Influence of Wind-Driven Inundation and Coastal Geomorphology on Sedimentation in Two Microtidal Marshes, Pamlico River Estuary, NC

Marsh sediment accumulation is predominately a combination of in situ organic accumulation and mineral sediment input during inundation. Within the Pamlico River Estuary (PRE), marsh inundation is dependent upon event (e.g., storms) and seasonal wind patterns due to minimal astronomical tides (<10 cm). A better understanding of the processes controlling sediment deposition and, ultimately, marsh accretion is needed to forecast marsh sustainability with changing land usage, climate, and sea level rise. This study examines marsh topography, inundation depth, duration of inundation, and wind velocity to identify relationships between short-term deposition (tile-based) and long-term accumulation (²¹⁰Pb and ¹³⁷Cs) recorded within and adjacent to the PRE. The results of this study indicate (1) similar sedimentation patterns between the interior marsh and shore-side marsh at different sites regardless of elevation, (2) increased sedimentation (one to two orders of magnitude, 0.04–4.54 g m^?2 day^?1) within the interior marsh when the water levels exceeded the adjacent topography (e.g., storm berm), and (3) that short-term sea level changes can have direct effects on sediment delivery to interior marshes in wind-driven estuarine systems.     

The role of the Mississippi River in wetland loss in southeastern Louisiana,U.S.A.

The suspended load of the Lower Mississippi River has decreased almost 80 percent since 1850. The long-term suspended sediment record can be loosely subdivided into three phases: a historic interval prior to 1900, a predam period (1930–1952) and a postdam period (1963–1982). The suspended load decreased 43 percent from the historic to the predam period and 51 percent from the predam to the postdam period. The decreases in suspended load after 1952 coincide with the construction of reservoirs and dams on the Missouri and Arkansas rivers. Earlier decreases may be the result of changes in land use measurement practices. The decrease in suspended load and the elimination of overbank flow by the construction of artificial levees are considered to be major causes of coastal wetland loss in southeastern Louisiana. During the historic period sediment accumulation of the marsh surface was greater than the rate of water level rise. During the pre and postdam periods, the rate of water level rise exceeded sediment accretion on the marsh surface. Although the elimination of overbank sediment clearly exacerbated the wetlands loss, an accelerated rate of water level rise during the past 25 years has been a dominant factor. Based on estimates of available overbank sediment, it is suggested that the most viable management strategy for the wetlands would be the diversion of sediment into selected areas where the land loss is most critical.     

Modern diatom assemblages from Chilean tidal marshes and their application for quantifying deformation during past great earthquakes

Tidal marsh sediments from south‐central Chile provide evidence for multiple great earthquakes. Diatom transfer functions, statistical models of the relationship between species preserved in the sediment and elevation, provide quantitative estimates of coseismic vertical land‐level change associated with individual earthquakes. However, in south‐central Chile, our ability to quantify land‐level change is currently limited by a lack of understanding of the environmental variables controlling the distribution of diatoms, an essential prerequisite for converting variations in fossil diatom assemblages into quantitative estimates of past elevation changes. We present a new modern diatom dataset for the region and explore the implications of the scale of the dataset used in transfer function models on the reconstructions of land‐level change. Modern training sets containing samples from a regional scale are superior to sub‐regional and local‐scale training sets, providing closer estimates for known deformation during the great 1960 Chilean earthquake, a higher proportion of good modern analogues and uncertainty terms up to 42% smaller than previously published reconstructions. Copyright © 2017 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.

     

海岸带陆海相互作用(LOICZ)研究及我们的策略

介绍了全球变化研究中关于“海岸带”的定义，海岸带在地球系统研究中的重要地位及其生态系统的脆弱性。我国海岸带地跨三大气候带，海岸类型多种多样，不但有黄河、长江等大河入海，每年有巨大的向海物质通量（包括从大气中的粉尘输入），有宽阔的陆架，有陆架区和近洋之间强烈的物质和能量交换，而且沿海人口密集，大河流域经济活动频繁，人类活动和自然因素冲突集中。近年来海岸带环境和生态系统已经发生了巨大变化。今后，在全球变化条件下为使我国的海岸带环境和生态系统进入良性循环和制定科学的长期管理政策，亟待通过陆海相互作用研究提高对其未来变化的预测能力。文中根据国际ＬＯＩＣＺ运行计划和我国的特点，提出开展我国ＬＯＩＣＺ研究的策略和主要科学问题。     

