High Tidal Range Research Articles

Submarine Groundwater Discharge at a Mega‐Tidal Beach

ABSTRACTTidally influenced groundwater systems in coastal environments represent important mixing zones of fresh groundwater and circulating seawater, manifesting as submarine groundwater discharge (SGD). Water circulation induced by tidal pumping enhances the exchange of chemicals between aquifers and coastal waters and thereby influences the biogeochemistry of coastal zones. Here, we report the results of an SGD field study conducted at a steep, mega‐tidal sand and gravel beach along the Canadian coast of the Bay of Fundy, a region with the world's highest tides (semi‐diurnal tidal ranges exceeding 10 m). Several physical and geochemical measurement techniques were employed to document the spatiotemporal SGD variability. SGD was directly sampled from seepage meters installed over multiple tidal cycles and two summer campaigns. SGD rates were estimated from tracer mass balances for radon (August 2020) and radium isotopes (July 2021) over multiple tidal cycles. Tidally averaged SGD estimates from seepage meters ranged from 12 to 87 cm d−1, with an average of 42 cm d−1, while radon tracing yielded a tidally averaged rate of 86 cm d−1. SGD estimates from radium tracing ranged from 23 to 43 cm d−1 along the shoreline and 6 to 71 cm d−1 offshore, depending on the estimated residence times. Radionuclide analyses of seepage meter waters suggest that the residence time of seawater circulation through the aquifer is less than 1 day. SGD measurements in mega‐tidal settings are rare, and the results suggest that the combination of the steep slopes, highly permeable sediments and high tidal range drive very high seepage rates for diffusive SGD. Salinity gradients in the intertidal zone demonstrate that SGD is primarily comprised of circulated seawater with negligible fresh groundwater. Although the freshwater proportion of SGD is relatively low, the large volumetric rates of total SGD can still contribute large amounts of terrestrially derived and remineralized nutrients to coastal waters.

Kandungan nitrogen saat pasang dan surut di Sungai Mahakam Kota Samarinda

This study aims to determine the levels of nitrogen compounds in the Mahakam river at high and low tide, and to compare it with the quality standard East Kalimantan Timur Regulation Number 02 0f 2011 concerning Water Quality Management and Water Pollution Control. The data obtained in the field and the results of the analysis in the laboratory are displayed in the form of tables and graphs. The data is presented based on a descriptive picture to get conclusions from the results of the study, with an independent sample t-test and compared the average between the two cases. The levels of Ammonia, Nitrite and Nitrate at high tide were significantly lower than at low tide. lower than at low tide. Ammonia levels at high tide ranged from 0.382- 0.424 mg/L, and have exceeded the quality standard threshold of regional Regulation of East Kalimantan Province Number 02 of 2011. Nitrite levels at high tide range from 0.027- 0.068 mg/L and ar low tide 0.04 - 0.068 mg/L, and still meet the quality standards of East Kalimantan Province Regulation Number 02 0f 2011.Nitrate levels at high tide range from 0.89 – 1.20 mg/L and at low tide 1.00 – 1.20 mg/L, which still meets the quality standards of East Kalimantan Province Regualation No. 01 of 2011. The levels of Ammonia, Nitrite and Nitrate at high and low tide were not significantly different.

Macroalgal cover on coral reefs: Spatial and environmental predictors, and decadal trends in the Great Barrier Reef.

Macroalgae are an important component of coral reef ecosystems. We identified spatial patterns, environmental drivers and long-term trends of total cover of upright fleshy and calcareous coral reef inhabiting macroalgae in the Great Barrier Reef. The spatial study comprised of one-off surveys of 1257 sites (latitude 11-24°S, coastal to offshore, 0-18 m depth), while the temporal trends analysis was based on 26 years of long-term monitoring data from 93 reefs. Environmental predictors were obtained from in situ data and from the coupled hydrodynamic-biochemical model eReefs. Macroalgae dominated the benthos (≥50% cover) on at least one site of 40.4% of surveyed inshore reefs. Spatially, macroalgal cover increased steeply towards the coast, with latitude away from the equator, and towards shallow (≤3 m) depth. Environmental conditions associated with macroalgal dominance were: high tidal range, wave exposure and irradiance, and low aragonite saturation state, Secchi depth, total alkalinity and temperature. Evidence of space competition between macroalgal cover and hard coral cover was restricted to shallow inshore sites. Temporally, macroalgal cover on inshore and mid-shelf reefs showed some fluctuations, but unlike hard corals they showed no systematic trends. Our extensive empirical data may serve to parameterize ecosystem models, and to refine reef condition indices based on macroalgal data for Pacific coral reefs.

