Dynamic Coastal Regions Research Articles

Assessment of erosion-accretion patterns, land dynamics, and climate change impacts on the islands of the south-central coastal zone of Bangladesh using remote sensing techniques

This study investigates morphological changes, erosion-accretion patterns, and climate change impacts on Bangladesh’s dynamic coastal regions focusing on the Meghna Estuary and islands like Sandwip, Urir Char, and Swarna Dweep. Using remote sensing and GIS techniques, the research analyzes short-term (5-year) and long-term (30-year) changes from 1991 to 2021. Satellite imagery reveals significant erosion and accretion rates. Sandwip experienced high erosion (up to 29.48 km2 every 5 years) until 2006 but recent stability. Urir Char faced substantial erosion (up to 22.73 km2 every 5 years) until 2001 in the southeast and accretion in the north. Swarna Dweep showed minimal erosion but significant accretion. The islands exhibited migration tendencies: Swarna Dweep southeast, Sandwip northeast, and Urir Char northwest. Cyclones, including the 1991 event, Sidr, and Aila, significantly reshaped coastal morphology. Climate change impacts include increasing rainfall trends (up to 0.8572 mm/year on Sandwip), rising temperatures (up to 0.005 °C/year on Urir Char), and accelerated sea-level rise (up to 11.93 mm/year on Sandwip). The study emphasizes the importance of monitoring, coastal management, and adaptation strategies for Bangladesh’s dynamic coastline in the face of ongoing environmental changes.

Strategies for Mitigating Na and K Pollution in Marine Sediments along the Maharashtra Coast: A Comprehensive Review

Abstract: This comprehensive review delves into the intricate dynamics of heavy metal contamination, with a specific focus on sodium (Na) and potassium (K) pollution in marine sediments along the Maharashtra coast. Examining both anthropogenic and natural sources, the study emphasizes the urgency of addressing the escalating levels of Na and K in coastal ecosystems. The pivotal role of plants and their phytochemical constituents in mitigating the environmental consequences is explored, shedding light on adaptive strategies and potential interventions. Through an in-depth analysis of phytochemical adaptations, metal uptake and accumulation, rhizospheric processes, and the potential for phytoremediation, this work unravels the promising avenues for sustainable environmental management in the dynamic coastal regions.

Sea-level trends and variability along the coast of Vietnam over 2002–2018: Insights from the X-TRACK/ALES altimetry dataset and coastal tide gauges

The changes in coastal sea levels are now considered a significant concern for densely-populated coastal regions such as Vietnam, which hosts a long coastline and two large deltaic areas. In this study, we used high-resolution (20-Hz) altimetry data from the X-TRACK/ALES product to investigate the trends and variability of sea-level anomalies (SLAs) along the Vietnam coast from 2002 to 2018. We conducted comparisons of SLAs from X-TRACK/ALES with SLAs from four coastal tide gauges, and the results present a good root mean square error (0.03 m on average) and good statistically significant correlation (for p < 0.05) with an average value of 0.66. There is an exception for the Quy Nhon site (r ∼ 0.5) as its closest altimetry points lie in the open ocean. Regarding trend calculations, the tide gauge sites exhibit two-to-three times larger trends than altimetry points, indicating a significant deviation from the coast to the open ocean. We then examined the contribution of various forcing factors by stepwise regression analysis for the 2002 – 2018 and 2008–2018 periods. The stepwise model can explain the observed data in the latter period (about 63 % on average). As local factors, SST and meridional wind stress appear important, whereas PDO and ENSO are significant as remote factors, particularly at the southern sites. However, we could not find the best common forcing factors for all sites suggesting the inconsistent mechanisms causing sea-level variability along the Vietnam coast. Our study demonstrates complicated regional sea-level variability and emphasizes the benefit of high-resolution altimetry data in studying dynamic coastal regions.

