August 2021 to July 2022
NZFFA water testing NO3-N mg/L Year Three 2021 t0 2022
The August 2020 “bottom line” for nitrate DIN for rivers (virtually the same as NO3-N) is 2.4 mg/L
The bottom line for lakes is 700 to 800 mg / m3 [1.80 mg/L = 1,800 mg / m3]
Surface waters exceeding this bottom line are recorded in red since August 2020
The apparent improvement in the Selwyn River nitrate results simply reflects the relative proportion of groundwater to water from surface flooding, (i.e. When the upper and lower Selwyn River flows are connected).
The increased nitrate results along the Lower Lake Road probably reflects markedly increased flows from recent rains and no take up by plants during a cold part of the year. In the summer most of these drains are dry or are reduced to a trickle.
Ecologist agree that ecosystem health begins to become affected by direct nitrate toxicity from 0.6 to 1.0 mg/L NO3-N
There are no precise limits due to a lack of studies and the influence other water quality parameters such as pH, Hardness, dissolved O2, etc..
Aquatic invertebrates are lost first, then amphibians, then early life stages of fish such as trout.
A Canadian Government sponsored study (2010) found Lake Trout and Whitefish eggs and fry become affected from 2.90 mg/L
The Canadian Government has adopted a bottom line for nitrate of 3.0 mg/L to protect salmonid fish as a result.
A recent peer reviewed study (2020) found no nitrate sensitive invertebrates in the MIC index in 19/20 Canterbury streams.