Freshwater marsh succession

The reliability of vegetation maps produced through remote sensing methods is contingent upon the results of a formal accuracy assessment. Such an accuracy assessment is conducted by field inspection and examination of detailed aerial photography of randomly selected locations that represent the variability of vegetation signatures within the marsh.  USFWS identified this work as necessary for them to compare to Dr. Kitchen's earlier work to the Tier I findings and verify the overall study. 

Marsh salinity field data collection

The goal of this work is to provide sufficient data to allow for determination of the relationship between interstitial salinity in the marshes and salinity within the adjacent river channels.

Marsh vegetative survey

The goals of this work are to (1) update and expand the existing information regarding the distribution of plant species within the tidal fresh water and brackish marshes of the Savannah National Wildlife Refuge, and (2) continue to define the environmental factors that determine the plant distributions.

Marsh vegetation survey by USFWS

This work will establish 6 additional study sites comprised of 6 transects and an array of 24 shallow wells for monitoring of interstitial salinity. Salinity monitoring and vegetation sampling will be conducted. Digital videography work will be collected to provide baseline data on the feasibility of using this technique to conduct routine monitoring of vegetation study sites. USFWS researchers will participate in formal accuracy assessment and sediment/marsh variability reconnaissance efforts with ATM researchers.

SNWR freshwater marsh continued vegetation monitoring

SNWR freshwater marsh water level study

SNWR freshwater marsh topography survey

A key component of the spatial aspect of the marsh succession model will be marsh topography. Survey grade elevations will be made at each of the 10 FWS vegetation monitoring sites along the floodplain.  These marsh elevations will be tied to the results of the water level study to define hydrologic signatures.  The topographic survey will be conducted using GPS survey equipment.

SNWR freshwater marsh sediment characterization/mapping

The data to date strongly indicate that vegetation distribution is heavily influenced by sediment characteristics.  Two primary sediment characteristics will be investigated in this work: (1) the locations of sediments that support floating vegetation mats, and (2) the locations of sediments that support the production of hydrogen sulfide gas or methane gas.  Some investigators hypothesize that floating vegetation mats are able to support relatively high plant diversities because, since they float, they are flooded less often than plants that are rted into a firm substrate.  The marshes of highest plant diversity within the study area exist as floating vegetation mats.  This work will map the areas of floating mats for incorporation into the marsh succession model.  Field mapping will be conducted in conjunction with collection of Rapid Assessment Plot data and other ongoing fieldwork.  Ground penetrating radar (GPR) may be used to assist in mapping substrate types in selected locations.  GPR data will be augmented and verified by extraction of sediment cores.  In addition, production of hydrogen sulfide or methane gas may be a very sensitive indicator of areas that are receiving inputs of saline water during incoming tides.  This work will also provide for collection of sediment samples at various locations throughout the study area.  These samples will be analyzed in the lab for their potential for producing either hydrogen sulfide or methane gas and assessed for their contribution to production of floating mats.

SNWR freshwater marsh transplanting experiments

This work is intended to translocate and transplant intact cores of plant/substrate units in such a fashion as to cross transplant within, between, and among tidal marsh types (fresh, intermediate and brackish) while documenting subsequent vegetation responses, if any over time.  In addition to confirming or clarifying correlational results of the other field studies, this technique was found to be extremely valuable to previous studies (Pearlstine et al. 1990) for providing time-lines for vegetation responses as well as indications of ecological community structural changes due to hydrologic alterations.  

SNWR freshwater marsh continued salinity monitoring

SNWR freshwater marsh salinity spatial synoptic sampling

SNWR freshwater marsh tree gap analysis

SNWR freshwater marsh sediment characterization/Mapping (Spatial synoptic analysis)

In addition to the sediment sampling initiated previously at each of the 10 FWS permanent study sites, a synoptic series of regularly grid-spaced sites will be sampled in conjunction with seasonal (early and late growing season) vegetation sampling along the upstream/downstream gradient.  These data will be used to create a substrate characterization set of GIS layers to define transition and breakpoint regions representing the spatial boundaries of marsh zones from fresh to sub saline conditions.  This work is essential to developing a spatial characterization of marsh substrate types across the various gradients of hydro periods, salinities, riverine inputs, and tidal influences (tidal subsidies).  This information is essential to the implementation of spatially based vegetation succession modeling.

SNWR freshwater marsh vegetation change analysis

This work will continue a study already initiated by the USFWS based on other sources of funding.  The work will be based on analysis of aerial photography and satellite imagery to determine changes in vegetation signatures over time.  A primary aspect of the analysis will focus on the changes in the shrub swamp located in the transition zone between the tidal forest and the tidal freshwater marsh.  Some field observations have indicated that the shrub cover has been increasing in this area.  Comparisons between historical imagery and current imagery will be made to confirm and quantitate this trend.

Marsh succession modeling

The goals of this work are to integrate data collected under the field data collection works into wetland impact prediction model.  This model will be a geographic information system (GIS)-based spatial model that will predict changes in wetland vegetation distribution caused by salinity and water level changes associated with harbor deepening.  A further goal of the model will be to study potential long-term (50-year) changes in vegetation distribution resulting from sea level rise.

SNWR freshwater marsh nekton study

In order to determine the nektonic usage of the various marsh types, replicate flume net traps (as per McIvor et al. 1989) will be placed in critical tidal exchange points between the dredged channel networks and the adjacent expansive intertidal marshes.  The net traps will be set on the marsh surface-proper, situated transverse to specific topographic depressions where tidal flows tend to be confined and collected between the marshes and adjacent channels.  The sides of the mouth of the traps will extend to the lower tidal elevation limit of the emergent vegetation to the upper limit of the high tide water surface elevation.  Cod-end pieces will be attached variously to the ends of the trap to collect nekton entrained through the flume on the rise and fall of the tides.  Flume traps will be established at selected points, as described above, in each of the three marsh types along the salinity gradient.  These sites should occur in the proximity of established vegetative sampling transects. Data obtained from the traps will be coordinated with other investigators sampling fish communities in the river and sub tidal reaches of the canal network to determine what portion of the fish species pool occupy and use the marsh surface.

SNWR freshwater marsh migratory bird study