Aeolian sand drift from the intertidal zone on a temperate beach: Potential and actual rates

This paper compares the amount of sand that is potentially moved into a coastal dune system from a beach using estimates based solely on the wind force, with actual measured amounts. The actual sand inputs are determined by measuring sand level changes each month over a period of eighteen months, along a 1760-m section of foredune on Braunton Burrows, Southwest England. The calculation procedure used to estimate the potential rates of sand drift is based on the capacity of the wind force to transport sand using a published transport equation (White, 1979). The results show that the actual movement rates are markedly smaller than the potential rates for all months except in the summer. Meteorological variables and the watertable level in the adjacent dune system are used in an empirically derived regression equation in an attempt to explain the large discrepancy between the potential and actual movement rates. The resulting corrected potential movement rates are a closer estimate to the actual rates, but there remains much unexplained variance.     

Effects of nutrients on crude oil biodegradation in the upper intertidal zone

To enhance biodegradation, nutrients in the form of slow-release fertilizer (SRF) were applied to oil-contaminated microcosms (3%, v/v) which simulated intertidal environmental systems. Although nutrient concentrations in the interstitial water were not proportional to those in amended SRF, microbial activity, growth of oil-degrading microorganisms, and oil-degradation rate were closely related to the concentration of nutrients in the interstitial water. Adding nutrients at higher dose (microcosm I, 144.4 mg C/kg sand/day, versus microcosm II, 8.5 mg C/kg sand/day) had a positive effect on oil degradation rate, which was especially obvious during the early phase of treatment. Use of pristane, phytane, and nor-hopane as biomarkers enabled the detection of significant treatment differences in hydrocarbon biodegradation, which were not reliable enough when the data were normalized to sand mass.     

Preliminary study on responses of marine nematode community to crude oil contamination in intertidal zone of Bathing Beach, Dalian

This study investigated the responses of marine nematodes to crude oil contamination in polluted and relatively uncontaminated sites in Dalian Xingang, China, 40 days after an oil spill. Samples were taken at different tide levels on the beach and at different positions along the beach. We present the results of a comparison of nematode assemblages from undisturbed sediment from the Xiajiahezi Bathing Beach with those from sediment from the Xinghai Bathing Beach contaminated with crude oil. A total of 1666 nematodes from 26 genera were found in this study. Results showed significant differences in nematode assemblages between samples from undisturbed controls and those from the polluted area. Nematode abundance, number of species, diversity and species richness decreased significantly with increasing levels of crude oil contamination. Fifteen genera were eliminated and seemed to be composed of species intolerant to crude oil contamination; only the abundance of Marylynnia sp. increased slightly.     

Overwash processes along a gravel beach in south-east Ireland

Recent overwashing, and to a more limited extent overtopping, has occurred on a gravel-dominated beach just west of Carnsore Point in south-east Ireland. At relatively low points swash excursions have breached the duneline and extensive gravel fans have formed on landward-facing slopes. Also, at interbreach positions, swash ramps have been built-up in front of previously eroding dune cliffs, allowing overtopping at heights of up to 5 m above MHWOST, spreading a veneer of sediment over the adjacent dune ridge. In both cases events appear to be preceded by erosion and backbeach sand and gravel deposition. Stratigraphic, textural and fabric analyses assist in identifying environmental conditions that prevailed during overwash throat and fan, and overtopping ramp, sedimentation.     

