Joanna Grigg
Time is better spent identifying risks to freshwater quality on your farm and making appropriate management changes, not testing the stream.
Susie Le Cren, agricultural land management consultant with LandVision Ltd, has been compiling farm environment plans (FEP) for sheep, beef and deer farmers affected by the Kaikoura earthquake, from Marlborough to Canterbury, and for clients in the North Island.
She said there is no requirement to test surface water quality as part of a routine farm environment plan at this stage and she seldom recommends it to farmers.
“We already know the management practices that can have a negative effect on water quality, so it’s best to spend time and energy on making sure it doesn’t happen.”
‘Understand your critical source areas; where potential contaminant pools like below yards, stock camps, silage pits and the winter cropping area.’
“My personal view is that water testing be voluntary, or do it if identifying or monitoring a specific issue.”
There are two ways contaminants typically get in a waterway; either by overland surface runoff or via diffuse water movement through the soils, she said. The surface runoff can collect phosphate, sediment, bacteria and some nutrients as it flows, while diffuse runoff can take dissolved nutrients such as nitrate and sulphate.
“Understand your critical source areas; where potential contaminant pools like below yards, stock camps, silage pits and the winter cropping area.”
There are many options to filter out contaminants including intercepting the runoff into a sediment catch pond, where it can settle before any overflow meets the flowing water, or through a riparian strip of vegetation.
Le Cren is reluctant to suggest surface water testing be compulsory because of the variation in test results seen from the same water body.
Results can vary due to flow rate, water temperature, pH or between test sites and this makes it very difficult to get a consistent appraisal of the waterway.
“It is far better to focus on best or good management practices as these have a direct link to water quality.”
Having said that, surface water testing kits are a lot cheaper than they used to be and can give results for a range of parameters including nitrates, nitrites, phosphate and E. coli. Le Cren said some farmers may like to test water, for their personal interest. If you do test, Le Cren suggests testing the direct surface runoff below a critical point area, such as a drain. Testing should be done in the same place, at the same flow and same season, in the mid-stream area. Farm and climate conditions and activities throughout the catchment at the time of testing should be noted down.
“Look for trends, don’t get fixated on one result.”
“You just have to be very careful how you interpret the results as, in a short space of time, they can vary a lot.”
A basic test will include Total N and/or TKN, Ammoniacal-N, Nitrate-N, Nitrite-N, Total P, Dissolved Reactive P, E. coli and Turbidity. If monitoring for sediment contamination then include suspended solids and turbidity. If monitoring faecal contamination then look at total coliforms, specific coliforms such as Campylobacteria. However, E. coli is generally considered adequate as the primary marker for general in-stream health, she said.
It is important to follow the testing protocol and procedures to avoid inaccurate test results. Collect samples from midstream flow rather than eddies or back-flows. When looking at whole-farm contaminant loss find a site at the most ‘downstream end’ or ‘exit point’ of the property. Most properties require a number of sample sites in different waterways to represent all sub-catchments on the property. ‘Up-stream’ or ‘entry point’ sampling may be required as well to assess changes in contaminant concentrations resulting directly from the farm.
The Proposed National Environmental Standards for Freshwater suggests farm plans map the water ways, the fences next to waterways and the places stock cross water. It proposes that a FEP include the location of source protection zones for human drinking water and the location of any critical source areas for nutrient loss, soil loss or both.
Farmers then have to assess the risk of contaminant losses from the farm, with consequent impacts on freshwater ecosystem health, associated with activities carried out on the farm.
Le Cren said lysimeters installed in-ground are ideal for high risk sites or for research but they are expensive, very technical to use and more of a long-term monitoring tool.
Understanding soils and drainage patterns is where farmers should better spend their energy, she said.
A clay pan, pugged or compacted soils create ponding, which increases run-off with rain. Hydroscopic soils, typically seen during a drought, act like corrugated iron sheets initially with a rain.
“Avoid over grazing these soils.”
Any soil with a high water table, often seen in low lying ground, is also at risk of ponding and surface run-off.
She challenges farmers to list management strategies to reduce sediment and nutrient loss to waterways.
“All farmers should be able to recite a list of good management practices, unless they’ve been hiding under a rock recently.”
Challenge to farmers: how many of these can you list?
Examples of good management practices for minimising contamination to waterways.
- Ground cover: Manage periods of exposed soil between crops/pasture to reduce risk of erosion, overland flow and leaching. (e.g. space planted trees, windbreaks, cover crops)
- Leave grassed areas around rocks, gullies and riparian margins.
- Sediment: Identify risk of overland flow of sediment and faecal bacteria and minimise transport of these to water bodies e.g. sediment traps or interception drains, headlands or diversion bunds.
- Select appropriate paddocks for intensive grazing, recognising and mitigating possible nutrient and sediment loss from critical source areas.
- Locate laneways so that run-off is filtered by a vegetated strip.
- Nutrients: Monitor soil phosphorus levels and maintain them at or below the optimum for the farm system.
- Manage the amount and timing of irrigation to meet plant demands and minimise risk of leaching and runoff.
- Provide alternative stock-water sources, shade and shelter away from waterways where possible.
- Place salt blocks and supplementary feed away from riparian margins.
- When developing paddocks, retain native vegetation such as tussock and shrub habitat in gullies, steep and higher country as this will regulate run off of water, help retain water quality, reduce soil movement and provide filter areas prior to water entering streams.
