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Managing Sediments & Nutrients

Sediment is soil that has been washed off the land by rain water, taking nutrients with it. Sediment has damaging impacts on water quality and the health of streams, rivers, estuaries and coastal waters.

Soil is the basis of all farming profitability and takes thousands of years to be created, so farmers benefit by doing all they can to hold soil on their land. 

Sediment

Sediment is no good for stream habitats and fish life. As an example most of the Tukituki Catchment has high levels of riverbed sediment.  The muddy water irritates the gills of fish and invertebrates, and makes it harder for fish to find food; imagine trying to eat a sandwich sitting in a sand storm. When sediment settles, it fills the nooks and crannies that bugs and fish live in; basically taking that sandwich away!  An experiment near Hamilton showed that 90% of fish left a channel after it received fine sediment deposits.

Rivers eventually flow to the sea and carry that sediment out to the coast. The Regional Council’s 2016 State of the Environment Report shows estuaries around Hawke’s Bay becoming ‘muddier’. Fine sediment accumulation can be detrimental to coastal fisheries, so reducing erosion and preventing sediment from reaching waterways in the first instance is one of the regional council’s top priorities. We are also researching the impact of sediment on our coastal fisheries.

Riparian management

Good margins (buffers/gaps) between waterways and productive land are critical for ecosystem health. Fencing off waterways to prevent stock entering them is essential to ensure a healthy plant barrier and also stop animals excreting in the water.

Fencing off streams, planting trees and improving ground conditions along waterways is good operational practice and land stewardship, and will help fish and bugs live happily. An experiment near Taranaki showed that removing riparian habitat resulted in 75% less inanga (the main whitebait species) in a waterway.

Reducing Sediment Loss

  • Understand where water from your property flows and where sediment goes downstream. What impacts might it be having on neighbours or the wider environment?
  • Check the banks of waterways flowing through your property – are they eroding? If they are, exclude stock to help vegetation establish. This can just be done using a hot wire – it does not necessarily need to be a permanent fence, although in time that would be good (replaceable biodegradable hot wires and stakes are on the market). Planting trees also helps stabilise badly-eroding banks.
  • Do you have any major hill slips near waterways? Contact us for help and advice.
  • If possible, have 20m buffer strips/gaps between waterways and tracks, lanes, or any other potential sources of sediment such as worked paddocks or winter crops.  
  • Manage winter crop grazing to reduce run off.  Rain running over grazed crops will take soil downstream.  Graze from the top of the slope first so a margin of crops or long grass at the bottom can help capture runoff.  

Reducing Nitrogen and Phosphorus in water

Nitrogen and phosphorus are both critical for plants. Farming systems aim to make the most of them because obviously it costs money to apply fert. Unfortunately, nutrients don’t always stay where they are intended and can be attached to sediment in water.

Once in waterways, nutrients can trigger excessive algal growth in both tributaries near the source and further downstream in the main river channel. Ultimately, these nutrients find their way to estuaries and the ocean which causes other problems.

Although algal growth is naturally occurring, too much algae in the water smothers habitat and reduces life-supporting capacity. It looks slimy, may smell bad and may result in Phormidium (black mat) growth, which can be toxic to people and animals.

Currently, either phosphorus or nitrogen, or both, are above target levels in waterways in most of the Tukituki catchment.

Photos: 1) long green filamentous algae 2) phormidium

Reducing Nutrient Loss

  • Understand where water from your property flows – where do nutrients go?  What problems do they cause for neighbours or in waterways near you?
  • Understand your soil by getting professional soil testing. 
  • Get expert/professional advice to ensure that your fertilisers are appropriate for the soils and the crops they are being applied too.  This could save you money as well.
  • Avoid applying nutrients - fertiliser or effluent - when plants are not actively growing, i.e. not between May and August, or when heavy rain is forecast.
  • Consider using a spreadmark operator and get trackmap.
  • Keep good records of any fertiliser use which helps a farm environment plan provider put together a good nutrient budget.
  • Winter grazing is permitted but know the rules for feedlots.  See rules here -  https://www.hbrc.govt.nz/assets/Document-Library/Information-Sheets/Land/Winter-grazing-handoutv3.pdf

Reducing Bacteria in Water

E. coli in water is an indicator of disease-causing organisms associated with faeces in our waterways.  People can become sick after swimming in water with bacteria and other pathogens from faeces.  The regional council uses faecal source tracking as a way of figuring out what type of beast (eg. human, bird, cow) E. coli comes from. 

In Hawke’s Bay faecal contamination mainly comes from livestock, and cows in particular.  E. coli and other faecal bacteria can live for several weeks in water, and stay alive while being carried a long distance downstream from its source. So stock accessing and excreting in small streams a long way from swimming holes in rivers or from coastal beaches still poses a risk to human health.

Reducing Bacteria Contamination

  • Wherever practical, prevent direct stock access to waterways – a single hotwire may be sufficient if fencing is too difficult or expensive.
  • Faeces is concentrated on tracks, races and laneways. Do you have tracks or races running alongside streams? Could you possibly move it? If not, is it fenced off? Check to make sure that runoff from the track/race does not flow into waterways – if it does create a bund (earth wall) to direct runoff onto a pasture area instead.
  • Stream crossings that you use fairly often that are not bridged or culverted will be another problem area.  Plan to fence off access and put in a bridge or culvert crossing.
  • If your stockyards and/or woolshed are close to a stream, check where the runoff goes next time it rains.  To stop contaminants flowing into water, make a bund to divert the runoff into pasture instead.
  • Close off any offal pits/rubbish tips close to a stream if these are nearly full.  Create the next one well away from waterways, and where the groundwater table is not high (otherwise it can come up into the bottom of the pit). If you have a fairly new pit, consider replacing it with one in a safer location away from water.
  • Make sure your septic tank/waste water system does not receive stormwater and is cleaned out regularly.

 

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