Introduction
This project began in October 1999 with our efforts to obtain the necessary permits to begin the study. We were required by NC State Law to obtain a major CAMA permit before we could undertake movement and placement of sand on the study plots. In mid-March 2000, our permit request was granted and we received Permit number 41-00 from the North Carolina Department of Environment and Natural Resources and the Coastal Resources Commission. Because of the permitting delay, we were not able to initiate sand placement until early May 2000. Below is a summary of our efforts and data collected prior to and following sediment placement.
Study Area
Figure 1 (end of this report) shows the configuration of the test plots referred to throughout this report. Each plot is approximately 7m X 7m square. A one-meter wide buffer area runs the interior perimeter of each plot. All data (physical, chemical, and biological) are collected from within the buffer area. Boardwalks have been constructed within each plot to facilitate sampling efforts and to limit damage to the plant canopy. Nonetheless, some damage to the vascular plant fringing the plot buffer zones occurred during placement activities. Subsequent trampling of perimeter vegetation has also occurred and appears to be related to the presence of curious "non-project" personnel drawn to the site by the boardwalks and PVC markers. Thus far, the integrity of the interior of each site has not been compromised.
Physical Data
Sediment was distributed manually on the marsh surface at high tide over two 3-day periods in mid to late May. After sediment emplacement, sediment thicknesses were verified in the field. For future sampling efforts, each plot has been divided into three subsections: thick (8-10cm), Intermediate (3-6 cm), and Thin (1-2 cm). Table 1 shows preliminary thickness measurements obtained from single cores collected in each subsection of each plot. Additional thickness measurements are underway in order to obtain representative thicknesses across the sites. Sediment thicknesses will be measured every six months for the duration of the project.
Table 1. Sediment thickness overlying each plot by sediment addition treatment given in (mm).
*indicates measurements are approximations from disturbed cores.
Petri-dish sediment traps were deployed from the boardwalks in each plot in order to assess sediment deposition prior to sand additions. The sediment trap deployments occurred in late April 2000. Sediment traps were deployed at low tide and retrieved 24 hours later (again at low tide). Sediment deposition rates are given in Table 2. These data indicated that deposition rates in the deteriorated sites were slightly greater than deposition rates in the non-deteriorated sites prior to sediment additions. It is likely that these data reflect the higher degree of sediment mobility in the soupy deteriorating sites. Sediment trap surveys will continue to be conducted every other month for the duration of the project. The first post addition trap survey will be in mid August 2000.
Granulometry and compositional attributes of pre-addition substrate and source material for the sediment additions have been provided in prior reports. The granulometry and organic content of surface samples will be examined every six months for the duration of the project.
Redox potential and pH of the substrate is measured monthly for each "thickness" within each plot. Additional measurements are collected in adjacent control areas. Initial measures indicate that the emplaced sediment becomes anoxic quite quickly after emplacement. The sand overlays in the deteriorated plots exhibit lower redox potentials than the sand overlays in the nondeteriorated plots. Nevertheless, both sites are anoxic.
Benthic Biomass
Pre-sediment addition samples were collected in each of the study plots (I-IV) in January, March, and April 2000. Post-sediment addition samples were collected in on May 10, June 1, June 15, July 19, and August 8, 2000. Twenty-one randomly placed cores were collected within each plot. Each core measures 2.5cm in diameter. Seven cores are taken from within each thickness zone (10cm, 4-5cm, and 1-2cm). Seven additional cores are taken from each of the control areas. These cores are analyzed to determine chlorophyll a levels. Additional cores have been stored and will be used for pigment analysis using HPLC. Benthic biomass sampling will continue monthly for the next year. Preliminary biomass data are shown below.
Diatom Taxonomy
The benthic diatom group began pre-sediment-emplacement sampling of the study site on January 22, 2000 to establish baseline conditions. Two-three randomly placed samples were collected in each plot. The plots were sampled again in the same manner on April 8.
The first post-sediment-emplacement samples were taken on May 20. Four samples were taken from plots III and IV, one each from thick (10cm sediment), medium (4-5cm), thin (1-2cm), and control (0cm) areas of the plots. This sampling strategy is repeated on each sampling date. Additional samplings of all four plots were done on June 1, 7, and 15, again taking four samples from each plot (thick, medium, thin and control). The latest sampling took place on August 3rd, and again four samples were taken from each plot. The table below summarizes the sampling to date.
All samples from the January, April, May and Junes dates have been cleaned and processed. Microscope slides have been prepared from the January and April materials. We are in the process of preparing slides of the May and June materials, and the August 3 samples will be cleaned and chemically processed in the next three weeks. Diatom identification and quantification will begin in the next three weeks.
Future sampling is planned as follows:
Week of September 18
Week of November 6
Week of January 22
Week of March 5
Week of April 30 (Final Sampling)
All future samplings will follow the same protocol as those from June 1 (four samples from each plot).
Benthic Invertebrates
Benthic core samples have been collected from all four of the established plots (two degraded and two non degraded). All samples were taken 6-8 weeks after sediment addition, allowing the site to recover from the act of sediment addition and to provide an initial baseline for comparison. Plots III and IV were sampled 26 June while plots I and II were sampled 14 July respectively based on timing of sediment addition. To reduce impacts to the sites only six cores were taken from each plots (2 thick, 2 intermediate, and 2 thin sediment additions) for a total of 24 preliminary samples. Processing of these samples is continuing and will be completed prior to the next scheduled sampling.
The second of benthic samples will be collected in May 2001. This will allow the sites nine months for recovery and recruitment of benthic fauna. Measurements of sediment addition depth (actual amount of sediment placed on site) were collected at the along with benthic cores. See results in attached table.
Vascular Plant Surveys
Vascular plant surveys have been conducted bi-monthly within each plot since the sediment additions. Stem density, ratio of live to dead stems, and plant heights are measured in 12.5cm X 12.5cm quadrats. Five random measurements are made for each thickness range in each of the four plots (n=15 per plot). Five additional measurements are made in each control area. Thus far, two plant surveys have been conducted (June and August, 2000). These data are currently being compiled and will be provided in our next six month progress report.
Project Dissemination
We continue to update our project webpage as data become available. General information about this project and preliminary data were presented at two professional meetings. The first presentation was a talk given at the southeastern sectional meeting of the Geological Society of America (Charleston, SC). The second presentation was a poster given at the annual Benthic Ecology Meeting in April 2000 (Wilmington, NC). We are in contact with Ms. Susan Lovelace (NCNEER) about the possibility of disseminating our progress via audio and video links as part of her CICEET project. In addition, we are tentatively scheduled to make a presentation about our project to the NC Coastal Resources Commission in September.
Figure 1. Study plots configuration. Sites I and II were degraded prior to sediment addition. Sites III and IV were non-degraded prior to sediment addition.
