In the Resource Management Act 1991, under Schedule 3, water quality classes, Class AE Water (water being managed for aquatic ecosystem purposes) states: "There shall be no undesirable biological growth as a result of any discharge of a contaminant into water."
This worthy AE Standard is currently not accepted, therefore contaminants such as nitrogen, phosphorus and other pollutants are ending up in our waterways and groundwater. This is resulting in undesirable biological growths. A significant amount of money is being spent to lessen the effects.
Undesirable biological growths include periphyton.
Periphyton is a group of organisms in aquatic environments specialised to live on and exploit much larger surfaces. Groups of organisms include fungi, bacteria, protozoa and algae. The most conspicuous group is algae.
It is this group which is usually the focus of most studies of periphyton and draws the most public attention.
The main contributing factor of undesirable biological growths in our waterways comes from the excessive application of fertilisers to land, in particular nitrogen and phosphorus.
There is a relationship between what a plant needs for optimum growth and the water-holding capacity of the soil around the root zone. In order to protect our environment, this relationship needs to be thoroughly understood.
When too much nutrient is applied over the plant's uptake level, and over the holding capacity of the root zone to retrain these nutrients, the risk of leaching is increased.
When this situation is coupled with the application of irrigation water over the plant uptake level and over the soil's capacity to retain this water, the irrigation water flushes nutrients out of the soil.
This nutrient-rich water ends up in our waterways. Our aquatic systems are extremely sensitive to nitrogen and phosphorus - it only takes a slight increase to have a notable effect.
Rather than focusing on the effects with ongoing, expensive and short-term solutions, it would make more sense to address this now.
When a farming system is working well, very little is required in the way of inputs. An example of a long-term solution is good soil management. By looking after the soil through increasing its humus level, a number of positives can be achieved.
It provides valuable nutrients and prevents the soil from drying out in times of drought. Soil with a humus content of 1 per cent can retain about 100,000 litres of water/ha - equivalent to 25mm of rainfall.
There are numerous farming techniques that result in excellent harvests, with reduced expenses and minimal nitrogen pollution.
How much longer are we going to allow our waterways to become unnecessarily polluted, to simply satisfy a "mindset" for over-fertilised land?
- David W Renouf worked for NZAPB managing an apple electronic pre-sizer plant, which had colour fibre optics and 25 staff. He also comes from a farming background and is a long-term researcher of fresh water.
- Views expressed here are the writer's opinion and not the newspaper's. Email: editor@hbtoday.co.nz