A 5000 year record of intertidal peat stratigraphy and sea level change from northwest Alaska

Coastal environments of northwest Alaska preserve a detailed record of sea level change during the past 5000 ¹⁴C yr. Rapid burial of intertidal marshes by storm overwash processes, a short open water period, and the arctic maritime climate contribute to the preservation of marine and eolian facies. Eustatic and storm-controlled changes in sea level can be identified from interbedded sequences of marsh peat and coastal flood deposits on barrier islands and estuaries along northwest Seward Peninsula. Mean eustatic sea level has risen about 1.5 m during the last 5000 years, at an average of ca. 0.028 cm yr⁻¹, based on the depth and age relationship of a suite of 23 peat horizons sampled from a 140 km-long reach of coast. Nearshore erosion and sedimentation are controlled by secular variations in wave climate. Peaks in tidal amplitude and storminess correlate with transgressive sedimentary regimes and occurred during the periods 3300–1700, 1200–900, and since about 400 ¹⁴C yr BP. Short-term fluctuations in relative sea level are superimposed on the long-term regional eustatic trend, and record the coastal response to variable rates of sea-level change during the late Holocene.     

Marsh aggradation and sediment distribution along rapidly submerging Louisiana gulf coast

A coastwide study of the relationship between marsh aggradation and water level changes along the rapidly deteriorating Louisiana gulf coast was conducted. Rate of vertical marsh accretion determined from¹³⁷Cs dating was compared to water level changes or submergence. Results identified marsh locations that are not keeping pace with submergence. Coastwide vertical accretion rates on the order of 0.7–0.8 cm/yr are not sufficient to keep pace with water level increases occurring at rates in most locations of over 1.0 cm/yr. Submergence rates were four to five times greater than eustatic sea level change for the Gulf of Mexico. Louisiana gulf coast marshes are likely to continue deteriorating unless means are implemented for distributing Mississippi River sediment to the marsh. It is estimated that sediment equivalent to less than 10 percent of the present annual suspended load of the Mississippi would provide enough sediment for marsh accretionary processes to compensate for submergence or water level increase.     

Massive Upland to Wetland Conversion Compensated for Historical Marsh Loss in Chesapeake Bay,USA

Sea level rise leads to coastal transgression, and the survival of ecosystems depends on their ability to migrate inland faster than they erode and submerge. We compared marsh extent between nineteenth-century maps and modern aerial photographs across the Chesapeake Bay, the largest estuary in North America, and found that Chesapeake marshes have maintained their spatial extent despite relative sea level rise rates that are among the fastest in the world. In the mapped region (i.e., 25% of modern Chesapeake Bay marshland), 94 km² of marsh was lost primarily to shoreline erosion, whereas 101 km² of marsh was created by upland drowning. Simple projections over the entire Chesapeake region suggest that approximately 100,000 acres (400 km²) of uplands have converted to wetlands and that about a third of all present-day marsh was created by drowning of upland ecosystems since the late nineteenth century. Marsh migration rates were weakly correlated with topographic slope and the amount of development of adjacent uplands, suggesting that additional processes may also be important. Nevertheless, our results emphasize that the location of coastal ecosystems changes rapidly on century timescales and that sea level rise does not necessarily lead to overall habitat loss.     

Sedimentology and depositional environments of the Maastrichtian Patti Formation, southeastern Bida Basin, Nigeria

