EVALUATION OF LAKE SEDIMENT COMPOSITION AND PRODUCTIVITY USING HIGH RESOLUTION DIFFUSE SPECTRAL REFLECTANCE DATA FROM CLELAND LAKE, SOUTHWESTERN CANADA

The first derivative of Diffuse Spectral Reflectance (DSR) data defines the spectral shape of the sample. It is an efficient method of quantitatively analyzing the organic matter content, clay minerals, carbonates and iron oxides in sediment. DSR was measured at 0.5 cm resolution using a hand held spectrophotometer, for lake sediment obtained from Cleland Lake, British Columbia, Southwestern Canada. The instrument generates reflectance spectra at 10 nm intervals throughout the visible spectrum (400 to 700 nm). Varimax-rotated principal component analysis of the reflectance data generated four factors that explain 95.9% of the total variance. Factor 1 explains 37% of the variance and correlates (r = 0.90) with the combined spectrum of bacillariophycea (diatom pigment) and the inverse spectrum of phycocyanin (cyanobacterial pigment). The negative correlation further demonstrates the competitive relationship between diatoms and cyanobacteria. Factor 2 explains 26.7% of the variance and correlates (r = 0.88) with Dolomite+Kaolinite+Phycocyanin. Factor 3 contributes 24.8% of the variance and has an inverse correlation with chlorite+muscovite+amphibiolite+chlorophyllide-a (r = -0.79). Factor 3 contributes 7% of the variance and correlates with sphalerite+Illite+green algae pigments (r = 0.98). Sediment brightness (L*); a proxy for carbonate and organic matter content positively correlates with factors 1 and 2 (r = 0.60, r = 0.67, respectively). The down core variations of L* display five distinct periods of below average (43%) L*. All these periods which are associated with troughs in factor 1, 2 and loss on ignition based percent organic matter content, suggests periods of low productivity. Cleland Lake is located within the well known Driftwood creek magnesite deposit. This deposit consists of minor and trace amounts of pyrite, iron oxide, dolomite, calcite, chert, chlorite and mica (Simandl, 2002). Therefore, muscovite and dolomite observed in the second and third factors could be derived from this formation. Deposition of these minerals likely correlate with wet climatic conditions, where enhanced runoff delivered sediment to the lake. Geochemical analysis of magnesite samples from Cleland Lake show trace amounts of Zn (50 ppm, Simandl, 2002), which corroborate with our interpretation of factor 4.