Modelling the effect of the tidal cycle on the high phytoplankton biomass area of Cape Trafalgar (SW Iberian Peninsula)

Physical–biological interactions in the ocean are known to be crucial for understanding ecosystem processes. This is particularly relevant in the highly dynamic coastal regions, where the biogeochemical processes associated with higher-frequency perturbations such as tidal waves play a key role in primary production. In this study, we examine the influence of the tide-topography interaction on the high productivity area of Cape Trafalgar (NW limit of the Strait of Gibraltar, Iberian Peninsula) using a high-resolution ocean circulation model coupled to an ecosystem model. The obtained results highlight the relevance of the tidal cycle explaining the high phytoplankton biomass that characterises this region through an active and periodic forcing, resulting in a pulsating upwelling system. Our model shows that the interaction of the westward zonal component of the tidal current (uvel) with the submarine ridge (i.e., Barbate High) that characterises this region, which is perpendicular to the coast, results in the pumping of deep, cold, salty, and nutrient-rich waters to the well-illuminated subsurface waters, fuelling phytoplankton growth. At the same time, the interaction of the westward tidal current with the ridge leads to the development of a cyclonic eddy, which enables the redistribution of the upwelled waters over and to the east of Barbate High. The fortnightly tidal period has been identified as the most influential because (an effective) tidal-pumping process only takes place when the westward uvel is ∼ 0.42 m s−1, a condition attained between ∼ 3 days before and after the moment of maximum tidal flow during spring tides. Simultaneously, the energy and the associated horizontal and vertical mixing of the cyclonic gyre also vary with the tidal cycle, being stronger during spring tides. Both tidally driven processes, i.e., the cyclical upslope advection of deep nutrient-rich water and the influence of the cyclonic gyre, are the main mechanisms that lead to the development of a persistent phytoplankton-rich tongue over Barbate High. Consequently, Cape Trafalgar acts as a source of nutrient- and phytoplankton-rich waters to the surrounding waters.

Human-induced salinity changes impact marine organisms and ecosystems.

Climate change is fundamentally altering marine and coastal ecosystems on a global scale. While the effects of ocean warming and acidification on ecology and ecosystem functions and services are being comprehensively researched, less attention is directed toward understanding the impacts of human-driven ocean salinity changes. The global water cycle operates through water fluxes expressed as precipitation, evaporation, and freshwater runoff from land. Changes to these in turn modulate ocean salinity and shape the marine and coastal environment by affecting ocean currents, stratification, oxygen saturation, and sea level rise. Besides the direct impact on ocean physical processes, salinity changes impact ocean biological functions with the ecophysiological consequences are being poorly understood. This is surprising as salinity changes may impact diversity, ecosystem and habitat structure loss, and community shifts including trophic cascades. Climate model future projections (of end of the century salinity changes) indicate magnitudes that lead to modification of open ocean plankton community structure and habitat suitability of coral reef communities. Such salinity changes are also capable of affecting the diversity and metabolic capacity of coastal microorganisms and impairing the photosynthetic capacity of (coastal and open ocean) phytoplankton, macroalgae, and seagrass, with downstream ramifications on global biogeochemical cycling. The scarcity of comprehensive salinity data in dynamic coastal regions warrants additional attention. Such datasets are crucial to quantify salinity-based ecosystem function relationships and project such changes that ultimately link into carbon sequestration and freshwater as well as food availability to human populations around the globe. It is critical to integrate vigorous high-quality salinity data with interacting key environmental parameters (e.g., temperature, nutrients, oxygen) for a comprehensive understanding of anthropogenically induced marine changes and its impact on human health and the global economy.

