Vegetation Cover and Elevation in Long-Term Experimental Nutrient-Enrichment Plots in Great Sippewissett Salt Marsh,Cape Cod,Massachusetts: Implications for Eutrophication and Sea Level rise

Nitrogen inputs restructure ecosystems and can interact with other agents of ecological change and potentially intensify them. To examine the effects of nitrogen combined with those of elevation and competition, in 2005 we mapped vegetation and elevation within experimental plots that have been fertilized since 1970 in Great Sippewissett salt marsh, Cape Cod, MA, USA and compared the resulting effects on marsh vegetation. Decadal-scale chronic nutrient enrichment forced changes in cover and spatial distribution of different species. With increasing enrichment, there was a shift in species cover primarily involving loss of Spartina alterniflora and an increase in Distichlis spicata. Percent cover of near monocultures increased with nitrogen fertilization, owing mainly to the proliferation of D. spicata. The experimental fertilization prompted a shift from the short form of S. alterniflora to taller forms, hence increasing above-ground biomass, where this species managed to remain. Chronic enrichment increased upper and lower limits of the elevation range within which certain species occurred. The shift to increased cover of D. spicata was also associated with faster accretion of the marsh surface where this species was dominant, but not where S. alterniflora was dominant. Interactions among nutrient supply, elevation, and competition altered the direction of competitive success among different species of marsh plants, and forced changes in the spatial distribution and composition of the salt marsh plant communities. The results imply that there will be parallel changes in New England salt marshes owing to the widespread eutrophication of coastal waters and the increasing sea level rise. Knowing the mechanisms structuring marsh vegetative cover, and their role in modification of salt marsh accretion, may provide background with which to manage maintenance of affected coastal wetlands.     

Shifting nutrient limitation and eutrophication effects in marsh vegetation across estuarine salinity gradients

In light of widespread coastal eutrophication, identifying which nutrients limit vegetation and the community consequences when limitation is relaxed is critical to maintaining the health of estuarine marshes. Studies in temperate salt marshes have generally identified nitrogen (N) as the primary limiting nutrient for marsh vegetation, but the limiting nutrient in low salinity tidal marshes is unknown. I use a 3-yr nutrient addition experiment in mid elevation,Spartina patens dominated marshes that vary in salinity along two estuaries in southern Maine to examine variation in nutrient effects. Nutrient limitation shifted across estuarine salinity gradients; salt and brackish marsh vegetation was N limited, while oligohaline marsh vegetation was co-limited by N and phosphorus (P). Plant tissue analysis ofS. patens showed plants in the highest salinity marshes had the greatest percent N, despite N limitation, suggesting that N limitation in salt marshes is partially driven by a high demand for N to aid in salinity tolerance. Fertilization had little effect on species composition in monospecificS. patents stands of salt and brackish marshes, but N+P treatments in species-rich oligohaline marshes significantly altered community composition, favoring dominance by high aboveground producing plants. Eutrophication by both N and P has the potential to greatly reduce the characteristic high diversity of oligohaline marshes. Inputs of both nutrients in coastal watersheds must be managed to protect the diversity and functioning of the full range of estuarine marshes.     

Wave Attenuation at a Salt Marsh Margin: A Case Study of an Exposed Coast on the Yangtze Estuary

To quantify wave attenuation by (introduced) Spartina alterniflora vegetation at an exposed macrotidal coast in the Yangtze Estuary, China, wave parameters and water depth were measured during 13 consecutive tides at nine locations ranging from 10 m seaward to 50 m landward of the low marsh edge. During this period, the incident wave height ranged from <0.1 to 1.5 m, the maximum of which is much higher than observed in other marsh areas around the world. Our measurements and calculations showed that the wave attenuation rate per unit distance was 1 to 2 magnitudes higher over the marsh than over an adjacent mudflat. Although the elevation gradient of the marsh margin was significantly higher than that of the adjacent mudflat, more than 80% of wave attenuation was ascribed to the presence of vegetation, suggesting that shoaling effects were of minor importance. On average, waves reaching the marsh were eliminated over a distance of ∼80 m, although a marsh distance of ≥100 m was needed before the maximum height waves were fully attenuated during high tides. These attenuation distances were longer than those previously found in American salt marshes, mainly due to the macrotidal and exposed conditions at the present site. The ratio of water depth to plant height showed an inverse correlation with wave attenuation rate, indicating that plant height is a crucial factor determining the efficiency of wave attenuation. Consequently, the tall shoots of the introduced S. alterniflora makes this species much more efficient at attenuating waves than the shorter, native pioneer species in the Yangtze Estuary, and should therefore be considered as a factor in coastal management during the present era of sea-level rise and global change. We also found that wave attenuation across the salt marsh can be predicted using published models when a suitable coefficient is incorporated to account for drag, which varies in place and time due to differences in plant characteristics and abiotic conditions (i.e., bed gradient, initial water depth, and wave action).     

