The Total Nitrogen in water is comprised of dissolved inorganic (nitrites, nitrates and ammonia) and organic nitrogen. High organic nitrogen levels are due to decomposition of aquatic life and sewage runoff while inorganic levels are enhanced by erosion and residential runoff (fertilizers).
The above data shows the levels of nitrogen from site 1 to site 8. Site 2 (Punawai) has the highest concentration of Total Nitrogen, almost always exceeding the state geometric mean criteria. An overlay of the Total Nitrogen and Inorganic Nitrogen plots reveal that in Site 1 and 2 the amount of organic nitrogen is not significant. However, in sites 3, 4 and 5, a substantial increase in the Total Nitrogen levels is observed. This implies that levels of organic Nitrogen (most likely from decomposition of dead vegetation) prevail in these sites. Upstream site 4 (Restoration) is the area densely covered with alien floral species and rubbish (along the Long Bridge).