Monitoring the success of salt marsh restoration by evaluating trophic relationships: a multiple stable isotope approach

Principal Investigator: Mary-Jane James-Pirri, Graduate School of Oceanography, University of Rhode Island

Federal Collaborator: Charles Roman, USGS Patuxent Wildlife Research Center & Graduate School of Oceanography, University of Rhode Island & Richard McKinney, US Environmental Protection Agency, Region 1 Atlantic Ecology Division.

Project summary:

As a result of sea level rise, human mediated changes and pollution, the health of many salt marshes along the northeastern Atlantic seaboard has been compromised. Fortunately, restoration of these degraded salt marshes to re-establish ecosystem function is proceeding at a rapid rate. The National Park Service and US Fish and Wildlife Service have ongoing salt marsh restoration programs at Cape Cod NS (MA), Sachuest Point NWR (RI), Parker River NWR (MA) and Fire Island NS (NY) to name a few. To date however, few restoration programs have developed comprehensive data sets allowing them to quantify the ecological success of their efforts. Such data are essential for understanding the processes that control habitat restoration, and for ultimately predicting restoration responses; critical pieces for insuring that resource managers make science-based decisions regarding future restoration of salt marsh habitats.

Hatches Harbor Reference Marsh	Hatches Harbor Culvert	Herring River Reference Marsh	Herring River Restricted Phragmites Marsh

Existing restoration and monitoring efforts evaluate vegetation changes and the response of nekton communities. They do not provide information regarding energy transfer between trophic levels. Recently, collection of such information has become possible through measures of naturally occurring stable isotopes of carbon, nitrogen, and sulfur (d13C, d15N, d34S). These isotopes provide an understanding of linkages between observed vegetation changes and the response of higher trophic levels (fish, decapods, etc.); relying on the fact that animals retain the isotope values of the foods they assimilate. For these reasons, the purpose of this project is to use multiple stable isotopes as a monitoring tool to complement the existing marsh restoration program at Cape Cod NS.

Three study sites representing a continuum of conditions will be established at Cape Cod NS. Nauset Marsh is a large, well-flushed, fairly typical and undisturbed, Spartina marsh with abundant fish species and invertebrates. Hatches Harbor salt marsh is partially tide restricted with reduced tidal flow to the upstream portion. Some upstream flow was re-introduced in 1998. Extensive pre and post tidal restoration data are available for this marsh. The Herring River salt marsh is severely tide-restricted, from a dike, on the upstream end. The upstream vegetation is dominated by woody species, terrestrial grasses, and brackish/freshwater marsh vegetation.

At each site, samples of primary producer (Spartina Alterniflora, S. patens, Juncus gerardi, Phragmites australis, Ruppia maritima, macroalgae and water column phytoplankton) and consumer organisms (Palaemonetes pugio, Crangon crangon, Geukensia demissa, Carcinus maenas and Fundulus heteroclitus) representing different trophic levels were collected in August 2002. Producer and consumer samples consisted of several leaves, organisms, or individuals pooled into one sample. Three pooled samples for each target species were collected from each habitat at the three sites.

Consumer Sampling
Hatches Harbor	Hatches Harbor (2)	Sachuest Point Marsh	Sachuest Point Marsh (2)

Isotopic analysis of d13C and d15N was conducted at the US EPA-Narragansett laboratory; d34S samples were analyzed by Iso-Analytical in the United Kingdom. Carbon, nitrogen and sulfur isotopic composition were determined by continuous flow isotope ratio mass spectrometry. Carbon isotope ratio is reported as parts per thousand deviation (d13C ‰) from the reference standard PDB. The nitrogen isotope ratio of the tissue is expressed as a part per thousand (‰) difference from the composition of a recognized reference material, N2 in air. All samples were analyzed in duplicate and quality assurance was maintained by determining the precision calculated as a single standard deviation of all replicate values. Data will be interpreted from 2-dimensional isotope plots showing relationships among isotopic ratios for the primary producers and consumers. A two-way ANOVA will be employed to evaluate seasonal differences and differences in isotopic ratios among sites.

Researchers anticipate that isotopic ratios will differ between sites and that a gradient in the ratios will exist from the relatively undisturbed sites to those severely disturbed. It is also expected that tropic linkages will also differ along the gradient of marshes and between degraded and relatively undisturbed systems. By examining a gradient of marshes they hope to identify how production is supported in each system (e.g. is production primarily Spartina based in undisturbed systems where as in degraded systems it is Phragmites based). These results will enhance understanding of the function (or non-function) of degraded marsh systems in relation to tropic linkages. Additionally, measure of stable isotopes will provide a new tool to monitor and evaluate salt marsh restoration activities.

Student Involvement

Wozniak, A., MJ James-Pirri, C. Roman, S. Wainright, and R. McKinney. Monitoring the success of salt marsh restoration by evaluating trophic relationships: a multiple stable isotope approach. Estuarine Research Federation, September 14-18, 2003. Seattle, Washington.