Succession and productivity on perturbed and naturalSpartina salt-marsh areas in New Jersey

Vegetation growth on spoil placed on aSpartina patens andS. alterniflora marsh in Barnegat Bay, New Jersey, was examined for two years following spoil deposition. In areas where spoil was leveled to match the elevation of the marsh, the percent cover by the end of the first growing season ranged from 60 to 90%. By the second year, cover was 100% in all study plots. Even during the first year, there was no difference in species diversity or vegetation species in the experimental and control areas. The percentage of shrubs did not increase on the perturbed (spoil) areas compared to the control plots. During the first year, but not the second, live and dead biomass was greater in the perturbed areas compared to the control plots. In an area where the spoil was thicker succession was exceedingly slow and there was only about 5% grass cover by the end of the first growing season. BecauseSpartina colonizes primarily by rhizome growth, the comparatively slow recovery was attributed to the inability of the grass to penetrate the thick spoil layer.     

Succession of microphytobenthos in a restored coastal wetland

Sediment microphytobenthos, such as diatoms and photosynthetic bacteria, are functionally important components of food webs and are key mediators of nutrient dynamics in marine wetlands. The medium to long-term recovery of benthic microproducers in restored habitats designed to improve degraded coastal wetland sites is largely unknown. Using taxon-specific photopigments, we describe the composition of microphytobenthic communities in a large restoration site in southern California and differences in the temporal recovery of biomass (chlorophylla), composition, and taxonomic diversity between vegetatedSpartina foliosa salt marsh and unvegetated mudflat. Visually distinct, spatially discreet, microphytobenthic patches appeared after no more than 7 mo within the restoration site and were distinguished by significant differences in biomass, taxonomic diversity, and the relative abundance of cyanobacteria versus diatoms. Sediment chlorophylla concentrations within the restored site were similar to concentrations in nearby natural habitat 0.2–2.2 yr following marsh creation, suggesting rapid colonization by microproducers. RestoredSpartina marsh very rapidly (between 0.2 and 1.2 yr) acquired microphytobenthic communities of similar composition and diversity to those in naturalSpartina habitat, but restored mudflats took at least 1.6 to 2.2 yr to resemble natural mudflats. These results suggest relatively rapid recovery of microphytobenthic communities at the level of major taxonomic groups. Sediment features, such as pore water salinity andSpartina density, explained little variation in microphytobenthic taxonomic composition. The data imply that provision of structural heterogeneity in wetland construction (such as pools and vascular plants) might speed development of microproducer communities, but no direct seeding of sediment microfloras may be necessary.     

Analysis of tidal marsh vegetation patterns in two Georgia estuaries using aerial photography and GIS

Aerial photographs and GIS analysis were used to map the distribution of tidal marsh vegetation along the salinity gradients of the estuaries of the Altamaha and Satilla Rivers in coastal Georgia. Vegetation maps were constructed from 1993 U.S. Geological Survey Digital Orthophoto Quarter Quads, 1∶77,000-scale color infrared photographs taken in 1974 and 1∶24,000-scale black and white photographs taken in 1953, Changes between years were identified using a GIS overlay analysis. Four vegetation classifications were identified and groundtruthed with field surveys: salt marsh (areas containing primarilySpartina alterniflora), brackish marsh (Spartina cynosuroides andS. alterniflora), Juncus (Juncus roemerianus), and fresh marsh (Zizania aquatica, Zizaniopsis miliacae, and others). There was no evidence for an upstream shift in marsh vegetation along the longitudinal axis of either estuary over the time frame of this analysis, which implies there has not been a long-term increase in salinity. Although the inland extent of each marsh zone was further upstream in the Satilla than the Altamaha, they corresponded to similar average high tide salinities in each estuary: areas classified as salt marsh occurred from the mouth up to where average high tide salinity in the water was approximately 15 psu;Juncus ranged from 21 to 1 psu; brackish marsh ranged from 15 to 1 psu; and fresh marsh was upstream of 1 psu. Approximately 63% of the 6,786 ha of tidal marsh vegetation mapped in the Altamaha and 75% of the 10,220 ha mapped in the Satilla remained the same in all 3 yr.Juncus was the dominant classification in the intermediate regions of both estuaries, and shifts between areas classified asJuncus and either brackish or salt marsh constituted the primary vegetation change between 1953 and 1993 (87% of the changes observed in the Altamaha and 95% of those in the Satilla). This analysis suggests that the broad distribution of tidal marsh vegetation along these two estuaries is driven by salinity, but that at the local scale these are dynamic systems with a larger number of factors affecting the frequently changing borders of vegetation patches.     

