Processes In Coastal Waters Research Articles

Experimental Validation of Float Array Tidal Current Measurements in Agate Pass, Washington

Abstract Tidal currents, particularly in narrow channels, can be challenging to characterize due to high current speeds (>1 m s−1), strong spatial gradients, and relatively short synoptic windows. To assess tidal currents in Agate Pass, Washington, we cross evaluated data products from an array of acoustically tracked underwater floats and from acoustic Doppler current profilers (ADCPs) in both station-keeping and drifting modes. While increasingly used in basin-scale science, underwater floats have seen limited use in coastal environments. This study presents the first application of a float array toward small-scale (<1 km), high-resolution (<5 m) measurements of mean currents in energetic tidal channel and utilizes a new prototype float, the μFloat, designed specifically for sampling in dynamic coastal waters. We show that a float array (20 floats) can provide data with similar quality to ADCPs, with measurements of horizontal velocity differing by less than 10% of nominal velocity, except during periods of low flow (0.1 m s−1). Additionally, floats provided measurements of the three-dimensional temperature field, demonstrating their unique ability to simultaneously resolve in situ properties that cannot be remotely observed. Significance Statement The purpose of this research was to validate measurements of tidal currents in a fast-flowing tidal channel using a prototype technology composed of 20 drifting underwater sensors called μFloats (“microFloats”) and five surface buoys against standard devices (acoustic Doppler current profilers). Float measurements matched those from the standard devices within 10% of the mean water speed and simultaneously provided three-dimensional mapping of temperature in the test region. Results demonstrate how moderate numbers of simultaneously deployed μFloats can provide high-resolution sensing capacity that will improve our understanding of physical, chemical, and biological processes in coastal waters.

Emissions of Nitric Oxide from Photochemical and Microbial Processes in Coastal Waters of the Yellow and East China Seas.

Nitric oxide (NO) is an atmospheric pollutant and climate forcer as well as a key intermediary in the marine nitrogen cycle, but the ocean's NO contribution and production mechanisms remain unclear. Here, high-resolution NO observations were conducted simultaneously in the surface ocean and the lower atmosphere of the Yellow Sea and the East China Sea; moreover, NO production from photolysis and microbial processes was analyzed. The NO sea-air exchange showed uneven distributions (RSD = 349.1%) with an average flux of 5.3 ± 18.5 × 10-17 mol cm-2 s-1. In coastal waters where nitrite photolysis was the predominant source (89.0%), NO concentrations were remarkably higher (84.7%) than the overall average of the study area. The NO from archaeal nitrification accounted for 52.8% of all microbial production (11.0%). We also examined the relationship between gaseous NO and ozone which helped identify sources of atmospheric NO. The sea-to-air flux of NO in coastal waters was narrowed by contaminated air with elevated NO concentrations. These findings indicate that the emissions of NO from coastal waters, mainly controlled by reactive nitrogen inputs, will increase with the reduced terrestrial NO discharge.

Landsat 8 Data as a Source of High Resolution Sea Surface Temperature Maps in the Baltic Sea

Sea surface temperature (SST) is a key hydrological variable which can be monitored via satellite. One source of thermal data with a spatial resolution high enough to study sub-mesoscale processes in coastal waters may be the Landsat mission. The Thermal Infrared Sensor on board Landsat 8 collects data in two bands, which allows for the use of the well-known nonlinear split-window formula to estimate SST (NLSST) using top-of-the-atmosphere (TOA) brightness temperature. To calibrate its coefficients a significant number of matchup points are required, representing a wide range of atmospheric conditions. In this study over 1200 granules of satellite data and 12 time series of in situ measurements from buoys and platforms operating in the Baltic Sea over a period of more than 6 years were used to select matchup points, derive NLSST coefficients and evaluate the results. To filter out pixels contaminated by clouds, ice or land influences, the IdePix algorithm was used with Quality Assessment Band and additional test of the adjacent pixels. Various combinations of flags were tested. The results show that the NLSST coefficients derived previously for coastal areas, characterised by a more humid atmosphere, might overestimate low SST values. Formulas derived for the Baltic Sea produced biases close to 0 °C and RMSEs in the range of 0.49–0.52 °C.

