Optical characterization of a precipitation event in a moderately hypersaline lake

The role of mineral precipitation events in creating large patches of bright green water in the Salton Sea was investigated by comparing in situ inherent optical properties (IOPs) and constituent concentrations within and outside a green water region. While absorption was similar in both regions, scatter and backscatter were ∼2 and 3 times higher in green water, respectively. Ratios of scatter to absorption and backscatter to absorption had nearly identical spectral shapes but much higher magnitudes within green water. CIE chromaticity values were similar between stations, but luminance was 2.4 times greater in green water. Therefore, differences in observed water color were mostly due to increased brightness within green water. Further analyses of IOPs indicated that particles were small at both stations (average diameter ∼0.3 m), but a larger proportion of particles present in green water were inorganic. Scanning electron microscopy analysis revealed the presence of small (up to 5 m) particles consistent with gypsum. Because precipitated minerals only increase backscatter and do not by themselves affect water color, simple reflectance ratios will not always detect these events. Therefore, the magnitude of reflectance must be incorporated into analyses of precipitation events.