meth_2.30 Nutrient Analysis via Flow Injection Analysis (University of Technology, Sydney)
Contributor(s): University of Technology, Sydney
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Water samples for nutrient analysis were collected in triplicates, approximately weekly (n= 65) between September 2018 and March 2020. The triplicates originate from 3 locations, ~160 meters apart from each other in the Georges River Estuary (Figure X). A 10 L container was rinsed with sea water and used to retrieve sample water from ~2 meters depth, ~5 meters offshore. From each location, five litres of sample water were transported to the laboratory at UTS, where it was filtered through a 100 µm mesh. All containers were acid-washed and rinsed with the sample water before use. Subsequently, 100 ml of water per triplicate was filtered through a sterile, 0.22 µm Sterivex-GP pressure filter (Merck) using a MasterFlex L/S Multichannel Peristaltic Pump 7535-08 (Cole-Parmer, Vernon Hills IL, USA). Filtrate for each triplicate was stored in 2, 50 ml Falcon tubes at -20 °C until analysis.
Duplicate samples for Orthophosphate (-PO4-3), Ammonia (NH3), Nitrate and Nitrite (Nitrate-Nitrite, NOx) and Nitrite (NO2–) concentrations were measured colourimetrically using Lachat QiuckChem 8500 Series 2 flow injection analysis (FIA) and Omnion 4.0 (Lachat Instruments, Loveland CO, USA) in 2022. The average value of the duplicate results was reported in ug/L.
Soluble or dissolved reactive phosphorus (SRP) consists mostly of inorganic orthophosphate, which is the form of phosphorus that is directly available for algae (Carlson and Simpson, 1996; Koenig et al., 2014). The concentration of SRP (µg P/L) was determined using the phosphomolybdenum blue method; reagents were prepared as per QuikChem Method 31-115-01-1-G, 2003 (USEPA method equivalent: EPA-NERL: 365.5, Zimmerman and Keefe, 1997).
Ammonia concentration was determined following the manufacturer’s manual (QuikChem® Method 31-107-06-1-G). The reagents used to measure nitrate and nitrite (NOx) and Nitrite (NO2–) concentrations (µg N/L) were prepared based on QuikChem Method 31-107-05-1-A, 2003 (USEPA method equivalent: EPA-NERL: 353.4, Zang et al., 1997). After conversion from ug/L to umol/L, Nitrate (NO3–) concentrations were calculated based on subtraction of the Nitrite value from the Nitrate-Nitrite value. The limit of detection (LOD) was 5 µg/L for all nutrients.
Throughout the sample analysis, regular quality control methods were applied, such as calibration standards at the beginning of each analysis furthermore duplicates, field blanks and spike recoveries after every ~20 samples. The efficiency of the cadmium column, installed in the nitrate line, was checked at least 3 times per analysis. All glassware used during the preparation of reagents was acid-washed using 10 %v/v hydrochloric acid (HCl) solution and rinsed at least 3 times with Milli-Q water to prevent any contamination. Light-sensitive reagents were stored in dark glass containers. The results were monitored in Omnion 4.0, and peak captures were adjusted when it was necessary.
For consistency with the AM database, unit conversions are conducted for some parameters using the International Council for the Exploration of the Sea (ICES) conventions (https://www.ices.dk/data/tools/Pages/Unit-conversions.aspx; detailed in Table 2.30_1).
Values below the detection limit of 5 µg/L, were marked with the Australian Microbiome below detection limit sentinel value (1 E-10).
Table 2.30_1
| Parameter | Reported units | AM units | Conversion formula |
| Nitrite (N02) as N | µg/L | µmol/L | NO2 value / 14.006720 |
| Nitrate-Nitrite (NOx) as N | µg/L | µmol/L | NOx value / 14.006720 |
| Nitrate as N | µg/L | µmol/L | (NOx value – NO2 value)/ 14.006720 |
| Dissolved reactive phosphorus as P (PO4) | µg/L | µmol/L | PO4 value / 30.973762 |
| Ammonia and ammonium as N | µg/L | µmol/L | DEP AWQ value / MW N 14.006720 |
* Atomic Weight of Nitrogen = 14.006720, Atomic Weight of Phosphorous = 30.973762