CICEET Progress Report for the period 3/01/09 Through 8/31/09
Project Title: Comparative Functional Assessment of Differential Sediment Slurry Application to Rapidly Subsiding Brackish Marshes
Principal Investigator(s): Irv Mendelssohn, Sean Graham, Aixin Hou
Project Start Date: September 1, 2007
Report Compiled By: Sean Graham
Contributing team members and their role in the project: Greg Grandy (Technology Advisor), Martin Maxwell (Graduate Student), and John Cross (Graduate Student)
Figures |
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
Objectives
Objective 1: Our first objective for this reporting period was to continue monitoring surface elevation change, applied sediment compaction, and plant, soil, and microbial response to the applied sediment at the marsh enhancement site. Since our last report, we have completed two quarterly samplings in May and August 2009. There have been no unanticipated delays or difficulties associated with this objective. Select data from various soil, plant, and microbial measurements collected in February, May, and August 2009 are described below. When possible the most recent data collected on August 13, 2009 are presented.
Surface Elevation Change and Subsurface Subsidence: Measurements collected on August 13, 2009, approximately one year after dredging, still show highly significant positive linear relationships with applied sediment thickness (Figure 1). When compared to measurements included in the last report, it appears that the effects of hurricane Ike are slowly dissipating. However, the same general trends are still holding, although some additional subsidence has occurred. Regression slopes now show that 1.0 cm of applied sediment increased surface elevation by approximately 0.4 cm with 0.6 cm of subsidence, compared to 0.5 cm of elevation change and 0.5 cm of subsidence in February 2009, six months after sediment application.
Soil Bulk Density: Approximately 72% of the variation in soil bulk density (soil mass/soil volume) from the top 15 cm of soil was explained by the thickness of applied sediment in soil cores collected on August 13, 2009 (Figure 2). The positive linear relationship was highly significant and shows that an increase in bulk density of 0.02 g cm-3 occurred with each 1 cm of applied sediment.
Soil Chemistry: Soil exchangeable phosphorus (labile P), when normalized for bulk density, displayed a highly significant positive linear trend with sediment thickness in soils cores collected to a depth of 15 cm on May 27, 2009 (Figure 3). The linear regression explained approximately 40% of the variability in soil P as being due to increasing sediment thickness. In contrast, there was no relationship between soil exchangeable ammonium-nitrogen (NH4+-N) and applied sediment thickness (data not shown).
Soil Red-ox Potential (Eh): Soil red-ox provides an indication of soil flooding and soil anaerobiosis. Therefore we were not surprised to find that there was no relationship between Eh and applied sediment thickness (data from August 13, 2009). Rather, a highly significant linear increase occurred with increasing surface elevation (Figure 4).
Aboveground Plant Biomass: Total aboveground biomass harvested on May 27, 2009, declined significantly with increasing applied sediment thickness (Figure 5). This result, however, was not surprising due to the method of sediment application. The applied sediment was dispersed directly above each plot using a dispersion manifold to evenly distribute the sediment throughout the plot (see 9-1-08 Progress Report). In plots that received the greatest amount of sediment, the vegetation was almost completely buried, while in those that received little sediment the vegetation was little affected. It is likely that this trend will not hold through the duration of this project.
Plant Decomposition: In general, above- and belowground tissue decomposition displayed similar trends after 6 months (Figure 6). A significant decrease in the rate of belowground decomposition occurred with increasing applied sediment thickness. However, the relationship between aboveground decomposition and applied sediment thickness was not significant due to high variability.
Microbial Structure and Function: Epifluorescent image capture for direct bacterial counts has been completed for the February 2009 samples (Figure 7). This process will continue throughout the year as the proper procedures are established. Hand counting microbes in the 4000 total images will begin this fall. Extraction of microbial DNA in soil samples collected in February and May 2009 was undertaken during the summer. We are currently preparing samples for GeoChip analysis; a new and promising molecular technique. This technique allows for the study of microbial community structure and diversity at a resolution never before available. Not only will we be able to quantify the diversity of organisms expressing the dissimilatory sulfate reductase gene (dsrA) as was originally proposed, but also organisms involved in the biogeochemical cycling of carbon, nitrogen, and phosphorus.
