Western Inlet Research Articles

The influence of environmental conditions on the benthic foraminiferal distribution from the recent sediments of Lake Bardawil, Eastern Mediterranean Sea, Egypt

Lake Bardawil, similar to the other Mediterranean Egyptian lakes, is a unique wetland, separated from theMediterranean Seaby a narrowsandbarwith very restricted water exchange that allowed the development of a shallow-hypersaline lagoon. Late Pleistocene tectonics activities divided the lake into two main basins; the eastern and western basins. Twelve surface sediment samples were collected along the Lake and subjected to sediment texture and benthic foraminiferal analyses. In general, benthic foraminifera were abundant in the surface sediments of Lake Bardawil and were characterized by low diversity. The statistical analysis revealed two biotopes that distinguished between the eastern and western basins' environments. The eastern basin biotopes were characterized by fine bottom sediments with the predominance of salinity-tolerant assemblages, thus demonstrating hypersaline stressful restricted environment. The western biotope exhibited coarser bottom sediments associated with relatively narrow salinity-tolerant assemblages. This reflected sandy and less saline sediment of uncontaminated environments, as the western basin was exposed to active hydrodynamic regime that developed more magnitudes of water exchange with the Eastern Mediterranean Sea through the western inlet. Based on the results of this study, the biomonitoring of Lake Bardawil could be assessed by the analysis of its benthic foraminifera as a bioindicator tool that may help in the improvement of the Lake's conditions.

Ummeland voyaging, maritime ‘monks’, and the emergence of the town of Marstrand

For many centuries, the Limfjord was a strait dividing Jutland in a northerly and a southerly part. As such, it constituted the safest and most frequented sea route between the North Sea and Baltic Sea regions. During the first part of the 12th century, its western inlet silted up, creating today’s Limfjord, thus forcing vessels to take a more northerly route around the dangerous Skaw – a route that had previously been avoided. The present study suggests that this so-called ummeland voyaging had considerable economic and geo-political consequences for the Viken region. In particular, it argues that ummeland voyaging was the main driver to the establishment of the town of Marstrand in the southern part of this region. The hypothesis presented thus contradicts much of the previous research on Marstrand’s urbanisation, which instead states that the town derived from a fishing hamlet.

Decline in Surface Melt Duration on Larsen C Ice Shelf Revealed by The Advanced Scatterometer (ASCAT)

Surface melting has been contributing to the surface lowering and loss of firn air content on Larsen C Ice Shelf since at least the mid‐1990s. Where the amount of melting and refreezing is significant, the firn can become impermeable and begin to support ponds of surface meltwater such as have been implicated in ice shelf collapse. Although meteorological station data indicated an increase in melt on the Antarctic Peninsula over the second half of the 20th century, the existing Ku‐band Quick Scatterometer (QuikSCAT) time series is too short (1999–2009) to detect any significant 21st century trends. Here we investigate a longer 21st century period by extending the time series to 2017 using the C‐band Advanced Scatterometer (ASCAT). We validate our recent observations with in situ weather station data and, using a firn percolation model, explore the sensitivity of scatterometry to water at varying depths in the firn. We find that active microwave C‐band (5.6‐cm wavelength) instruments can detect water at depths of up to 0.75 m below a frozen firn layer. Our longer scatterometry time series reveals that Larsen C Ice Shelf has experienced a decrease in melt season length of 1–2 days per year over the past 18 years consistent with decreasing summer air temperatures. Only in western inlets, where föhn winds drive melt, has the annual melt duration increased during this period.

