Performance Verification Statement for the Real Tech Real Nitrate Analyzer GL Series

Ref. No. [UMCES] CBL 2017-050

ACT VS17-05

Deployment at Chesapeake Biological Laboratory (CBL)

An 84 day moored field test was conducted in Chesapeake Bay from July 18 to October 10,

2016. The deployment was located at 38.32°N, 76.45°W attached to the side of a floating pier at

the mouth of the Patuxent River (Figure 13.) The site was brackish with an average water depth of

2.2 m at the test site.

Figure 13.

Aerial view of CBL deployment site (left) and instrument deployment rack off the dock during

deployment (right).

Time series results of ambient conditions for tidal height, temperature, salinity, turbidity

and chlorophyll are given in figure 14. Temperature ranged from 20.0 to 31.3°C, salinity from

12.7 to 16.9 PSU, turbidity from 0.5 to 936.3 NTU and chlorophyll from 0.2 to 97.1 µg/L over the

duration of the field test.

The Real-NO3 operated continuously for 69 days until 9/24 when air purge system

malfunctioned. The system was bypassed per manufacturer’s instructions and the instrument

restarted on 9/30. The instrument returned 22,345 observations out of a possible 24,144 based on

approximate 5 minute sampling intervals for a data completion rate of 93%. For the entire

deployment, 1796 data points were missing, and 3 were flagged as bad. Time series results of the

Real-NO3 and corresponding reference NO

results are given in figure 15 (top panel). For the

interval deployed, the range of accepted values reported by the Real-NO3 was 0.000 to 0.254

mgN/L, compared to 0.001 to 0.038 mgN/L within reference samples.

The bottom panel of figure 14 presents the time series of the difference between the Real-

NO3 and reference NO

for each matched pair (n=100 comparisons out of a total of 103 with 3

missing instrument results during the inoperable). The average and standard deviation of the

measurement difference for the deployment was 0.083 ±0.022 mgN/L, with the total range of

differences between 0.018 to 0.166 mgN/L. There no significant trend in measurement difference

over time during the deployment (p=0.681; r

=0.002).