Vertically detailed in situ measurements of gelbstoff: demonstrating the impact of a runoff event

Abstract

The successful performance of a rapid profiling light absorption instrument in making vertically detailed measurements of gelbstoff (dissolved yellow material) in a mesotrophic water supply reservoir is demonstrated. In situ measurements of gelbstoff spectra (gλ; m− 1) for the photosynthetically active radiation wavelength (λ) interval (400–700 nm), and values of g440, matched closely values obtained through traditional laboratory spectrophotometric analyses. The advantages of the high vertical resolution capability of the in situ absorption instrument (∼10 measurements per meter of depth) was demonstrated through the depiction of the vertical details (subsurface peak about 2.25 m thick) of the enrichment in gelbstoff that occurred following a major runoff event, associated with the entry of inflow(s) as a plunging interflow. Values of g440 increased at the depth of the subsurface peak by nearly 100% as a result of this event. The detailed vertical resolution of gelbstoff is valuable to managers of water supply lakes and reservoirs to support selection of intake depths to avoid delivery of water with high levels of color, and to researchers investigating the origins, fate and transport of this material.