We measured the exchange of inorganic nutrients and particulate matter between the Spartina alterniflora marshes and the adjacent estuary of Cumberland Island, Georgia, USA, beginning in January 1991. Tidal fluxes were quantified using throughflow flumes at 3 sites within 10 km of one another. These sites represent a spatial gradient in geologic age, sediment characteristics, marsh topography and elevation, and exposure to open water that is often found in transgressive marshbarrier complexes. They exhibited large variabhty in frequency and duration of tidal inundation and in susceptibhty of the marshes to wind and wave erosion. The flumes were sampled seasonally and on consecutive days, and we present flux data from 7 samplings. We also investigated short-term temporal variab~lity in nutrient and particulate fluxes by sampling one flume 4 times in 6 days. Temporal vanability in total and organic suspended sediment fluxes, which was largely related to quickly changing wind and wave conditions, was greater than spatial variability measured during the same time. Dissolved constituent fluxes were generally more variable across space, suggesting that day-to-day variabhty in dissolved nutrient exchanges was not a major contribution to spatial variability. Dissolved inorganic nutrient fluxes (as ammonium, nitrate+nitrite, and soluble reactive phosphorus) followed a spatial pattern of highest nutrient uptake at the geologically young marsh site. This marsh also consistently imported &ssolved organic carbon. This site has the lowest absolute elevation of the 3 sites and a ramp-like topographic profile, and its young geologic age suggests that it is also ecologically immature. Fluxes of dissolved constituents at this site were negatively related to the area of marsh inundated, switching to export when large areas of the young marsh were inundated for long periods of time. This marsh also generally exported total and organic s e d~n~e n t s ; data from the other 2 sites were more variable. Sedlrnent fluxes from the older marsh sites were positively related to slack high tide water level and area inundated, switching from particulates release to uptake only when the highest portions of these marshes were inundated. Most Cumberland Island marshes thus appear to take up sedirnents only when tidal heights exceed about 2.3 m above National Geodetic Vertical Datum, corresponding to tides where the moon is within 20 % of new or full phase. Our data also suggest definite differences in the way the geologically young marshes interact with the inundating water column compared to geologically older marshes in the same estuarine system.

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Louisiana is facing a land loss crisis with 5,000 km2 lost since the 1930s, and another 10,000 km2 may disappear over the next 50 years. In response, the state developed a Comprehensive Master Plan for a Sustainable Coast, which includes predictions for how wildlife species respond to futures with or without restoration action. However, the 2017 Master Plan did not include a bird species representative of brackish or freshwater wetland habitats. Our objective therefore was to evaluate the potential for the Bald Eagle (Haliaeetus leucocephalus) to serve as an indicator of freshwater wetland health, and to develop a model to predict Bald Eagle responses to land cover change 20 and 50 years into the future, with or without restoration action. Using nest location data collected by the Louisiana Department of Wildlife and Fisheries from the Barataria Basin, we modeled the relationship between Bald Eagle nest occurrence and land cover using boosted regression trees. Model performance was strong, explaining 54.4 ± 0.1% of the deviance in nest occurrence, and showed that Bald Eagle nests were more common in areas with greater fresh forested wetland, freshwater marsh, and flotant marsh land cover. Future suitability for nesting Bald Eagles was higher in 20 and 50 years with restoration action compared to without, although suitability in both years was lower than contemporary suitability, regardless of restoration action. Our model suggests that comprehensive restoration action is needed, including the implementation of Mississippi River diversions, to sustain high densities of nesting Bald Eagles in coastal Louisiana.

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