Numerical simulation of shoreline responses in the vicinity of the western artificial inlet of the Bardawil Lagoon, Sinai Peninsula, Egypt

This paper introduces an appropriate visualization of the tidal inlets including the characterization of internal siltation and the remediation of associated non-affirmative consequences due to the existence of its protective jetties, such as down-side erosion and up-side accretion. Accordingly, the 2D hydrodynamic circulation models CMS-Flow and CMS-Wave have been initially set up to describe the morphodynamics situation inside the artificial western inlet (inlet (1)) of the Bardawil Lagoon, which is situated along the Mediterranean coastline of the Sinai Peninsula, in the presence and absence of the jetties. Simultaneously, the Littoral Processes and Coastline Kinetics (DHI-LITPACK) numerical model is essentially applied to predict the shoreline responses in the vicinity of inlet (1) to numerous different scenarios considering both hard (i.e., groins and detached breakwaters) and soft (i.e., sand nourishment and sand bypassing systems) measures during the period from 2010 to 2030. The study has revealed that the use of hard measures to the east of the inlet would induce exceedingly high recession rates of the shoreline. Nevertheless, the use of a one-time nourishment of 250,000 m3 in the areas between short groins (with lengths of 90 m and an interval of 400 m) during their construction would optimally reduce the expected area of erosion by approximately 91.85%. Meanwhile, a single groin with a length of 200 m and a westward drift distance of 450 m to the west of the inlet would be superior with regard to optimizing the sedimentary stock compared to an annual dredging rate of 100,000 m3/year. Finally, an optimization model has been constructed using a Mamdani-type fuzzy inference system to determine the cheapest and most efficient solution with the minimum impact on the sandy barrier zone of inlet (1).

High-resolution numerical modelling of the barotropic tides in the Gulf of Gabes, eastern Mediterranean Sea (Tunisia)

A high-resolution 2D barotropic tidal model was developed for the Gulf of Gabes and used to characterise hydrodynamic processes and tidal dynamics. The model is based on the Regional Ocean Modelling System. It is forced at the open boundaries by the semidiurnal M2 and S2 astronomical components while meteorological forcing has been neglected. The model results show good agreement with observations confirming that it reproduces the gulf's main tidal characteristics reasonably well. In fact, the simulated semidiurnal tidal components M2 and S2 generate important sea level variations and coastal currents. Tidal propagation is directed to the gulf's western sector while tidal resonance occurs in its inner sector where the M2 and S2 amplitudes are about 50 and 36 cm, respectively. Phase maxima (170°–185°) are located inside Boughrara Lagoon for both the simulated M2 and S2 tides. The strongest currents are found in shallow coastal regions and at the lagoon's western inlet. During spring tides, currents are around 10–20 cm s−1 in the gulf center and up to 50 cm s−1 inside the lagoon.

Water exchanges between a multi-inlet lagoon and the ocean: the role of forcing mechanisms

Understanding the influence of the main drivers controlling the circulation and the transport in coastal lagoons is a necessary step towards the description of the dynamics of their ecosystems. Thus, the influence of the main physical drivers on the water exchanges in a multi-inlet barrier island (western sector of the Ria Formosa coastal lagoon, Portugal) was investigated. Several scenarios of tide, wind, bathymetry and point source discharges were simulated using a three-dimensional circulation model and a particle-tracking model. The circulation is adequately reproduced by the hydrodynamic model, with root mean square errors of about 5–8 cm for the water levels and 5–10 cm/s for the cross-sectional averaged velocities in the western inlets and main channels. Wind has a negligible effect on the modelled water levels and cross-sectional velocities, with differences smaller than 1 % between the simulations with and without wind. However, results show that wind influences significantly the transport by affecting the residual circulation, with distinct effects depending on the wind direction. Upwelling favourable winds (with west component) increase the landward transport through the Faro-Olhao inlet and promote a larger dispersion of the water-borne material inside the lagoon. The residual circulation between the three inlets of the western sector of the lagoon is also significantly affected by the bathymetry. Results show a decrease of about 50 % of the tidal prism of the Ancao inlet between 2002 and 2011, which reduces its capacity to export waterborne material to the adjacent coastal area and increases the residence times in some areas of the lagoon, with potentially adverse effects on the ecosystems’ health. The dispersion of potential contaminants from point sources inside the lagoon to the coastal area depends on the combined effect of the tidal phase and amplitude and the location of the source. Mean residence times for the discharges from the wastewater treatment plants of the western sector ranged from 7 to 18 days. These findings improve the understanding of the influence of the physical forcings in the circulation and transport dynamics of multi-inlet coastal systems.

