Nutrient Cycling in Estuarine and Coastal Marine Ecosystems

Although secondary production of marine and estuarine ecosystems is the result of energy and carbon flux from lower trophic levels, the rate of primary production may be controlled by the availability of disssolved inorganic (and perhaps organic) nutrients. In this report we briefly review the status of knowledge and relevant questions pertaining to nutrient flux and transformation processes in shallow marine systems. Our emphasis is on nitrogen although we conclude that further research is also needed for phosphorus and silicon. We begin by presenting a conceptual schematic for the nitrogen cycle in these systems (Figure 1). The diagram is organized by vertically separating characteristics of the upper mixed layer from those of the demersal and benthic systems. Even though particulate nitrogen is divided into various living and abiotic compartments, fluxes among those particulate components are not emphasized here. Concentrations and fluxes are discussed one pathway at a time.