Objective 2: Our second objective for this reporting period was to initiate the larger scale marsh pond restoration project in association with the National Audubon Society’s Gulf Coast Initiative. To that end, we have selected a site location in Audubon’s Rainey Wildlife Sanctuary near our current marsh enhancement project. This area was severely impacted by Hurricane Ike and resulted in the formation of a new pond area approximately 6.5 ha in size (Figure 8). We have received permit approval to initiate restoration activities utilizing sediment slurry conveyance technology. Javeler Construction Company, Inc. has completed construction and retrofit of the 24 ft tender boat that will be used to position the mini-dredge barge. Construction of the barge is also complete and the power unit and dredge have been installed. However, testing of the dredge has been delayed due to necessary modifications made to the hydraulics system that operate the dredge. We are tentatively planning a system test at a location outside of the study area in late September or early October.
John Cross, a first-year Ph.D. student in the Department of Oceanography and Coastal Sciences at LSU, will investigate the ecological response to sediment slurry addition at the marsh pond restoration site. His research will focus on the beneficial utilization of dredged material in coastal wetland restoration, creation, and nourishment with restoration ecology as his primary specialization. John’s background is well suited for this project. He has a Master’s degree from the Department of Environmental Sciences at LSU and has work experience in dredging, excavation construction, and environmental management. John was also instrumental in the development of the portable, self-contained dredge system that we will be using on the marsh pond restoration project. We look forward to working with John and are confident that his skill set will be an asset to our team and toward the completion of this project.
Knowledge dissemination activities during this reporting period.
Martin Maxwell gave a poster presentation at the annual Society of Wetland Scientists (SWS) and International Wetland Biogeochemistry Conference in Madison, WI, in June 2009. His poster was entitled ”Fine-scale determination of sulfate reduction rates in a stressed olighohaline marsh after sediment slurry addition.” Martin collected cores from a sub-set of plots at the Rainey Wildlife Sanctuary marsh enhancement study area and determined potential sulfate reduction rates at discrete (3 cm) depth increments to ascertain if the rate microbial sulfate reduction was dependent upon depth. His overall conclusion from this study was that the rate of potential sulfate reduction was not depth dependent in the top 15 cm of soil. Although these data were preliminary in nature, Martin is currently exploring the possible reasons for this result.
Have the results/data gathered during this reporting period indicated that a change to your original approach is necessary? If so, who was involved in the decision-making process? Please explain.
No additional changes to our approach were necessary during this reporting period. All changes have been outlined in previous reports.
Please describe collaboration activities with target stakeholders during this period. Has interaction with stakeholders during this period brought about any changes to the project? Have the stakeholders confirmed the relevance of the technology or approach you are working on?
Our collaborative activities with the National Audubon Society are continuing. On July 30, 2009 we met with Dr. Paul Kemp and Ms. Karen Westphal from the National Audubon Society (NAS), Ron Boustany and Loland Broussard from the Natural Resources Conservation Service (NRCS), Clint Galliano from Net Gaines, LLC, and John Cross (new graduate student) to discuss progress on the marsh enhancement project and technical issues associated with the larger scale marsh pond restoration project. Karen Westphal (NAS) gave a short presentation detailing the site location of the marsh restoration project and the permit acquisition process. The NRCS representatives were enthusiastic about the potential use of small dredges to restore remote wetland areas with limited access. In fact, Ron Boustany (NRCS) is in the process determining if our restoration site can also be utilized as a Coastal Wetland Planning, Protection and Restoration Act (CWPPRA) Demonstration Project to test a new sediment containment device being developed by Net Gains, LLC.
Please describe technical and non-technical objectives for the next reporting period and outline your work plan to meet identified objectives.
Objective 1: Continue monitoring on a quarterly basis surface elevation change, applied sediment compaction, and the plant, soil, and microbial response to the applied sediment at the marsh enhancement site. During the next reporting period, we plan to complete samplings in November 2009 and February 2010.
Objective 2: Perform a system test of the new dredge. Finalize the experimental design of the marsh pond restoration project. Install the necessary site infrastructure (i.e., boardwalk, sediment containment device, surface elevation benchmark, settling disks, etc.) and commence dredging.
Objective 3: Begin preparing a manuscript for submission to a peer-reviewed journal that details the initial surface elevation change and subsurface compaction following sediment slurry application.