Surface melt and ponding on Larsen C Ice Shelf and the impact of föhn winds

AbstractA common precursor to ice shelf disintegration, most notably that of Larsen B Ice Shelf, is unusually intense or prolonged surface melt and the presence of surface standing water. However, there has been little research into detailed patterns of melt on ice shelves or the nature of summer melt ponds. We investigated surface melt on Larsen C Ice Shelf at high resolution using Envisat advanced synthetic aperture radar (ASAR) data and explored melt ponds in a range of satellite images. The improved spatial resolution of SAR over alternative approaches revealed anomalously long melt duration in western inlets. Meteorological modelling explained this pattern by föhn winds which were common in this region. Melt ponds are difficult to detect using optical imagery because cloud-free conditions are rare in this region and ponds quickly freeze over, but can be monitored using SAR in all weather conditions. Melt ponds up to tens of kilometres in length were common in Cabinet Inlet, where melt duration was most prolonged. The pattern of melt explains the previously observed distribution of ice shelf densification, which in parts had reached levels that preceded the collapse of Larsen B Ice Shelf, suggesting a potential role for föhn winds in promoting unstable conditions on ice shelves.

Remote sensing assessment of sediment variation in the Pearl River Estuary induced by Typhoon Vicente

A MODIS-based algorithm was developed to investigate the impact of Typhoon Vicente on the total suspended solid concentration in the Pearl River Estuary. This algorithm used two high resolution bands at 645 nm and 555 nm to map the concentrations. Regression between the remote sensing reflectance and in situ total suspended solid concentration showed good correlation (R2 = 0.91), indicating that the algorithm was valid for the high turbid waters in the Pearl River Estuary. MODIS-derived maps showed different total suspended solid concentration anomalies in different sub-regions of the estuary during the passage of Typhoon Vicente. In western inlets, the increase of total suspended solids (maximum values of 22.20 g m−3 before and 55.71 g m−3 after the typhoon) was possibly related to the larger rainfall discharge from the Pearl River. In Lingdingyang, the increase of total suspended solids (maximum values of 19.60 g m−3 before and 44.59 g m−3 after the typhoon) might be the result of typhoon-induced resuspension. In the southeastern portion of the Estuary, due to the typhoon-induced current, a significant decrease of total suspended solid area (decreased by 10 g m−3) was observed. Different changes were observed in different sub-regions under the influence of the typhoon, implying the complicated hydrological environment is an important feature in the Pearl River Estuary.

The decline of the Nile crocodile population in Loskop Dam, Olifants River, South Africa

The apparent decline in the number of Nile crocodiles present in the Loskop Dam prompted a study to determine the number, size and distribution of Nile crocodiles now present in the reservoir. The number of crocodiles in the Loskop Dam was surveyed using aerial counts and spotlight counts. Surveys revealed the presence of a very low total number of crocodiles and also a poor distribution of crocodiles in the different size classes over almost 30 years since 1981. Eight surveys carried out between 2001 and 2010 revealed that the distribution pattern of crocodiles in the Loskop Dam did not vary between winter and summer. These distribution patterns indicate that crocodiles occur most frequently in the eastern and western inlets and not in the main basin of the dam. Thirteen crocodiles were re-introduced into the dam during March 2007; however the August 2009 spotlight survey results indicated that none of these animals had survived.Keywords: Crocodylus niloticus, numbers, size classes, density, distribution

Yangtze Delta, China: Taihu lake-level variation since the 1950s, response to sea-level rise and human impact