Erosion-accretion pattern in the tidal-rivers of Indian Sundarban in relation to estuarine hydrodynamics

Mapping the changes in the deltaic-coastal zone under changing hydrodynamic conditions is crucial for developing a concise picture of coastal vulnerability. The present study provides a comprehensive idea of changing scenario of rivers in the world's largest delta-Sundarban, using a variety of remotely sensed data and measurements, and relating these changes to hydrodynamic conditions. Bathymetric changes have also been estimated using Landsat imageries, calibrated with bathymetric chart data. We document a substantial dynamic variation between western and eastern sections of the Sundarban tidal rivers, as well as between the northern and southern parts. As such, banks adjoining the Saptamukhi and Thakuran rivers in the west have accreted by +43.48 ​km2 and +6.13 ​km2 respectively, while the net change in the eastern rivers like Matla, Gosaba, and Hariabhanga river systems shows a loss of −51.54 km2, –13.92 km2, and –13.82 km2, respectively, over the last century. Erosion rates have decreased from the southern seafront zone to the northern interior parts due to the low wave exposure, and high tidal range. The accretion rate has increased on the same ground. The depth of these rivers has also changed significantly. For instance, the depth of most sections along the Thakuran river has increased from 5 to 7 m to about 7–10 m during the period 1987–2016. The findings of this study will help researchers all around the world in understanding the centurial dynamics of tidal rivers, and by comparing these to other deltas, it will be possible to emphasize the relative vulnerability of major deltas to current sea level rise.

A Case Study of Tidal Analysis Using Theory-Based Artificial Intelligence Techniques for Disaster Management in Taehwa River, South Korea

Monitoring tidal dynamics is imperative to disaster management because it requires a high level of precision to avert possible dangers. Good knowledge of the physical drivers of tides is vital to achieving such a precision. The Taehwa River in Ulsan City, Korea experiences tidal currents in the estuary that drains into the East Sea. The contribution of wind to tide prediction is evaluated by comparing tidal predictions using harmonic analysis and three deep learning models. Harmonic analysis is conducted on hourly water level data from 2010–2021 using the commercial pytides toolbox to generate constituents and predict tidal elevations. Three deep learning models of long short-term memory (LSTM), gated recurrent unit (GRU), and bi-directional lstm (BiLSTM) are fitted to the water level and wind speed to evaluate wind and no-wind scenarios. Results show that Taehwa tides are categorized as semidiurnal tides based on a computed form ratio of 0.2714 in a 24-h tidal cycle. The highest tidal range of 0.60 m is recorded on full moon spring tide indicating the significant lunar pull. Wind effect improved tidal prediction NSE of optimal LSTM model from 0.67 to 0.90. Knowledge of contributing effect of wind will inform flood protection measures to enhance disaster preparedness.

Physical controls and a priori estimation of raising land surface elevation across the southwestern Bangladesh delta using tidal river management

