Rain falls onto deforested land and carries sediment into waterway.
Livestock can also increase erosion.
Sediment reduces water clarity.
Fine sediment can suffocate fish and increased nutrients cause undesirable plants and algae to grow.
Riparian planting provides shade, shelter, and food for wildlife.
Fencing keeps livestock away from our waterways.
Tree and shrub roots filter nitrogen and other pollutants from water run-off and reduce soil erosion.
Shade from strategic trees and plants at the toe of the slope provide fish habitat and prevent algae growth.
As water erodes the land it carries sediment into our rivers, lakes and harbours. This sediment is made up of fine silt, sand, and/ or clay. The erosion process is natural, but human activity can greatly increase it. On dairy farms we have issues with river bank erosion, sediment run-off from cultivation of crops and soil damage by cows, particularly in winter.
This is a problem because when we get heavy rainfall and run-off the sediment moves from the land into our waterways.
This clogs up rivers, lakes and harbours and makes them look brown and dirty. But the biggest impact is when sediment forms a mat over the waterway bed, and can make the habitat unsuitable for fish and other life.
In the past, our native wetlands played a major role in protecting our waterways from sediment. Unfortunately, more than 90 percent have been drained over the last 150 years. Sediment does eventually disperse from some waterways but it takes a long time – especially when we’re talking about decades and centuries worth of sediment loss.
Sediment run-off is an issue for farmers.
No dairy farmer wants to lose the soil their livelihood is built on.
So a lot of work is being done on the best ways to reduce it.
Our farmers have invested in protecting stream and river banks, especially those prone to erosion.
Riparian planting has helped make them more stable, and waterway fencing keeps cows from grazing and trampling over them Water clarity is the main indicator for sediment levels in our waterways and the Ministry for the Environment and Stats NZ "our fresh water 2017" report says:
"Model-based estimations of river water clarity showed 5.7 percent of river length did not meet the Australian and New Zealand guidelines."
OF NATIVE WETLANDS
DRAINED IN LAST 150 YEARS.
Water Clarity Trends
(241 RIVER SITES)
MINISTRY FOR THE ENVIRONMENT AND STATS NZ
"OUR FRESH WATER 2017" REPORT.
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