Tidal marshes constitute important recreational and economic resources that provide significant economic and social benefits for many coastal states. In the southeastern United States alone, approximately 17.2 million acres of marsh and estuarine habitat exist, and the economy of many coastal communities is based on commercial fisheries that rely on high quality marsh habitat. As population growth and development have increased in the coastal zone in recent years, however, multi-use coastal management practices have negatively impacted the natural processes of marsh accretion. In southeastern North Carolina, for example, inorganic sediment inputs to back barrier marshes have been reduced by coastal engineering practices (Hackney and Cleary, 1987) thereby limiting the development of new marshes and the ability of existing marshes to keep up with sea level rise.

One way by which sediment deficits may be offset is by artificially introducing inorganic sediment, specifically dredged material, in deteriorating marshes. The benefits of this method are two-fold. First, marsh stability is enhanced and second, the "spoil" is used beneficially. The goal of this study is to develop a methodology of sediment placement that offsets elevation losses in deteriorating marshes without decreasing productivity and/or diminishing functionality. The specific objectives of this study are 1) to determine maximum sediment addition depths in tidal marshes that optimize elevation maintenance without compromising microalgal and vascular plant biomass, or community structure of resident fauna, 2) to determine how frequency of marsh nourishment affects biotic responses, and 3) to disseminate project results to a range of potential users through multimedia and on-site experience. This research will consist of several experiments designed to test the effect of spraying sediments in discrete increments, at different rates, on the surfaces of deteriorating and stable tidal marshes in the Masonboro Estuarine Research Reserve, NC. The response of vascular plants, microalgae, and benthic fauna to sediment additions will be assessed. Changes in sediment delivery and soil chemistry will also be examined. This project will constrain the volumes of sediment, and rates of input, that can restore degrading marsh without adversely effecting ecosystem function. This report summarizes the progress of our research project through the period of August 1, 1999 to January 31, 2000.

 

Permit Applications: The initiation of this project was delayed until October 1999 due to delays and closures caused by the passage and lingering effects of Hurricanes Dennis and Floyd on coastal North Carolina. In mid-October, we began the process of acquiring the necessary permits to conduct the proposed research. After contacting John Taggart, Director of the North Carolina Estuarine Research Reserve, we were advised to meet with Mr. Robert Stroud, District Manager of the NC Division of Coastal Management and Mr. Jeffrey Richter, Project Manager for the Wilmington Field Office of the US Army Corps of Engineers. A meeting was held in early November at which time we were informed that our project would require a major CAMA permit to conduct fill operations in a state wetland as the state of North Carolina lacks a permitting mechanism that encompasses research activities. None of the state of federal representatives at that meeting anticipated any problem in our obtaining the necessary CAMA permit. In early December, we submitted our permit application to place fill material in 5 plots covering approximately 2,200 square feet. Since that time, we have received notification from Mr. Richter of the USACE, that our project can be covered by an existing general permit once we receive authorization from the state. In addition, Mr. Rick Shaw of the NC Division of Water Quality, has notified us that a permit from his office is not necessary. We are now awaiting comment on our permit application from the remaining required state and federal agencies.

Personnel: Two graduate students and two undergraduate students have been hired to work on this project. The two graduate students, Ms. Gina Panasik and Ms. Heather Reesey, are enrolled in the Marine Science MS program at UNCW and will use data from this project in their thesis work. Ms. Reesey is working on microalgal taxonomy under the direction of Dr. R.A. Laws and Ms. Panasik is working on microalgal productivity under the direction of Dr. L. Cahoon. The undergraduate students are working under the direction of Drs. Leonard and Posey. Currently, these students are assisting in site preparation, preliminary data collection, and data analyses.

Site Preparation: This study is being conducted in the Masonboro Island Component of the North Carolina National Estuarine Research Reserve (Figure 1 and Figure 2). Marshes in the study area consist of monospecific stands of S. alterniflora which are dissected by numerous tidal creeks and bays. Our study consists of a series of sediment addition experiments conducted in two different marsh areas with similar elevations; one characterized by S. alterniflora die back and the other by healthy stands of cordgrass. At this time, we have selected and delineated the boundaries of our five experimental test plots (Figure 3). In order to minimize the effect of S. alterniflora tiller invasion from adjacent plots (Padgett and Brown, 1999) and the potential for spatial artifacts, each of the test areas measures 21' X 21'. Three test areas have been established in non-deteriorating S. alterniflora marsh and two in deteriorating S. alterniflora marsh. Each plot has been subdivided into 12 smaller sampling areas measuring 3' X 3' . Each sampling area is at least 3' from a "non-sprayed" boundary and 3' from any adjacent plot. Three replicate sampling areas will be used for each sediment treatment and the control. At this time, each sampling area has been marked with graduated rods to ready each site for sediment placement. Within the next several weeks, we will begin emplacement of sand on the marsh surface. Experimental treatments will consist of a 3 cm overlay of material, a 6 cm overlay of material, a 9 cm overlay of material, and a control with no addition.