Abstract. The Ganges–Brahmaputra–Meghna delta in Bangladesh is one of the largest and most densely populated deltas in the world and is threatened by relative sea level rise (RSLR). Renewed sediment deposition through tidal river management (TRM), a controlled flooding with dike breach, inside the lowest parts of the delta polders (so-called beels) can potentially counterbalance the RSLR. The potential of TRM application in different beels across southwestern Bangladesh has been estimated previously but requires further exploration. Neither the seasonal and spatial variations in physical drivers nor the non-linear character of physical drivers and several sensitive parameters for sediment deposition have been taken into account so far. We used a 2D morphodynamic model to explore the physical controls of the following five parameters on the total sediment deposition inside the beels during TRM: river tidal range (TR), river suspended sediment concentration (SSC), inundation depth (ID), width of the inlet (IW), and surface area of the beel (BA). Our model results indicate that these five parameters and their interactions are significant for sediment deposition per day (SPD), where SSC and BA have a high impact, TR and ID have a moderate impact, and IW has a low impact on sediment deposition. Non-linear regression models (NLMs) were developed using the results of 2D models to quantify how sediment deposition inside the beels depends on these parameters. The NLMs have an average coefficient of determination of 0.74 to 0.77. Application of the NLMs to 234 beels in southwestern Bangladesh indicates that TRM operation in beels located closer to the sea will retain more sediment as a result of decreasing SSC further inland. Lower average land surface elevation is one of the reasons that the beels in the western part retain more sediment. Smaller beels have a higher potential to raise the land surface elevation due to the non-linear increase in sediment deposition per day (SPD) with beel area. Compartmentalization of larger beels may increase their potential to raise the land surface elevation. Thus, the length of time of the TRM application in a cyclic order will need to vary across the delta from 1 to multiple years to counterbalance RSLR, depending on the current beel land surface elevation and local TRM sediment accumulation rates. We found that operating TRM only during the monsoon season is sufficient to raise the land surface in 96 % and 80 % of all beels by more than 3 and 5 times the yearly RSLR, respectively. Applying TRM only seasonally offers huge advantages as to keeping the land available for agriculture during the rest of the year. The methodology presented here, applying regression models based on 2D morphodynamic modeling, may be used for the low-lying sinking deltas around the world to provide an a priori estimation of sediment deposition from controlled flooding to counterbalance RSLR.

Spatio-temporal variability of the salinity intrusion, mixing, and estuarine turbidity maximum in a tide-dominated tropical monsoon estuary

The hydrodynamic processes of tropical estuaries in developing Asian countries are rarely reported due to their complex shape, high tidal range, long monsoon season with high river flows, and lack of infrastructure and technology. Therefore, this study investigates the seasonal and neap-spring tidal variability of salinity intrusion, mixing and formation of estuarine turbidity maximum (ETM) in a multi-branched estuarine system, Tanintharyi River estuary, Myanmar during the neap-spring tidal cycle in both dry and wet seasons of 2019. The salinity intrusion, mixing and ETM in the estuary exhibited both spatial and temporal (neap-spring tidal and seasonal) variability. The ETM zone was located at the high salinity region during the dry season whereas it was located at the low salinity region during the wet season. Hence, the ETM zones are not associated with a singular salinity, which is a different phenomenon that has been previously reported in tide-dominated estuaries. The spatial variability of salinity intrusion, mixing, and ETM in different branches at the same time during each season can be attributed to the effect of the length and shape of each branch. Finally, these hydrodynamic processes in the estuary were influenced by the strong tidal flow during the dry season whereas the river flow slightly dominated the tidal flow during the wet season.

An assessment of coastal vulnerability using geospatial techniques

The Sundarbans, a UNESCO world heritage site, is of immense importance for its ecological and economic utilities. This paper attempts to identify, assess and classify the degree of vulnerability along the 269 km coastal stretches of Indian Sundarbans using GIS-based composite index. This study implies five physical and one social variable (geomorphology, regional elevation, absolute sea level rise, erosion-accretion, tidal range and population density) for calculating Coastal Vulnerability Index (CVI). The results indicate that nearly half of the coastlines (114 km) are under moderate to very high vulnerability regime. Inhabited mouzas like Beguakhali and Sibpur are found to be highly vulnerable on account of its high population densities, reclaimed coastline, moderate elevation, moderate erosion and medium tidal range. Lower elevation and higher rate of sea level rise were responsible for high vulnerability in uninhabited islands like Bhangadauni, Gosaba-E, Island-2 and Harin-W. Among the geomorphic categories, supra-tidal areas mostly belong to the high vulnerability category. This study provides valuable information to the decision makers and planners for understanding the problems and formulating suitable management strategies for this area. It also clarifies the major forcing factors and concludes that prioritization should be done based on relative importance, even if complete management is not feasible.

