9412028 Simenstad This project will continue and expand upon a previous four year NSF Land-Margin Ecosystem Research (LMER) study (1990- 1994) of the importance of estruarine turbidity maxima (ETM) to river estuaries and coastal ecosystems, as exemplified by the Columbia River estuary. In these continuing investigations , the project will build on past results and will concentrate the research on five areas: * particle aggregation/disaggregation as a key linkage between ETM physics, geochemistry and ecology; * biogeochemical and ecological processes affected by ETM dynamics; * modeling of these proecesses to quantify mass, constituent and energy fluxes, and chemical transformations, with respect to selected scenarios of watershed and global climate change; * interactions of ETM with surrounding estuarine habitats, watershed and the coastal ocean; * selected comparisons with other estuaries, particularly LMER sites. The Columbia River estuary is characteristic of a major class of land-margin ecosystmes (river estuaries) and differs in many respects from other LMER sites. Because of its distinctiveness and scale, and the importance of large river estuaries to coastal oceans, comparisons of critical processes and properties in the Columbia River estuary with those of LMER sites and selected oterh estuaries will contribut significantly to understanding global variability in land-margin systems and their responses to anthropogenic inputs and changes. Comparative efforts will focus on analysis of particle dynamics, microbial-loop processes, and trophic transfers across LMER systems. Results of these comparisons will be embedded in an estuarine classificiation system that ecnompasses physical, sedimentological and geochemical aspects of temperate estuaries. ***
