CICEET Progress Report for the period 9/01/08 Through 2/15/09

Project Title: Comparative Functional Assessment of Differential Sediment Slurry Applications to Rapidly Subsiding Brackish Marshes
Principal Investigator(s): Irv Mendelssohn
Additional Investigator(s): Sean Graham, Aixin Hou
Project Start Date: 9/1/07

Figures

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

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Figure 7

Figure 8

Figure 9

Tasks to meet objectives
Tasks completed during this reporting period include the following:
1) Sediment-Slurry applications

• No additional sediment was applied during this reporting period due to site damage caused by hurricane Ike.

2) Surface elevation change and sediment compaction:

• Re-survey marsh plots relative to NAVD 88.
• Measure the thickness of applied sediment.

3) Litter bags, in-growth bags, cotton strip, and sedimentation tile installation:

• Install four root in-growth bags in each plot to measure belowground plant production. Two in-growth bags will be removed from each plot per year.
• Install seven above- and seven belowground decomposition bags in each plot to measure rates of plant decomposition. Decomposition bags will be removed after 2 wk, 1 mo, 3 mo, 6 mo, 1 yr, and 2 yr.
• Install two ceramic tiles (15 cm x 15 cm) positioned on the sediment surface within each plot to measure rates of sedimentation on a quarterly basis.
• Insert 1 cotton strip into the sediment to depth of approximately 30 cm at each plot as a secondary measure of cellulose degradation. Cotton strips will be removed after approximately 14 days.

4) Sampling:

• Harvest aboveground biomass
• Collect soil cores for physico-chemical analysis
• Remove decomposition bags
• Remove cotton strips
• Collect interstitial water samples for chemical analysis
• Measure soil red-ox potential
• Collect soil cores for microbial analysis.

Progress on Tasks
1) Sediment-slurry applications: The canal that served as the source of the dredge material is now filled with wrack and debris deposited by hurricane Ike, and is no longer navigable. As a result, we were unable to continue dredging operations at our site.

2) Surface elevation change and sediment compaction: Measurements of surface elevation change and sediment compaction were made on 8/29/08 prior to hurricane Ike, on 10/30/08 to assess the impacts of hurricane Ike, and again on 2/5/09 as part of our quarterly sampling.

3) Litter bag, in-growth bag, cotton strip, and sedimentation tile installation: Installation occurred on 1/20/09 and 1/21/09.

4) Sampling: Our first quarterly sampling was completed on 2/19/09. We are currently analyzing these samples.

Have the results/data gathered during this reporting period changed the project objectives when compared to your original proposal? Please explain.
Given the impacts of the recent hurricanes here, specifically hurricane Ike, we resurveyed our sampling plots to measure post-hurricane surface elevations and sediment deposition. We compared these measurements to pre-hurricane measurements to determine if the hurricane damage to the experiment would jeopardize the completion of the study. We are pleased to report minimal damage to the marsh enhancement component of the research, which entailed adding sediment to an existing, but deteriorating brackish marsh. However, considerable new sediment was transported into many of those plots (Figure 1). Unfortunately, the hurricane-deposited sediment modified the amount of applied sediment that each plot received and their resultant surface elevations. Therefore, the original experimental design with pre-set surface elevation treatments will have to be modified. However, we feel confident that the initial goal and intent of the research can be maintained, albeit with a less rigorous statistical design, i.e., we will now use a multivariate approach to assess the effects of different intensities of sediment addition on marsh structure and function rather than an ANOVA approach. We don't expect this to be an impediment, however, to addressing the research questions as stated in the proposal.

In contrast, the marsh pond restoration component of the research, received enough damage to make these plots unusable (Figure 2). To compensate for this change in our activities, we are working with the National Audubon Society on a larger scale marsh pond restoration project at Rainey Wildlife Sanctuary using similar sediment delivery methods (see Dissemination activities). The end result, we believe, will provide the information that is needed concerning the use of sediment-slurries for the restoration of brackish and low salinity marsh habitats.

