New Zealand’s water has taken a massive hit in areas of urban settlement and pastoral farming.
There are many causes including: cutting down forests; introduced pests and plants; disposal of human sewage; removing water for irrigation and electricity generation; industrial discharges; urban stormwater; the drainage of wetlands and farming practices.
Sediment and E coli reduce wildlife and water clarity. Lack of shade and excess nutrients contribute to the growth of weed and algal blooms. They may also contribute to the creation of poisonous cyanotoxins. In short, pollution makes waterways unpleasant and at times unsafe.
Depending on local conditions, it may take decades to see the impacts of current practices on water quality.
Over the past two decades most measures of water quality have been declining. More recently some of those measures have started to stabilise and a few have improved. This is probably because farmers have fenced and planted some rivers, keeping their stock out. However, indicators of ecosystem health still show a worsening trend.
In recent decades the impact of human sewage and industrial waste has reduced. This leaves the increased intensity and coverage of dairy farming as the most likely cause of any continuing problems. There has been a substantial change in land use, especially in some regions, from low intensive sheep and beef farming to highly intensive and irrigated dairy farming.
Why are cows a problem? More cows means more urine going onto the land, which means more nitrogen leaching into our waterways.Read More: Our Findings – Why Did it Happen?
MFE vs NIWA data – is water quality still declining?
The NIWA data set includes a more comprehensive range of variables which have been consistently measured, so their results are more robust. NIWA analysis shows that water quality declines in an area as more land is put into pasture.
MFE analyses indicate that these trends may have recently reversed or stabilised for some particular variables (phosphorus, bacteria and ammonia). This may be a result of improved fencing and riparian planting, as well as better effluent management.
However these are just 3 variables. Even according to MFE results the best indicator we have of ecosystem health – the Macroinvertebrate Index, is still deteriorating.