Temporal oceanographic variation using satellite imagery data in the central Mexican Pacific convergence zone

The oceanographic variation of the central Mexican Pacific (CMP) is mainly driven by the California Current and the Mexican Coastal Current, which generate a convergence zone. Little information is available regarding changes in oceanographic variables at the mesoscale level in the CMP. Therefore, this study characterized 6 oceanographic variables (sea surface temperature, chlorophyll concentration [Chl], primary productivity [PP], diffuse attenuation coefficient [K490], and particulate inorganic/organic carbon concentration [PIC, POC]) in the CMP from 2010 to 2017 and their relationships with El Niño/Southern Oscillation (ENSO). The variables were standardized to monthly pixel values of 0.08 latitude degrees, and the study area covered 48,846.48 km2. Friedman tests were used to compare the temporal variation in the variables, while Spearman correlations were used to evaluate the relationship between each variable and the Multivariate ENSO Index (MEI). A cross-correlation analysis was performed to determine the temporal lag between the oceanographic variables and the MEI. The cyclicity of the variation in the CMP was determined by spectral analysis. All variables showed significant differences between months and years. Two seasons defined by temperature were also detected: a cold season (December–June), in which high values of these variables were observed, and a warm season (July–November), in which low values of these variables were observed. No variables were correlated with the MEI; however, a 4-month time lag was identified between the variables and the MEI. The cyclicity of the variables corresponded to the cold and warm seasons. The cold phase of ENSO increased the values of PP, Chl, and K490 up to 4 times compared to those of other years. Taken together, the observed variation in oceanographic conditions makes the CMP one of the most dynamic coastal regions of the Mexican Pacific.

Continuous Change Mapping to Understand Wetland Quantity and Quality Evolution and Driving Forces: A Case Study in the Liao River Estuary from 1986 to 2018

Coastal wetland ecosystems, one of the most important ecosystems in the world, play an important role in regulating climate, sequestering blue carbon, and maintaining sustainable development of coastal zones. Wetland landscapes are notoriously difficult to map with satellite data, particularly in highly complex, dynamic coastal regions. The Liao River Estuary (LRE) wetland in Liaoning Province, China, has attracted major attention due to its status as Asia’s largest coastal wetland, with extensive Phragmites australis (reeds), Suaeda heteroptera (seepweed, red beach), and other natural resources that have been continuously encroached upon by anthropogenic land-use activities. Using the Continuous Change Detection and Classification (CCDC) algorithm and all available Landsat images, we mapped the spatial–temporal changes of LRE coastal wetlands (e.g., seepweed, reed, tidal flats, and shallow marine water) annually from 1986 to 2018 and analyzed the changes and driving forces. Results showed that the total area of coastal wetlands in the LRE shrank by 14.8% during the study period. The tidal flats were the most seriously affected type, with 45.7% of its total area lost. One of the main characteristics of wetland change was the concurrent disappearance and emergence of wetlands in different parts of the LRE, creating drastically different mixtures of wetland quality (e.g., wetland age composition) in addition to area change. The reduction and replacement/translocation of coastal wetlands were mainly caused by human activities related to urbanization, tourism, land reclamation, and expansion of aquaculture ponds. Our efforts in mapping annual changes of wetlands provide direct, specific, and spatially explicit information on rates, patterns, and causes of coastal wetland change, both in coverage and quality, so as to contribute to the effective plans and policies for coastal management, preservation, and restoration of coastal ecosystem services.

Monitoring Total Suspended Sediment Concentration in Spatiotemporal Domain over Teluk Lipat Utilizing Landsat 8 (OLI)