Distribution,Abundance, and Habitat Characterization of the Saltmarsh Topminnow, <Emphasis Type="Italic">Fundulus jenkinsi</Emphasis> (Everman 1892)

The saltmarsh topminnow (Fundulus jenkinsi) is federally listed as a Species of Concern due to a its rarity, impacts from human activities, and lack of information on its biology and ecology. From 2007 through 2008, we used Breder traps to fish the marsh edge on a falling tide in four regions from Louisiana through the Florida panhandle during winter, spring, and summer periods. Out of 2,108 Breder traps deployed, 661 F. jenkinsi were collected as far east as Escambia Bay, Florida, with Weeks Bay, National Estuarine Research Reserve (NERR), Alabama, yielding the highest F. jenkinsi abundance. Principal component analysis (PCA) was used to ordinate physical–chemical data into two meaningful components: a geomorphic axis (water depth, bank slope, and plant stem density) and a seasonal/spatial axis of species occurrence (water temperature, salinity, and turbidity). PCA showed a higher mean catch-per-unit-effort (CPUE) in environments comprised of low to moderate stem density (<25 stems/0.25 m⁻²), depth (<25 cm), bank slope (<15°), turbidity (<30 NTU), and salinity (<16) coupled with spring and early summer water temperatures (>15°C). F. jenkinsi CPUE was significantly higher in Spartina cynosuroides marsh edge compared with five other habitat types, even though it was one of the least sampled habitats. This species appears to be collected more frequently and in higher CPUE in small dendritic creeks off of main channels than suggested by our previous work in main channel edge habitat. This suggests that small creeks are important vectors for marsh access and supports the value of the dendritic nature of salt marshes to marsh residents.     

Effects of an Omnivorous Katydid,Salinity, and Nutrients on a Planthopper-<Emphasis Type="Italic">Spartina</Emphasis> Food Web

Top–down and bottom–up effects interact to structure communities, especially in salt marshes, which contain strong gradients in bottom–up drivers such as salinity and nutrients. How omnivorous consumers respond to variation in prey availability and plant quality is poorly understood. We used a mesocosm experiment to examine how salinity, nutrients, an omnivore (the katydid Orchelimum fidicinium) and an herbivore (the planthopper Prokelisia spp.) interacted to structure a simplified salt marsh food web based on the marsh grass Spartina alterniflora. Bottom–up effects were strong, with both salinity and nutrients decreasing leaf C/N and increasing Prokelisia abundance. Top–down effects on plants were also strong, with both the herbivore and the omnivore affecting S. alterniflora traits and growth, especially when nutrients or salt were added. In contrast, top–down control by Orchelimum of Prokelisia was independent of bottom–up conditions. Orchelimum grew best on a diet containing both Spartina and Prokelisia, and in contrast to a sympatric omnivorous crab, did not shift to an animal-based diet when prey were present, suggesting that it is constrained to consume a mixed diet. These results suggest that the trophic effects of omnivores depend on omnivore behavior, dietary constraints, and ability to suppress lower trophic levels, and that omnivorous katydids may play a previously unrecognized role in salt marsh food webs.     