Dissemination activities during this reporting period (please include the number of participants where applicable).
Contact with End Users: The National Audubon Society has embraced the concept of developing a small dredge to restore degraded wetlands within an experimental context that allows accurate and scientifically defensible assessments of this method's capacity to restore marsh structure and function. However, our portable dredge does not have the power to expand the scale of experimental restoration to a level that landowners and marsh managers can see significant marsh restoration. Hence, based on our initial concept, Dr. Paul Kemp, vice president and director of Audubon's Gulf Coast Initiative, has contracted a Louisiana engineering firm to construct a "mini-dredge" that is larger and more powerful than our portable dredge, yet is considerably smaller than commercially available dredges. Dr. Kemp notes that landowners in Louisiana are extremely interested in this method to restore wetlands and their functions. And, Audubon has encouraged us to initiate experimental trials in low salinity marshes on and off the Rainey Wildlife Refuge to address the uncertainties associated with the use of this restoration method and to compensate for the losses associated with hurricane Ike.

Student Activities: Martin Maxwell, a first-year Master's student in the Dept. of Environmental Science at LSU, will investigate the microbiological aspects of this project. He was awarded a fellowship through the Coastal Science Assistantship Program (CSAP) to carry out his thesis research on this project. The fellowship is provided jointly by the Louisiana Department of Natural Resources and Louisiana Sea Grant. One of the goals of CSAP is to address issues related to planning, designing, and constructing coastal restoration projects that will benefit Louisiana Office of Coastal Restoration (LADNR) in the future. As part of the fellowship, Martin is required to intern for 240 hours at a LADNR office. The contacts made through this work will undoubtedly provide for an exchange of ideas that will ultimately benefit CICEET, Sea Grant, and the State of Louisiana.

Difficulties
The site damage caused by Hurricane Ike constituted a major setback to our project. As a result of the storm surge, large areas of marsh were scoured (Figure 3) while other areas that were open water bodies (e.g. our pond plots) were covered with debris. The canal that served as our access point and the source of the dredge material is now filled with wrack and debris, and is no longer navigable (Figure 4). A sizable portion of our boardwalk system was also destroyed (Figure 5), and our water level recorder was broken. This damage required several months of rebuilding the site infrastructure necessary to continue this project.

Data Generated to date
Surface Elevation and Sediment Thickness:
Surface elevation and sediment thickness measurements collected on August 29, 2008, 16 days after dredging ended and prior to hurricane Ike show highly significant linear relationships between surface elevation change, subsurface subsidence, and sediment thickness (Figure 6). The slope of the elevation change versus sediment thickness regression line shows that for every 10 cm of sediment added, surface elevation increased by approximately 5 cm. The disparity between the thickness of sediment added and the observed increase in elevation results from subsurface compression, or subsidence, of the native material below the applied sediment layer. Thus, for every 10 cm of applied sediment added to the marsh surface approximately 5 cm of compression, or subsidence, occurred below the sediment layer. However, the y-intercepts of the regression lines indicate that within our range of applied sediment approximately 1 cm of additional subsidence occurred regardless of thickness.

Surface elevation and sediment thickness measurements were again collected on October 30, 2008, forty-seven days after hurricane Ike made landfall, to determine if the hurricane impact would jeopardize the completion of this project (Figure 7). Based on these measurements, we concluded that hurricane sediment deposition did not alter the elevation relationships enough to invalidate the results of this project. However, Figure 7 shows that even though the regression slopes remained relatively unchanged, an overall increase in surface elevation occurred relative subsurface subsidence, i.e., the regression lines are reversed compared to pre-hurricane measurements. This increase in surface elevation is most likely due to the deposition of lightweight organic sediment. A ~25% reduction in the R2 fit statistics further suggests that sediment deposition occurred differentially across the plots.

Surface elevation and sediment thickness measurements were collected on February 5, 2009, as part of our 1st quarterly sampling (Figure 8). Similar to our previous two measurements, the slopes of the regression lines show an approximate 1:0.5 relationship between surface elevation change, subsurface subsidence and sediment thickness, although at this time 2 cm of additional subsidence occurred regardless of sediment thickness. Since October, approximately 3.5 cm of subsidence occurred across all plots, based on changes in the regression intercepts between the last two measurements. This high rate of subsurface subsidence was likely due to low water levels that have persisted for the last several months (Figure 9).

Plant, Soil, and Interstitial Water Sampling:
We harvested aboveground biomass from 0.1 m² sub-plots and measured plant height and cover in two 1 m² sub-plots within each plot. Soil cores were collected soil to a depth of 15 cm for nutrient, organic matter, and texture analysis. Separate ~75 cm soil long cores were collected for bulk density analysis. Soil red-ox measurements were taken at 10 cm below the soil surface, and because of low water, interstitial water samples were collected from 20-30 cm below the soil surface for nutrient analysis. Above- and belowground plant decomposition bags were removed at 2 wk and 1 mo, and cotton strips were removed after 14 days. We are currently processing these samples and will include this data in our next report.

