AMT12 Nutrient (micro- and nano-molar) measurements from CTD bottle and surface underway samples
Originator's Protocol for Data Acquisition and Analysis
Water samples were taken from the Sea-Bird CTD rosette system and from the non-toxic supply tap. They were sub-sampled into acid-clean 60 ml HDPE (nalgene) sample bottles. Analysis for nutrients was completed within 3 hours of sampling in all cases. Clean handling techniques were employed to avoid contamination of the samples.
The main nutrient analyser was a 5-channel Bran and Luebbe AAIII segmented flow autoanalyser. This cruise was the first in which this new instrument was deployed. The analytical chemical methodologies used were according to Brewer and Riley (1965) for nitrate, Grasshoff (1976) for nitrite, Kirkwood (1989) for phosphate and silicate, and Mantoura and Woodward (1983) for ammonium.
Nanomolar ammonium concentrations were obtained using an adapted method from Jones (1991); this uses a fluorescent analysis technique following ammonia gas diffusion out of the samples, passing across a hydrophobic Teflon membrane due to differential pH chemistry. Unfortunately, this system could only be used in the early stages of the cruise as the fluorometer broke down.
Nanomolar nitrate+nitrite, nitrate and phosphate concentrations were obtained on some samples using a 3-channel nanomolar analyser. This method combines sensitive segmented flow colorimetric analytical techniques with a Liquid Waveguide Capillary Cell (LWCC). The phosphate waveguide did not produce consistently reliable results.
References Cited
Brewer P.G. and Riley J.P., 1965. The automatic determination of nitrate in sea water. Deep-Sea Research, 12, 765-772.
Grasshoff K., 1976. Methods of seawater analysis. Verlag Chemie, Weiheim: 317 pp.
Jones R.D., 1991. An improved fluorescence method for the determination of nanomolar concentrations of ammonium in natural waters. Limnology and Oceanography, 36, 814-819.
Kirkwood D.S., 1989. Simultaneous determination of selected nutrients in seawater. ICES CM1989/C:29, 12pp.
Mantoura R.F.C. and Woodward E.M.S., 1983. Optimisation of the indophenol blue method for the automated determination of ammonia in estuarine waters. Estuarine, Coastal and Shelf Science, 17, 219-224.
BODC Data Processing Procedures
Data were submitted to BODC in Microsoft Excel spreadsheet format. Sample metadata were checked against information held in the database - there were no discrepancies. Parameter codes defined in BODC parameter dictionary were assigned to the variables. Data from the nanomolar ammonium and LWCC systems were submitted in units of nmol/l. Nano-molar data were divided by 1000 to convert the units to µmol/l for storage in the database. Users should be aware that these LWCC measurements are valid to the fourth decimal place. The data were assigned parameter codes defined in BODC parameter dictionary. Data loaded into BODC's database using established BODC data banking procedures.
A parameter mapping table is provided below;
| Originator's Parameter | Units | Description | BODC Parameter Code | Units | Comments |
|---|---|---|---|---|---|
| Ammonium (AAIII) | µmol l -1 | Concentration of ammonium {NH 4 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | AMONAATX | µmol l -1 | - |
| Ammonium (nano-molar system) | nmol l -1 | Concentration (nM sensitivity) of ammonium {NH 4 } per unit volume of the water body [dissolved plus reactive particulate phase] by nanomolar ammonium system after Jones (1991) | AMONNATX | µmol l -1 | nmol l -1 converted to µmol l -1 (conversion used * 1/1000) |
| Nitrate+Nitrite (AAIII) | µmol l -1 | Concentration of nitrate+nitrite {NO 3 +NO 2 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | NTRZAATX | µmol l -1 | - |
| Nitrate+Nitrite (LWCC nano-molar system) | nmol l -1 | Concentration (nM sensitivity) of nitrate+nitrite {NO 3 +NO 2 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis with liquid waveguide capilliary cell | NTRZLWTX | µmol l -1 | nmol l -1 converted to µmol l -1 (conversion used * 1/1000) |
| Nitrite (AAIII) | µmol l -1 | Concentration of nitrite {NO 2 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | NTRIAATX | µmol l -1 | - |
| Nitrite (LWCC nano-molar system) | nmol l -1 | Concentration (nM sensitivity) of nitrite {NO 2 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis with liquid waveguide capilliary cell | NTRILWTX | µmol l -1 | nmol l -1 converted to µmol l -1 (conversion used * 1/1000) |
| Phosphate (AAIII) | µmol l -1 | Concentration of phosphate {PO 4 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | PHOSAATX | µmol l -1 | - |
| Phosphate (LWCC nano-molar system) | nmol l -1 | Concentration (nM sensitivity) of phosphate {PO 4 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis with liquid waveguide capilliary cell | PHOSLWTX | µmol l -1 | nmol l -1 converted to µmol l -1 (conversion used * 1/1000) |
| Silicate (AAIII) | µmol l -1 | Concentration of silicate {SiO 4 } per unit volume of the water body [dissolved plus reactive particulate phase] by colorimetric autoanalysis | SLCAAATX | µmol l -1 | - |
Data Quality Report
The dataset has been checked by the data originator - any suspect data values were removed from the data set before submission to BODC.
The detection limits for measurements from the AAIII Bran and Luebbe autoanalyser have are 0.02 µmol l -1 , except the colorimetric ammonium which has a detection limit of 0.08 µmol l -1 . Samples in the database with a flag of "<" had concentrations below the specified detection limits.
At low concentrations, the values obtained by the LWCC are likely to be more accurate than those from the AAIII analyser.
Problem Report
Not relevant to this data set.
