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Contaminants

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5 min read

Hotspots for contaminant losses Stock – dung and urine Bridges and culverts Races Irrigation water Effluent irrigation Effluent ponds Stand-off areas Crops Supplements feed storage Fertiliser storage Fertiliser application Offal pits Impacts of losing excess nutrients Sources of excess sediments Sources excess faecal matter Measures of stream health

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
inefficient use having to
increase fertilizer application
to compensate for N and P
or letting valuable nutrients in
effluent go to waste.
• Excess plant growth in
streams can increase the
frequency of flooding and
erosion, this comes at a cost
when it wipes out fences,
riparian plants and introduces
weeds onto pasture.
• Degraded water quality
from bad environmental
management can negatively
impact on international
markets and reduce the
value of New Zealand
milk products.

N

• Urine and dung from stock

• N in fertilizer

• Farm dairy effluent

• 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

• Ammonia (a form of
organic N)
can be toxic to fish and
stream insects (fish food)
High concentrations of
nitrates in groundwater
used for drinking poses a
significant health risk.

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,
which tends to settle on the
inside of bends, can:
◦ Affect flow and cause flooding,
◦ Destabilise and increase erosion
on the outside bends worsening the issue,
◦ Impact on the ability of the drain to
function which can lead to flooding.

• Excess sediment indicates there
is erosion somewhere in your property,
this will mean increased repair and
maintenance cost e.g. on scoured
races, hillsides and banks.
There are also potential vet or stock
loss cost from injury or lameness
caused by these areas.

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.

Last updated: Sep 2023
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