COLORS OF NATURAL-WATERS .2. OBSERVATIONS OF SPECTRAL VARIATIONS IN BRITISH-COLUMBIA RIVERS

Subsurface volume reflectance spectra in the range 400-740 nm were dir ectly measured on four separate occasions at each of fourteen river st ations in British Columbia during 1986 and 1987. Chromaticity analyses were performed on volume reflectance spectra to define aquatic colour in terms of a dominant wavelength and its associated purity. An attem pt was made to explain water colour variations in British Columbia riv er systems based upon elevation, drainage area, glacial-feed, groundwa ter intrusion, turbidity, and basin type. It is shown that simple sub- basins which are glacier-fed and meltwater-dominated generally display dominant wavelengths in the interval 480-550 nm (i.e. colours usually perceived to be in the range blue to turquoise to green), a consequen ce of low to moderate turbidity comprised predominantly of suspended i norganics. Simple sub-basins which are non glacier-fed and groundwater -dominated display dominant wavelengths in the interval 550-570 nm (i. e. colours perceived to be in the range green to brown), a consequence of low to high particulate turbidity in conjunction with substantial concentrations of dissolved organics. Most of the large river basins o f the Canadian Cordillera are comprised of a complex of sub-basins, an d thus represent the integration of inputs from several sources. These complexes are shown to display dominant wavelengths in the restricted wavelength interval 573-578 nm. Such an ''end-point'' dominant wavele ngth causes the river water to be perceived as brownish in colour.