Estuarine and coastal systems play important roles in society, serving as port facilities, productive fisheries and rookeries, and scenic recreational areas. However, these same values to society mean that these areas can be significantly affected by human activities. Inputs of nutrients, organic matter, and trace metals are among these impacts. The MagMix project seeks to understand the transport and cycling of nutrients and trace elements and relate that to biogeochemical and optical properties in river-dominated coastal systems. The area of study is the outflow region of the Mississippi and Atchafalaya rivers in the northern Gulf of Mexico. The Mississippi River carries high concentrations of plant nutrients derived from fertilizer use on farms in the heartland of the US. These excess nutrients stimulate plant growth in the surface waters of the Louisiana Shelf. These plants, in turn, sink to the bottom waters of the shelf where they serve as food for respiring organisms. The input of this excess food then stimulates an excess of respiration thereby depleting the shelf bottom waters of oxygen during the summer. These oxygen-depleted (or hypoxic) waters then become a dead zone avoided by animals. The overall goal of this research project is to better understand the mixing processes and their relationship to optical and biogeochemical properties as the waters of the Mississippi River and the Atchafalaya River enter the Gulf of Mexico.