Formation events of shoreline sand waves on a gravel beach

Kilometric-scale shoreline sand waves (KSSW) have been observed in the north-east flank of the Dungeness Cuspate Foreland (southeastern coast of the UK). They consist of two bumps separated by embayments with a 350–450-m spacing. We have analysed 36 shoreline surveys of 2-km length using the Discrete Fourier Transformation (DFT), from 2005 to 2016, and seven topographic surveys encompassing the intertidal zone, from 2010 to 2016. The data set shows two clear formation events. In order to test the role of high-angle waves on the KSSW formation, the 10-year wave series is propagated from the wave buoy located at 43 m depth up to a location in front of the undulations at 4 m depth using the SWAN wave model. The dominating SW waves arrive with a very high incidence angle (～ 80°) while the NE waves arrive almost shore normal. The ratio R, which measures the degree of dominance of high-angle waves with respect to low-angle waves, correlates well with the shoreline DFT magnitude values of the observed wavelength undulations. In particular, the highest R values coincide with the formation events. Finally, a linear stability model based on the one-line approximation is applied to the Dungeness profile and the 10-year propagated wave series. It predicts accurately the formation moments, with positive growth rates in the correct order of magnitude for wavelengths similar to the observed ones. All these results confirm that the shoreline undulations in Dungeness are self-organized and that the underlying formation mechanism is the high-angle wave instability. The two detected formation events provide a unique opportunity to validate the existing morphodynamic models that include such instability.     

A tracer study in an Alaskan gravel beach and its implications on the persistence of the Exxon Valdez oil

Despite great efforts including bioremediation, the 1989 Exxon Valdez oil spills persist in many gravel beaches in Prince William Sound, Alaska, USA. To explore this mystery, a lithium tracer study was conducted along two transects on one of these beaches. The tracer injections and transports were successfully simulated using the 2-dimensional numerical model MARUN. The tracer stayed much longer in the oil-persisting, right transect (facing landwand) than in the clean, left transect. If the tracer is approximately regarded as oils, oils in the upper layer would have more opportunities to enter the lower layer in the right transect than in the left one. This may qualitatively explain the oil persistence within the right transect. When the tracer is regarded as nutrients, the long stay of nutrients within the right transect implies that the oil persistence along the right transect was not due to the lack of nutrients during the bioremediation.     

A preliminary study of heavy metal contamination in Yangtze River intertidal zone due to urbanization

Three short sediment cores (<20 cm) were collected in the high, middle and low tidal flats in the Yangtze River Estuary near the Southern (Nanqu) Sewage Outlet, one of the three largest sewage outlets in Shanghai, China. All samples were analyzed for Al, Cu, Pb, Zn, 210Pb and 7Be. The 210Pbxs profile shows a non-steady-state sedimentation pattern in the study area and 7Be is only found in the upper 1 cm layer of sediment in high and middle tidal flats. In this study, we found that Cu, Pb and Zn contaminants are present in the upper 20 cm of the tidal flat sediment and, after normalizing with Al, the contamination is more striking in the upper approximately 5 cm sediment. Relationships between the metal (Cu, Pb and Zn) enrichment factor and 210Pbxs activity suggest that contamination increases with time. Factor analyses shows that differences in sediment grain size have insignificant effects on Cu and Pb concentrations, but have some influence on Zn concentration in the study area. This preliminary study shows that urbanization and recent coastal wetland reclamation have had an environmental impact on this area.     

Performance of intertidal topography video monitoring of a meso-tidal reflective beach in South Portugal

This study discusses site-specific system optimization efforts related to the capability of a coastal video station to monitor intertidal topography. The system consists of two video cameras connected to a PC, and is operating at the meso-tidal, reflective Faro Beach (Algarve coast, S. Portugal). Measurements from the period February 4, 2009 to May 30, 2010 are discussed in this study. Shoreline detection was based on the processing of variance images, considering pixel intensity thresholds for feature extraction, provided by a specially trained artificial neural network (ANN). The obtained shoreline data return rate was 83%, with an average horizontal cross-shore root mean square error (RMSE) of 1.06 m. Several empirical parameterizations and ANN models were tested to estimate the elevations of shoreline contours, using wave and tidal data. Using a manually validated shoreline set, the lowest RMSE (0.18 m) for the vertical elevation was obtained using an ANN while empirical parameterizations based on the tidal elevation and wave run-up height resulted in an RMSE of 0.26 m. These errors were reduced to 0.22 m after applying 3-D data filtering and interpolation of the topographic information generated for each tidal cycle. Average beach-face slope tan(β) RMSE were around 0.02. Tests for a 5-month period of fully automated operation applying the ANN model resulted in an optimal, average, vertical elevation RMSE of 0.22 m, obtained using a one tidal cycle time window and a time-varying beach-face slope. The findings indicate that the use of an ANN in such systems has considerable potential, especially for sites where long-term field data allow efficient training.     

