Export of nutrients and suspended sediment from the Herbert River catchment, northern Queensland, during a flood event associated with Cyclone Sadie (1994)

Brief description

Water samples were collected by both AIMS and CSIRO in the Herbert River catchment 10-15 days before the Cyclone Sadie flood. During the flood event, the John Row Bridge was the only site continuously accessible through the peak flow. Independent concurrent sampling was carried out by AIMS and CSIRO at the John Row Bridge, allowing for comparison of the different sampling and analytical methods used by each agency. Time-series sampling commenced 10 h before the flood peak (approximately 13 h after the initial rise began) and continued for two and a half days, covering most of the flow event. Following the Cyclone Sadie flood, sampling was continued at this and other sites at lower frequency for a further three weeks, which included a second, smaller flood event. Surface water samples were collected at bridges, in clean plastic containers, from the mid- or deepest point of the river. At sites where bridge access was restricted, the sampling container was thrown out into the main flow of water and retrieved by rope.Water samples were analysed to determine: dissolved inorganic nitrogen (DIN)= (NH4+NO2+NO3), dissolved inorganic phosphorus (DIP)=PO4=orthophosphate; silicate; total dissolved nitrogen (TDN); total dissolved phosphorus (TDP); particulate nitrogen (PN); particulate phosphorus (PP); suspended sediment; potassium; and salinity. pH was also measured.Concentrations of dissolved organic nitrogen (DON) and phosphorus (DOP) were calculated as the difference between the total dissolved and dissolved inorganic nutrients. Water discharge in the Herbert River was monitored at two flow gauging stations, one located immediately upstream of the John Row Bridge (116001E) and the other at Gleneagle on the upper Herbert (116004C). This study was targeted at estimating nutrient and sediment export from the Herbert River catchment during a major flood event. Tropical cyclone Sadie degenerated into an intense rain depression over the North Queensland coast on 31 January 1994. A flood plume from the Herbert River and adjacent streams extended approximately 20 km offshore on 2 February 1994. Further heavy rain occurred some two weeks following the cyclone, particularly in the Ingham area causing a second flood of smaller magnitude than that associated with cyclone Sadie.At the time of this study, water-borne nutrients and sediments within the lower catchment of the Herbert River were being sampled by three research agencies, AIMS, CSIRO (Townsville) and the Bureau of Sugar Experimental Stations (BSES, Ingham). The collaborative sampling program of AIMS/BSES, carried out at John Row Bridge, Abergowrie Bridge and Nash's Bridge, was primarily concerned with assessing riverine export of nutrients and suspended sediment to the Great Barrier Reef lagoon. The broader CSIRO program sought to resolve the major source areas for sediments leaving the lower catchment.Stream gauging data was supplied by the Queensland Department of Natural Resources Hydrography Section, Mareeba. Rainfall data was supplied by the Hinchinbrook Shire Council.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: Sampling:The AIMS sampling methodology is described in:Furnas MJ, Mitchell AW and Skuza M (1995) Nitrogen and phosphorus budgets for the Great Barrier Reef. Great Barrier Reef Marine Park Authority Research Publication No. 36. 194 pp.AIMS sampling involved collection of duplicate water samples and taking duplicate subsamples from each for analysis. Immediately after collection, water samples for dissolved nutrients (two each for dissolved inorganic nitrogen, dissolved organic nitrogen and silicate) were filtered through pre-combusted (450°C) Whatman GF/F filters (pore size ~0.7 µm). Particulate nutrient samples were obtained separately by vacuum-filtering known volumes of river water (20 to 100 ml) onto pre-combusted GF/F filters. All nutrient samples, apart from those kept aside for silicate determinations, were immediately frozen on dry ice and stored frozen until analysis. Samples of suspended sediment were collected by filtering known volumes of river water (20-100 ml) onto pre-weighed 47 mm diameter polycarbonate membrane filters (pore size 0.4 µm). The filters were folded and stored in clean scintillation vials at ambient temperature until dried and reweighed.In the CSIRO sampling procedures, single 1 litre water samples were taken. The water samples were kept in a portable refrigerator (3°C) and transported back to the laboratory, where they were processed the day after collection. Duplicate subsamples for analysis of dissolved nutrients were filtered through pre-combusted Whatman GF/F filter papers and the filtrates frozen until chemical analysis. Two GF/F filter papers from each sample were retained for analysis of particulate material.Analyses:The AIMS analytical methodology is described in:Furnas MJ, Mitchell AW and Skuza M (1995) Nitrogen and phosphorus budgets for the Great Barrier Reef. Great Barrier Reef Marine Park Authority Research Publication No. 36. 194 pp.The standard wet chemical procedures used are described in:Treguer P and Le Corre, P (1975) Manuel d'analyse des nutritifs dans l'eau de mer (utilisation de l'Autoanalyzer II Technicon). Lab. d'Oceanologie Chem., Univ. de Bretagne Occidentale, Brest, France.These procedures were implemented on a Skalar segemented flow analyser as described in:Ryle VD, Mueller HR and Gentian P (1981) Automated analysis of nutrients in tropical seawater. Australian Institute of Marine Science Oceanography Series No. AIMS-OS-82-2. 24 pp.Concentrations of dissolved N, P and Si were determined. Separate sets of subsamples were analysed for dissolved inorganic nitrogen ([DIN] = NH4 + NO2 + NO3) and phosphorus ([DIP] = PO4 = orthophosphate) and for total dissolved nitrogen (TDN) and phosphorus (TDP). These last two analyses followed 16 h of oxidation with high-intensity UV light as described in:Armstrong FAJ, Williams PM and Strickland JDH (1966) Photo-oxidation of organic matter in sea water by ultra-violet radiation: analytical and other applications. Nature (London) 211, 481-483.Walsh TW (1989) Total dissolved nitrogen in seawater: a new high temperature combustion method and a comparison with photo oxidation. Marine Chemistry 26, 295-312.Concentrations of dissolved organic nitrogen (DON) and phosphorus (DOP) were calculated as the difference between the total dissolved and dissolved inorganic nutrients ([DON] = [TDN] - [DIN]; [DOP] = [TDP] - [DIP]). Concentrations of particulate nitrogen (PN) were determined by high-temperature combustion of the material retained on glass-fibre filters, with the aid of an Antek Model 707 nitrogen analyser. Particulate phosphorus (PP) was determined colorimetrically after acid-persulfate digestion of the filtered suspended material. See:Parsons TR, Maita Y and Lalli C (1984). A manual of chemical and biological methods for seawater analysis. Pergamon, London.Menzel DW and Corwin N (1965) The measurement of total phosphorus in seawater based on the liberation of organically bound fractions by persulfate oxidation. Limnology and Oceanography 10, 280-282.Concentrations of suspended sediment were determined gravimetrically from the difference between weights of loaded and unloaded membrane filters, after the filters were dried at 60°C for 24 h.Filtered samples collected by CSIRO were analysed for concentrations of ammonium and oxidized nitrogen (nitrate + nitrite), orthophosphate and Kjeldahl N and P by using an Alpkem segmented flow analyser and following methods described in:Anon. (1984) Methods for Chemical Analysis of Water and Wastes. (US Environmental Protection Agency: Cincinnati.)Prior to analysis, the filtered particulate matter was broken down by Kjeldahl acid digestion.

Notes

Credit
Mitchell, Alan W, Mr (Principal Investigator)

Credit
Skuza, Michele (Custodian)