QA/QC Chlorophyll

by | Oct 25, 2010

Sensor Information:
We currently deploy five types of sensors which measure Chlorophyll a fluorescence. These are summarized in the following table:

Click sensor name for link to manufacturer website WETLabs ECO FLNTU (& puck) Turner Designs Cyclops 7 Turner Designs Algaewatch MultiExciter2 Turner Designs Phytoflash3
Excitation Wavelength 470 nm 460 nm 430 nm 435 nm 420-530 nm
Detection Wavelength 695  nm
@ 80-85 deg.
620-715 nm @ 90 deg. > 665 nm @ 90 deg. 650 ~ 1000 nm 640-730 nm @ 90 deg.
Accuracy +/-0.2 ug/L or 3% of reading (greater of) +/-0.2% FS
Sensor Format Outward looking Flow through Flow through Outward looking Flow through

1 As part of a LOBO mooring
2The multi-exciter excites at multiple wavelengths and uses the resulting aborbances to indicate the types of phytoplankton present.  The 435nm excitation is used to measure the total Chlorophyll a.
3The primary purpose of the phytoflash instrument is to measures photosynthetic efficiency (fv/fm), however, the initial fluorescence (Fo) measurement made by the Phytoflash can be used as a chlorophyll a measurement.



Calibration Evaluation:

Of the five different sensor types deployed at the SATURN stations, the FLNTU and MultiExciter are factory calibrated to units of chlorophyll a concentration (ug/L) using a fluorescent dye as a proxy for chlorophyll.  The remainder measure chlorophyll a in relative fluorescent units only (rfu’s). Data from these sensors are therefore not directly comparable, both between sensor types and even between deployments of individual sensors of the same sensor type.   It is also worth noting that the FLNTU and MultiExciter calibrations against a fluorescent proxy of a laboratory culture may not accurately reflect the in situ chlorophyll a originating from different algal sources in the estuary.

Current quality control protocols attempt to ensure that within individual sensor deployments data are relatable.  This is done through monitoring the sensor response to DI water at Saturn03 & Saturn04.  These measurements will capture periods of sensor offset or the onset of fouling.  It is important to note, however,  that the DI readings do not verify that the slope of the response has not changed over time. These sensors have LED light sources and photodiode detectors and are expected to be relatively stable over time.

For some periods of time, monthly water samples are collected from SATURN-03 and SATURN-04 for the measurement of extracted chlorophyll (link to full protocol).  These samples are sometimes used to calculate and apply a field calibration to the chlorophyll data to convert it to chlorophyll concentration (ug/L).  Because of the dynamic nature of the estuary and shifting conditions known to affect chlorophyll  measurements (temperature, turbidity, different algal communities to name a few) these field calibrations should be considered approximate, but they do allow for some degree of comparison of data from different stations/sensors.  Details on these calibrations can be found at the links below.

Protocols to allow for the direct comparison of data from different sensors and sensor types are in development. In addition upgrades to the database to more accurately display data (only comprable data on the same plot) and to allow for access to field calibrated data are underway.


Chlorophyll QA/QC Archive

PDF Dates Description
 s1-chlcal01 through July 2012 FLNTU: evaluation of manufacturer calibration
s2-chlcal02 Apr. – Oct. 2012 FLNTU: evaluation of manufacturer calibration
 s2-chlcal01 July – Oct. 2010 FLNTU: evaluation of manufacturer calibration
  s3-chlcal01_v2 Oct.2010 – Oct.2012 updated version of field calibration against extracted chlorophyll; released August 2016.  Replaced s3-chlcal01_v1
        s3-chlcal02_v2 Aug.2012-Jan2015 updated version of field calibration against extracted chlorophyll; released August 2016.  Replaced s3-chlcal02_v1
s3-chlcal03_v2 Jan2015-Jan2016 updated version of field calibration against extracted chlorophyll; released August 2016.  Replaced s3-chlcal03_v1
s3-chlCal04 Jan2016-Aug2016 AlgaeWatch calibration for 2016; sensor recovered & replaced in early August 2016
s3_chlCal05 Aug2016-Jan2016 Cyclops 7 chlorophyll fluorometercalibration; sensor deployed Aug2016 through Jan. 2018
s3_chlCal06 Feb2016-Jul2018 preliminary calibration for Cyclops 7 chl. fluorometer deployed 1/31/18
  s3-chl02 7/11/11 – 10/15/11 sensor fouled: corrections for some periods
  s3-chl01 9/24/10 – 9/28/10 correction for sensor fouling
  s4-chlcal01-v2 1/1/10 – 1/1/13 updated version of field calibration against extracted chlorophyll; released August 2016.  Replaced s4-chlcal01_v1
s4-cal02-v2 1/1/13 – 1/1/16 updated version of field calibration against extracted chlorophyll; released August 2016.  Replaced s4-chlcal02_v1
  s4-chl10 4/13/12 – 7/13/12 shift in sensor response
  s4-chl09 10/22/10 – 12/13/10 sensor fouled: no correction
  s4-chl08 8/4/10 – 8/12/10 correction for sensor fouling
  s4-chl07 7/25/10 – 7/29/10 correction for sensor fouling
  s4-chl06 7/18/10 – 7/21/10 correction for sensor fouling
  s4-chl05 6/30/10 – 7/12/10 sensor fouled: no correction
 s4-chl04 6/12/10 – 6/17/10 correction for sensor fouling
 s4-chl03 5/13/10 – 5/19/10 correction for sensor fouling
 s4-chl02 10/14/09 – 11/23/09 sensor fouled: no correction
  s4-chl01 10/3/09 – 10/9/09  correction for sensor fouling
s7-chl01 1/14/15 – 7/29/15 scaling of sensor output to align with later data from the station
s10-chl02 8/28/16-12/16/16 alignment of sensor output from cyclops and FLNTU flourometers