Dynamics of intertidal drainage channels on a multi‐barred macrotidal beach

The intertidal drainage channels on a macrotidal bar–trough (ridge‐and‐runnel) beach were monitored during a 17‐day survey. Type 1 channels were persistent, dominantly longshore systems essentially limited to the wide intertidal zone between mean high and low water neap tidal levels. The cumulative length of this channel type fluctuated as a function of topographically controlled through‐flow or flow impedance in troughs, and showed no correlation with the semi‐lunar tidal cycle. Smaller, ephemeral type 2 channels appeared as dominantly cross‐shore systems incising bars on the narrower upper and lower beach zones during spring tides. They disappeared during neap tides through infill by waves and aeolian activity. The only significant phase of type 1 channel mobility occurred during a brief moderate‐energy storm at the start of the survey. The effect of this mobility on beach morphology was inextricably linked to that of waves and currents. Meander bend migration, forced by wave‐ and longshore‐current‐induced migration of a bar during the storm, resulted in important but highly localized morphological change that was only a minor part of an irregular saw‐tooth pattern of change that affected the entire beach profile, and that was largely controlled by wave processes and longshore currents. The flow velocities in channels on this beach are too weak to generate the formation and longshore migration of high‐energy bedforms. Channel mobility and impact on beach morphology are expected to increase under storm conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Design and application of a direct-push vadose zone gravel permeameter

A borehole permeameter is well suited for testing saturated hydraulic conductivity (K(sat)) at specific depths in the vadose zone. Most applications of the method involve fine-grained soils that allow hand auguring of test holes and require a small water reservoir to maintain a constant head. In non-cohesive gravels, hand-dug test holes are difficult to excavate, holes are prone to collapse, and large volumes of water are necessary to maintain a constant head for the duration of the test. For coarse alluvial gravels, a direct-push steel permeameter was designed to place a slotted pipe at a specific sampling depth. Measurements can be made at successive depths at the same location. A 3790 L (1000 gallons) trailer-mounted water tank maintained a constant head in the permeameter. Head in the portable tank was measured with a pressure transducer and flow was calculated based on a volumetric rating curve. A U.S. Bureau of Reclamation analytical method was utilized to calculate K(sat). Measurements with the permeameter at a field site were similar to those reported from falling-head tests.     

Bathymetric control of surf zone retention on a rip-channelled beach

Simulations from a numerical model address the impact of nearshore morphology on surf zone retention on, open coast, rip-channelled beaches exposed to shore-normal waves. In the model, rip channels are regularly spaced alongshore with a given spacing λ. For a given reference case bathymetry (λ= 200 m), rip current circulations retain floating material at a hourly rate R of about 80 % which is in line with most existing field and laboratory studies in similar settings. The influence of a surf zone rip-channel morphology on surf zone retention is evaluated by a number of morphologic parameters. Results show that rip spacing is important. The ratio of the surf zone width X _s to rip spacing λ controls surf zone retention with R rapidly increasing with increasing X _s /λ up to a threshold of about 1 above which R levels off to become asymptotic to 100 %. The impact of the presence of a rip head bar is profound but nonlinear. The onset of wave breaking across the rip head bar drives a weak seaward located circulation providing major pathways for surface water exiting the surf zone compartment. Additional simulations suggest that alongshore variations in the offshore bathymetry are important. Patterns in the wave field enforced by wave refraction and potentially wave breaking across offshore bathymetric anomalies can provide a conduit for transporting floating material out of the surf zone and into the inner shelf region. This has major implications for surf zone flushing by inner-bar rips on multiple-barred beaches and on beaches facing bathymetric anomalies on the inner shelf.     

