In late 2022 it was recognized that the NH4 values appeared to be too high for the 2016 NTN network data. Investigation determined that the data was calculated with an incorrect value of the Method Detection Limit (MDL) for NH4. The incorrect value was set at 0.19mg/L, while the correct value was actually 0.019 mg/L. This MDL value corresponded to sample ID’s between TP0370SW and TQ4360SW, which were collected for the majority of 2016. Weekly samples in this sample range were identified and corrected in 2022 for incorrect NH4 values.
In February 2023, some samples beyond the range of TQ4360SW were also found to be using an MDL value of 0.19mg/L, while the correct value was actually 0.018mg/L. The affected samples were generally collected between the end of 2016 and the start of 2017. These additional weekly samples have been identified and corrected in February 2023 for incorrect NH4 values.
Based on the above weekly sample updates, the following aggregate NH4 values were affected. These have been recalculated and updated in February 2023:
MONTHLY
- Dec 2015 for sites MD99, OH71, OR09 due to a single sample update for each site in Dec 2015
- Jan 2016 thru Dec 2016 – Various
- Jan 2017 – Various
SEASONAL
- 2016 Season 1 (Dec 2015 – Feb 2016) – Various
- 2016 Season 2 (Mar 2016 – May 2016) – Various
- 2016 Season 3 (Jun 2016 – Aug 2016) – Various
- 2016 Season 4 (Sep 2016 – Nov 2016) – Various
- 2017 Season 1 (Dec 2016 – Feb 2017) – Various
ANNUAL
- 2015 – Not updated due to small number of sample changes.
- 2016 – Various
- 2017 – Various
WATER YEAR
- 2016 – Various
- 2017 – Various
This is specific for the NTN network only. This MDL error is not present with the AMoN network data.
The map data for these periods (raster / grid files) have not been updated at this time. This news item will be updated when those updates are completed.