, 2012). Discharges from major episodic floods in the large catchments (Burdekin and Fitzroy) contributed the highest contaminant Pexidartinib loads, but occur as sporadic pulses. However, chronic stresses, resulting from areas of more intense land uses in the smaller, wetter, more developed catchments may also have a significant impact on the GBR. Improved flow estimates and water quality data have been integrated into
new load estimates of 10 water quality constituents (TSS, various nutrient species and PSII herbicides) for 35 river basins, and distinguish between natural and anthropogenic loads (Kroon et al., 2012a). In comparison to pre-European load estimates, TSS increased by 5.5 times to 17,000 tones per year, TN by 5.7 times to 80,000 tones per year, total phosphorus (TP) by 8.9 times to 16,000 tones per year, and PSII herbicides is 30,000 kg per year. Davis et al. (2012) examined the temporal variability in herbicide delivery to the GBR from one of the major sugarcane growing regions in the GBR catchment. Atrazine and its degradation products
and diuron contributed approximately 90% of the annual herbicide load from the catchment, with the highest exports during ‘first-flush’ events. Diuron had the highest concentrations and was the most frequently detected herbicide in sediments collected from catchment waterways and adjacent estuarine–marine environments. Significant sediment find more and nutrient loads to the GBR lagoon are exported during
over-bank floods, when discharge can be significantly underestimated by standard river gauges. Wallace et al. (2012) estimates that most GBR rivers potentially need a flood load correction as over 15% of their mean annual flow occurs as overbank flows. While improvements in the statistical techniques will allow greater certainty in calculating changes over time in catchment loads, simulations using current monitoring data indicated that the chances of detecting trends of reasonable magnitudes over these time frames are very small (Darnell et al., 2012). Riverine freshwater plumes are the major transport mechanism for nutrients, sediments and pollutants into the GBR lagoon and connect the PAK6 land with the receiving coastal and marine waters. Knowledge of the area of the GBR lagoon exposed to freshwater, and its interannual variability, is important for understanding the ecological responses of coastal and marine ecosystems to land-based pollutants. Schroeder et al. (2012) estimate and map the freshwater extent for the entire GBR lagoon area from daily satellite imagery, applying a physics-based coastal ocean colour algorithm that simultaneously retrieves chlorophyll-a, non-algal particulate matter and coloured dissolved organic matter (CDOM) and use CDOM as a surrogate for salinity.
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