Field measurements of intertidal bar evolution on a high‐energy beach system

Nearshore bars play a pivotal role in coastal behaviour, helping to protect and restore beach systems particularly in post‐storm conditions. Examination of bar behaviour under various forcing conditions is important to help understand the short‐ to medium‐term evolution of sandy beach systems. This study carried out over a nine‐week period examines, the behaviour of three intertidal bars along a high energy sandy beach system in northwest Ireland using high‐frequency topographic surveys and detailed nearshore hydrodynamic modelling. Results show that, in general, there was onshore migration for all the bars during the study period, despite the variability observed between bars, which was driven mostly by wave dominated processes. Under the prevailing conditions migration rates of up to 1.83 m day^?1 and as low as 0.07 m day^?1 were observed. During higher wave energy events the migration rates of the bars decelerated in their onshore route, however, under lower wave energy conditions, they quickly accelerated maintaining their shoreward migration direction. Tidal influence appears to be subordinate in these conditions, being restricted to moderating the localized wave energy at low tides and in maintaining runnel configurations providing accommodation space for advancing slip faces. The study highlights the intricate behavioural patterns of intertidal bar behaviour along a high energy sandy coastline and provides new insights into the relative importance of wave and tidal forcing on bar behaviour over a relatively short time period. Copyright © 2016 John Wiley & Sons, Ltd.     

太湖北部湖区水体中浮游细菌的动态变化

2003年1月-12月对太湖北部湖区8个采样点进行了每月1次、为期一年的水体中浮游细菌数量的测定,并同步对溶解性有机碳(DOC),总氮,总磷,叶绿素a和温度进行了测定,结果表明:浮游细菌数量存在明显的季前变化和空间差异,夏秋季浮游细菌数量比冬春季高,最高值出现在夏季的7月份,平均值为7．43×106cell／ml,最低值出现在3月份,平均值为3．14×106cells／ml,最低值与最高值差异达73％;污染严重的河口区浮游细菌数量明显高于湖心区,最高值出现在河口的6#点,平均值为5.51×106cells／ml,比湖心区最低值8#点高83．2％,并呈现从河口、湾内至湖心随水体污染程度减轻而逐步递减的趋势;浮游细菌数量与温度和浮游植物量显著相关．而与水体中营养盐无关,预示着太湖水体中的营养盐已处于较高的水平,不再是浮游细菌生长的限制因素,而来源于浮游植物的有机碳可能是其生长的重要碳源．     

Frequency content of stress waves in the nearest zone of a spherical explosive source in gravel sandy soil

Zusammenfassung Bei Verfolgung der Entstehung und Formierung der durch eine explosive Kugelquelle erregten Druckwellen steht die Frage ihres Frequenzgehalts im Vordergrund. Der Frequenzgehalt dieser Wellen wurde durch die Abhängigkeit ausgedrückt (2), die die Änderungen der relativen Breite des Amplitudenspektrums (1) vom Gewicht und von der Entfernung der Quelle angibt. Aus(2) erfolgt, dass der Frequenzgehalt der Druckwellen mit wachsender Entfernung und Grösse der Ladung exponential sinkt, wobei die Steilheit dieses Abfalls für höhere Grössen der Ladung kleiner ist. Das Herabsetzen des Frequenzgehalts dieser Wellen verursacht, dass die maximate spektral Dichte in grösseren Entfernungen von der Quelle markanter wird.     

Groundwater,salt and contaminant transport in a coastal aquifer system with a low-permeability layer in the intertidal zone

Low-permeability layer (LPL), formed by natural deposit or artificial reclamation and commonly found below the intertidal zone of coastal groundwater system, can retard the ingress of seawater and contaminants, and shorten the travel time of the land-sourced contaminant to the marine environment compared with a homogenous sandy coastal aquifer. However, there is limited understanding on how an intertidal LPL, a condition occurred in a coastal aquifer at Moreton Bay, Australia, influences the groundwater and contaminant transport across the shallow beach aquifer system. We characterized the aquifer hydrological parameters, monitored the in situ groundwater heads, and constructed a 2-D numerical model to analyses the cross-shore hydrological processes in this stratified system. The calibrated model suggests that in the lower aquifer, the inland-source fresh groundwater flowed horizontally towards the sea, upwelled along the freshwater–saltwater interface, and exited the aquifer at the shore below the LPL. Whereas in the upper aquifer, the tidally driven seawater circulation formed a barrier that prevented fresh groundwater from horizontal transport and discharge to the beach above the LPL, thereby directing its leakage to the lower aquifer. A contaminant represented by a conservative tracer was ‘released’ the upper aquifer in the model and results showed that the spreading extent of the contaminant plume, the maximum rate of contaminant discharge to the ocean, and its plume length decreased compared with a simulation case in a homogenous sandy aquifer. Sensitivity analysis was also conducted to investigate the characteristics of the LPL, including its continuity and hydraulic conductivity, which were found to vary along the beach at Moreton Bay. The result shows that with a lower hydraulic conductivity and continuous layer of LPL reduced the groundwater exchange and contaminant transport between upper and lower aquifer. The findings from the combined field and modelling investigations on the impact of an intertidal LPL on coastal aquifer systems highlight its significant implications to alter the groundwater and mass transport across the land–ocean interface.     