Geographic Variability in Salt Marsh Flooding Patterns may Affect Nursery Value for Fishery Species

Flooding of salt marshes controls access to the marsh surface for aquatic organisms and likely regulates the value and use of this habitat for juvenile fishery species. We examined geographic variability in marsh access by measuring tidal flooding characteristics in 15 Spartina alterniflora marshes in the southeastern US between South Texas and lower Chesapeake Bay. Flooding duration and flooding frequency were correlated with the elevation of the marsh edge in relation to mean low water and with the tidal range. Mean annual flooding duration over the years 2006–2008 was highest in Texas (91.5% in Aransas Bay) and North Carolina (89.3% in Pamlico Sound) and lowest in Timbalier Bay, LA (54%) and the lower Carolinas and Georgia (55–57%). We used published data on densities of blue crabs and penaeid shrimps as a measure of habitat selection, and there was a positive relationship between marsh selection and flooding duration.     

Distribution of natural uranium,thorium, lead,and polonium radionuclides in tidal phases of a Delaware salt marsh

Natural radionuclides in the uranium and thorium series were measured in solid tidal phases (suspended particles, bottom sediment, surface microlayer colloids) of a salt marsh in lower Delaware. The purpose was to identify potential processes responsible for trace element cycling (sources, redistribution and exchange) in salt water marshes and with their coastal waters. Generally, concentrations of U, Th,²¹⁰Pb, and²¹⁰Po on the tidal solid phases suggest a general mechanism by which tidal marshes appear to be trapping the nuclides into their interiors. The processes may include transport of enriched fine particles into the marsh, capture by salt marsh grass and chemical fixation by redox processes at the sediment surface. Specifically, the uranium contents of most of the samples are similar with activity ratios²³⁴U²³⁸U≧1, indicating a mixture of detrital and nondetrital (authigenic) uranium inputs such as seawater or ground water. Since the²³⁰Th daughter is generally deficient by about 50%, the authigenic enrichment process appears to favor uranium and is potentially linked to the extensive diagenetic sulfur redox cycle of salt marsh sediments. The²¹⁰Po/²¹⁰Pb activity ratio is less than one on Spartina adsorbed solids, and could suggest a general process in salt marshes which favors²¹⁰Pb enrichment by atmospheric fallout over enrichment of²¹⁰Po on time scales of weeks which correspond to complete tide marsh exchange. A²²⁸Th/²³²Th activity ratio of less than unity on the solids adsorbed onto marsh grass suggests a net process whereby diffusive loss of the intermediate daughter²²⁸Ra from the adsorbed solids to tidal waters dominates over potential²²⁸Th scavenging by suspended sediment.     

Salt Marsh Fucoid Algae: Overlooked Ecosystem Engineers of North Temperate Salt Marshes

Salt marsh fucoid algae are a conspicuous component of north temperate marshes, yet comparatively little research has been conducted to examine their ecological effects. We examined the influence of salt marsh fucoids on physical conditions and the biotic community in a manipulative experiment conducted in a southern Maine back-barrier salt marsh. The biomass of salt marsh fucoids was higher than that of aboveground Spartina alterniflora in the zone where we conducted the experiment. Average daytime temperatures at the sediment surface were significantly reduced by the presence of salt marsh fucoids. Density and biomass of standing-dead S. alterniflora was significantly higher when salt marsh fucoids were removed. In contrast, the abundance of various species of epifauna and infauna were significantly enhanced by the presence of salt marsh fucoids. A regional survey indicated that results from the study site may be conservative because the biomass of salt marsh fucoids was lowest among other back-barrier marshes. Salt marsh fucoids are little studied ecosystem engineers whose presence affects the microclimate and biotic community, especially the animals that constitute the basal components of the salt marsh trophic relay.     

Nekton of new seagrass habitats colonizing a subsided salt marsh in Galveston Bay, Texas

