Sedimentation rates and heavy metals in a macrotidal salt marsh: Bay of Fundy,Canada

Macrotidal salt marshes play an important role in sedimentary processes in estuaries and can act as a sink for fine sediments and contaminants. This study examines sedimentation rates and the history of heavy metal accumulation in the Allen Creek salt marsh in the Bay of Fundy, Canada. Pb-210 and Cs-137 measurements and accelerated mass spectrometer (AMS) dating indicate a sedimentation rate of about 1.1 cm/year, which is consistent with independent observations. Elevated normalized concentrations of As in the upper section of the deposit may reflect an increase in organic matter content while a consistent decrease in Mn toward the surface of the section may be due to a decrease in natural supply. A peak in metal concentrations in the early to mid twentieth century is attributed to inputs from local foundries.     

Methane and carbon dioxide flux from a macrotidal salt marsh,Bay of Fundy,New Brunswick

Fluxes of methane (CH₄) and carbon dioxide (CO₂) to the atmosphere at 52 sites within a salt marsh were measured by a dark static chamber technique from mid July to mid September. Mean CH₄ fluxes ranged from 0.2 mg m^?2 d^?1 to 11.0 mg m^?2 d^?1, with an overall average of 1.6 mg m^?2 d^?1. Flux of CH₄ was inversely correlated (r²=0.23, p = 0.001) with salinity of the upper porewater at the site, suggesting the dominant role of SO₄ ^2? in inhibiting methanogenesis in salt-marsh sediments. The combination of salinity and water table position was able to explain only 29% of the variance in CH₄ emission. Mean soil flux of CO₂ ranged from 0.3 g m^?2 d^?1 to 3.7 g m^?2 d^?1, with an overall average of 2.5 g m^?2 d^?1; it was correlated with aboveground biomass (positive, r²=0.38, p = 0.001) and position of the water table (negative, r² = 0.55, p = 0.001). The combination of biomass and water table position accounted for 63% of the variance in CO₂ flux. There were high variations in gas flux within the six plant communities. The sequences were CH₄: upland edge > panne > pool > middle marsh > low marsh > high marsh, and CO₂: middle marsh > low marsh > upland edge > high marsh > panne > pool. Compared to other salt-marsh systems, this Bay of Fundy marsh emits small amounts of CH₄ and CO₂.     

Climatic controls of the middle marsh zone in the Bay of Fundy

The ecological importance of Plantago maritima within a salt marsh on the Bay of Fundy is documented through measurements of cover, density, and biomass. During late August 1993, peak standing crops of Plantago were as high as 532 g m^?2, and composed as much as 96% of the biomass of a stand of vegetation. Plantago is a dominant component of the marsh vegetation at an elevation just above the Spartina alterniflora-dominated low marsh, and is found as a dominant when growing in association with a number of plant species characteristic of the high marsh. We hypothesize that the existence of this community is dependent upon regular ice-shearing of Spartina patens, which would otherwise competitively exclude Plantago. This hypothesis is supported by the elevational limits of Plantago dominance and the geographical limitation of Plantago communities to portions of the northwestern Atlantic subjected to winter temperatures which average below 0°C.     

Erosion and deposition of fine-grained sediments from the Bay of Fundy

Simulations of the erosion, transport and deposition of fine-grained sediment, such as that of Greenberg & Amos and the Hydraulics Research Station, have illustrated a general lack of reliable field data. Consequently, some standard equations and constants used in modelling the sedimentation character of fine-grained cohesive sediment were evaluated based on data from two field studies and a flume experiment with undisturbed sediment from the Bay of Fundy. Initial results showed that the resistance to erosion of intertidal fine-grained sediment is controlled largely by the degree of subaerial exposure and the consequent dehydration and compaction. The sediment shear strength was high (4 kPa), but generally decreased seawards across the intertidal zone. The resistance of intertidal mud to erosion can be 80 times greater than sub-tidal counterparts. The rate of sediment erosion varied as a complex function of the applied bottom shear stress. At stresses immediately above the critical, the erosion rate decreased asymptotically with time. At higher excess stresses, the erosion rate was linear with respect to time. Thus sediment erosion cannot be represented by a single coefficient. The Krone method of computing sedimentation rates of suspended material was shown, by comparisons with direct measurement, to overpredict by 29%. All variables used in his method were measured in the evaluation with the exception of the critical deposition stress (τ_d). The closest comparisons were obtained when τ_d was assigned a value of 0.1 N m^?2 following Creutzberg & Postma. The in situ still-water particle settling rate (V_o) was constant with respect to time (2.1 × 10^?3 m s^?1). However, the settling tube measures of settling rate, compared to in situ results, underpredicted particle settling by an order of magnitude (2.7 × 10^?4 m s^?1). The reason for this discrepancy is not apparent from our results.     