The Maastrichtian Patti Formation, which consists of shale - claystone and sandstone members, constitutes one of the three Upper Cretaceous lithostratigraphic units of the intracratonic southeastern Bida Basin, in central Nigeria. Well exposed outcrops of this formation were investigated at various locations around the confluence of the Niger and Benue Rivers. The lithostratigraphic sections were measured and their peculiar sedimentological features such as textures, physical and biogenic sedimentary structures, facies variations and associations were documented and used to interpret the depositional environments and develop a paleogeographic model. Some selected representative samples of the sedimentary depositional facies were also subjected to grain size analysis.Three shoreline sedimentary depositional facies composed of shoreface, tidal channel, and tidal marsh to coastal swamp facies were recognized in the study area. Continental sedimentary depositional facies such as fluvial channel, swamp, and overbank were also documented. The sandstones of the shoreface and tidal channel facies are medium- to coarse-grained, moderately sorted (standard deviation ranges from 0.45–1.28 averaging 0.72), and quartzarenitic. The fluvial channel sandstone facies are coarse- to very coarse-grained, mostly poorly sorted (standard deviation ranges from 0.6–1.56 averaging 1.17), and subarkosic. Typical sedimentary structures displayed by the shoreface and tidal channel facies include burrows, clay drapes, hummocky and herringbone cross stratifications, whereas the fluvial channel sandstone facies are dominated by massive and planar cross beddings. The tidal marsh to coastal swamp shales and ferruginised siltstone facies are fossiliferous and bioturbated, whereas the nonmarine swamp siltstones contain vegetal imprints and lignite interbeds. The overbank claystone facies are massive and kaolinitic.In the study area, a regressive to transgressive model is proposed for the Patti Formation. This model correlates with stratigraphically equivalent sediments of the Ajali and Mamu Formations in the adjacent Anambra Basin to a great extent.     

Distribution and abundance of tidal marshes along the coast of maine

Planimetry studies of coastal geology maps prepared by the Maine Geological Survey show that there is more than an order of magnitude more tidal marsh area in the state of Maine than documented in previously published estimates. The highly convoluted coast of Maine, which is approximately 5,970 km long, contains almost 79 km² of salt marsh, far more than any other New England state, New York, or the Bay of Fundy region. Reasonable estimates for the per-unit primary productivity of salt marshes lead to projections of total marsh productivity on the order of 10¹⁰ g dry weight yr^?1 for the Maine coast and 10¹¹ g dry weight yr^?1 for the Gulf of Maine as a whole. Distribution of tidal marsh area is strongly controlled by coastal geomorphology, which varies considerably along the coast of Maine. The salt marsh area is concentrated in the southwestern coastal region of arcuate bays, where marshes have developed behind sandy beaches. A series of long islands and bedrock peninsulas in the south-central portion of the coast also provides sheltered areas where large marshes occur. Northeast of Penobscot Bay salt marshes become more numerous and smaller in average areal extent. A lack of protection from waves, along with limited sources of glacio-fluvial and glacio-marine sediments, restricts the occurrence of salt marshes in that region to the frignes of coves and tidal rivers.     

Land subsidence due to groundwater withdrawal: potential damage of subsidence and sea level rise in southern New Jersey, USA

 Land subsidence due to groundwater withdrawal combined with a global sea level rise creates a serious environmental problem in the coastal region. Groundwater withdrawal results in fluid pressure change in the layers. The pressure change in the layers induces both elastic and inelastic land compaction. The elastic compaction can be recovered if the water level rises again and inelastic compaction becomes permanent. Groundwater response to barometric pressure change is used to estimate the elastic compaction in this study. The storativity, specific storage and other layer and hydrological information are used to estimate the inelastic compaction of the layers due to fluid withdrawal. The discussed methods are applied to estimate and predict the subsidence potentials resulting from overdrafting of the groundwater in the southern New Jersey. The estimated subsidence is about 2–3 cm near the location of monitoring wells in Atlantic, Camden, Cumberland and Cape May Counties over the past 20 years. If the current trend of water-level drop continues, the average subsidence in southern New Jersey in the vicinity of some monitoring wells will be about 3 cm in the next 20 years. The rise of global sea level is about 2 mm/year on average. Because of the very gentle slope in southern NJ, the combination of subsidence and sea level rise will translate into a potentially substantial amount of land loss in the coastal region in each 20 year period. This combination will also accelerate the coastal flooding frequency and the erosion rate of the New Jersey coastal plain, and pose a serious threat to the coastal economy. Received: 15 December 1997 · Accepted: 30 June 1998     

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).     

