Dispersal of suspended sediments and nutrients in the Great Barrier Reef lagoon during river-discharge events: conclusions from satellite remote sensing and concurrent flood-plume sampling

Abstract

Intense wet-season rainfall in January 2005 caused rivers in the Mackay–Whitsunday region of Queensland, Australia, to produce large discharges to the Great Barrier Reef (GBR) lagoon. The regional land use is dominated by sugarcane cultivation, beef grazing and urban uses. The high nutrient (nitrogen and phosphorus) fluxes from these land uses via river runoff produced a massive phytoplankton bloom in the GBR lagoon, which, after 9 days, had spread 150 km offshore. The plume and algal bloom surrounded inner-shelf reefs of the GBR such as Brampton Island Reef and its spread was tracked with a variety of satellite sensors including MODIS, SeaWiFS and Landsat over the 9-day period. The ability to be able to access imagery from a large number of satellite sensors allowed almost daily estimates of the extent of plume to be made, despite periods of cloud. Analysis of water samples from the plume revealed elevated (2–50 times higher) concentrations of Chlorophyll a (and hence phytoplankton biomass), up to 50 times higher than in non-flood conditions, nutrients (2–100 times higher) and herbicide residues (10–100 times higher) compared with GBR lagoon waters in non-discharge conditions. The concentration data from the samples and estimated exposure periods from the satellite images allowed estimates of the exposure of GBR marine ecosystems (coral reefs, the pelagic community, seagrass beds and mangrove forests) to the terrestrial contaminants to be made.

Evidence of Large-Scale Chronic Eutrophication in the Great Barrier Reef: Quantification of Chlorophyll a Thresholds for Sustaining Coral Reef Communities

“…Results from recent water quality monitoring surveys (Brodie et al 2007(Brodie et al , 2010 show that nutrient concentrations in riverine flood plumes in the GBR lagoon greatly exceed the suggested NTC-P and NTC-N values and the resultant Chl a values are 1-2 orders of magnitude higher than the suggested upper ETC-Chl a concentration. The results also demonstrate an inverse relation between salinity and P-PO 4 and some DIN species demonstrating that the river flow is a probable source of readily bioavailable nutrients.…”

Small river plumes off the northeastern coast of the Black Sea under average climatic and flooding discharge conditions

“…This rain-induced flooding discharge of small rivers can significantly influence the land-ocean fluxes of fluvial water, sediments, nutrients, and pollutants as well as modify the structure and intensity of coastal transport pathways for certain world regions, at least on a short-term scale, as addressed in a number of relevant studies (e.g., Milliman and Syvitski, 1992;Meybeck et al, 2003;Brodie et al, 2010;Hilton et al, 2011;Bao et al, 2015;Warrick and Farnsworth, 2017).…”

Water Quality and River Plume Monitoring in the Great Barrier Reef: An Overview of Methods Based on Ocean Colour Satellite Data

“…This paper has described qualitative outcomes derived from remotely-sensed data, which could potentially provide the spatial and temporal information required to achieve consistency of reporting across the GBR. Plumes in the GBR are now mapped remotely by the use of ocean colour [31,48,101] and by the use of remote-sensed CDOM measurements, acting as a proxy for salinity and freshwater extent [29,51] and more recently by the use of tracer values extracted from hydrodynamic models [53,70,102]. This review reported on outcomes associated with the wet season true colour products produced to support the MMP water quality program; however, the advances in regional paramaterisation of the Level 2 products has also been an important step in the provision of a baseline of annual water quality measurements.…”