Stations in optically shallow water, where the signal is affected by light reflection from the sea floor, were excluded. A Type II linear regression of log-transformed satellite and Secchi values was applied, to then estimate GBR Z10% as: equation(1) GBRZ10%=10∧[(log10(Z10%)-a0)/a1]where a0 and a1 are slope and intercepts of satellite data against Secchi (values: 0.518 and 0.811 for SeaWiFS, and 0.529 and 0.816 for MODIS-Aqua).
GBR Z10% was implemented into the NASA satellite processing software (SeaDAS) and applied to the full time series of MODIS-Aqua data (01 July 2002 to 21 November 2012). The large Burdekin River with its 133,400 km2 catchment area is the single greatest HCS assay source of suspended sediments into the GBR lagoon (mean: 4 million tonnes yr−1, representing ∼25% of total loads entering into GBR; Kroon et al., 2012). A mask was generated for the continental shelf off the Burdekin Natural Resource Management region (∼17.9–20.1°S and 146.3–149.3°E), extending from the shore to the 200 m depth selleck screening library contour, and excluding coral reefs (Fig. 1). To the best of our knowledge, grid points in optically shallow water were also
excluded. The final data contained 25,621 grid points each covering a 1-km2 area. Data availability varied greatly between days and months due to cloud cover. Environmental data were obtained as follows: bathymetry data (meters below mean sea level) for each grid point were obtained from a high-resolution digital elevation model for the GBR at a resolution of 0.001-arc degrees (about 100 m) (Beaman, 2012). Daily data of freshwater discharge volumes of the Burdekin, Houghton, Ross and Black Rivers were provided by the State of Queensland, Department of Environment and Heritage Protection (DEHP).
Annual loads of suspended solids, total nitrogen and total phosphorus of the Burdekin River were obtained for 2003–2009 from Kuhnert et al. (2012) and for 2010–2011 from DEHP at the Clare/Home Hill gauge and monitoring station (Table 1). Hourly data on wave heights and wave frequencies were obtained from the DEHP from a wave rider buoy in the center of the study region (8 km O-methylated flavonoid off the coast, at 19.1487° latitude South, 147.0576° longitude East). Daily rainfall data from Townsville Airport station and hourly wind speed data from Cape Ferguson were obtained from the Australian Bureau of Meterology (http://www.bom.gov.au/oceanography/projects/abslmp/data/index.shtml). Daily tidal amplitudes as a proxy for tidal currents (one daily value for the whole region) were calculated from hourly predicted sea level data derived from a DEHP-operated storm tide gauge site in Townsville Harbour (19.2538°S, 146.8295°E). Gaps in the tidal range data were input from estimates generated from a harmonic tide clock and tide predictor (Flater, 2007) after correcting for an offset calculated over all available tide measurements.