Late Pleistocene raised beaches of coastal Estremadura,central Portugal

We present new stratigraphic, sedimentological, and chronological data for a suite of tectonically raised beaches dating to Marine Isotope Stages 5, 4, and 3 along the Estremadura coast of west-central Portugal. The beach deposits are found in association with ancient tidal channels and coastal dunes, pollen bearing mud and peat, and Middle Paleolithic archaeological sites that confirm occupation of the coastal zone by Neanderthal populations. The significance of these deposits is discussed in terms of the archaeological record, the tectonic and geomorphic evolution of the coast, and correlation with reconstructions of global climate and eustatic sea-level change. Direct correlation between the Estremadura beach sections is complicated by the tectonic complexity of the area and the age of the beach deposits (which are near or beyond the limit of radiocarbon dating). Evidence from multiple sites dated by AMS radiocarbon and optical luminescence methods suggests broad synchroneity in relative sea-level changes along this coast during Marine Isotope Stage 3. Two beach complexes with luminescence and radiocarbon age control date to about 35 ka and 42 ka, recording a rise in relative sea level around the time of Heinrich Event 4 at 39 ka. Depending on assumptions about eustatic sea level at the time they were deposited, we estimate that these beaches have been uplifted at rates of 0.4–4.3 mm yr^?1 by the combined effects of tectonic, halokinetic, and isostatic processes. Uplift rates of 1–2 mm yr^?1 are likely if the beaches represent sea level stands at roughly 40 m below modern, as suggested by recent eustatic sea level reconstructions. Evidence from coastal bluffs and the interior of the study area indicates extensive colluvial, fluvial, and aeolian sedimentation beginning around 31 ka and continuing into the Holocene. These geomorphic adjustments are related to concomitant changes in climate and sea level, providing context that improves our understanding of Late Pleistocene landscape change and human occupation on the western Iberian margin.     

A Climate Change Adaptation Strategy for Management of Coastal Marsh Systems

Sea level rise is causing shoreline erosion, increased coastal flooding, and marsh vulnerability to the impact of storms. Coastal marshes provide flood abatement, carbon and nutrient sequestration, water quality maintenance, and habitat for fish, shellfish, and wildlife, including species of concern, such as the saltmarsh sparrow (Ammodramus caudacutus). We present a climate change adaptation strategy (CCAS) adopted by scientific, management, and policy stakeholders for managing coastal marshes and enhancing system resiliency. A common adaptive management approach previously used for restoration projects was modified to identify climate-related vulnerabilities and plan climate change adaptive actions. As an example of implementation of the CCAS, we describe the stakeholder plans and management actions the US Fish and Wildlife Service and partners developed to build coastal resiliency in the Narrow River Estuary, RI, in the aftermath of Superstorm Sandy. When possible, an experimental BACI (before-after, control-impact) design, described as pre- and post-sampling at the impact site and one or more control sites, was incorporated into the climate change adaptation and implementation plans. Specific climate change adaptive actions and monitoring plans are described and include shoreline stabilization, restoring marsh drainage, increasing marsh elevation, and enabling upland marsh migration. The CCAS provides a framework and methodology for successfully managing coastal systems faced with deteriorating habitat, accelerated sea level rise, and changes in precipitation and storm patterns.     

Quantification of the Attenuation of Storm Surge Components by a Coastal Wetland of the US Mid Atlantic

Coastal wetlands are receiving increased consideration as natural defenses for coastal communities from storm surge. However, there are gaps in storm surge measurements collected in marsh areas during extreme events as well as understanding of storm surge processes. The present study evaluates the importance and variation of different processes (i.e., wave, current, and water level dynamics with respect of the marsh topography and vegetation characteristics) involved in a storm surge over a marsh, assesses how these processes contribute to storm surge attenuation, and quantifies the storm surge attenuation in field conditions. During the Fall of 2015, morphology and vegetation surveys were conducted along a marsh transect in a coastal marsh located at the mouth of the Chesapeake Bay, mainly composed of Spartina alterniflora and Spartina patens. Hydrodynamic surveys were conducted during two storm events. Collected data included wave characteristics, current velocity and direction, and water levels. Data analysis focused on the understanding of the cross-shore evolution of waves, currents and water level, and their influence on the overall storm surge attenuation. Results indicate that the marsh area, despite its short length, attenuates waves and reduces current velocity and water level. Tides have a dominant influence on current direction and velocity, but the presence of vegetation and the marsh morphology contribute to a strong reduction of current velocity over the marsh platform relative to the currents at the marsh front. Wave attenuation varies across the tide cycle which implies a link between wave attenuation and water level and, consequently, storm surge height. Storm surge reduction, here assessed through high water level (HWL) attenuation, is linked to wave attenuation across the front edge of the marsh; this positive trend highlights the reduction of water level height induced by wave setup reduction during wave propagation across the marsh front edge. Water level attenuation rates observed here have a greater range than the rates observed or modeled by other authors, and our results suggest that this is linked to the strong influence of waves in storm surge attenuation over coastal areas.     

