A critical yet poorly quantified aspect of the Earth system is the influence of river‐borne constituents on coastal biogeochemical dynamics. Coastal waters contain some of the most productive ecosystems on Earth and are sites of intense downward particle fluxes and organic accumulation. Also, in many parts of the world, coastal ecosystems are experiencing unfavorable changes in water quality some of which can be linked directly to the transport of waterborne constituents from land. These include the well‐publicized, increasing frequency of hypoxia events in the Gulf of Mexico [Goolsby, 2000], harmful algal blooms [Smayda, 1992], diminished water quality and changes in marine biodiversity [Radach et al., 1990].