Total suspended sediment (TSS) is a water quality parameter that is used to understand sediment transport, aquatic ecosystem health, and engineering problems. The majority of TSS in water bodies is due to natural and human factors such as brought by river runoff, coastal erosion, dredging activities, and waves. It is an important parameter that should be monitored periodically, particularly over the dynamic coastal region. This study aims to monitor spatiotemporal TSS concentration over Teluk Lipat, Malaysia. To date, there are two commonly used methods to monitor TSS concentration over wide water regions. Firstly, field sampling is known very expensive and time-consuming method. Secondly, the remote sensing technology that can monitor spatiotemporal TSS concentration freely. Although remote sensing technology could overcome these problems, universal empirical or semiempirical algorithms are still not available. Most of the developed algorithms are on a regional basis. To measure TSS concentration over the different regions, a new regional algorithm needs to develop. To do so, two field trip was conducted in the study area concurrent with the passing of Landsat 8. A total of 30 field samples were collected from 30 sampling points during the first field trip and 30 samples from 30 samplings from the second field trip. The samples were then analyzed using an established method to develop the TSS algorithm. The data obtained from the first field trip were then used to develop a regional TSS algorithm using the regression analysis technique. The developed algorithm was then validated by using data obtained from the second field trip. The results demonstrated that TSS in the study area is highly correlated with three Landsat 8 bands, namely green, near-infrared (NIR), and short-wavelength (SWIR) bands, with R2 = 0.79. The TSS map is constructed using the algorithm. Analyses of the image suggest that the highest TSSs are mainly observed along the coastal line and over the river mouth. It suggested that the main contributing factors over the study area are river runoff and wave splash.

The spatiotemporal shore morphological changes at east Bhola Island in Meghna Estuary of Bangladesh’s central coast

This article focuses on the spatiotemporal shore erosion–accretion progression of east Bhola Island, located in the Ganges-Brahmaputra-Meghna (GBM) basin at the mouth of Meghna Estuary on the central coast of Bangladesh. The erosion–accretion in this dynamic coastal region has caused significant morphological changes and frequent shoreline displacement over the last 40 years. This research analyzed 13 LANDSAT satellite images spanning from 1989 to 2018 to evaluate the shoreline change rates for the east face of Bhola Island over the four selected periods, i.e., 1989–2000, 2000–2005, 2005–2010, and 2010–2018. In general, the upstream portion of the east Bhola Island experienced a higher shore erosion rate up to −139 m/year at the northeast face, close to the confluence of the GBM Rivers. At this portion, the Island’s geometric shape caused the stability of the shore vulnerable against the ebb tide-dominated high monsoon GBM River flows. In the interim, the southeast portion of the Island near the Bay of Bengal faced a slower rate of shore erosion up to −40 m/year because the upper part of the Island provided shelter to the downstream portion that diverts and minimizes the downward GBM River outfall flow intensities towards the sea. Construction of barrages on the major upstream rivers resulted in the widening of the Bhola’s adjoining rivers through lean dry periods and increased wet season flows may be liable for a severe shoreline erosion of −171 m/year in 1989–2000. Further, higher annual rainfall and prolonged floods in 1998 and 2004 increased the shoreline erosion rate to −249 m/year from 2000 to 2005. Nevertheless, after considerable erosion from 1989 to 2005, recently implemented and ongoing shore protection works along the east face of the Island declined the erosion rate drastically to −41 m/year, while some sections achieved shore stability in the latest period of 2005–2018.

Development of livelihood vulnerability index for the coastal fishermen communities of Bangladesh using spatial information technique

The livelihood of the people in the dynamic coastal regions of Bangladesh is highly dependent on nature and thus is vulnerable to climatic events. The research study developed the Fishermen Livelihood Vulnerability Index (LVI) to measure the vulnerability of the fishing communities living in the coastal regions of Bangladesh. The weighted average method was used to measure the FLVI and the binary logistic regression was used to find out the determinants of vulnerability. The variables to measure vulnerability such as exposure, sensitivity, and adaptive capacity were taken from the IPCC climate vulnerability framework. The results, based on the findings of a survey of 164 households from 3 coastal districts (Patuakhali, Khulna & Cox's Bazar) indicated that the coastal fishing communities are more vulnerable (FLVI = 0.48) compare to the people living in other parts of Bangladesh. The study also revealed that the livelihood activities of the coastal fishermen are mainly affected by the impacts of natural disasters. Spatial maps were prepared to show the distribution of the vulnerable areas with indicating the houses according to their level of vulnerability. The study also identified the most significant factors of vulnerability. As part of the analysis, it was found that the variables that had the most significant impact on fishermen livelihood vulnerability were natural disasters, diseases due to climate change, NGO and microcredit, income, and piracy problem. The study also identified that vulnerability factors are highly influenced by spatial characteristics and thereby identification of location specific factors is crucial in assessing and calculating vulnerability score. The study concluded that if location specific fishermen vulnerability factors are identified after certain interval with the active engagement of local communities can generate valuable information for developing appropriate strategy to secure their livelihood in a sustainable way.

