Created Salt Marsh Research Articles

Multivariate analysis of U.K. salt marsh sediment contaminant data with reference to the significance of PCB contamination.

A data set acquired to establish an inventory of pollutants in salt marsh sediments has been evaluated using two numerical techniques, principal component analysis and discriminant analysis. Results indicate that sites proximate to the River Thames exhibit a greater degree of contamination, and numerical analysis supports the hypothesis that the river has been the major source of contaminants to the region. The presence of the contaminants within salt marsh sediments may be of concern due to changes in flood defense techniques. The use of managed realignment, where the line of flood defense is moved back to higher ground which requires only a low, minimal cost, sea-wall protected by newly created salt marsh from former farmland, is not free from problems of historical pollution. Mature salt marsh, laid down during previous decades, may be eroded and reworked within the new coastal geomorphology created by breaching existing seawalls and what were previously considered to be sinks of pollutants may have become sources. However, evaluation of the sediment burden of PCB within the salt marshes of the U.K. Essex coast indicates that they are not likely to be a major source of pollutants should sediments be remobilized during managed realignment programs.

Exploiting wild population diversity and somaclonal variation in the salt marsh grass Distichlis spicata (Poaceae) for marsh creation and restoration

The salt marsh grass Distichlis spicata was regenerated from tissue culture and propagated in a greenhouse. Selected regenerants, along with selections from six wild populations, were grown for two years in a common garden flood-irrigated thrice weekly with tidal creek water. Selected wild and regenerated plants were also planted in a created salt marsh. Significant differences among regenerant and wild population selections were found in several functionally important salt marsh plant characteristics, including potential detritus production, belowground organic matter production, canopy structure, and decomposition rate. A combination of characteristics not found in the wild populations was evident in a regenerated line that exhibited both a high detritus production potential and a high decomposition rate. The amount of variation that occurred among regenerants from one parental line via somaclonal variation was similar to that which occurred among the wild population selections. Results of this study suggest that tissue culture may provide a means of producing marsh grasses with specific characteristics for directing the functional development of newly created salt marshes.

Temporal development of salt marsh value for nekton and epifauna: utilization of dredged material marshes in Galveston Bay, Texas, USA.

Densities of nekton and other fauna were measured inthree created salt marshes to examine habitatdevelopment rate. All three marshes were located onPelican Spit in Galveston Bay, Texas, USA and werecreated on dredged material from the Gulf IntracoastalWaterway. The youngest marsh was planted on 1-mcenters in July of 1992. At the time sampling wasinitiated in fall 1992, the marshes were 9, 5, andless than 1 year in age; sampling continued in thefall and spring through spring 1994. Animaldensities were measured within the vegetation at twoelevations using an enclosure sampler. In the fall of1992, 4 months following the planting of the 92Marsh,densities of most marsh organisms were lower in thismarsh compared with the older two marshes. Significantly lower densities were observed fordominant crustaceans (including three species of grassshrimps, two species of commercially-important penaeidshrimps, thinstripe hermit crabs Clibanarius vittatus,and juvenile blue crabs Callinectes sapidus), adominant fish (Gobionellus boleosoma), and thedominant mollusc (Littoraria irrorata). By the fallof 1993, however, densities of most nekton specieswere similar among the three created salt marshes. Incontrast, reduced densities of less mobile epifauna(C. vittatusand L. irrorata) persisted in the 92Marshthroughout the 2 years of sampling. The patterns ofnekton utilization exhibited in these marshes suggestthat the 92Marsh reached its maximum habitat supportfunction for these animals in less than 1 year. Comparisons of the older marshes with natural marshesin the bay system, however, suggest that all three ofthese created marshes are functioning at lower levelsthan natural marshes in terms of supporting productionof commercially important fishery species such aspenaeid shrimps and C. sapidus.

Co-development of wetland soils and benthic invertebrate communities following salt marsh creation

The development of wetland soil characteristics andbenthic invertebrate communities were evaluated increated Spartina alterniflorasalt marshes inNorth Carolina ranging in age from 1 to 25 years-old.A combination of measurements from different-agecreated marshes as well as periodic measurements overtime on two marshes were used to (1) document rates ofwetland pedogenesis, especially soil organic matter,and, (2) explore relationships between soil andbenthic invertebrate community development. Soilmacro-organic matter (MOM, the living and dead rootand rhizome mat), organic C and N increased and bulkdensity decreased during the 25 years following marshestablishment. The most dramatic changes in bulkdensity, MOM, C and N occurred within the upper 10 cmof the soil with lesser changes below this depth.Created marshes were sinks for organic C (90–140g·m-2·yr-1) and N (7–11g·m-2·yr-1) but not for P (0–1g·m-2·yr-1). The density of benthicinvertebrates (>250 μm) and subsurface-depositfeeding oligochaetes also increased over time oncreated salt marshes. Invertebrate and oligochaetedensity were strongly related to MOM content(r2= 0.83–0.87) and soil organic C(r2= 0.52–0.82) and N (r2= 0.62–0.84). Thesefindings suggest that, in created salt marshes,development of the benthic invertebrate community istied to marsh soil formation, especially accumulationof organic matter as MOM and soil. Field studies thatmanipulate the quantity and quality of soil organicmatter are needed to elucidate the relationshipbetween salt marsh pedogenesis and benthicinvertebrate community development.