Controls on salt marsh accretion: A test in salt marshes of Eastern Canada

We used¹³⁷Cs-dating to determine vertical accretion rates of 15 salt marshes on the Bay of Fundy, the Gulf of St. Lawrence, and the Atlantic coast of Nova Scotia. Accretion rates are compared to a number of factors assumed to influence vertical marsh accretion: rates of relative sea-level rise, climatic parameters (average daily temperatures and degree days) and latitude (related to insolation and day length), sediment characteristics (organic matter inventory, bulk, mineral, and organic matter density), distance of the core site from the nearest source of tidal waters, and the tidal range. Uniques to our study is a consideration of climatic parameters and latitude, which should influence organic matter production, and thus vertical accretion rates. Significant predictors of accretion rates (in order of importance) were found to be organic matter inventory, distance from a creek, and range of mean tides. Contrary to conclusions from previous studies, we found that accretion rates decreased with increasing tidal range, probably because we considered a wider span of tidal ranges, from micro- to macrotidal. Although four marshes with low organic matter inventories also show a deficit in accretion with respect to relative sea-level rise, organic matter is not limiting in two-thirds of the marshes studied, despite shorter growing seasons.     

Early use by fish of a mitigation salt marsh,Humboldt Bay,California

Fish numbers and biomass in a mitigation salt marsh, Humboldt Bay, California, were examined from July 1981 to October 1982 and were compared with a nearby established marsh to determine whether the restored marsh provided adequate mitigation for habitat lost due to construction of a nearby marina. The use by fish of channels adjacent to the two marshes and the channel at the Woodley Island Marina construction site, for which mitigation was required, were also compared. The mitigation marsh, adjacent to Freshwater Slough channel, was 5.2 km from the marina site. Fishes were sampled by otter trawl, ichthyoplankton net, fixed channel nets, drop traps, and beach seines. Thirty-one fish species and two crab species were collected. Wide ranges in seasonal salinities and water temperatures, and differences in marsh elevation influenced fish use of the mitigation marsh area. The intertidal area of the mitigation marsh, dominated by euryhaline sticklebacks and topsmelts, did not replace intertidal and subtidal habitat lost by marina construction, which had more stable salinities and water temperatures and was used extensively by juvenile English sole.     

Direct counts of bacteria in the sediments of a North Carolina salt marsh

The number of bacteria in sediments of a North Carolina salt marsh was determined by direct counts with epifluorescent illumination and acridine orange stain. Cell number decreased from 8.36–10.90×10⁹ cells/cm³ of sediment at the surface to 2.19–2.58×10⁹ cells/cm³ of sediment at a depth of 20 cm. No significant difference was found among four stations located on a transect which crossed the marsh and spanned subtidal to intertidal sediments.     

Sedimentology and stratigraphy of a transgressive, muddy gravel beach: Waterside Beach, Bay of Fundy, Canada

Sediments exposed at low tide on the transgressive, hypertidal (>6 m tidal range) Waterside Beach, New Brunswick, Canada permit the scrutiny of sedimentary structures and textures that develop at water depths equivalent to the upper and lower shoreface. Waterside Beach sediments are grouped into eleven sedimentologically distinct deposits that represent three depositional environments: (1) sandy foreshore and shoreface; (2) tidal‐creek braid‐plain and delta; and, (3) wave‐formed gravel and sand bars, and associated deposits. The sandy foreshore and shoreface depositional environment encompasses the backshore; moderately dipping beachface; and a shallowly seaward‐dipping terrace of sandy middle and lower intertidal, and muddy sub‐tidal sediments. Intertidal sediments reworked and deposited by tidal creeks comprise the tidal‐creek braid plain and delta. Wave‐formed sand and gravel bars and associated deposits include: sediment sourced from low‐amplitude, unstable sand bars; gravel deposited from large (up to 5·5 m high, 800 m long), landward‐migrating gravel bars; and zones of mud deposition developed on the landward side of the gravel bars. The relationship between the gravel bars and mud deposits, and between mud‐laden sea water and beach gravels provides mechanisms for the deposition of mud beds, and muddy clast‐ and matrix‐supported conglomerates in ancient conglomeratic successions. Idealized sections are presented as analogues for ancient conglomerates deposited in transgressive systems. Where tidal creeks do not influence sedimentation on the beach, the preserved sequence consists of a gravel lag overlain by increasingly finer‐grained shoreface sediments. Conversely, where tidal creeks debouch onto the beach, erosion of the underlying salt marsh results in deposition of a thicker, more complex beach succession. The thickness of this package is controlled by tidal range, sedimentation rate, and rate of transgression. The tidal‐creek influenced succession comprises repeated sequences of: a thin mud bed overlain by muddy conglomerate, sandy conglomerate, a coarse lag, and capped by trough cross‐bedded sand and gravel.     