AMPHIBIAN DISTRIBUTION IN THE GEORGIA SEA ISLANDS: IMPLICATIONS FROM THE PAST AND FOR THE FUTURE

We summarized amphibian distributions for 12 coastal islands in Georgia, USA. Occurrence among islands was correlated with life history traits, habitats, island size, distance to other islands, and island geological age. Species’ distributions were determined from published literature. Island sizes and vegetation types were derived from 2011 Georgia Department of Natural Resources habitat maps, which included both federal and state vegetation classification systems. Species occurring on more islands tended to have greater total reproductive output (i.e., life span &gt;4 years, and annual egg production &gt;1,000 eggs) and adults had tolerance of brackish environs. Larger islands had great­er area of freshwater wetlands, predominantly short hydroperiod (&lt;6 months). Species tied to long hydroperiod wetlands (&gt;6 months) were more restricted in their distribution across islands. Overall, larger islands supported more species, but the correlation was weaker for geologically younger Ho­locene islands (age &lt;11,000 years). While Euclidean distance between islands does not necessarily preclude inter-island dispersal, inhospitable habitat for amphibians (brackish tidal marshes and creeks interspersed with wide rivers) suggests that inter-island dispersal is very limited. The paucity of recent occurrence data for amphibians in this dynamic coastal region, let alone standardized annual moni­toring data, hinders efforts to model species’ vulnerability in a region susceptible to sea level rise and development pressure. The most common survey method, standardized amphibian vocal surveys, will detect Anuran reproductive efforts, but is unlikely to ascertain if breeding was successful or to detect salamanders. While it will not replace actual population data, consideration of critical life-history traits and breeding habitat availability can be used to direct management to support long-term species per­sistence in changing environs. Even common amphibians in coastal conservation areas of Georgia are vulnerable to increasing population isolation caused by unsuitable habitat.

Compact Open-Path Sensor for Fast Measurements of CO2 and H2O using Scanned-Wavelength Modulation Spectroscopy with 1f-Phase Method.

We report here the development of a compact, open-path CO2 and H2O sensor based on the newly introduced scanned-wavelength modulation spectroscopy with the first harmonic phase angle (scanned-WMS-θ1f) method for high-sensitivity, high temporal resolution, ground-based measurements. The considerable advantage of the sensor, compared with existing commercial ones, lies in its fast response of 500 Hz that makes this instrument ideal for resolving details of high-frequency turbulent motion in exceptionally dynamic coastal regions. The good agreement with a commercial nondispersive infrared analyzer supports the utility and accuracy of the sensor. Allan variance analysis shows that the concentration measurement sensitivities can reach 62 ppb CO2 in 0.06 s and 0.89 ppm H2O vapor in 0.26 s averaging time. Autonomous field operation for 15-day continuous measurements of greenhouse gases (CO2/H2O) was performed on a shore-based monitoring tower in Daya Bay, demonstrating the sensor’s long-term performance. The capability for high-quality fast turbulent atmospheric gas observations allow the potential for better characterization of oceanographic processes.

