Project Title: Marsh Renourishment Through Dredged Material Disposal
Principal Investigator(s): Lynn A. Leonard, Martin H. Posey, Troy D. Alphin, Lawrence B. Cahoon, Richard A. Laws

Accomplishments
Scheduled Tasks:

• Statistical analyses of vascular plant data collected over the duration of the project.
• Statistical analyses of microalgal biomass data collected over the duration of the project.
• Analysis of soil geochemistry measurements.
• Statistical analysis of sediment trap data.
• Stastical analysis of benthic infaunal data.
• Identification of microalgal taxonomy.
• Analysis of "pulsed sediment" experiments

Progress on Tasks

• Data collection and analyses have proceeded on schedule.
• Benthic infaunal identifications completed.
• Final collection of surface sediment grab samples was conducted in January 2002.
• Surface sample grain size and organic content analyses completed.
• Final post-project topographic surveys were conducted in April 2002.
• Statistical analyses of vascular plant data, benthic infaunal data, microalgal biomass, and grain size data are in progress.
• Taxonomic identification of diatoms continues.
• Submission and acceptance of an abstract for the National Geological Society of America Meeting in Denver, CO in October 2002. The title of the presentation is: THIN LAYER DREDGE MATERIAL DISPOSAL IMPACTS ON TIDAL MARSH PROCESSES; Ref: Abstract No: 46373 and is authored by Alex Croft.

Difficulties Encountered
We are now in the final phase of this project and are nearing completion in our data analysis. Our work has been progressing very smoothly and we have encountered very few difficulties over the last six-months of this project. Although not one of the original project objectives, we have begun an analysis of the surface hydrology at our sites due to our manipulations. We will likely continue this aspect of the project beyond the formal end date.

Anticipated Success in Meeting Project Objectives in Scheduled Project Period
We are on track to complete project objectives within the project period.

Preliminary Results
Vascular Plant Data
Vascular plant data were collected from June 2000 through October 2001 (Figure 1). Throughout the first growing season following the sediment placement, stem densities in the deteriorated sites were lower then those in the non-deteriorated sites. During the winter months, stem densities in both the non-deteriorated and deteriorated sites experienced die back associated with the colder temperatures. During the second growing season, stem densities increased in the deteriorated sites relative to the densities measured during the previous growing season. An increase in stem density also occurred in the non-deteriorated sites during the second growing season. Although stem densities increased in both deteriorated and non-deteriorated sites that received sediment, the greater increase occurred within the deteriorated sites. Further, stem densities have become more uniform for all sites over time. No clear relationship between stem density and treatment is apparent.

Sediment Surveys
Topographic surveys were conducted within each test plot. Elevation data have been generated for the well locations where piezometers were placed. These data have been linked to the water level data to quantify inundation frequency and hydroperiod within each site.

Sediment Traps
Quarterly measures of sediment deposition using petridish sediment traps have been completed. Sediment deposition was measured from October 2000 through October 2001 (Figure 2). In general, deposition in deteriorated sites exceeded deposition in the non-deteriorated sites. It is our contention that these measurements actually reflect sediment mobility rather then sediment deposition. The deteriorated sites are probably more prone to resuspention of sediment due to the patchiness of above and below ground biomass. This is apparent for the deteriorated sites first growing season where higher sedimentation corresponds with lower plant densities. In the second growing season, higher sedimentation rates were again associated with the deteriorated sites, although the difference between deteriorated and non-deteriorated sites was less pronounced. When comparing the growing seasons, rates of sedimentation in the deteriorated sites appear to have decreased, while rates in the non-deteriorated rates have remained constant. These patterns may reflect a limitation of localized sediment resuspension in the deteriorated sites due to increased plant densities.

Benthic Biomass
Monthly benthic biomass sample collection has been completed. Samples collected through October 2001 were analyzed for benthic chlorophyll production and reported earlier. In general, the data show a drop in benthic microalgal biomass immediately after sediment additions, followed by a quick and large rebound. This period was followed by a period of fairly stable biomass level, except for the very cold period in December, 2000. These data are in general agreement with microalgae data previously collected near the study site. Statistical analyses of these data indicate that sediment additions resulted in significant increases in microalgal biomass in both deteriorated and non-deteriorated sites, but that the thickness of emplaced sediment had little or no effect.

Benthic invertebrates
Benthic cores were collected and sorted as part of our efforts to assess the feasibility of using incremental additions of the sediment to help mitigate the effects of subsidence on already degraded marshes. Cores were collected in areas where sediment was placed on the surface of the both degraded marshes and adjacent healthy control areas. Three different levels of sediment addition were examined: thin sediment addition (<1"), medium sediment addition (2-3''), and thick sediment addition (4'). The benthic core samples are being used to evaluate the direct acute impacts of the sediment addition within this system and possible longer-term recovery impacts from one-time additions.

Because the infaunal community represents the basic food resource for juvenile fishes and crustaceans utilizing the marsh habitat it was imperative to evaluate how sediment additions may impact this community and subsequently the nursery function of the marsh. Samples were collected at degraded and non-degraded sites 6 week following sediment addition (July 2000) and again 10 months following sediment addition (May 2001). At each site multiple samples were taken from each of the sediment addition treatments. Preliminary analysis showed that overall the benthic infaunal community within degraded and non-degraded sites were similar having many of the same species in both areas regardless of the sediment addition. However degraded marsh sites tended to have few taxa per sample overall and somewhat lower abundance than non-degraded sites at the 6-week recovery sampling. Samples from the 10-month recovery show did seem to reflect an increase in total abundance of infauna for both degraded and non-degraded sites regardless of the sediment addition. This increase is not surprising because many infaunal taxa experience a recruitment pulse in both the fall and spring of the year. Also the size of the sediment addition plots was relative small allow a great deal of recruitment of the adults from the adjacent marsh area. Both of these factors are key elements for the recovery of the benthic infauna. Currently we are conducting Analysis of Variance on rank abundance to detect consistent differences in abundance patterns and treatments and sites as well as functional guild analysis to detect possible shifts in the dominance among the organisms with varying life history strategies.

Tasks and activities for next reporting period

Tasks for the next reporting period

• Complete statistical analysis of all results
• Presentation at the Geological Society of America Annual Meeting in Denver, CO.
• Prepare and submit final report

Work plan to accomplish tasks
All PIs are conducting analyses and preparing the final report.

Concerns or difficulties
None.

Expenditures
All expenditures have been completed and met expectations for the work accomplished to date.