Collaborative Research: A dual-dye approach to measuring in situ light fields: development and preliminary field testing

A lot of attention has been focused on light measurements and models of light fields because of light?s significant role in primary and secondary production and photochemical reactions of natural organic matter in aquatic ecosystems. However, these studies have relied upon Eulerian measurements rather than Lagrangian ones and have not taken into account the effect of currents and other physical processes on light-particle interactions. Researchers from the University of Minnesota, Duluth and Old Dominion University plan to develop and test light integrators that will measure the light exposure/light history of parcels of water in a Lagrangian sense by deploying two fluorescent dyes in a known ratio within freshwater and seawater. One of the dyes to be deployed will be light sensitive and decay in the presence of photosynthetically active radiation (fluorescein or amino-G) while the other one will be photostable (rhodamine-WT). Laboratory experiments will be carried out to characterize the dyes in fresh, brackish, and salt water to (1) establish the wavelengths that are responsible for fluorescein and rhodamine-WT decay in sunlight; (2) assess whether the dyes are subject to loss due to biological processes and/or adsorption of the dyes onto particles; (3) determine the effects of temperature, pH, ionic strength, and light dose/intensity; and (4) ascertain the feasibility of the dual dye method for describing the light field in the water column mixed layer. The result of this project will be the development of a potentially transformative new technique for quantifying the water-column light history that impacts light sensitive organisms and chemical species. With dual-dye pairs within the oceanographic and limnological tool box, we can develop a more predictive understanding of the relationships between light and primary production, photoinhibition, CDOM photobleaching and the photochemical fate of anthropogenic compounds in the aquatic environment.

As regards broader impacts, results from the study would be presented to 'Freshwater Folks', a meeting attended by members of the water research and water management community of Northern Minnesota and disseminated via a website that would be created. The new analytical technique would be included into advanced chemistry courses. One graduate and one undergraduate student from the University of Minnesota, Duluth (UMD) and one graduate student from Old Dominion University would be supported and trained as part of this project. Undergraduate students would also participate in the study and would be supported by the Summer Undergraduate Research Program (SURP) at UMD. High school seniors and K-12 science teachers would be involved in the laboratory work