A New Approach for Estimating Soil Salinity Using A Low-Cost Soil Sensor In Situ: A Case Study in Saline Regions of China’s East Coast

Accurate and timely information on soil salinity is crucial for vegetation growth and agricultural productivity in coastal regions. This study investigates the potential of using Wifi POGO, an in situ electromagnetic sensor, for soil salinity assessment over saline coastal regions in eastern China. The sensor readings, soil moisture, and temperature-corrected apparent electrical conductivity (ECa) were used to generate models for EC1:5 (a surrogate for soil salinity) estimation. Two salty areas with distinct soil textures, sandy loam (Shuntai) and clay (Dongxin), were selected. This study revealed that the difference between soil salinity and the in situ measured soil ECa (i.e., EC1:5-ECa) had a strong curvilinear relationship with soil moisture. Such a relationship allows for the direct estimation of soil salinity from soil ECa with the aid of soil moisture information. Both ECa and soil moisture can be measured in situ using a Wifi POGO, a low-cost ground-based soil sensor. By using the leave-one-out cross-validation (LOOCV), the achieved root mean square error (RMSE) and relative RMSE (RRMSE) in EC1:5 estimation were 0.0109 S/m and 19.24% respectively in Shuntai, and 0.0157 S/m and 16.05%, in Dongxin. This new method offers a simple, cost-effective and reliable tool for assessing soil salinity in dynamic coastal regions.

Seasonal dynamics of carbonate chemistry, nutrients and CO2 uptake in a sub-Arctic fjord

Environmental change can have a significant impact on biogeochemical cycles at high latitudes and be particularly important in ecologically valuable fjord ecosystems. Seasonality in biogeochemical cycling in a sub-Arctic fjord of northern Norway (Kaldfjorden) was investigated from October 2016 to September 2018. Monthly changes in total inorganic carbon (CT), alkalinity (AT), major nutrients and calcium carbonate saturation (Ω) were driven by freshwater discharge, biological production and mixing with subsurface carbon-rich coastal water. Stable oxygen isotope ratios indicated that meteoric water (snow melt, river runoff, precipitation) had stratified and freshened surface waters, contributing to 81% of the monthly CT deficit in the surface layer. The timing and magnitude of freshwater inputs played an important role in Ω variability, reducing AT and CT by dilution. This dilution effect was strongly counteracted by the opposing effect of primary production that dominated surface water Ω seasonality. The spring phytoplankton bloom rapidly depleted nitrate and CT to drive highest Ω (~2.3) in surface waters. Calcification reduced AT and CT, which accounted for 21% of the monthly decrease in Ω during a coccolithophore bloom. Freshwater runoff contributed CT, AT and silicates of terrestrial origin to the fjord. Lowest surface water Ω (~1.6) resulted from organic matter remineralisation and mixing into subsurface water during winter and spring. Surface waters were undersaturated with respect to atmospheric CO2, resulting in modest uptake of –0.32 ± 0.03 mol C m–2 yr–1. Net community production estimated from carbon drawdown was 14 ± 2 g C m–2 yr–1 during the productive season. Kaldfjorden currently functions as an atmospheric CO2 sink of 3.9 ± 0.3 g C m–2 yr–1. Time-series data are vital to better understand the processes and natural variability affecting biogeochemical cycling in dynamic coastal regions and thus better predict the impact of future changes on important fjord ecosystems.

The application of data innovations to geomorphological impact analyses in coastal areas: An East Anglia, UK, case study

Rapidly advancing surveying technologies, capable of generating high resolution bathymetric and topographic data, allow precise measurements of geomorphological change and deformation. This permits great accuracy in the characterisation of volumetric change, sediment and debris flows, accumulations and erosion rates. However, such data can be utilised inadequately by coastal practitioners in their assessments of coastal change, due to a lack of awareness of the appropriate analytical techniques and the potential benefits offered by such data-driven approaches. This was found to be the case for the region of East Anglia, UK, which was analysed in this study. This paper evaluates the application of innovative geomorphological change detection (GCD) techniques for analysis of coastal change. The first half of the paper contains an extensive review of GCD methods and data sources used in previous studies. This leads to the selection and recommendation of an appropriate methodology for calculation of volumetric GCD, which has been subsequently applied and evaluated for 14 case study sites in East Anglia. This has involved combining open source point cloud datasets for broad spatial scales, covering an extended temporal period. The results comprise quantitative estimates of volumetric change for selected locations. This allows estimation of the sediment budgets for each stretch of coastline focused upon, revealing fluctuations in their rates of change. These quantitative results were combined with qualitative outputs, such as visual representations of change and we reveal how combining such methods assists identification of patterns and impacts linked to specific events. The study demonstrates how high-resolution point cloud data, which is now readily available, can be used to better inform coastal management practices, revealing trends, impacts and vulnerability in dynamic coastal regions. The results also indicate heterogeneous impacts of events, such as the 2013 East Coast Storm Surge, across the study area of East Anglia.

