The biggest problem facing our water bodies today is nutrient pollution – specifically from nitrogen and phosphorus. On land, they are valuable nutrients, helping plants to grow. But when there is too much of them in water, they become pollutants, leading to excessive growth of weeds, slime and algae.
Nitrogen can occur in forms that are highly soluble in water and so can travel via groundwater as well as across surfaces – it can be thought of as the elusive nutrient, and is difficult to mitigate. Phosphorus, on the other hand, clings to soil, which is then washed into waterways – it can be thought of as the sticky nutrient, and is easier to mitigate.
The biggest source of nitrogen in New Zealand’s waterways is urine from farm animals. Nitrogen rich urine can wash straight through soil and into the groundwater before plants have a chance to take it up as fertiliser. In recent years, the rapid growth in dairy farming has led to a big increase in the concentration of nitrogen in waterways in many parts of the county.