Different coastal marsh sites reflect similar topographic conditions under which bare patches and vegetation recovery occur

Abstract. The presence of bare patches within otherwise vegetated coastal marshes is sometimes considered to be a symptom of marsh dieback and the subsequent loss of important ecosystem services. Here we studied the topographical conditions determining the presence and revegetation of bare patches in three marsh sites with contrasting tidal range, sediment supply, and plant species: the Scheldt estuary (the Netherlands), Venice lagoon (Italy), and Blackwater marshes (Maryland, USA). Based on GIS (geographic information system) analyses of aerial photos and lidar imagery of high resolution (≤2×2 m pixels), we analyzed the topographic conditions under which bare patches occur, including their surface elevation, size, distance from channels, and whether they are connected or not to channels. Our results demonstrate that, for the different marsh sites, bare patches can be connected or unconnected to the channel network and that there is a positive relationship between the width of the connecting channels and the size of the bare patches, in each of the three marsh sites. Further, pixels located in bare patches connected to channels occur most frequently at the lowest elevations and farthest distance from the channels. Pixels in bare patches disconnected from channels occur most frequently at intermediate elevations and distances from channels, and vegetated marshes dominate at highest elevations and shortest distances from channels. In line with previous studies, revegetation in bare patches is observed in only one site with the highest tidal range and highest sediment availability, and it preferentially occurs from the edges of small unconnected bare patches at intermediate elevations and intermediate distances from channels. Although our study is only for three different marsh sites with large variations in local conditions, such as tidal range, sediment availability, and plant species, it suggests that similar topographic conditions determine the occurrence of bare patches. Such insights may inform decision makers on coastal marsh management on where to focus monitoring of early signatures of marsh degradation.

The importance of weather and tides on the resuspension and deposition of microphytobenthos (MPB) on intertidal mudflats

Abiotic variables, such as weather and tidal forces, are potentially as important as biotic factors (growth, predation, competition) in driving the variability of microphytobenthic (MPB) biomass on intertidal flats. Patterns of spatial distribution and temporal variability in MPB Chl. a, sediment Extracellular Polymeric Substances (EPS) and benthic diatom species composition were investigated during daily sampling spanning neap to spring tide periods on intertidal mudflats in the Colne Estuary, U.K., in three different seasons, with a particular focus on the influence of wind, rainfall, sun hours in the days prior to sampling, and tidal range. Spatial distribution (at < 1 m and <5 m scales) made the greatest contribution to biomass variability, followed by temporal (inter-monthly) variability. MPB Chl. a and EPS concentrations were positively correlated with sun-hours and tidal range, and negatively with rainfall and wind speed. Higher benthic MPB biomass was associated with lower suspended solid and Chl a loads, indicating biostabilisation of surface sediment. Suspended sediment loads and suspended Chl. a concentrations were positively correlated, and were significantly higher during neap rather than spring tides. Sediment settlement rates were higher during neap tides and related to suspended sediment load. The percent similarity in the benthic and suspended diatom assemblages (species relative abundance, RA) increased linearly with suspended solid load, with highest similarity during neap tides, with pennate benthic diatom taxa (Gyrosigma balticum, G. scalproides and Pleurosigma angulatum) dominant, indicating local sediment resuspension. During Spring tides, species similarity was lower, with a higher RA of planktonic centric diatoms (Actinoptychus, Coscinodiscus and Odontella) and lower sediment loads. Despite greater volumes of water movement during high tidal range periods, the highest levels of localised resuspension and remobilisation of MPB biomass across the mudflats occurred during low tidal range neap tide periods, when wind-induced waves were a key factor, particularly with shallower water depths over the intertidal mudflats.

Spatial Variation in Coastal Dune Evolution in a High Tidal Range Environment

Coastal dunes have global importance as ecological habitats, recreational areas, and vital natural coastal protection. Dunes evolve due to variations in the supply and removal of sediment via both wind and waves, and on stabilization through vegetation colonization and growth. One aspect of dune evolution that is poorly understood is the longshore variation in dune response to morphodynamic forcing, which can occur over small spatial scales. In this paper, a fixed wing unmanned aerial vehicle (UAV), is used to measure the longshore variation in evolution of a dune system in a megatidal environment. Dune sections to the east and west of the study site are prograding whereas the central portion is static or eroding. The measured variation in dune response is compared to mesoscale intertidal bar migration and short-term measurements of longshore variation in wave characteristics during two storms. Intertidal sand bar migration is measured using satellite imagery: crescentic intertidal bars are present in front of the accreting portion of the beach to the west and migrate onshore at a rate of 0.1–0.2 m/day; episodically the eastern end of the bar detaches from the main bar and migrates eastward to attach near the eastern end of the study area; bypassing the central eroding section. Statistically significant longshore variation in intertidal wave heights were measured using beachface mounted pressure transducers: the largest significant wave heights are found in front of the dune section suffering erosion. Spectral differences were noted with more narrow-banded spectra in this area but differences are not statistically significant. These observations demonstrate the importance of three-dimensionality in intertidal beach morphology on longshore variation in dune evolution; both through longshore variation in onshore sediment supply and through causing longshore variation in near-dune significant wave heights.

