ABSTRACT

A Long Term Ecological Research site will be established on the central Georgia coast in the vicinity of Sapelo Island. This is a barrier island and marsh complex with the Altamaha River, one of the largest and least developed rivers on the east coast of the US, as the primary source of fresh water. The linkages between local and distant upland areas mediated by water - surface water and ground water - delivery to the coastal zone will be investigated. The relationship between variability in environmental factors driven by river flow, primarily salinity because we can measure it at high frequency, and ecosystem processes and structure will be examined. This will accomplished by comparing estuary/marsh complexes separated from the Altamaha River by one or two lagoonal estuary/marsh complexes that damp and attenuate the river signal. This spatial gradient is analogous to the temporal trend in riverine influence expected as a result of development in the watershed. A monitoring system will be implemented that documents physical and biological variables. The time trends and spatial distributions of these variables and of their variance structure will be used to address questions about the factors controlling distributions, trophic structure, diversity, and biogeochemistry.
An existing GIS-based hydrologic model will be modified to incorporate changes in river water resulting from changes in land use patterns that can be expected as the watershed develops. This model will be linked to ecosystem models and will serve as a heuristic and management tool. Another consequence of coastal development is that as river flow decreases, groundwater flow increases and becomes nutrified. The effects of ground water discharge from the surficial aquifer in relatively pristine (Sapelo Island) will be compared against more urbanized (mainland) sites to assess the relative importance of fresh water versus nutrients to productivity, structure and biomass turnover rate in marshes influenced by groundwater. The effect of marine processes (tides, storm surge) on mixing across the fresh/salt interface in the surficial aquifer will be investigated. Additional physical studies will relate the morphology of salt marsh - tidal creek channel complexes to tidal current distributions and exchange. These findings will be incorporated into a physical model that will be coupled to an existing ecosystem model.
This land/ocean margin ecosystem lies at the interface between two ecosystems in which distinctly different groups of decomposers control organic matter degradation. Fungal decomposers largely dominate the terrestrial ecosystem, while bacterial decomposers dominate the marine ecosystem. Both groups are important in salt marsh-dominated ecosystems. Specific studies will examine, at the level of individual cells and hyphae, the relationship bacteria and fungi in the consortia that decompose standing dead Spartina and other marsh plants and, examine how, or if, this changes along the salinity gradient.

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