Subsidence and erosion of intertidal salt marsh at Galveston Island State Park, Texas, created new areas of subtidal habitat that were colonized by seagrasses begining in 1999. We quantified and compared habitat characteristics and nekton densities in monospecific beds of stargrassHalophila engelmanni and shoalgrassHalodule wrightii as well as adjacent nonvegetated substrates. We collected 10 replicates per habitat type during April, July, October, and December 2001. Most habitat characteristics varied with season. Water temperature, salinity, and dissolved oxygen were similar among habitat types. Turbidity and depth were greatest inH. engelmanni beds and least inH. wrightii beds.H. engelmanni exhibited shorter leaves and higher shoot density and biomass core⁻¹ thanH. wrightii. Densities of almost all dominant species of nekton (fishes and decapods) were seasonally variable, all were higher in seagrass habitats than in nonvegetated habitats, and most were higher in one seagrass species than the other. Naked gobyGobiosoma bosc, code gobyGobiosoma robustum, bigclaw snapping shrimpAlpheus heterochaelis, and blue crabCallinectes sapidus, were most abundant inH. engelmanni. Brown shrimpFarfantepenaeus aztecus, brackish grass shrimpPalaemonetes intermedius, and daggerblade grass shrimpPalaemonetes pugio were most abundant inH. wrightii. PinfishLagodon rhomboides and pink shrimFarfantepenaeus duorarum were equally abundant in either seagrass. Most dominant nekton varied in size by month, but only two (L. rhomboides andC. sapidus) exhibited habitat-related differences in size. Nekton densities in these new seagrass habitats equaled or exceeded densities associated with historical and current intertidal smooth cordgrassSpartina alterniflora marsh. Continued seagrass expansion and persistence should ensure ecosystem productivity in spite of habitat change.     

Salt marsh litter and detritivores: A closer look at redundancy

Most primary production of angiosperms in coastal salt marshes enters the detritivore food web; studies of this link have predominantly focused on one plant species (Spartina alterniflora) and one detritivore species (Littoraria irrorata). In mesocosm experiments, we studied the rates and pattern of decomposition of litter derived from four plant species common in southeastern United States coastal salt marshes and marsh-fringing terrestrial habitats. Crustanceans and gastropods were selected as detritivores feeding on, and affecting degradation of, the litter of two monocotyledons and two dicotyledons. Despite interspecific similarities in consumption, detritivores exhibited species-specific effects on litter chemistry and on the activity of litter-colonizing microbiota. The chemical composition of feces depended upon both the litter type and the detritivores’ species-specific digestive capabilities. Growth rates and survival of detritivores differed among litter species. Different salt marsh detritivores are likely to have different effects on decomposition processes in the salt marsh and cannot be regarded as functionally redundant nor can the litter of different plant species be regard ed as redundant as food for marsh detritivores.     

A review of environmental and genetic factors that affect height inSpartina alterniflora loisel. (Salt marsh cord grass)

The salt marsh cord grass,Spartina alterniflora Loisel., occurs in markedly distinct short and tall growth forms. Both forms have the same number of chromosomes, although polyploidy is well established in the genus. Previous studies have shown that height is primarily affected by nitrate availability and environmental stresses such as increased soluble salt concentrations. These studies have shown that, within a marsh, height differences cannot be attributed to genetic, chromosomal differences or electrophoretic banding. However, more subtle genetic differences may be involved. Other studies suggest that between marshes,S. alterniflora, in response to a latitudinal gradient on the Atlantic coast, has evolved ecotypes differing in height, color and flowering period. This review paper points out that plant height inS. alterniflora may be determined by a combination of environmental and genetic factors.     

Life history strategies of estuarine nekton: The role of marsh macrophytes,benthic microalgae,and phytoplankton in the trophic spectrum

The stable isotope signatures of marine transient and resident nekton were used to investigate trophic linkages between primary producers, marsh macrophytes, phytoplankton, benthic microalgae, and consumers within the Delaware Bay. A whole estuary approach was used to compare the flux of nutrients from primary producers to juvenile weakfish (Cynoscion regalis), bay anchovy (Anchoa mitchilli), and white perch (Morone americana) in open waters of the lower and upper Bay and adjacent salt marshes dominated by eitherSpartina alterniflora orPhragmites australis. Our results suggest that trophic linkages vary significantly along the salinity gradient, reflecting the transition fromSpartina toPhragmites-dominated marshes, and secondarily, in a marsh to open water (offshore) direction at a given salinity. Superimposed on this pattern was a gradient in the proximate use of organic matter that depended on life history traits of each species ranging from pelagic to benthic in the order bay anchovy > weakfish > white perch.     