Microbial Diversity and Sulfate Reduction:
Duplicate 15 cm sediment cores were collected from each plot for a number microbiological assays. A sub-sample from each core was used to determine bacterial sulfate reduction rates. A separate sub-sample was plated for a direct bacterial count. A third sub-sample was frozen at -80° C for 16S rDNA analysis of microbial community structure and PCR extraction of sulfate reducing bacteria. We are currently processing these samples and will include this data in our next report.

Project Objectives for Next Reporting Period

Objectives
1) Continue monitoring surface elevation change, applied sediment compaction, and plant-soil-microbial interactions.
2) Initiate larger scale marsh pond restoration project.

Work Plan to Meet Objectives
1) Continue monitoring surface elevation change, applied sediment compaction, and plant-soil-microbial interactions on a quarterly basis. During the next reporting period we plan to complete samplings in May and August 2009.

2) Audubon has contracted Javeler Construction Company, Inc., New Iberia, LA, to construct a mini-dredge capable of conveying sediment-slurries at a scale that mimics real-world sediment-slurry applications (i.e. treatment plots ca. 0.5 ha in size). The dredge includes a small barge (25 ft x 8 ft), on which the pump is located, and small tender boat (24 ft) necessary to navigate shallow waters to position the dredge. Construction of the dredge pump and barge is almost complete, and a bid has been issued to begin fabrication of the tender boat. We are now in the process of selecting suitable sites. Upon final site selection, we will begin the permitting process and install infrastructure necessary to monitor to the site. We do not anticipate any additional permitting delays, as we are now familiar with the permitting process. We hope to finish dredging before the end of the next reporting period.

Dissemination Objectives for next reporting period
We will continue to work with the National Audubon Society on the completion of the larger-scale restoration project.

Overall Project Timeline Update
Given the damage caused by hurricane Ike, in addition to delays with permitting outlined in the last progress report, a one-year no-cost extension will be necessary to complete our proposed objectives.

Expenditures
Expenditures are in the range anticipated for the work accomplished to date. As of 1/31/09 we have expended $97,198.34

End User Advisor Feedback
End User Advisor: Greg Grandy
Organization: Louisiana Department of Natural Resources, Coastal Engineering Division
Location: Baton Rouge, LA 70802
Phone number: (225) 342-6412
E-mail: gregory.grandy@la.gov

At this stage, what are the potential applications for this research? Please discuss how you and others could potentially use the technology.
At this stage, the potential applications are the same as they were stated previously. Wetland loss often begins with deterioration and fragmentation of wetland areas, however, most restoration projects to date have not focused on restoring deteriorating areas but rather re-creating wetland that have already converted to open water. Marsh creation projects often require construction of extensive retention dikes and pose implementation problems due to poor geotechnical conditions and difficulties in maintaining dikes during construction. Though, if done properly, thin layer sediment nourishment has the potential to restore deteriorating marshes, reduce project costs, minimize adverse impacts and be more constructible. Further, thin layer sediment nourishment is a technique that can be used to increase elevations through the addition of sediment to a submerging marsh to ameliorate the negative conditions created by sea level rise and subsidence. This technology could be used in any deteriorating marsh in coastal Louisiana.

What are the key challenges to application of this technology? Please consider the technology itself as well as issues related to regulation, politics, socio-economic pressures, trends in the field etc.
The key challenges to wide scale application of this technology are similar to what was noted previously: securing landrights, permitting and funding for deteriorating sites are key challenges to applying the technology. From a technical standpoint, the work being done to validate the construction compaction from thin layer deposition is going to be of great utility in the design of future marsh nourishment projects. From a regulatory standpoint, the research that is being funded through this program can be provided to natural resource agencies to give them more background on the effectiveness and applicability of thin layer dredging.

Has anything changed about this project's potential applicability since the last reporting period (not applicable to the first Progress Report)?
No.

Questions/comments/suggestions for the researchers?
None that haven't previously been addressed.

PI Response to End User Advisor Feedback
We appreciate Greg's comments.