High-resolution sequence stratigraphy of a complex, incised valley succession, Cobequid Bay — Salmon River estuary, Bay of Fundy, Canada

The post-glacial succession in the Cobequid Bay — Salmon River incised valley contains two sequences, the upper one incomplete. The lower sequence contains only highstand system tracts (HST) deposits which accumulated under microtidal, glacio-marine deltaic conditions. The upper sequence contains two, retrogradationally stacked parasequences. The lower one accumulated in a wave-dominated estuarine environment under micro-mesotidal conditions. It belongs to the lowstand system tract (LST) or early transgressive system tract (TST) depending on the timing and location of the lowstand shoreline, and contains a gravel barrier that has been overstepped and preserved with little modification. The upper parasequence accumulated in the modern, macrotidal estuary, and is assignable to the late TST. Recent, net progradation of the fringing marshes indicates that a new HST has begun. The sequence boundary separating the two sequences was formed by fluvial incision, and perhaps also by subtidal erosion during the relative sea level fall. Additional local erosion by waves and tidal currents occurred during the transgression. The base of the macrotidal sands is a prominent tidal ravinement surface which forms the flooding surface between the backstepping estuarine parasequences. Because fluvial deposition continued throughout the transgression, the fluvial-estuarine contact is diachronous and cannot be used as the transgressive surface. The maximum flooding surface will be difficult to locate in the macrotidal sands, but is more easily identified in the fringing muddy sediments. These observations indicate that: (1) large incised valleys may contain a compound fill that consists of more than one sequence; (2) relative sea level changes determine the stratal stacking patterns, but local environmental factors control the nature of the facies and surfaces; (3) these surfaces may have complex origins, and commonly become amalgamated; (4) designation of the transgressive surface (and thus the LST) is particularly difficult as many of the prominent surfaces in the valley fill are diachronous facies boundaries; and (5) the transgression of complex topography may cause geologically instantaneous changes in tidal range, due to resonance under particular geographical configurations.     

Trace elements in surface sediments of Navarino Bay,Greece

The distribution of a number of trace elements in the Navarino Bay surface sediments is examined and their source and association with the major phases is determined. Cobalt follows Al in its distribution, having its highest vaues towards the center and deeper parts of the bay; Zn and Cu have their highest values at the effluent outfalls of a distillery and an olive oil and olive kernel factory (at the port of Yalova), being decreased away. The highest concentration of Ni is found near the town Pylos, while the highest concentrations of Rb and Y are observed at the mouths of rivers Yalovas and Xerias. Organic matter has its highest content at the port of Pylos, while no significant variations have been observed in the distribution of Sn and Ga. It is demonstrated that there is an anthropogenic input of Zn, Cu, and Corg in the bay. Zn and Cu are discharged by a distillery and an olive oil and olive kernel factory, at Yalova. Organic matter is mainly derived from domestic sewage. Ni enters the bay from its southern coasts and might be derived from weathering of bauxite deposits present in the adjacent limestones. Rb and Y are transported by the rivers Yalovas and Xerias from the northeastern adjacent land area; Ni, Co, and Cu show positive correlation with Al, suggesting their incorporation in clay minerals, while Rb shows positive correlation with Si, suggesting its incorporation in silicate detrital minerals. The following areas in the bay are considered to be heavily polluted: (1) the port and a large zone near Pylos (domestic sewage); (2) the port and a small area near Yalova (domestic sewage and industrial effluents); and (3) the eastern coast of the island Sphaktiria (oil). The domestic sewage pollution in Navarino Bay is of the same level as that in other Greek bays.     

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.     

