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Table 1 Plume water types as described in Devlin et al. ( 2012a ) and Álvarez-Romero et al. ( 2013 ), detailing the water quality and optical properties which define the plume characteristics within each plume type (e.g., Clarke et al. 1970 ; Morel and Prieur 1977 ; Froidefond et al. 2002 ; McClain 2009 )

From: Combining in-situ water quality and remotely sensed data across spatial and temporal scales to measure variability in wet season chlorophyll-a: Great Barrier Reef lagoon (Queensland, Australia)

Colour classes

Water type

Description

Colour properties

1 to 4

Primary

Sediment-dominated waters: characterised by high values of coloured dissolved organic matters (CDOM) and total suspended sediment (TSS), with TSS concentrations dropping out rapidly as the heavier particulate material flocculates and settles to the sea floor (Devlin and Brodie 2005;Brodie and Waterhouse 2009). Turbidity levels limit the light (KdPAR) in these lower salinity waters, inhibiting production by primary producers and limiting chl-a concentrations.

Greenish-brown to beige waters: Sediment particles are highly reflective in the red to infra-red wavelengths of the light spectrum. Sediment-dominated waters have a distinctive brown/beige colour, depending upon the concentration and mineral composition of the sediments.

5

Secondary

Chlorophyll-a-dominated waters: characterised by a region where CDOM is elevated with reduced TSS concentrations due to sedimentation. In this region, the increased light in comparison to primary water type condition (but still under marine ambient conditions) and nutrient availability prompt phytoplankton growth measured by elevated chl-a concentrations.

Bluish-green waters: Due to this green pigment, chlorophyll/phytoplankton preferentially absorb the red and blue portions of the light spectrum (for photosynthesis) and reflect green light. Chl-a-dominated waters will appear as certain shades, from blue-green to green, depending upon the type and density of the phytoplankton population.

6

Tertiary

CDOM-dominated waters: Offshore region of the plume that exhibits no or low TSS that has originated from the flood plume and above ambient concentrations of chl-a and CDOM. This region can be described as being the transition between secondary water type and marine ambient conditions.

Dark yellow waters: CDOM are highly absorbing in the blue spectral domain. CDOM-dominated waters have a distinctive dark yellow colour.