February 21, 2024

A new study of New Zealand’s freshwater quality has painted a sobering picture, showing that E coli is seeping through three-quarters of the land and into waterways at higher levels than national regulations allow.

The report, funded by the government-backed organisation Our Land and Water, looked at how rivers, lakes, and estuaries are polluted by four major contaminants, including E coli, a bacteria found in the intestines of many animals and humans that can cause serious illness.

It highlights the challenge New Zealand faces in bringing contaminant levels down in line with the guidelines outlined in the National Policy Statement for Freshwater Management.

“The big picture that we see in terms of water quality is the impact of agriculture, which is quite ubiquitous because agriculture occupies about 35% of our total land use,” said Ton Snelder, director of LWP, a company involved in creating the report.

“There are other land uses in particular, urban land use that can also have quite a significant impact on water quality,” he said.

Along with E. coli, the report looked at levels of nitrogen, phosphorus and sediment at 850 water monitoring sites across the country and modelled how those contaminates might affect New Zealand’s 650,000 river segments, 961 lakes and 419 estuaries. Nitrogen and phosphorus naturally occur in soil, but dangerous levels are often attributed to farming byproducts, such as cattle urine. Sediment is another naturally occurring pollutant that can reach unhealthy levels due to human-caused erosion as well as urban and agricultural land use.

The report found that substantial reductions of at least one of the four contaminants were required in almost all regions of the country to meet national regulations. Maps generated by the report’s data demonstrate the human impact on waterways – the sparsely populated west coast of New Zealand’s South Island shows low levels of the contaminants. However, areas such as Canterbury, which has intensive dairy farming, and Auckland, the country’s largest city, show high levels of either nitrogen or E. coli.

Reducing contaminants falls to local councils, which are required to regulate farms and urban areas to improve freshwater. Richard McDowell, a chief scientist at Our Land and Water and professor at Lincoln University, said nitrogen and phosphorus in waterways can decrease when farmers use less fertiliser and ensure cattle effluent from dairy sheds does not run into waterways.

Land use change, such as switching from dairy to forestry or crops where suitable, can improve water quality, McDowell said, acknowledging the balance between environmental and social challenges. In recent years, farmers have blamed rural unemployment on high numbers of cattle farms converting to forestry.

Unrelated to the study, New Zealand has seen a handful of swimming areas off-limits due to water pollution. Traces of human faeces were recently found in the waters of Corsair Bay, a popular Christchurch swimming spot. In Auckland, a burst sewage pipe near the Hauraki Gulf spewed raw sewage into the harbour for weeks until the issue was temporarily fixed. In parts of the upmarket mountain town of Queenstown, a “boil water notice has been in place since mid-September due to an outbreak of cryptosporidium, which can cause diarrhoea and stomach cramps. The likely cause is human or animal faeces.

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