Land use change assessment in coastal mangrove forests of Iran utilizing satellite imagery and CA–Markov algorithms to monitor and predict future change

Mangrove forest stores large organic carbon stocks in a setting that is highly vulnerable to climate change and direct anthropogenic influences. As such there is a need to elucidate the causes and consequences of land use change on these ecosystems that have high value in terms of ecosystem services. We examine the areal pattern of land types in a coastal region located in southern Iran over a period of 14 years to predict future loss and gain in land types to the year 2025. We applied a CA–Markov model to simulate and predict mangrove forest change. Landsat satellite images from 2000 to 2014 were used to analyze the land cover changes between soil, open water and mangroves. Major changes during this period were observed in soil and water which could be attributed to rising sea level. Furthermore, the mangrove area in the more seaward position was converted to open water due to sea-level rise. A cellular automata model was then used to predict the land cover changes that would occur by the year 2025. Results demonstrated that approximately 21 ha of mangrove area will be converted to open water, while mangroves are projected to expand by approximately 28 ha in landward direction. These changes need to be delineated to better inform precise mitigation and adaptation measures.     

Seasonal and Annual Fluxes of Nutrients and Organic Matter from Large Rivers to the Arctic Ocean and Surrounding Seas

River inputs of nutrients and organic matter impact the biogeochemistry of arctic estuaries and the Arctic Ocean as a whole, yet there is considerable uncertainty about the magnitude of fluvial fluxes at the pan-Arctic scale. Samples from the six largest arctic rivers, with a combined watershed area of 11.3?×?10⁶?km², have revealed strong seasonal variations in constituent concentrations and fluxes within rivers as well as large differences among the rivers. Specifically, we investigate fluxes of dissolved organic carbon, dissolved organic nitrogen, total dissolved phosphorus, dissolved inorganic nitrogen, nitrate, and silica. This is the first time that seasonal and annual constituent fluxes have been determined using consistent sampling and analytical methods at the pan-Arctic scale and consequently provide the best available estimates for constituent flux from land to the Arctic Ocean and surrounding seas. Given the large inputs of river water to the relatively small Arctic Ocean and the dramatic impacts that climate change is having in the Arctic, it is particularly urgent that we establish the contemporary river fluxes so that we will be able to detect future changes and evaluate the impact of the changes on the biogeochemistry of the receiving coastal and ocean systems.     

Tower-based conditional sampling for measuring ecosystem-scale carbon dioxide exchange in coastal wetlands

Long-term measurements of CO₂ exchange between coastal wetlands and the atmosphere are necessary to improve our understanding of the role these ecosystems play in the global carbon cycle, and the response of these systems to environmental change. We conducted research to adapt and evaluate tower-based conditional sampling as a method for measuring net CO₂ exchange (NCE) at the ecosystem scale on a continuous basis. With conditional sampling, NCE is determined from the product of the standard deviation of vertical wind velocity, the difference in CO₂ concentration between updrafts and downdrafts in the constant flux portion of the boundary layer above the surface, and an empirical coefficient. We constructed a system that used a sonic anemometer to measure vertical wind velocity (w) and control a high-speed three-way valve that diverted air from updrafts and downdrafts into separate sample lines, depending on the direction ofw. an infrared gas analyzer was used to measure the concentration difference. The conditional sampling system was installed and tested in a marsh in the Nueces River Delta near Corpus Christi, Texas, as part of a long-term study of effects of freshwater inflow on CO₂ flux. System accuracy was evaluated by comparing conditional sampling measurements of water vapor flux with independent estimates obtained with the Bowen ratio method. Average daily flux estimates for the two methods agreed to within 13%. Measurements showed that freshwater inflow due to flooding of the Nueces River increased NCE by increasing CO₂ assimilation and decreasing CO₂ efflux. Over a 65-d period, daily NCE varied from a maximum gain of 0.16 mol CO₂ m⁻² d⁻¹ during flooding to a maximum loss of −0.14 mol CO₂ m⁻² d⁻¹ when the marsh dried. Our study showed that conditional sampling was well suited for quantifying CO₂ exchange in coastal wetlands on a diel, daily, and seasonal basis.     