Net Community Production in a Productive Coastal Ocean From an Autonomous Buoyancy‐Driven Glider

AbstractNet community production (NCP), an analog of carbon export out of the surface ocean, is often estimated using budgets of dissolved oxygen. Accurate estimates of oxygen‐based NCP, especially in dynamic coastal regions, require constraints on vertical transport of water with O2 out of equilibrium with the atmosphere, nonsteady state change in the oxygen inventory, heating/cooling‐driven O2 disequilibrium, and the rate of bubble injection from wave activity. The latter two are typically evaluated by using discrete measurements of the O2/Ar ratio in lieu of O2 only. Because sophisticated sampling and measurement techniques are required to make these measurements, they are often limited in spatiotemporal resolution. However, high‐resolution estimates of NCP may be useful in determining small‐scale patchiness in export. In this study, we calculated high‐resolution NCP in coastal Southern California using dissolved oxygen measurements made by an autonomous buoyancy‐driven Slocum glider and an empirical relationship derived using discrete measurements of O2/Ar in the surface mixed layer to remove the influence of bubble injection, which accounted for approximately one fourth of the O2 supersaturation observed. Using estimates of vertical transport from wind speed‐based parameterizations, previously validated using a 7Be budget, we were able to correct for the physical biases to the signal, which are known to significantly influence dissolved oxygen budgets in this region. Our results agree well with previously published NCP estimates for the study area but also reveal higher‐frequency variability that discrete sampling was unable to resolve, suggesting that this approach may be useful in other regions with well‐constrained vertical transport rates.

Environmental Feature Exploration With a Single Autonomous Vehicle

In this paper, a sliding mode-based guidance strategy is proposed for the control of an autonomous vehicle. The aim of the autonomous vehicle deployment is the study of unknown environmental spatial features. The proposed approach allows the solution of both boundary tracking and source-seeking problems with a single autonomous vehicle capable of sensing the value of the spatial field at its position. The movement of the vehicle is controlled through the proposed guidance strategy, which is designed on the basis of the collected measurements without the necessity of preplanning or human intervention. Moreover, no a priori knowledge about the field and its gradient is required. The proposed strategy is based on the so-called suboptimal sliding mode controller. The guidance strategy is demonstrated by computer-based simulations and a set of boundary tracking experimental sea trials. The efficacy of the algorithm to autonomously steer the C-Enduro surface vehicle to follow a fixed depth contour in a dynamic coastal region is demonstrated by the results from the trial described in this paper.

Assessing the quality of bottom water temperatures from the Finite-Volume Community Ocean Model (FVCOM) in the Northwest Atlantic Shelf region

