A REVIEW OF RECENT DEVELOPMENTS IN ESTUARINE SCALAR FLUX ESTIMATION

The purpose of this contribution is to review recent developments in c alculation of estuarine scalar fluxes, to suggest avenues for future i mprovement, and to place the idea of flux calculation in a broader phy sical and biogeochemical context. A scalar flux through an estuarine c ross section is the product of normal velocity and scalar concentratio n, sectionally integrated and tidally averaged. These may vary on inte rannual, seasonal, tidal monthly, and event time scales. Formulation o f scalar fluxes in terms of an integral scalar conservation expression shows that they may be determined either through ''direct'' means (me asurement of velocity and concentration) or by ''indirect'' inference (from changes in scalar inventory and source/sink terms). Direct deter mination of net nux at a cross section has a long and generally discou raging history in estuarine oceanography. It has proven difficult to e xtract statistically significant net (tidally averaged) fluxes from mu ch larger flood and ebb transports, and the best mathematical represen tation of flux mechanisms is unclear. Observations further suggest tha t both lateral aid vertical variations in scalar transport through est uarine cross sections are large, while estuarine circulation theory ha s focused on two-dimensional analyses that treat either vertical or la teral variations but not both. Indirect estimates of net fluxes by det ermination of the other relevant terms in an integral scalar conservat ion balance may be the best means of determining scalar import-export in systems with residence Limes long relative to periods of tidal mont hly fluctuations. But this method offers little insight into the inter action of circulation modes and scalar fluxes, little help in verifyin g predictive models, and may also be difficult to apply En some circum stances. Thus, the need to understand, measure, and predict anthropoge nic influences on transport of carbon, nutrients, suspended matter, tr ace metals, and other substances across the land-margin brings a renew ed urgency to the issue of how to best. carry out estuarine scalar flu x determination. An interdisciplinary: experiment is suggested td test present understanding, available instruments, and numerical models.