Tampa Bay Coastal Wetlands: Nineteenth to Twentieth Century Tidal Marsh-to-Mangrove Conversion

Currently, mangroves dominate the tidal wetlands of Tampa Bay, Florida, but an examination of historic navigation charts revealed dominance of tidal marshes with a mangrove fringe in the 1870s. This study's objective was to conduct a new assessment of wetland change in Tampa Bay by digitizing nineteenth century topographic and public land surveys and comparing these to modern coastal features at four locations. We differentiate between wetland loss, wetland gain through marine transgression, and a wetland conversion from marsh to mangrove. Wetland loss was greatest at study sites to the east and north. Expansion of the intertidal zone through marine transgression, across adjacent low-lying land, was documented primarily near the mouth of the bay. Generally, the bay-wide marsh-to-mangrove ratio reversed from 86:14 to 25:75 in 125?years. Conversion of marsh to mangrove wetlands averaged 72?% at the four sites, ranging from 52?% at Old Tampa Bay to 95?% at Feather Sound. In addition to latitudinal influences, intact wetlands and areas with greater freshwater influence exhibited a lower rate of marsh-to-mangrove conversion. Two sources for nineteenth century coastal landscape were in close agreement, providing an unprecedented view of historic conditions in Tampa Bay.     

Paleoenvironmental history of submerged ruins on the Northern Euboean gulf coastal plain,central Greece

Hewn blocks from submerged ruins associated with the name Thronion are exposed during low, low tide along the northeastern shoreline of the fan delta which separates the Gulf of Euboea from the Maliakos Gulf, central Greece. Although the date of these ruins is not known, their submergence indicates that they predate the most recent marine transgression. Late Holocene sediments of the coastal plain adjacent to the ruins were studied using 34 auger cores drilled along two 1.3 and 1.1 km shore-normal sections. Cores were described in the field and sampled for sedimentologic and microfossil analyses. These analyses show that late Holocene transgressive marine and strandline units interfinger inland with deposits of a brackish water embayment. Subsequent progradation of the shoreline is marked by overlying slightly brackish to freshwater marsh sediments. A soil horizon developed on these marsh sediments defines a period of aerial exposure and land stability. Late Roman to Byzantine sherds (ca. 4th-13th Century A.D.) within the buried soil and a high phosphate content suggest that this soil developed in association with human habitation. the buried soil may be the surface on which the now-submerged ruins were built. the deposits below the buried soil indicate that prior to the period of soil formation, most of this area was under water and the paleoshoreline was landward of its present position. the ruins were later covered by lake or marsh deposits radiocarbon dated as 1400 A.D. the depth of the dated wood samples, 2.5–3.0 meters below the surface, indicates rapid sediment accumulation (ca. 40–55 cm/100 yrs) over the past 550 years. A small exposure of the ca. 1400 A.D. marsh silt and overlying post-1950 land fill near the ruins is the result of post-1400 A.D. erosion and recession of the shoreline. the lower pre-occupational and post-1400 A.D. transgressions were caused by a combination of eustatic sea level rise, tectonic subsidence, and fluctuations of sediment supply to this portion of the Kenourion fan delta.     

Testate amoebae as estuarine water‐level indicators: modern distribution and the development of a transfer function from a freshwater tidal marsh (Scheldt estuary,Belgium)

Little is known about the century‐scale response of water levels in inland estuaries to sea‐level change and human modifications to estuarine morphology. This study explored the ability of using testate amoebae (Protozoa, Rhizopoda) from sediments of a freshwater tidal marsh as indicators of water level in an inland estuary. The hypothesis was that modern testate amoeba assemblages change with surface elevation (approximately the duration of tidal flooding) within a freshwater tidal marsh. Variation in testate amoeba assemblages in relation to multiple environmental variables and sediment characteristics was studied through redundancy analysis. This demonstrated that a significant part of the variation in modern testate amoeba assemblages could be explained by flooding frequency, surface elevation, organic content and particle size of the soil. Transfer functions, partial least squares and weighted average regressions were made to show that testate amoebae can be used for reconstruction of water level (with an accuracy of 0.05 Normalized Elevation). A preliminary test of application of the transfer function to palaeo testate amoeba assemblages showed promising results. Testate amoebae from a freshwater tidal marsh provide a potentially powerful new tool for estuarine water‐level reconstructions. Copyright © 2011 John Wiley & Sons, Ltd.