Abstract The Finite-Volume Community Ocean Model (FVCOM) is an advanced coastal circulation model widely utilized for its ability to simulate spatially and temporally evolving three-dimensional geophysical conditions of complex and dynamic coastal regions. While a body of literature evaluates model skill in surface fields, independent studies validating model skill in bottom fields over large spatial and temporal scales are scarce because these fields cannot be remotely sensed. In this study, an evaluation of FVCOM skill in modeling bottom water temperature was conducted by comparison to hourly in situ observed bottom temperatures recorded by the Environmental Monitors on Lobster Traps (eMOLT), a program that attached thermistors to commercial lobster traps from 2001 to 2013. Over 2 × 10 6 pairs of FVCOM-eMOLT records were evaluated by a series of statistical measures to quantify accuracy and precision of the modeled data across the Northwest Atlantic Shelf region. The overall comparison between modeled and observed data indicates reliable skill of FVCOM (r 2 = 0.72; root mean squared error = 2.28 °C). Seasonally, the average absolute errors show higher model skill in spring, fall and winter than summer. We speculate that this is due to the increased difficulty of modeling high frequency variability in the exact position of the thermocline and frontal zones. The spatial patterns of the residuals suggest that there is improved similarity between modeled and observed data at higher latitudes. We speculate that this is due to increased tidal mixing at higher latitudes in our study area that reduces stratification in winter, allowing improved model accuracy. Modeled bottom water temperatures around Cape Cod, the continental shelf edges, and at one location at the entrance to Penobscot Bay were characterized by relatively high errors. Constraints for future uses of FVCOM bottom water temperature are provided based on the uncertainties in temporal-spatial patterns. This study is novel as it is the first skill assessment of a regional ocean circulation model in bottom fields at high spatial and temporal scales in the Northwest Atlantic Shelf region.

WATERLINE DETECTION AND MONITORING IN THE GERMAN WADDEN SEA USING HIGH RESOLUTION SATELLITE-BASED RADAR MEASUREMENTS

Abstract. High resolution TerraSAR-X/TanDEM-X as well as Sentinel-1 remote sensing Synthetic Aperture Radar (SAR) data are used to determine and monitor the waterline in the Wadden Sea. In this very unique and dynamic coastal region in the southeastern North Sea, tidal flats extend several kilometers away from the coast during low tide with features like tidal inlets and sand banks. Under the influence of tidal water currents transporting large amounts of eroded material, inlets and sand banks move over time; heavy storms can even cause large variations in their extensions in merely a few hours. Observation of these obstacles is crucial for maritime security as high ship traffic is caused by the ports of Hamburg, Bremerhaven, Wilhelmshaven and others. Conventional monitoring campaigns with ships or airplanes are economically expensive and can only provide limited coverage. We present an automatic algorithm with Near Real-Time capability for extracting the waterline at the time of recording from SAR images, which allows for a fast and large scale determination of changes in coastal outlines. The comparison of recent acquisitions of TerraSAR-X and Sentinel-1 to bathymetry data of the Elbe estuary obtained in 2010 reveals significant changes in tidal flat structures.

Picophytoplankton as Tracers of Environmental Forcing in a Tropical Monsoonal Bay.

In order to better understand the picophytoplankton (PP) dynamics in tropical monsoon influenced coastal regions, samples were collected daily (June-September 2008: monsoon, December 2008: post-monsoon and April 2009: pre-monsoon) from a fixed station in Dona Paula Bay, India. Eight PP abundance peaks comprising Prochlorococcus-like cells, picoeukaryotes, and three groups of Synechococcus occurred. The chlorophyll biomass and PP abundance were negatively influenced by reduced solar radiation, salinity and water transparency due to precipitation and positively influenced by the stabilized waters during precipitation break/non-monsoon periods. Responses to environmental conditions differed with PP groups, wherein the presence of Synechococcus-PEI (phycoerythrin) throughout the year suggested its ability to tolerate salinity and temperature variations and low light conditions. Synechococcus-PEII appearance toward monsoon end and non-monsoon during high water transparency suggests its tidal advection from offshore waters. Dominance of Synechococcus-PC (phycocyanin) at intermediate salinities under low water transparency during MON and high salinities in PrM coinciding with high nitrate concentrations implies a greater influence of light quality or nutrients. Cyanobacteria and not picoeukaryotes were the dominant picophytoplankton in terms of numbers as well as biomass. This study suggests that PP could be used as tracers of environmental forcing driven by tides and freshwater influx and also highlights the importance of high-frequency samplings in dynamic coastal regions through which transient responses can be captured.