Ms Mary Gurrie:

That is the assessment we have described. We take a sample from an area where we see high nitrate or phosphorous levels or there is a problem with the biology and we look for possible sources of nitrogen in its catchment. We know cattle numbers, the number of septic tanks, whether there is forestry or peat and whether it is an urban area. We know what is happening, as there are a number of data sets that tell us what is going on in the area, and we then we can work out the source, for example, how much nitrogen is being produced by that number of cattle and what the emissions from septic tanks or wastewater treatment plants are.