Differences in the avian communities of natural and createdSpartina alterniflora salt marshes

Birds were surveyed by censusing strip transets, monthly from October 1990 through September 1991 in seven created and seven natural salt marshes located in lower Galveston Bay. All birds observed using the transect, the airspace above the transect, and 5m of bay bottom adjacent to the transect were recorded. Species richness and species diversity were calculated for each salt marsh and compared between natural and created sites. Species richness and diversity were greater in natural salt marshes due to the occurrence of migratory waterfowl, wintering shorebirds, and typical marsh species such as rails and marsh sparrows. Birds using created salt marshes consisted primarily of gulls and terns, especially during the nesting season. Bird density was greater in natural marshes during fall and winter months, while created marshes had higher bird density from March through July. Created salt marshes provided bird habitat, however not necessarily for the same species assemblage as natural salt marshes.

Exploiting Tissue Culture-generated Variation and Natural Plant Population Diversity for Wetland Creation

Several salt marsh functions were found to be directed by the genotype of the vascular plant. Tissue culture regenerants of Distichlis spicata and Sporobolus virginicus, along with plants from natural populations of these species, were compared in a common garden study. Significant differences among genotypes were found in several characteristics of importance in the functioning of the salt marsh food web. Specifically, potential detritus production, belowground organic matter production, and canopy structure were affected. Selections from five morphologically distinct populations of Spartina patens, including one tissue culture regenerant, also maintained differences in a common marsh setting. In a newly created salt marsh near Lewes, Dela., three populations of short-form Spartina alterniflora from different latitudes (Massachusetts, Delaware, and Georgia) were planted. After 5 years in the new site, the plants maintained distinct morphologies characteristic of plants at their site of origin; e.g., aboveground biomass, canopy structural characteristics, and root and rhizome biomass, composition, and distribution. The magnitude of marsh functional processes associated with the latitude of the population source persisted in the created wetland. The edaphic algal community, the activity of the aerial microbial decomposers, and the edaphic community respiration were significantly influenced by vascular plant genotype in the created marsh, and they reflected the values characteristic of these functions at the latitude of origin of the vascular plants. Indications are that higher trophic levels may also be affected. In creating new wetlands, this plant genetic variation can be used to accentuate different functions, thus optimizing wetland values on the specific site and at the landscape ecology scale.

Succession of macrobenthos in a created salt marsh

Succession of macrobenthos in a created salt marsh

The importance of edge for natant macrofauna in a created salt marsh

The relationship between marsh edge and animal use was examined in a plantedSpartina alterniflora marsh located in the Galveston Bay system of Texas. A completely randomized block experimental design was used with each of four blocks containing a control and experimental sector. Marsh edge was increased through the construction of channels in experimental sectors. Channel construction had no detectable effect on marsh surface elevation. Effects of these simulated tidal creeks on habitat use were examined by sampling nekton at high tide with drop enclosures both on the marsh surface and within the channels. Crustaceans dominated the nekton, and use of the marsh surface in experimental sectors was significantly higher than in controls; densities of brown shrimpPenaeus aztecus, white shrimpP. setiferus, and daggerblade grass shrimpPalaemonetes pugio were 4.6 to 13 times higher near the channels. Polychaete densities in marsh sediments were also significantly higher near channels, and densities of decapod predators were positively correlated with densities of these infaunal prey. Thus, channel effects on natant decapods may have been related to the distribution of prey organisms. However, increased densities of natant fauna along the channel edge may simply reflect a requirement for departure from the marsh surface at low tide. Marshsurface densities of small bait fishes, bay anchovyAnchoa mitchilli and the inland silversideMenidia beryllina, also increased near channels, but highest densities of these fishes were in the creeks themselves. The abundance and distribution of juvenile blue crabsCallinectes sapidus and gulf marsh fiddler crabsUca longisignalis were not affected by the addition of experimental channels. Overall, the study results indicate that habitat value of created salt marshes can be enhanced by incorporating tidal creeks into the marsh design.