Burying response of an intertidal gastropod to freshwater and copper contamination

The effects of sublethal concentrations of freshwater and copper on the burying responses of the intertidal marine gastropod, Polinices incei, are presented. Such responses are inhibited by both pollutants and the two also act additively. Behavioural responses obtained in a 30 min assay were found to be good predictors of the results of 96 h lethal assays. The results are discussed in light of previous work.     

Short‐term rock surface expansion and contraction in the intertidal zone

Transverse micro‐erosion meter (TMEM) stations were installed in rock slabs from shore platforms in eastern Canada. The slabs were put into artificial sea water for 1, 6 or 11 hours, representing high, mid‐ and low tidal areas, respectively. The TMEMs were used to record changes in surface elevation as the rocks dried during the remainder of the 12 h of a semi‐diurnal tidal cycle. A similar technique was used on the same rock types at intertidal TMEM stations in the field, as the rocks dried during low tide. Argillite and basalt surface contraction was from 0 to 0·04 mm: there was little surface expansion. Sandstones contracted by up to 0·03 mm in the field, but there was almost no contraction in the laboratory. Argillite and basalt contraction tended to be greatest in the upper intertidal zone, and to increase with rates of longer‐term surface downwearing, but there was little relationship with rock hardness or air temperature and humidity. Changes in elevation at the same points at TMEM stations in the laboratory and field were quite consistent from one tidal cycle to the next, but there were considerable variations within single tidal cycles between different points within each station. The data suggest that contraction within the elevational zone that is normally submerged twice a day by the tides is by alternate wetting and drying. Short‐term changes in elevation are generally low compared with annual rates of downwearing owing to erosion, but they may generate stresses that contribute to rock breakdown. Copyright © 2007 John Wiley & Sons, Ltd.     

Decadal‐scale gravel beach evolution on a tectonically‐uplifting coast: Wellington,New Zealand

Uplift of the shoreline in tectonically‐active areas can have a profound influence on geomorphology changing the entire process dynamics of the coast as the landforms are removed from the influence of the sea. Over decadal timescales it is possible for the landforms to return to their pre‐earthquake condition and this paper examines the re‐establishment of mixed sand and gravel beaches on the coast of Wellington, New Zealand, subsequent to an uplift event in 1855. Over 60 topographic profiles were surveyed, seven sets of aerial photographs from a 67 year period were mapped and sediment size analyses conducted in order to quantify the nature of beach change following uplift, and associated relative sea level fall. These data were supported by surveys using ground penetrating radar. It is found that uplift raised the gravel beaches out of the swash zone thereby removing them from the littoral zone. Intertidal rocky reefs which occur between each embayment were also uplifted during the same event and completely interrupted the longshore transport system. Continued input of gravel material to the littoral zone allowed beaches to re‐establish sequentially along the coast as each embayment was infilled with sediment. This reconnection of the embayments with the longshore drift system is associated with the beach planform being initially drift dominated during infill but then switching to swash alignment once the embayment becomes infilled. This has resulted in shoreline accretion of over 100 m in some places, at rates of up to 4 m/yr, covering shore protection works built in the past few decades. The ability of the shore to adjust back to its pre‐uplift condition appears to be a function of the accommodation space created during uplift and the rate of sediment supply. Copyright © 2012 John Wiley & Sons, Ltd.