Title: Biogeochemical studies of the salt marsh and a barrier island at Cape Romain National Wildlife Refuge, South Carolina
Abstract: This report is divided into four chapters: (A) methods and results for the determination of baseline concentrations in Spartina alterniflora (smooth cordgrass) and associated sediments in the intertidal salt marsh; (B) methods and results for the determination of baseline element concentrations in soils and plants on Bull Island; (C) an integrated assessment of the biogeochemical studies at CRNWR, including stable sulfur isotope ratios, with respect to anthropogenic and natural sources of elements in vegetation, sediments, and soils; and (D) a data compilation of the raw chemical analysis results and a summary of quality control results obtained during the chemical analysis of the various samples.These studies were initiated to help define baseline elemental concentrations in the predominant intertidal salt marsh plant species and associated sediments and barrier island plants and soils at CRNWR.In addition, spatial scales of chemical variability in plants and sediments are defined.A minor objective of the work was to examine seasonal variability in plant chemistry by sampling a subset of sites at two times during the year.Results of these studies are integrated into an assessment of the potential for the trace elements being derived from natural or anthropogenic sources.Summary statistics and baseline 95 percent expected element concentration ranges are reported for S. alterniflora and associated sediments in the salt marsh and for Tillandsia usneoides (Spanish moss), Pinus taeda (loblolly pine), and surface soils on Bull Island.Element concentrations in plants and soils on Bull Island exhibited little spatial variability, whereas element concentrations in S. alterniflora and salt marsh sediments had significant spatial variability.The large spatial heterogeneity of element concentrations in the salt marsh media indicate that extensive sampling is required to reproducibly map or evaluate concentrations in these media.All field sampling was completed before the destructive forces of Hurricane Hugo hit Cape Remain National Wildlife Refuge on September 21, 1989.Re-sampling is required to assess the effects of Hurricane Hugo and validate existing baseline element concentration ranges or establish new baseline ranges.Although 5. alterniflora is the dominant plant species in CRNWR and a major source of food in the estuarine detrital-based food chain, it may not be a good biomonitor for anthropogenic trace metals additions to mis environment because of high turnover rates and relatively small metal uptake.In addition, sulfur concentrations in S. alterniflora and sediments were highly variable.Total sulfur concentration in these media is unlikely to be a useful monitor of anthropogenic sulfur additions owing to the great variability and the large oceanic input of sulfate.The biogeochemistry of the vegetation, sediments, and soils at CRNWR indicate that this environment is not highly contaminated with anthropogenic additions of trace elements.Lead and nickel concentrations in Spanish moss and lead and copper concentrations in the salt marsh sediments may be symptomatic of anthropogenic additions of these elements.Stable S isotope ratios of 5. alterniflora and sediments indicate that dissimilatory sulfate reduction in the sediment is an important process controlling the isotopic signature of the 5. alterniflora.Spanish moss and loblolly pine exhibited S isotope ratios that indicate seawater sulfate is not directly the predominant source of S for these two species.The isotopically light signatures of these plants compared to seawater S suggest an anthropogenic and/or a biogenic source of S.Although anthropogenic S emissions have been estimated to be a significantly greater source of S in the region than natural emissions, biogenic S flux is an important component of the salt marsh S cycle that is poorly understood and insufficient data are available to compare anthropogenic and natural sources of S at CRNWR.A better understanding of natural processes controlling the cycling of S and trace elements in the environments at CRNWR is required before the anthropogenic additions of elements can be accurately estimated.