Effects of Life History Strategy on Fish Distribution and Use of Estuarine Salt Marsh and Shallow-Water Flat Habitats

To assess the potential for habitat isolation effects on estuarine nekton, we used two species with different dispersal abilities and life history strategies, mummichog (Fundulus heteroclitus) and pinfish (Lagodon rhomboides) to examine: (1) distribution trends among estuarine shallow-water flat and various intertidal salt marsh habitats and (2) the influence of salt marsh habitat size and isolation. Collections were conducted using baited minnow traps set within nonisolated interior marshes (interior), nonisolated fringing marshes (nonisolated), isolated island marshes (isolated), and shallow-water flat habitats (flat) that were adjacent to isolated and nonisolated marshes. Size range of individuals collected included juvenile and adult F. heteroclitus (20–82-mm standard length) and L. rhomboides (22–151-mm standard length). During high tide, F. heteroclitus exclusively used marsh habitats, particularly high marsh, whereas L. rhomboides used marshes and flats. F. heteroclitus abundance followed an interior > nonisolated > isolated pattern. L. rhomboides abundance patterns were less consistent but followed a nonisolated > isolated > interior pattern. A size-dependent water depth relationship was observed for both species and suggests size class partitioning of marsh and flat habitats during high tide. Minimum water depth (~31 cm) restricted L. rhomboides populations in marshes, while maximum water depth (~69 cm) restricted F. heteroclitus population use of marshes and movement between marsh habitats. Disparities in F. heteroclitus young of year contribution between isolated compared to nonisolated and interior marsh types suggests isolated marshes acted as population sinks and were dependent on adult emigrants. Resident and transient salt marsh nekton species utilize estuarine habitats in different ways and these fundamental differences can translate into how estuarine landscape might affect nekton.     

Changing elevation,accretion, and tidal marsh plant assemblages in a South San Francisco Bay tidal marsh

Analyses of organic content, pollen, and the carbon-isotopic composition of a 3.5-m sediment core collected from a subsided tidal marsh located in South San Francisco Bay, California, have provided a 500-yr record of sediment accretion and vegetation change before, during, and after a rapid 1 m increase in sea level. Core chronology was established using¹⁴C dating of fossil plant material, the first appearance of pollen types produced by plants not native to California, and changes in lead concentrations coincident with anthropogenic contamination. Prior to the mid 19th century, rates of sediment accretion were between 1 and 4 mm yr⁻¹; sediment accretion accelerated to an average of 22 mm yr⁻¹ following the initiation of subsidence. Changes in tidal marsh vegetation also accompanied this depositional change. Vegetation shifted from a high to low marsh assemblage, as indicated by a larger percentage of grass pollen, rhizomes ofSpartina foliosa, and a strong C₄ signal. Between 1980 and 2001, Triangle marsh again developed high marsh vegetation, as indicated by higher percentages of the Amaranthaceane pollen type, seed deposition, includingSalicornia spp., and more negative carbon isotopic ratios.     

Comparison of Nekton Use for Cordgrass <Emphasis Type="Italic">Spartina alterniflora</Emphasis> and Bulrush <Emphasis Type="Italic">Scirpus mariqueter</Emphasis> Marshes in the Yangtze River Estuary,China

To test whether invasive Spartina alterniflora marshes were functionally equivalent to native Scirpus mariqueter marshes, the present study used bottomless lift nets (20 m²) during 12 high-tide events from August to October 2008 to compare nekton densities and biomass between the two marsh types in the Dongtan wetland. A total of eight species of fish, two species of shrimp, and three species of crab were collected. So-iny mullet Chelon haematocheilus, keeled mullet Liza carinata, Asian freshwater goby Acanthogobius ommaturus, and ridge-tail prawn Exopalaemon carinicauda dominated samples from the two marsh types and accounted for over 90% of the total catch. There were significantly greater densities and biomass (p < 0.05) of total nekton (all species combined) and two mullets (C. haematocheilus and L. carinata) in S. alterniflora marshes than in S. mariqueter marshes in August 2008, while no significant differences (p > 0.05) between the two marsh types were observed for densities and biomass of any species or total nekton in September and October 2008. Non-metric multidimensional scaling ordination did not show clear separation of samples between the two marsh types (r = 0.071, p = 0.159). Furthermore, there were no habitat-specific differences (p > 0.05) in the size distributions of the three numerically dominant species (C. haematocheilus, L. carinata, and A. ommaturus). We concluded that S. alterniflora marshes were utilized by nekton in a fashion similar to their utilization of native S. mariqueter marshes under similar physical conditions.     

