Water Quality dataset, Great Barrier Reef

Brief description

Each collection station is denoted by date, latitude and longitude. The data were sampled at several depths at each site: the number of samples was primarily, but not always, dependent on bottom-depth. A unique identifier has been assigned to each replicate.Variables: depth, dissolved inorganic phosphate (DIP), silicate, ammonium, nitrite, nitrate, dissolved inorganic nitrogen (DIN), dissolved organic carbon (DOC), temperature, salinity, particulate nitrogen (PN), particulate phosphorus (PP), particulate organic carbon (POC), zooplankton, total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), Chlorophyll a, phaeophytin, Secchi disk. Weather information is recorded on swell and wind.Information about the methods used are in the Data Quality section of this metadata record. To collect information about water quality on the Great Barrier Reef. To assist in better defining the range of conditions within which reefs normally exist and the extreme conditions likely to cause significant changes in biological reef communities. Chlorophyll a, PP, PN and Secchi data have been used for the e-Atlas: http://e-atlas.org.auData plot checks by year revealed seemingly abnormally high values of nitrogen-based parameters 1976-1987 with typical values >10 times those of later years. Since many other variables had no data for this period, the data for all parameters was restricted to the period 1988 to current.Methods are summarised in the data quality section of this metadata record.

Lineage

Maintenance and Update Frequency: asNeeded

Statement: Statement: 1989-2005 the water quality data was kept in Microcsoft Access (Bioocean database). From 2005 onward kept on Oracle (RWQPP database). Checks on PP and PN data prior to and including 1987 led to it being discarded.Discrete water samples were collected from two to three depths through the water column with Niskin bottles. Sub-samples taken from the Niskin bottles were analysed for dissolved nutrients and carbon (ammonium, nitrite, nitrate, phosphate, silicate, DON, DOP, DOC), particulate nutrients and carbon (PN, PP, POC), suspended solids (SS) and plant pigments (chlorophyll a, phaeophytin). Subsamples were also taken for laboratory salinity measurements using a Portasal Model 8410A Salinometer. Temperatures were measured with reversing thermometers from at least 2 depths. The sub-samples for dissolved nutrients were immediately filtered through a 0.45µm filter cartridge (Sartorius Mini Sart N) into acid-washed screw-cap plastic test tubes and stored frozen (-18ºC) until later analysis ashore. DOC samples were acidified with 100 ul of AR-grade HCl and stored at 4ºC until analysis. Inorganic dissolved nutrients (ammonium, nitrite, nitrate and phosphate, silicate) concentrations were determined by standard wet chemical methods (Treguer & LeCorre, 1975) implemented on a segmented flow analyser (Bran & Luebbe, 1997) after return to the AIMS laboratories. To avoid potential contamination during transport and storage, analysis of ammonium concentrations in triplicate subsamples per Niskin bottle were also immediately carried out on board the vessel using a fluorometric method based on the reaction of ortho-phthal-dialdehyde with ammonium (Holmes et al., 1999). These samples were analysed on fresh unfiltered seawater samples using specially cleaned glassware, because AIMS experience shows that the risk of contaminating ammonium samples by filtration, transport and storage is high. If available, the ammonium values measured at sea were used for the calculation of DIN.Analyses of total dissolved nutrients (TDN and TDP) were carried using persulphate digestion of water samples (Valderrama, 1981), which are then analysed for inorganic nutrients, as above. DON and DOP were calculated by subtracting the separately measured inorganic nutrient concentrations (above) from the TDN and TDP values. Dissolved organic carbon (DOC) concentrations were measured by high temperature combustion (680ºC) using a Shimadzu TOC-5000A carbon analyser. Prior to analysis, CO2 remaining in the sample water is removed by sparging with O2 carrier gas.The sub-samples for particulate nutrients and plant pigments were collected on pre-combusted glass fibre filters (Whatman GF/F). Filters were wrapped in pre-combusted aluminium foil envelopes and stored at -18ºC until analyses.Particulate nitrogen (PN), reported in µm, is determined by high-temperature combustion of filtered particulate matter on glass fibre filters using an ANTEK 707/720 Nitrogen Analyser (Furnas et al., 1995). The analyser is calibrated using AR Grade EDTA for the standard curve and marine sediment BCSS-1 as a control standard.Particulate phosphorus (PP), reported in µm, is determined spectrophotometrically as inorganic P (phosphate: Parsons et al, 1984) after digesting the particulate matter in 5% potassium persulphate (Furnas et al., 1995). The method is standardised using orthophosphoric acid and dissolved sugar phosphates as the primary standards.The particulate organic carbon content (POC) of material collected on filters is determined by high temperature combustion (950ºC) using a Shimadzu TOC-V carbon analyser fitted with a SSM-5000A solid sample module. Filters containing sampled material are placed in pre-combusted (950ºC) ceramic sample boats. Inorganic C on the filters (e.g. CaCO3) is removed by acidification of the sample with 2M hydrochloric acid. The filter is then introduced into the sample oven (950ºC), purged of atmospheric CO2 and the remaining organic carbon is then combusted in an oxygen stream and quantified by IRGA. The analyses are standardised using certified reference materials (e.g. MESS-1).Chlorophyll a and phaeophytin concentrations are measured fluorometrically using a Turner Designs 10AU fluorometer after grinding the filters in 90% acetone (Parsons et al., 1984). The fluorometer is calibrated against chlorophyll a extracts from log-phase diatom cultures (chlorophyll a and c). The extract chlorophyll concentrations are determined spectrophotometrically using the wavelengths and equation specified by Jeffrey and Humphrey (1975).Sub-samples for suspended solids were collected on pre-weighed 0.4µm polycarbonate filters. SS concentrations are determined gravimetrically from the difference in weight between loaded and unloaded 0.4 µm polycarbonate filters (47mm diameter, GE Water & Process Technologies) after the filters had been dried overnight at 60ºC.Zooplankton were sampled with vertical net hauls from bottom to surface with a 0.5m diameter net of 73µm mesh fitted with a Rigosha flowmeter. The zooplankton biomass were determined by duplicate hauls at all stations. Each net sample was filtered onto a pre-weighed disk of 73µm mesh and frozen. In the laboratory, the frozen mesh was dried (65ºC) and re-weighed to estimate zooplankton community biomass.Source Description: Bran & Luebbe (1997) Directory of Autoanalyser Methods, Bran and Luebbe GmbH, Norderstedt, GermanyFurnas MJ, Mitchell AW, Skuza M (1995) Nitrogen and Phosphorus Budgets for the Central Great Barrier Reef Shelf. Research Publication No. 36. Great Barrier Reef Marine Park Authority, TownsvilleHolmes RM, Aminot A, Kérouel R, Hooker BA, Peterson BJ (1999) A simple and precise method for measuring ammonium in marine and freshwater ecosystems. Can. J. Fish. Aquat. Sci. 56: 1801-1808Jeffrey SW & Humphrey GF (1975) New spectrophotometric equations for determiningParsons TR, Maita Y, Lalli CM (1984) A Manual of Chemical and Biological Methods for Seawater Analysis. Oxford, Pergamon PressTreguer P & LeCorre P (1975) Manuel D'Analyse des las nutirifs dans l'eau de mer (Utilisation de l'Autoanalyzer II Technicon), Lab. d'Oceanologie Chim., Univ. de Bretagne Occidentale, Brest, FranceValderrama JC (1981) The simultaneous analysis of total nitrogen and total phosphorus in natural waters. Marine Chemistry 10:109-122

Notes

Credit
Furnas, Miles J, Dr (Principal Investigator)