Application of Structure-from-Motion Terrestrial Photogrammetry to the Assessment of Coastal Cliff Erosion Processes in SW Spain

Del Río, L.; Posanski, D.; Gracia, F.J. and Pérez-Romero, A.M., 2020. Application of structure-from-motion terrestrial photogrammetry to the assessment of coastal cliff erosion processes in SW Spain. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1057–1061. Coconut Creek (Florida), ISSN 0749-0208.The episodic and irregular nature of cliff changes makes their assessment a challenging task, essential in order to cope with risks related to cliff erosion. In this work, structure-from-motion terrestrial photogrammetry was used to measure erosion processes in the Torre Bermeja cliff in SW Spain, where cliff instability poses a threat to people walking along the fronting beach. Two sites were investigated on 14 photogrammetric surveys conducted along a 9-month period in order to detect morphological changes in relation to external forces. The erosive events at both sites showed a strong episodic character, with some short periods reflecting intensive erosion and long periods of stability. Average figures for the observation period indicate a mean retreat of 2.8 mm/day at one of the sites and 0.5 mm/day at the other site. The differences were attributed to variations in the lithology and a higher wave exposure of the first site, due to a smaller fronting beach. A comparison of erosion and meteorological data of the survey period showed a positive correlation between mean retreat and maximum rainfall intensity. However, the storms with highest wave heights did not significantly affect the cliff foot, as most wave-related erosion occurred when a modal storm coincided with a high spring tidal range. Therefore, rainfall can be considered as the trigger for most of the erosion events at the study site, although the unstable conditions required for large-scale collapses are generated by wave attack in the first place. In this respect, it is assumed that climate change will lead to higher retreat rates in the investigated cliff, due to a rising mean sea level and a higher frequency of heavy rainfall events.

The hydrodynamics of the Bons Sinais Estuary: The value of simple hydrodynamic tidal models in understanding circulation in estuaries of central Mozambique

The Bons Sinais Estuary, located in the central Mozambique, with the highest tidal range in the Western Indian Ocean, is shallow (∼10m), long (∼28km) and receives freshwater only during the wet season. These characteristics give the Estuary distinctive hydrodynamics and ecological features. Current measurements and longitudinal CTD profiling were carried out during dry season, July 2011 and November 2012, and wet season, February 2012 and March 2013. The Estuary is partially to well-mixed most of the time, with Simpson Number (Si) ≤0.5. One-D, depth and width integrated, tidal hydrodynamic model, forced by the modelled tides at the mouth, was applied to understand the major mechanisms governing the estuarine dynamics. Barotropic forcing dominated the baroclinic pressure gradient forcing and the currents were found to be mostly tidal driven. Accordingly, the hydrodynamic model described the observed current velocities well in the dry season (R2≈0.95) and to a lesser degree in the wet season (R2≈0.80). The remaining 5%–20% may be attributed to other hydrodynamic forcing that were not captured in the tidal model, requiring further investigation at higher temporal and spatial scales to fully characterize the system dynamics. These may include the identified baroclinic forcing from freshwater inputs and the influence of the complex geometry at the study site. The initial hydrodynamic field study and simple modelling approach that was applied may inform studies of higher-order processes and management tools at the Bons Sinais Estuary, and similar systems (e.g. sediment dynamics and accommodation space, and diagnostic models), and the result can contribute to understanding the drivers of longer-term ecological and geomorphological dynamics of the estuary.