Hydrological records collected from water gauge stations since the 1950s demonstrate that the Taihu lake level is rising. The average rate of the lake-level rise is 0.4–1.1 mm/year during the non-flood season, resulting directly from a rise in sea level. High rates of 3.0–5.0 mm/year of rise are even recorded during the wet season. This indicates increasing human activities such as reclamation, sluicing and embanking, which significantly hinder the expulsion of extra lake water to the coast shortly after a rainfall. Generally, the lake level of the western inlet is higher than that of the eastern outlet. However, the lake-level difference between the west and east has been diminished annually from ∼10–15 cm in the 1950s to <3 cm at the present time. During non-flood seasons, the lake-level difference even appears to be reversed, indicating a retrogression of the lake flow from east to west. It is predicted that the Taihu drainage basin will lose much of its natural water-expelling ability in the next 50 years as the sea level continues to rise, and retrogression will likely occur during the flood season in the near future.

Ecology of three sea catfishes (Ariidae) in a tropical coastal ecosystem - Southern Gulf of Mexico

Catfishes of the Family Ariidae are characterized as eurythermal and euryhallne inhabitants of estuarine waters. In the Southern Gulf of Mexico (Terminos Lagoon) there are 3 species: Arius felis, A. melanopus, and Bagre rnarinus. Juveniles of A. melanopus occur in the fluvial-lagoon system (FLS) in areas with oysters Crassostrea virginica, while adults occur throughout the lagoon. A. melanopusreaches sexual maturity at 160 mm total length (TL) and reproduces in FLS in salinities 12 ppt, temperatures 2 30 C, and in less turbid areas dominated by Thalassia testudi~~um eadows. Males with eggs and/or embryos in their mouths are found In September. After the incubation period adults migrate toward the eastern inlet (marine) and luveniles toward the western inlet (estuarine). B. marjnus is found only in the western inlet (estuarine), central basin, and FLS of Terminos Lagoon. This specles reproduces along the coastline and enters the lagoon at the end of the rainy and winter storm or nortes season. Juveniles use the lagoon as nursery area. The Terminos Lagoon has a high diversity of habitats due to ecological interchange with rivers, swamps and the inner shelf. Three main strategies in the use of the system by catfishes in relation to reproduction and feeding may be characterized as: (1) spawning in the rivers and swamps followed by a migration of juveniles toward the central part of the estuarine system; (2) spawning in the estuarine system; and (3) s p a w ~ n g in the sea followed by migration of juveniles to the FLS for feeding. Estuarine fish that have separate reproduction, growth, and feeding areas generally occur in great abundance and have adapted by reducing interspecific competition and temporal and spatial niche partition. In tropical high diversity ecosystems, biological cycles are closely related to high productivity of coastal waters, large supply of organic matter, increased food availability, and protection from predators. The estuary-inner shelf or swamp-estuary migrations can be interpreted as small-scale anadromous adaptations.

Processes and History of Terminos Lagoon, Mexico

There is a net flow of Gulf of Mexico high salinity water into Terminos Lagoon through the eastern inlet, mixing with runoff from three large rivers, and a net flow of low-salinity lagoon water out through the western inlet. The average circulation is reflected in distribution patterns of salinity, sediment size distributions, forams, percent of calcium carbonate in the sediments, and water turbidity. Relatively high organic productivity is indicated by numerous large standing stocks of forams. The lagoon is on the boundary between biogenic carbonate sediments on the east and detrital river-borne sediments on the west. The modern lagoon barrier began during the Holocene on a foundation of calcilutite when sea level was at about -- 10 m. When it reached about its present level the inlets were east of the present ones. Predominant flow of lagoon water out through the western inlet as at present is indicated by river-borne detritus under a surface cap of biogenic carbonate on the western end of the barrier. The seaward side of the barrier is being eroded, except on the western end, where there is deposition. The lagoon is essentially filled with sediment, and most detritus being delivered by rivers is bypassing the lagoon. It is suggested that deposits similar to those in Terminos Lagoon can be identified in ancient sediments.