This metadata record describes physico-chemical and nutrient data collected through in situ monitoring by the Great Barrier Reef Marine Monitoring Program for Inshore Water Quality (MMP WQ). A full description of the MMP WQ and its associated datasets can be found in the parent metadata record linked above. Water quality sampling is conducted during both ambient conditions and river discharge events. Ambient monitoring refers to routine sampling during the wet and dry seasons outside of major flood events. Event-based monitoring occurs in response to major flood events to capture conditions within flood plumes; event-based monitoring occurs at the 55 routine site locations, plus 33 additional sites.

The MMP WQ uses in situ sampling to measure 17 key parameters:

physico-chemical: salinity, temperature, Secchi depth, total suspended solids (TSS), and coloured dissolved organic matter (CDOM);

nutrient: ammonium (NH4), nitrite (NO2), nitrate (NO3), dissolved inorganic phosphorus (DIP), silicate (Si), particulate nitrogen (PN), particulate phosphorus (PP), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), particulate organic carbon (POC), and dissolved organic carbon (DOC); and

biological: chlorophyll a (Chl-a).

Discrete water samples are collected with Niskin bottles at each site. Samples are collected from the surface (~0.5 m below water surface) and bottom (~1 m above the seabed) of the water column; although, for some event-based sampling only surface water samples are collected. Samples from the Niskin bottles are taken in duplicate and are analysed for the suite of water quality parameters listed above. Detailed descriptions of analytical chemistry procedures can be found in the program's annual published QA/QC report (see link below in Related Information).

Brief description of collection, storage and analysis method for parameters:

Salinity: 250 mL unfiltered sample, stored refrigerated at 4ºC in screw-top plastic bottle, analysed on Guildline Portasal Salinometer (temperature-compensated and calibrated using OSIL standard seawater as reference)

Temperature: Electronic reversing thermometer attached to Niskin

Secchi depth: The average of the vertical disappearance and reappearance depths of a Secchi disc

TSS: Filtered onto pre-weighed 47 mm 0.4 µm polycarbonate membrane filter, rinsed with deionised water, dried at 60ºC for 12 hours, gravimetric analysis

CDOM: 50 mL filtered sample (0.2 µm acrodisc), CDOM absorption coefficient at 443 nm calculated from absorbance measured by UV-visible absorption spectroscopy

NH4, NO3, NO2 and DIP: 10 mL filtered sample (0.45 µm minisart), stored frozen at -25°C, filtrate analysed on segmented flow analyser

Si: 10 mL filtered sample (0.45 µm minisart), stored refrigerated at 4ºC, filtrate analysed on segmented flow analyser (reported as Si)

PN and POC: 500 mL filtered onto 25 mm GF/F, stored frozen at -25ºC, analysed by high temperature combustion (Shimadzu TOC-L)

PP: 250 mL filtered onto 25 mm GF/F (0.7 µm), stored frozen at -25ºC, persulphate digestion of filter, colorific (molybdate blue) analysis on UV-Vis spectrophotometer

TDN and TDP: 10 mL filtered sample (0.45 µm minisart), stored frozen at -25ºC, persulphate oxidation/digestion with mixture of NaOH, boric acid and K2S2O8 in autoclave, analysed on segmented flow analyser

DOC: 10 mL filtered sample (0.45 µm minisart), acidified with 100 µL HCl, stored refrigerated at 4ºC, analysed by high temperature combustion (Shimadzu TOC-L)

Chl-a: 100 mL filtered onto 25 mm GF/F (0.7 µm), stored frozen at -25ºC, extraction into 10 mL of acetone, read on Turner Fluorometer using acidification method

Data can be downloaded from AIMS' main water quality database (see link below in Data Downloads). This link allows users to restrict searches to only MMP data rather than the entire database. Data are presented as depth-weighted means calculated using surface and bottom samples. Water quality data are collected in conjunction with the Great Barrier Reef Marine Monitoring Program for Inshore Coral Reefs see link below in Related Information).