Spatial and temporal patterns of transparency and light attenuation in the Salton Sea, California, 1997–1999

Abstract

Transparency, as measured by Secchi disk depth (SD), and light attenuation (Kd(PAR)) were measured in the Salton Sea in 1997–1999. Linear regression models were used to evaluate the relative importance of phytoplankton and non-phytoplankton substances in determining SD and Kd(PAR). Paired measurements of SD and Kd(PAR) made in 1999 were used to track relative changes in the importance of light absorption and scattering processes. Phytoplankton biomass was a poor predictor of both SD and Kd(PAR) at mid-lake stations, and this is most likely due to high concentrations of non-phytoplankton substances such as inorganic particulate matter in the Salton Sea. During strong windstorms in the warmer part of the year, the upper water column mixes with hydrogen sulfide-laden bottom waters, causing large crashes in plankton populations. This previously reported phenomenon also strongly affects the light regime through the production of gypsum crystals, which scatter large portions of penetrating light. Since a large amount of variation in both SD and Kd(PAR) is not explained by phytoplankton biomass, any use of this relationship to forecast future changes in water clarity through nutrient reductions must be done with caution.