SALT-MARSH PROCESSES - A REVIEW

Salt marshes are found between the high tide and the near-shore sublit toral zones along the coasts and up estuaries of continents, primarily in the temperate zone. They flourish in regions where much silt is ca rried to the coastal regions by rivers or where geological processes f avor erosion and suspension of silt. Salt marshes have multiple ecolog ical and economic values. They have a high rate of primary productivit y; provide habitats for many marine species (including commercially im portant organisms); assist in flood and erosion control; lessen the ef fects of stormwater surges; and improve water quality by filtering pol lutants, excess nutrients, and disease-causing microorganisms. In addi tion, this habitat is used for recreational and educational purposes b y millions of people who spend millions of dollars. Although the myria d functions and uses of this habitat attest to its tremendous importan ce, legal protection of salt marshes varies significantly throughout t he world. Salt-marsh processes are governed by the interactions betwee n ''natural'' physical, chemical, geological, and biological factors. Of importance to ecotoxicologists and other scientists is understandin g the intimate interaction between these various abiotic and biotic fa ctors. This paper reviews the functional processes of salt marshes and discusses recent research advances under the following major headings : (a) physical, geological, and chemical factors; (b) biotic factors ( including productivity of vascular plants, phytoplankton, epibenthic a lgae, and attached macrophytes; secondary production of primary and se condary consumers; and decomposition; (c) material cycling, biogeochem ical cycling, and nutrients; (d) long-term changes; and (e) interactio n with adjacent ecosystems.