Characteristics and context of high-energy, tidally modulated, barred shoreface deposits: Kimmeridgian–Tithonian sandstones, Weald Basin, southern U.K. and northern France

ABSTRACTThe influence of tides on the sedimentology of wave-dominated shorefaces has been emphasized in recent studies of modern shorelines and related facies models, but few ancient examples have been reported to date. Herein, we use a case study from the stratigraphic record to develop a revised facies model and predictive spatio-temporal framework for high-energy, tidally modulated, wave-dominated, barred shorefaces.Kimmeridgian–Tithonian shallow-marine sandstones in the Weald Basin (southern England and northern France) occur as a series of laterally extensive tongues that are 5–24 m thick. Each tongue coarsens upward in its lower part and fines upward in its upper part. The lower part of each upward-coarsening succession consists of variably stacked, hummocky cross-stratified, very fine- to fine-grained sandstone beds and mudstone interbeds that are moderately to intensely bioturbated by a mixed Skolithos and Cruziana Ichnofacies. This lower part of the succession is interpreted to record deposition on the subtidal lower shoreface, between effective storm wave base and fairweather wave base. The upper part of each upward-coarsening succession comprises cross-bedded, medium- to coarse-grained sandstones that are pervasively intercalated with mudstone-draped, wave-rippled surfaces (including interference ripples) which mantle the erosional bases of trough cross-sets. Bioturbation is patchy, and constitutes a low-diversity Skolithos Ichnofacies. Cross-bedded sandstones are arranged into cosets superimposed on steeply dipping (up to 10°) clinoforms that dip offshore and alongshore, and extend through the succession. These deposits are interpreted to record shallow subtidal and intertidal bars on the upper shoreface, which likely contained laterally migrating rip channels or formed part of a spit. The lower, upward-coarsening part of each sandstone tongue represents an upward-shallowing, regressive shoreface succession in which the internal bedding of upper-shoreface sandstones was modulated by tidal changes in water depth. The upper, upward-fining part of each sandstone tongue typically comprises an erosionally based bioclastic lag overlain by subtidal lower-shoreface deposits, and constitutes an upward-deepening succession developed during transgression.Regressive–transgressive sandstone tongues fringe the northeastern margin of the basin, which was exposed to an energetic wave climate driven by westerly and southwesterly winds with a fetch of 200–600 km. The high tidal range interpreted from the shoreface sandstone tongues is attributed to resonant amplification in a broad (150–200 km), shallow (18–33 m) embayment as the tidal wave propagated from the Tethys Ocean into the adjacent intracratonic Laurasian Seaway, of which the Weald Basin was a part.

Tidal Current Energy Resource Distribution in Korea

Korea is a very well-known country for having abundant tidal current energy resources. There are many attractive coastal areas for the tidal current power that have very strong currents due to the high tidal range and the acceleration through the narrow channels between islands in the west and south coasts of the Korean peninsula. Recently, the Korean government announced a plan that aims to increase the portion of electricity generated from renewable energy to 20% by 2030. Korea has abundant tidal current energy resources; however, as reliable resource assessment results of tidal current energy are not sufficient, the portion of tidal current power is very small in the plan. Therefore, a reliable resource assessment should be conducted in order to provide a basis for the development plan. This paper describes the resource assessment of tidal current energy in Korea based on the observational data provided by KHOA (Korean Hydrographic and Oceanographic Agency) and numerical simulation of water circulation. As the observational data were unable to present the detailed distribution of the complicated tidal current between islands, numerical simulation of water circulation was used to describe the detailed distribution of tidal current in Incheon-Gyeonggi and Jeollanam-do, where the tidal energy potentials are abundant. The west and south coastal areas of Korea were divided into seven regions according to the administrative district, and the theoretical tidal current potential was calculated using average power intercepted. The results of this research can provide the insight of the tidal current energy development plan in Korea.

Study of high tide level changes in estuary area in response to coastline deformation in Wenzhou Bay

Wenzhou Bay, which is located in the southern coast of China with rich tidal flat resources, is frequently influenced by human activities, leading coastline deformation and high tide level changes in estuary area. A two-dimensional tidal numerical model of high resolution including Wenzhou Bay and East China Sea was established based on the MIKE21 FM model. The model was calibrated with field data and then was employed to predict high tide level changes under the development plan of coastline deformation. According to the simulating results, high tide level and tidal range in the Ou River and the Feiyun River estuary area will decrease about 0.01~0.13 m and 0.01~0.18 m, whether in dry season or flood season. Further analysis from tide wave point illustrates that weaken of the tidal system outside estuary area will occur after the coastline deformation. The direction of tidal propagation will change from vertical to parallel to coastline, causing weaken reflection, leading to the decreases of tidal range and high tidal level.