Metal accumulation rates in northwest Atlantic pelagic sediments

Measurements of ²³⁰Th, ${}^{87}\text{Sr}{}^{86}\text{Sr}$ and twenty-four metals were made on cores from the Nares Abyssal Plain. The sediment is characterized by slowly-accumulating (0.3–0.7 g/cm² 10³ yr) pelagic red clays and rapidly deposited grey clays transported by turbidity currents. Despite their colour differences and the enrichment of Mn, Fe, Cu, Co, Ni, Zn, V and, to a lesser degree, the rare earths in the red clays, Sr isotope evidence demonstrates that the clays have the same terrigenous origin. The excesses of metals in the red clays have been attributed to metal removal from the water column and a comparison with the grey clays has enabled the authigenic fluxes of metals to be estimated. The fluxes obtained are in the ranges 20–50 μmol/cm² 10³ yr for Mn and Fe, 0.1–0.4 μmol/cm² 10³ yr for Cu, Co, Ni, Zn, V, Sr and Ce, 10–20 nmol/cm² 10³ yr for La and Nd, and 0.5-3 nmol/cm² 10³ yr for Sm, Eu, Gd, Dy, Er and Yb. Authigenic fluxes of Y, Nb, Cr, Zr, Rb, U and Th were not resolvable. Fluxes appear to be near constant on the Plain but comparison with other areas shows that they are quite variable both between and within ocean basins. The chief factor controlling authigenic fluxes is the geochemical abundances of the elements but fractionation within both the transition element and rare earth series can be recognized from inter-element comparisons and from differences in fluxes between Atlantic and Pacific red clays corresponding to the oceanic reactivities of the elements.     

The effect of tidal forcing on biogeochemical processes in intertidal salt marsh sediments

Background  

Early diagenetic processes involved in natural organic matter (NOM) oxidation in marine sediments have been for the most part characterized after collecting sediment cores and extracting porewaters. These techniques have proven useful for deep-sea sediments where biogeochemical processes are limited to aerobic respiration, denitrification, and manganese reduction and span over several centimeters. In coastal marine sediments, however, the concentration of NOM is so high that the spatial resolution needed to characterize these processes cannot be achieved with conventional sampling techniques. In addition, coastal sediments are influenced by tidal forcing that likely affects the processes involved in carbon oxidation.     

Evaluating salt marsh restoration in Delaware Bay: Analysis of Fish response at former salt hay farms

In a continuing effort to monitor the fish response to marsh restoration (resumed tidal flow, creation of creeks), we compared qualitative and quantitative data on species richness, abundance, assemblage structure and growth between pre-restoration and post-restoration conditions at two former salt hay farms relative to a reference marsh in the mesohaline portion of Delaware Bay. The most extensive comparison, during April–November 1998, sampled fish populations in large marsh creeks with otter trawls and in small marsh creeks with weirs. Species richness and abundance increased dramatically after restoration. Subsequent comparisons indicated that fish size, assemblage structure, and growth of one of the dominant species,Micropogonias undulatus, was similar between reference and restored marshes 1 and 2 yr post-restoration. Total fish abundance and abundance of the dominant species was greater, often by an order of magnitude, in one of the older restored sites (2 yr post-restoration), while the other restored site (1 yr post-restoration) had values similar to the reference marsh. The success of the restoration at the time of this study suggests that return of the tidal flow and increased marsh area and edge in intertidal and subtidal creeks relative to the former salt hay farms contributed to the quick response of resident and transient young-of-the-year fishes.     

Identification of microdetritus derived fromSpartina and its occurrence in the water column and intertidal sediments of Cumberland Basin,Bay of Fundy

A cellulose-specific staining procedure employing Herzberg’s chlor-zinc-iodide solution was developed to aid in the identification of microdetritus derived fromSpartina alterniflora and tested on samples of suspended and sedimented particulate matter collected in the Cumberland Basin at the head of the Bay of Fundy. Not all of the particles reacting positively to the stain could have been identified as originating fromSpartina on the basis of morphology alone, and the stain improved speed and confidence in identification even when particles could be identified morphologically.Spartina dominated particles greater than 100 μm while most of the smaller particles were amorphous aggregates of uncertain origin. In April 1985, at the start of the salt-marsh growing season, the average concentration of suspended microdetritus derived fromSpartina in Cumberland Basin surface water was 129 mg C m^?3 or 0.3–2.7% of the particulate organic carbon. The average concentration in intertidal sediments was 0.036 mg C g^?1 or 0.2–0.9% of the sediment organic carbon. Summing all reservoirs in the sediment (to a depth of 1 cm) and water column, the total amount of detritus originating fromSpartina in Cumberland Basin is 10–24% of the estimated annual net primary production of low marshS. alterniflora.     

