Inherent optical properties and optical mass classification of the waters of the Strait of Georgia, British Columbia, Canada Eduardo A. Loos ⇑ , Maycira Costa Department of Geography, University of Victoria, Victoria, BC, Canada V8P 5C2 article info Article history: Available online 26 September 2010 abstract Bio-physical and in situ hyperspectral optical data were measured during April and July, 2006, in the euphotic waters of central and southern Strait of Georgia, British Columbia, Canada. Particulate absorp- tion and scattering were derived from the optical measurements of beam attenuation and chromophoric dissolved organic matter (CDOM) absorption. The concentration of CDOM was measured with a fluorom- eter, and water samples were collected for total suspended material (TSM) and chlorophyll a (chl a). The results showed that waters closer to the Fraser River discharge presented the highest concentrations of TSM (18.2 mg L 1 ) and CDOM (32.1 ppb Quinine Sulphate Dihydrate Equivalent (QSDE)), whereas in dee- per waters and waters farther from the plume, both TSM (0.2 mg L 1 ) and CDOM (6.0 ppb QSDE) were relatively lower, and chl a relatively higher (11.3 lgL 1 ), reaching the lowest values at the bottom of the euphotic layer (0.3 lgL 1 ). The waters of the Strait of Georgia’s euphotic zone showed well-defined attenuation coefficients and absorption-to-scattering ratios, which allowed for the optical classification of riverine plume (OM1), estuarine (OM2), and northern and deeper (OM3) waters. Generally, particulate scattering dominated the attenuation of light in these waters. The particulate scattering was mostly influ- enced by inorganic particles, especially in OM1. High loads of inorganic particulate scatterers possibly increased the diffuse light into OM2. Conversely, the relatively higher absorption by CDOM in deeper waters indicates the possibility of competition with phytoplankton for short wavelength radiation. The data and analyses in this study provide important baseline optical information for the waters of the Strait of Georgia. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Coastal waters are very important with regard to ecological and economic issues. These waters are optically dominated by complex assemblages of organic and inorganic matter that has hindered the use of ocean colour satellites and remotely-sensed data for deriv- ing biogeophysical quantities (Bergmann et al., 2004; Chang et al., 2006). In spite of this, optical data have been used for coastal studies (Jerlov, 1976; Doxaran et al., 2006) and optical classifica- tion of water bodies (Chang et al., 2002; Reinart et al., 2003), thus providing information on marine primary productivity (Oliver et al., 2004), fisheries (Santos, 2000), coastal sedimentation and sediment dispersal (Bowers and Binding, 2006), harmful algal blooms (Cullen et al., 1997), organic matter content (Chen et al., 2004), raw sewage disposal (Baker and Spencer, 2004), and pollu- tion (Arst, 2003). Photosynthesis would not be possible without light. However, it is not so much the availability of light that is relevant as the mag- nitude and quality of the available light that will determine if phy- toplankton communities will flourish (Levinton, 2001). Water absorbs visible light (400–700 nm), and consequently there is a de- crease of light with depth. The presence of dissolved and particu- late materials will also have an impact on the light fields because they will not only absorb but also scatter light. These effects are not constant throughout the electromagnetic spectrum but differ quite significantly according to the material interacting with the available light (Mobley, 1995). Chromophoric dissolved organic matter (CDOM) and total suspended material (TSM) play an impor- tant role in the attenuation of photosynthetically-available radia- tion (PAR, 400–700 nm), and therefore on primary productivity (Coble et al., 2004). This has been demonstrated in several regions, such as the West Florida Shelf (Del Castillo et al., 2000), the East Sound, WA (Twardowski and Donaghay, 2001), the Rhode River, MD (Gallegos and Neale, 2002), the Baltic Sea (Woz ´ niak et al., 2003), the Lower St. Johns River, FL (Gallegos, 2005), and the Eng- lish Channel (Vantrepotte et al., 2007). CDOM competes with phytoplankton for photons, particularly in the blue region of the spectrum (400–500 nm; Blough and Del Vecchio (2002)). Furthermore, the absorption of light by CDOM leads to the breakage of molecular bonds and the photochemical formation of chemically-different organic compounds (Schofield et al., 2004) that can ultimately impact primary productivity (Bissett et al., 2001). Suspended material also affects primary 0079-6611/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.pocean.2010.09.004 ⇑ Corresponding author. Tel.: +1 250 853 3284; fax: +1 250 721 6216. E-mail address: ediloos@uvic.ca (E.A. Loos). Progress in Oceanography 87 (2010) 144–156 Contents lists available at ScienceDirect Progress in Oceanography journal homepage: www.elsevier.com/locate/pocean