Models of biogeochemical dynamics and chemical variability in coastal waters have traditionally relied on the assumption that small-scale mixing processes are sufficiently strong and isotropic to rapidly disperse centimeter to meter scale chemical gradients and thin layered vertical structure. Although this assumption of homogeneity may be reasonable in tidally well mixed estuaries, or within the well-mixed surface and bottom layers of some stratified systems, it may not be generally applicable to stratified coastal waters (Donaghay et al., 1992). A number of naturally occurring physical, biological, and chemical processes have the potential to influence the development, maintenance, and dissipation of micro- (cm to m) to fine-scale (1 to 10 m) chemical structure in stratified coastal waters. Since micro- and fine-scale structure in temperature, salinity, and density distributions result from small-scale physical mixing processes (Osborn, 1998), it is plausible that the vertical distributions of dissolved chemicals should have similarly scaled variability. Biogeochemical activity focused within thin plankton layers (Donaghay et al., 1992: Cowles and Desiderio, 1993; Cowles et al., 1998) should also cause and be influenced by similarly scaled gradients in chemical concentration and reactivity. This has clearly been demonstrated for methane (Sieburth and Donaghay, 1993), mercury (Mason et al., 1993), and iron (O’Sullivan et al., 1997) in the oxic-anoxic transition zone of the lower basin of the Pettaquamscutt Estuary. However, field observations of micro- to fine-scale chemical variability associated with physical micro- and fine-structure Alfred K. Hanson, Jr., and Percy L, Donaghay, Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA. and/or thin plankton layers have been limited in more open systems both by the difficulties in sampling at these scales and by the assumption that such structures cannot persist.