[1] Inshore estuarine, lagoonal, and reef waters of the Great Barrier Reef (Australia) were sampled between 2002 and 2005 during four dry and one wet tropical seasons. Relationships among three biogeochemical concentrations and five key water optical parameters measured at 129 stations were explored to optically characterize six predefined regions. A significant spatial and seasonal variability in some of the inherent optical properties and concentrations measured was found, reaching over two orders of magnitude in the estuaries. Total suspended solids concentrations ranged from 0.5 to $54 mg L À1 , TChl-a ranged from 0.05 to $9 mg m À3 , color dissolved organic matter (CDOM) ranged from 0.004 to 0.8 m À1 at 440 nm, and the backscattering coefficient ranged from 0.001 to 1.18 m À1 at 555 nm. Our data set was mainly composed of coastal stations (95%), leading to a poor correlation between the three concentrations (R 2 < 0.31). The range of variation in backscattering ratios, power law exponents, and the spectral slopes of CDOM and nonalgal particulate matter is comparable with findings from other coastal and open waters around the world. The empirical relationships between TChl-a and a ph (440) were found to differ from reference models, indicating differences in phytoplankton size structure and populations. High variability in backscattering ratios and associated power law exponents as well as particulate absorption ratios indicated different trends or relationships in particle size and composition between the different regions. Stations close to the reef matrix showed specific characteristics with concentrations typical of oceanic waters but CDOM spectral slopes similar to those of coastal environments.
[1] The variability in the inherent optical properties along an estuary-coast-ocean continuum in tropical Australia has been studied. The study area, the Fitzroy Estuary and Keppel Bay system, is a shallow coastal environment (depth < 30 m) with highly turbid waters in the estuary and blue oceanic waters in the bay and subject to macrotides. Biogeochemical and inherent optical properties (IOPs) were sampled in the near-surface layer spatially and across the tidal phase during the dry season. These determinations included continuous measurements of spectral absorption, scattering and backscattering coefficients, together with discrete measurements of spectral absorption coefficients of phytoplankton, nonalgal particles and colored dissolved organic matter, and concentrations of phytoplankton pigments and suspended matter. Because of a large variability in the characteristics of the water components on short spatial and temporal scales, we observe a large variability in the associated optical properties. From the estuary to the bay, particle scattering and dissolved absorption decreased by 2 orders of magnitude, and nonalgal particle absorption decreased by 3 orders of magnitude. We also observed a strong variability in particle single scattering albedo and backscattering efficiency (by a factor of 6) and in specific IOPs (IOPs normalized by the relevant constituent concentration) such as suspended matter-specific particle scattering and chlorophyll-specific phytoplankton absorption. Superimposed on this strong spatial variability is the effect of the semidiurnal tide, which affects the spatial distribution of all measured properties. These results emphasize the need for spatially and temporally adjusted algorithms for remote sensing in complex coastal systems.
The underwater light climate, which is a major influence on the ecology of aquatic systems, is affected by the absorption and scattering processes that take place within the water column.Knowledge of the Specific Inherent Optical Properties (SIOPs) of water quality parameters and their spatial variation is essential for the modelling of underwater light fields and remote sensing applications. We measured the SIOPs and water quality parameter concentrations of three large inland water impoundments in Queensland, Australia. The measurements ranged from 0.9-42.
Fluorometers are widely used in ecosystem observing to monitor fluorescence signals from organic compounds, as well as to infer geophysical parameters such as chlorophyll or CDOM concentration, but measurements are susceptible to variation caused by biofouling, instrument design, sensor drift, operating environment, and calibration rigor. To collect high quality data, such sensors need frequent checking and regular calibration. In this study, a wide variety of both liquid and solid fluorescent materials were trialed to assess their suitability as reference standards for performance assessment of in situ fluorometers. Criteria used to evaluate the standards included the spectral excitation/emission responses of the materials relative to fluorescence sensors and to targeted ocean properties, the linearity of the fluorometer's optical response with increasing concentration, stability and consistency, availability and ease of use, as well as cost. Findings are summarized as a series of recommended reference standards for sensors deployed on stationary and mobile platforms, to suit a variety of in situ coastal to ocean sensor configurations. Repeated determinations of chlorophyll scale factor using the recommended liquid standard, Fluorescein, achieved an accuracy of 2.5%. Repeated measurements with the recommended solid standard, Plexiglas Satinice® plum 4H01 DC (polymethylmethacrylate), over an 18 day period varied from the mean value by 1.0% for chlorophyll sensors and 3.3% for CDOM sensors.
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