A two-point in situ method for simultaneous analysis of radioactivity in seawater and sediment

A new in situ radioactivity analysis method was developed to determine the fractional contributions of gamma-ray emitters in seawater and sediment from total measured counts. A semi-empirical formula to determine the fractional count contributions was derived using the variation characteristics of the gamma-ray attenuation rate and geometrical efficiency with the measurement points. The proposed method was employed to make in situ gamma-ray measurements using a CeBr3 detector for radioactivity analysis of seawater and sediment at a coastal area with a relatively high tidal range. The full energy peak efficiency of the detector at measurement site was obtained using the GEANT4 simulation code. The radioactivity concentration of 40K in seawater and sediment was determined using the proposed method and laboratory analysis with sampling. The MDA of the in situ measurement for 137Cs and 131I was also estimated assuming they were deposited on the sediment surface-layer. The validation of this method was demonstrated by comparing with the sampling analysis results.

Karakteristik Hidrooseanografi di Perairan Pesisir Kabupaten agam

The research objectives to explore the characteristic of hydrooceanography in coastal of Agam Regency. The observations parameters included physical aspecs such as bathymetric, tide, wave, water current, Transparancy, and temperature; and so chemical aspecs such as pH, salinity, dissolved oxygen, and COD. Hydrooseanographic characteristics on Agam Regency coastal described the bathymetry was shallow to deep , high wave, high tidal range, water currents dependent on season, and water quality were in good criteria to life support of aquatic biota. Key words: Hydrooceanography, wave, tidal, water quality

Monitoring Retreat of Coastal Sandy Systems Using Geomatics Techniques: Somo Beach (Cantabrian Coast, Spain, 1875–2017)

The dynamics and evolution of a coastal sandy system over the last 142 years (1875–2017) were analyzed using geomatics techniques (historical cartography, photogrammetry, topography, and terrestrial laser scanning (TLS)). The continuous beach–dune system is a very active confining sand barrier closing an estuarine system where damage is suffered by coastal infrastructures and houses. The techniques used and documentary sources involved historical cartography, digitalizing the 5-m-level curve on the maps of 1875, 1908, 1920, 1950, and 1985; photogrammetric flights of 1985, 1988, and 2001 without calibration certificates, digitalizing only the upper part of the sandy front; photogrammetric flights of 2005, 2007, 2010, and 2014, using photogrammetric restitution of the 5-m-level curve; topo-bathymetric profiles made monthly between 1988 and 1993 using a total station; a terrestrial laser scanner (TLS) since 2011 by means of two annual measurements; and the meteorological data for the period of 1985–2017. The retreat of the sandy complex was caused by winter storms with large waves and swells higher than 6 m, coinciding with periods demonstrating a high tidal range of over 100 and periods with a large number of strong storms. The retreat was 8 m between December 2013 and March 2014. The overall change of the coastline between 1875 and 2017 was approximately 415 m of retreat at Somo Beach. The erosive processes on the foredune involved the outcrop of the rock cliff in 1999 and 2014, which became a continuous rocky cliff without sands. To know the recent coastal evolution and its consequences on the human environment, the combined geomatic techniques and future TLS data series may lead to the improvement in the knowledge of shoreline changes in the context of sea level and global changes.

Carbon stocks of mangroves and salt marshes of the Amazon region, Brazil.

In addition to the largest existing expanse of tropical forests, the Brazilian Amazon has among the largest area of mangroves in the world. While recognized as important global carbon sinks that, when disturbed, are significant sources of greenhouse gases, no studies have quantified the carbon stocks of these vast mangrove forests. In this paper, we quantified total ecosystem carbon stocks of mangroves and salt marshes east of the mouth of the Amazon River, Brazil. Mean ecosystem carbon stocks of the salt marshes were 257 Mg C ha-1 while those of mangroves ranged from 361 to 746 Mg C ha-1 Although aboveground mass was high relative to many other mangrove forests (145 Mg C ha-1), soil carbon stocks were relatively low (340 Mg C ha-1). Low soil carbon stocks may be related to coarse textured soils coupled with a high tidal range. Nevertheless, the carbon stocks of the Amazon mangroves were over twice those of upland evergreen forests and almost 10-fold those of tropical dry forests.