic • Ammonia (a form of |
Sources and potential impacts of excess sediments
| Sources on farm | Potential impacts on waterways | Potential impacts on your farm |
| • Slips and hillside erosion • Pugging and trampling • Surfaces of tracks, races and paddocks |
• Degrades water quality and clarity which makes water unsafe for swimming • Excessive sediment can smother the stream bed, reducing habitat for insects and fish • Excessive sediment can reduce visual feeding efficiency for fish • Excessive sediment can clog fish gills which suffocates them. |
• Excess sediment in streams, • Excess sediment indicates there |
Esherichia coli (E.coli) bacteria normally live in the intestines of healthy people and animals, the occurrence of E. coli is used as an indicator of faecal matter in waterways. E. coli and enterococci are indicators of human health risk from recreational contact with fresh water and marine water. They indicate the possible presence of pathogenic (disease-causing) bacteria, viruses, and protozoans that also live in human and animal digestive systems. Therefore, their presence in water bodies suggests that pathogenic microorganisms might also be present and that swimming and eating mahinga kai might be a health risk.
Faecal matter also has some other water quality implications which are explained in the following table. It is very likely that central government will require regional councils to set limits around faecal matter concentrations in all New Zealand bodies to amounts that allow secondary contact recreation activities (which includes activities such as fishing and tramping) to still occur.
Sources and potential impacts of excess faecal matter (and other bacteria)
| Sources on farm | Potential impacts on waterways | Potential impacts on your farm |
| • Dung from stock • Farm dairy effluent irrigation |
• Human health risk from swimming and drinking • Stock health risk if present in stock water |
• Water taken for human or stock drinking or milk cooling may need to be treated if there is excess faecal matter or other bacteria |
Measures of stream health
The figure below describes the factors influencing ecosystem health. The factors circle in yellow or blue can be affected (directly or indirectly) by actions taken on farm. E.coli is affected by actions taken on farm but do not affect ecosystem health, it affects human health.
