common
pollutants

What are the substances that are causing all the problems and how are they harmful to the environment? 

NITRATES

Nitrite and ammonia:  you’ve probably heard these words before. They are all different forms of inorganic nitrogen – the ‘good’ nutrients in fertilisers that are used to make plants grow. They are also formed when animal urine and dung breaks down (this is why manure is so good for the garden.)

So why are these nutrients a problem in the natural environment? The answer is that too much of anything in the wrong place is a bad thing. Inorganic nitrogen stimulates growth of both good and undesirable plants – including algae in rivers, streams and lakes which aren’t used to so many nutrients. If you have ever wondered why there is usually much more slimy green growth in a lowland creek or lake than a mountain stream, it’s mainly because one is being fed with lots of nutrients and the other isn’t. It’s the same story in Lakes Ellesmere and Forsyth where algal blooms regularly occur.

Inorganic nitrogen is also harmful to people if too much of it gets into the water we drink. ECan’s own studies show clearly that nitrate levels in groundwater are on the increase.

This has been described as a ‘time bomb’ that future generations will have to deal with.

PHOSPHORUS AND OTHER GROWTH FACTORS

It’s not just too much nitrogen that makes algae and other water plants grow so thickly. Plants are also stimulated by phosphorus (in phosphate fertilisers), and micronutrients like iron. Some of these also come from dung and fertiliser; and once again, too much in the wrong place is a bad thing. The more fertiliser farmers use, and the more dung and urine their animals drop, the more nutrients there are around. And phosphate in drinking water isn’t good for people either.

ENDOCRINE DISRUPTORS

Some pesticides, industrial chemicals, medicines and agricultural chemicals are hormone mimics and can disrupt the natural life processes of aquatic lifeforms. Overseas this has become a recognised problem, but not one New Zealand is yet alert to. In a report prepared for Water Rights Trust in 2003, ‘The Impact of Agriculture, Pollution and Water Extraction on the Future of Canterbury’s Waterways’, Professor Ian Shaw recommended further study of the potential problem. The report was made available to ECan at the time. The issue continues unanswered, and remains one of concern to Water Rights Trust.

SILT AND SEDIMENT

So far we’ve been talking about things that are dissolved in the water, and which you can’t see. But what about the stuff you can see?  Unlike mountain streams, which are clear, streams that run through farmland are often dirty from sediment. In fact it’s hard to find a really clear lowland stream anywhere in Canterbury any more. This is caused by mud and other ‘gunk’ stirred up by stock, and so on.

It makes the water look unappealing. But that’s the least of it. Silt is very harmful to many kinds of aquatic animals including fish and the larvae of freshwater insects. These animals are not adapted to live in muddy water. The silt clogs their gills so they can’t breathe properly or filter-feed. It coats stones and gravel on the bottom  and changes the habitat. Many species of animals disappear completely from  waterways where siltation is a problem. Biodiversity is badly impacted.

But the news isn’t all bad. Eliminate siltation and most rivers will get better. Most of the problem would be solved if only farmers would fence their rivers.  Fonterra has been pushing an accord to have most (90%) dairy farmers fence off their waterways by 2012. In the meantime half of them are meant to be fenced by 2007. Water Rights Trust is concerned that if Fonterra was taking its responsibility to the environment seriously, all farms would have their waterways fenced from stock access now.

DUNG

Too much animal dung is bad on land. But when it falls into water it’s even worse – and not just because of the nutrients in it. Dung is mostly made up of finely ground organic matter, coated with huge numbers of bacteria.  These bacteria soak up dissolved oxygen from the water. They strip out the very oxygen that the aquatic animals need.  The animals die and rot. The water smells sulphurous.  Plants in it die too. Then everything rots.