Optical characterization of black water blooms in eutrophic waters

Abstract

In the summer of 2007, blooms of "black" water in Lake Taihu entered into the potable water supply of Wuxi City and left more than 1million people without water. Attempts to monitor these black water blooms have not been successful due to their irregular nature. In May 2012, two black water blooms were observed in one of the lake's eutrophic bays. The bio-optical analyses of these blooms show that they were dominated by higher concentrations of dissolved organic matter and lower backscattering coefficients with respect to the surrounding lake conditions. We show the contribution of each optically active component to the perceived radiance and demonstrate that elevated absorption due to dissolved organic matter and phytoplankton combined with reduced backscattering led to the perception of these water areas as "black", while the true color was dark green. The present analysis indicates that formation of black water blooms is favored during springtime conditions in the macrophyte dominated areas of the lake's hypereutrophic bays.

Keywords: Aquatic vegetation; Biogeochemical cycles; Black water masses; Dissolved organic carbon.