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Figure 1: Location of Masonboro Island, NERR study site

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Figure 2: Location of plots on Masonboro Island. Source of image can be found at:
http://inlet.geol.sc.edu/NOC/masonboro_jan99.jpg

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Figure 3: Photographs of marsh plots on Masonboro Island. Upper panel shows deteriorating sites and lower panel shows non-deteriorating sites.

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Figure 4. Grain size characteristics of fill material.

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One of the three test areas in non-deteriorating S. alterniflora marsh will be used to examine the effect of adding sediment gradually through repeated pulses of sediment The experimental set-up will be the same as that described above except that sediment will be added in 3 bimonthly increments each equal to one-third of the desired total.

Equipment Acquisition: A Beckman Coulter LS200 Particle Sizing instrument was purchased by the University of North Carolina at Wilmington in November 1999 for use on this project. The instrument arrived in early January and is currently being installed in the new Myrtle Grove Marine Science Research facility. We are also fabricating a SET device that will be used to measure changes in surface elevation over the duration of the project.

Initial Sampling: Surface sediment samples have been collected within each sampling area in order to determine the "pre-spray" granulometry. Approximately 500g of material have been collected and stored on ice. These samples are currently being prepared for grain size analyses by removing large pieces of vascular plant material and digesting each sample in 10% hydrogen peroxide. Initial bulk densities of surface samples range from 0.99 + 0.23 g cm^-3 (deteriorating) and 1.36 + 0.18 g cm^-3 (undeteriorating). Grain size characteristics of fill material are given in Figure 4. Pre-fill sediment samples for analysis of microphytobenthos biomass and taxonomy have also been collected using 2.5 cm diameter cores. Six replicate cores, randomly selected from each plot, were collected in early January. Biomass will be measured as viable chlorophyll a using the double extraction spectrophotometric method of Whitney and Darley (1979). Species level microalgal taxonomy will be accomplished by standard light and electron microscopical techniques (Cahoon and Laws, 1993). Four additional 2.5 cm cores were collected from each plot, combined into a composite sample, and will be extracted for HPLC analyses of microalgal pigments in order to evaluate higher level taxonomic composition of the assemblages (Wright et al., 1991).

Dissemination: A web page has been created for this project and is being maintained by L. Leonard. (http://www.uncwil.edu/people/lynnl/ciceet.htm). The page includes a brief description of the project, objectives, site maps, photographs, progress updates, and available data. In addition, we will present preliminary project results and progress thus far in a poster entitled "Sediment Recycling: Marsh Renourishment Through Dredged Material Disposal" at the Benthic Ecology Meeting 2000 in Wilmington, NC March 9-12.

 

References Cited

Cahoon, L.B., and R.A. Laws 1993. Benthic diatoms from the North Carolina continental shelf: Inner and mid shelf. Journal of Phycology 29: 257-263.

Hackney, C.T. and W.J. Cleary 1987. Saltmarsh loss in Southeastern North Carolina lagoons: Importance of sea level rise and inlet dredging. J. Coastal Research 3(1): 93-97.

Padgett, D.E. and J.L. Brown. 1999. Effects of drainage and soil organic content on growth of Spartina alterniflora in an artificial salt marsh mesocosm. Amer. J. Botany (in press).

Whitney, D.E., and W.M. Darley 1979. A method for the determination of chlorophyll a in samples containing degradation products. Limnology and Oceanography, 24: 183-186.

Wright, S.W., S.W. Jeffry, R.E.C. Mantoura, C.A.N. Llewellyn, T. Bjornland, D. Repeta, and N. Welschmeyer 1991. Improved HPLC-method for the analysis of chlorophylls and acrotenoids from marine phytoplankton. Mar. Ecol. Prog. Ser. 77:183-196.