Occurrence ofSpartina macrodetritus in Bay of Fundy waters

Suspended macrodetritus (>600 μm) from extensiveSpartina alterniflora marshes is widespread in the Cumberland Basin region of the macrotidal upper Bay of Fundy. The average concentration is about 5 mg C per m³ and most is found in the lower two-thirds of the water column. The total amount in the Basin at high tide is approximately 8 metric tonnes of organic carbon which is less than 1% of the annual net aerial primary production of the fringingS. alterniflora marshes. The high visibility ofSpartina detritus in Cumberland Basin is caused by the extreme tides (average tidal range about 11 m) which export marsh vegetation and distribute it widely about the estuary, and by the pronounced turbidity which has been shown to limit phytoplankton growth.     

Carbon isotope composition of organic seston and sediments in a Georgia salt marsh estuary

The distribution of δ¹³C values for organic seston and sediment was determined in three sounds in the Spartina marsh estuaries along the Georgia coast, which had high, moderate, and low inputs of freshwater. Organic matter in all three sounds had similar carbon isotope compositions, for the most part within the range of marine values (δ¹³C of ?18%. to ?24%.). It appears that river flow does not introduce significant quantities of particulate C₃ plant material (δ¹³C of ?25%. to ?28%.) to Georgia estuaries. Evaluation of δ¹³C values of estuarine seston and three size fractions of sediment indicated that while Spartina carbon (δ¹³C of ?13%.) can be an important component of organic matter in intertidal sediments (mean δ¹³C of ?14.3%. to ?20.0%.), it is less so in subtidal sediments (mean δ¹³C of ?18.8%. to ?21.2%.), and it is hardly present at all in the seston (mean δ¹³C of ?24.5%.). δ¹³C values of dissolved inorganic carbon (DIC) in several water samples ranged between ?2.5%. and ?5.6%., suggesting that the isotope composition of estuarine DIC is influenced by respiratory CO₂ derived from metabolism of ¹³C-depleted plant carbon. Phytoplankton production utilizing this comparatively light DIC could be a source of relatively negative δ¹³C carbon in the estuary. Additional origins of estuarine organic matter greatly depleted in ¹³C compared to Spartina carbon remain to be identified.     

Tidal utilization of nekton in Delaware Bay restored and reference intertidal salt marsh creeks

Large-scale marsh restoration efforts were conducted to restore normal salt marsh structure and function to degraded marshes (i.e., former salt hay farms) in the mesohaline lower Delaware Bay. While nekton response has been previously evaluated for the marsh surface and subtidal creeks in these marshes, little effort has been focused on intertidal creeks. Nekton response in intertidal creeks was evaluated by sampling with seines to determine if restored (i.e., former salt hay farms restored in 1996) and reference (i.e., natural or relatively undisturbed) salt marshes were utilized by intertidal nekton in a similar manner. The overall nekton assemblage during June–October 2004–2005 was generally comprised of the same species in both the restored and reference marshes. Intertidal creek catches in both marsh types consisted primarily ofFundulus heteroclitus andMenidia menidia, with varying numbers of less abundant transient species present. Transient nekton were more abundant at restored marshes than reference marshes, but in insufficient numbers to cause differences in nekton assemblages. In both marsh types, low tide stages were characterized by resident nekton, dominated byF. heteroclitus, while high tide stages were characterized by a variable mix of transient and resident nekton. Assemblage level analyses indicated that intertidal creeks in restored and reference marshes were generally utilized in a similar manner by a similar nekton assemblage, so restoration efforts were deemed successful. This is in agreement with multiple comparative studies from the ame marshes examining fish, invertebrates, and vegetation in different marsh habitats.     

Characterization of organic matter in surface sediments of the Mackenzie River Basin, Canada

The particulate organic matter in < 63 µm surface sediments from the Mackenzie River and its main tributaries was studied using Rock-Eval pyrolysis and organic petrology. The organic matter in the sediments is dominated by refractory residual organic carbon (RC) of mainly terrigenous nature, as indicated by abundant inertinite, vitrinite, and type III kerogen. Sediments from the tributaries contained significantly more algal-derived organic matter than from the main channel of the river, highlighting the importance of low-energy system dynamics in the tributaries, which allows modest algal production, more accumulation, and better preservation of autochthonous organic matter. This is particularly true for tributaries fed by lacustrine systems, which showed the highest S1 and S2 fractions, and consequently higher total particulate organic carbon (POC) in the basin. Organic petrology of the sediment samples confirms abundant liptinitic materials (i.e., fat-rich structured algae, spores and pollen, cuticles, and resins). Forest fire and coal deposits are also confirmed to contribute to the basin. Assuming that suspended and fine surfacial sediments have a similar OC composition, the Mackenzie River is estimated to deliver a total POC flux of 1.1 Mt C/yr to its delta, of which 85% is residual carbon with liptinitic OC (S1 + S2) and S3 accounting for another 9% and 6%, respectively.