Dissolved and particulate nutrients in waters of the Whitsunday Island group, Great Barrier Reef (1988)

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In February 1988, 21 hydrographic stations were sampled within the Whitsunday Island group. The cruise track was laid out to sample the widest range of conditions possible.Initial sampling at each station involved full water column profiles of temperature, salinity and underwater scalar irradiance, obtained using a CTD profiler with an attached Biospherical QSP-200 underwater irradiance sensor. This was followed by the collection of discrete water samples from four to ten depths through the water column using Niskin bottles. These samples were used for analysis of dissolved inorganic nutrients. At some stations additional water samples were collected and subsamples were used for analysis of dissolved organic nitrogen (DON), dissolved organic phosphorus (DOP), chlorophyll, particulate organic nitrogen (PON) and particulate organic phosphorus (POP). Additional information collected for each station included location, acoustic depth, sample depth, sample time, wind speed, wind direction, swell height and swell direction.
The survey was carried out to obtain background data on concentrations of chlorophyll, organic and inorganic nitrogen, phosphorus and inorganic silicate in waters of the Whitsunday Island group. Stations were located to enable comparisons of water quality in the vicinity of anchorages (Nara Inlet) or islands with significant resort developments (Hamilton Island, West Molle Island and Hayman Island) with water sampled in the open water between islands.

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Maintenance and Update Frequency: notPlanned

Statement: Statement: Irradiance:Underwater irradiance measurements were corrected for variations in surface irradiance with a Biospherical GRS-240 reference sensor. The underwater instruments were lowered at 1m/sec and data was sampled at approximately 3 Hz. The raw data were processed to obtain corrected underwater values, then interpolated to values at a 1-meter depth interval for interpretation and analysis. Niskin Sample Preparation:Shortly after collection, unfiltered water samples (ca. 15ml) were drawn from each sampling bottle into acid-washed scintillation vials, which were immediately deep frozen for later analysis of dissolved inorganic nutrient concentrations ashore. At a number of stations, additional water samples were collected and filtered through ashed glass-fiber filters (Whatman GF/F) into acid-washed plastic sample vials and frozen for dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) analysis. Duplicate 100 ml subsamples of water were filtered onto Whatman GF/F filters and frozen for chlorophyll determinations. Duplicate 250 ml subsamples from each sampling depth were filtered onto ashed GF/F filters for particulate nitrogen (PON) determinations.Analytical Procedures:Inorganic nutrient (ammonia, nitrate, nitrite, phosphate, silicate) concentrations were determined by "standard" wet chemical methods implemented on a segmented flow analyzer (Ryle et al., 1981). Water samples for inorganic nutrient analyses were not prefiltered, as filtered samples, even when filtration was carried out by the cleanest possible methods, are often contaminated with small amounts of ammonium. For the dissolved organic nutrient analyses, the filtration apparatus (Millipore Swinnex) was soaked in 0.5N HCl prior to and between uses and filters (ashed Whatman GF/F) were washed with a small volume of sample prior to collection.Dissolved organic nitrogen and phosphorus concentrations were calculated by difference after oxidation of organic matter in the water samples by UV radiation (Armstrong et al., 1966). Water samples were oxidized overnight in a La Jolla Scientific UV irradiator, cooled and analyzed for total N and P as nitrate and phosphate. Prior to analysis for nitrate or phosphate, oxizided samples were re-frozen or stored refrigerated, which results in negligible loss of the nitrate and phosphate (e.g. Nowicki, 1986).Particulate nitrogen was determined by high temperature combustion of the organic matter caught on glass-fiber filters with an ANTEK Nitrogen Analyzer. The instrument was standardized with EDTA. Samples were stored frozen and lyophilized prior to analysis. Dissolved organic and inorganic nitrogen in water adsorbed to the filters and contaminating nitrogen introduced during sample storage and drying were corrected for by analyzing "wet filter blanks" stored and run in a manner similar to the unknown samples. Freshly combusted glass-fiber filters were not measurably contaminated with nitrogen at the instrument attenuation levels used.Particulate phosphorus was determined by inorganic phosphate analysis (Strickland and Parsons, 1972) after high temperature combustion (1 hr at 450°C) and acid persulfate chemical oxidation (Menzel and Corwin, 1965) of particulate matter collected on ashed Whatman GFIF filters.Chlorophyll a and phaeophytin concentrations were determined by fluorometry (Strickland and Parsons, 1972) after grinding of the filters in 90% v/v acetone.References:Armstrong FA, Williams, PM and JD Strickland (1966) Photo-oxidation of organic matter in seawater by ultra-violet radiation: analytical and other applications. Nature 211: 481.Menzel DW and N Corwin (1965) The measurement of total phosphorus in seawater based upon the liberation of organically bound fractions by persulfate oxidation. Limnol. Oceanogr. 10: 280-281.Nowicki BL (1986) Total dissolved and total particulate nitrogen and phosphorus. pp. 117-120. in: Manual of Biological and Geochemical Techniques in Coastal Areas, 2nd Ed. CE Lambert and CA Oviatt (eds.). MERL Series. Report No.1. MERL. Narragansett. Rhode Island.Ryle VD, Mueller HR and P Gentian (1981) Automated analysis of nutrients in tropical seawater. Australian Institute of Marine Science Oceanaography Series AIMS-OS-82-2. 24pp.Strickland JDH and TR Parsons (1972) A practical handbook for seawater analysis. 2nd Ed. Bull. Fish. Res. Bd. Canada 167. 311 pp.

Notes

Credit
Furnas, Miles J, Dr (Principal Investigator)