The distribution and utility of sea‐level indicators in Eurasian sub‐Arctic salt marshes (White Sea,Russia)

In support of efforts to reconstruct relative sea level (RSL), we investigated the utility of foraminifera, diatoms and bulk‐sediment geochemistry (δ¹³C, C:N and parameters measured by Rock‐Eval pyrolysis) as sea‐level indicators in Eurasian sub‐Arctic salt marshes. At three salt marshes (<15 km apart) in Dvina Bay (White Sea, Russia), we collected surface sediment samples along transects from subtidal to Taiga forest environments. Foraminifera at all sites formed bipartite assemblages, where elevations below mean high higher water (MHHW) were dominated by Miliammina spp. and elevations between MHHW and the highest occurrence of foraminifera were dominated by Jadammina macrescens and Balticammina pseudomacrescens. Five high‐diversity groups of diatoms were identified and they displayed pronounced variability amongst the study sites. Bulk‐sediment geochemistry recognized two groups (clastic‐dominated environments below MHHW and organic‐rich environments above MHHW). As one group included subtidal elevations and the other included supratidal elevations, we conclude that the measured geochemical parameters are not stand‐alone sea‐level indicators. Core JT2012 captured a regressive sediment succession of clastic, tidal‐flat sediment overlain by salt‐marsh organic silt and freshwater peat. The salt‐marsh sediment accumulated at 2804±52 years before present and preserved foraminifera (Jadammina macrescens and Balticammina pseudomacrescens) with good analogy to modern assemblages indicating that RSL was +2.60±0.47 m at this time. Diatoms confirm that marine influence decreased through time, but the lack of analogy between modern and core assemblages limited their utility as sea‐level indicators. Geochemical parameters also indicate a reduction in marine influence through time. We conclude that RSL reconstructions derived from salt‐marsh sediment preserved beneath Eurasian sub‐Arctic peatlands can provide valuable insight into the spatio‐temporal evolution of the Fennoscandian and Eurasian ice sheets.     

Rates, patterns, and impacts ofPhragmites australis expansion and effects of experimentalPhragmites control on vegetation, macroinvertebrates, and fish within tidelands of the lower Connecticut River

Phragmites expansion rates (linear at 1–3% yr⁻¹) and impacts of this expansion on high marsh macroinvertebrates, aboveground production, and litter decomposition fromPhragmites and other marsh graminoids were studied along a polyhaline to oligohaline gradient. These parameters, and fish use of creeks and high marsh, were also studied inPhragmites control sites (herbicide, mowing, and combined herbicide/mow treatments).Phragmites clones established without obvious site preferences on oligohaline marshes, expanding radially. At higher salinities,Phragmites preferentially colonized creekbank levees and disturbed upland borders, then expanded into the central marsh. Hydroperiods, but not salinities or water table, distinguishedPhragmites-dominated transects. Pooled samples ofPhragmites leaves, stems, and flowers decompose more slowly than other marsh angiosperms;Phragmites leaves alone decompose as or more rapidly than those of cattail. AbovegroundPhragmites production was 1,300 to 2,400 g m⁻² (about 23% of this as leaves), versus 600–800 g m⁻² for polyhaline to mesohaline meadow and 1,300 g m⁻² for oligohaline cattail-sedge marsh. Macroinvertebrates appear largely unaffected byPhragmites expansion or control efforts; distribution and densities are unrelated to elevation or hydroperiod, but densities are positively related to litter cover. Dominant fish captured leaving flooded marsh wereFundulus heteroclitus andAnguilla rostrata; both preyed heavily on marsh macroinvertebrates.A. rostrata andMorone americana tended to be more common inPhragmites, but otherwise there were no major differences in use patterns betweenPhragmites and brackish meadow vegetation. SAV and macroalgal cover were markedly lower within aPhragmites-dominated creek versus one withSpartina-dominated banks. The same fish species assemblage was trapped in both plus a third within the herbicide/mow treatment. Fish biomass was greatest from theSpartina creek and lowest from thePhragmites creek, reflecting abundances ofF. heteroclitus. Mowing depressedPhragmites aboveground production and increased stem density, but was ineffective for control.Phragmites, Spartina patens, andJuncus gerardii frequencies after herbicide-only treatment were 0.53-0.21; total live cover was <8% with a heavy litter and dense standing dead stems. After two growing seasonsAgrostis stolonifera/S. patens/J. gerardii brackish meadow characterized most of the herbicide/mow treatment area;Phragmites frequency here was 0.53, contributing 3% cover. Both values more than doubled after four years; a single treatment is ineffective for long-termPhragmites control.