Consistency of thresholds for eutrophication assessments, examples and recommendations

International harmonisation of management goals for eutrophication processes in coastal waters, requiring reduction of discharges and depositions of nutrients and organic matter, needs coordinated assessments and measures. This is especially necessary in open areas, connected by currents and mixing processes with trans-boundary exchanges. Management goals, defined nationally as local thresholds for nutrients and chlorophyll-a, had been applied recently (2006–2014) within international eutrophication assessments in the North Sea (OSPAR) and Baltic Sea (HELCOM). Consistency of thresholds for nitrogen nutrients and chlorophyll-a concentrations is tested by mixing diagrams and correlations between nitrogen nutrients (total and inorganic nitrogen) and chlorophyll-a. Results indicate mean consistent relations, but single deviations as in the continental coastal water of the North Sea surpassed means by a factor up to 5 for chlorophyll-a in relation to inorganic nitrogen. Thresholds differed across national borders significantly. Correlations of thresholds and assed data reflect the degree of regional deviations by comparison. Consistency of regionally applied thresholds can be achieved stepwise, by application of regionally correlated means, by adaptation to mixing and parameter relations, and finally by relations of thresholds to natural background concentrations. By this, consistency of international assessments can be improved generally, allowing coordinated management of open coastal waters.

MODELLING TRANSPORT AND FATE OF WOODY DEBRIS IN COASTAL WATERS

Woody debris is ubiquitous in coastal waters, and on shorelines proximate to forested regions. Logs and driftwood play a vital role in coastal and global ecosystems, and can provide valuable data to support studies of oceanography, geomorphology, ecology, history and archaeology. There is growing interest in the role that woody debris can play in nature-based coastal engineering solutions. However, large quantities of woody debris in coastal waters can pose significant hazards to communities, infrastructure, navigation and ecosystems. Thus, the changing abundance and distribution of coastal driftwood, driven by factors including human activities and climate change, has potential for both positive and negative consequences. A better understanding of coastal driftwood fate and transport processes is needed to inform management practices, uses, and sustainable ecosystem management. To date, research on physical transport of woody debris, has been concentrated on tsunami and inland (riverine) environments, where spatiotemporal scales and driving processes are significantly different from typical climatic or even extreme (storm) conditions in coastal waters. In this paper, we describe a series of scale physical model experiments, conducted to provide insight to debris transport processes in coastal waters under a range of controlled wave and water level conditions. The experiments were conducted in a 50.4-metre by 29.4-metre wave basin, in which a 1/30 scale model of a natural shoreline comprised of a shallow fringing reef, a sandy shoreline, and several small coastal structures (groynes and breakwaters) was constructed. Wooden dowels and tree branches, scaled to replicate the size distribution of woody debris observed on Pacific Northwest shorelines, were released in the model. Despite some limitations (e.g., model scale effects), the experimental test results provided several valuable insights to factors affecting debris mobility in coastal areas. The results will inform the parameterization of important physical processes in a numerical model being developed to predict the fate and transport of woody debris in coastal waters.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/hvBHZVObDhY

Estimation of colored dissolved organic matter using Sentinel-2 data in the coastal waters of Singapore

In coastal waters, colored dissolved organic matter (CDOM) is often present in moderate to high concentrations due to input from nearby landmasses and rivers. CDOM absorbs light sharply in the UV-blue region, causing waters to appear yellow or brown. This has a significant effect on optical and biogeochemical processes in coastal waters, as it inhibits the penetration of light within the water. It is thus important to be able to monitor CDOM levels on a regular basis. A model is presented linking Sentinel-2 reflectance data to the CDOM absorption coefficient. Such a model is useful for monitoring the CDOM absorption in coastal waters due to the frequency of Sentinel-2 passes and relatively high-spatial resolution. This model was developed and validated using concurrent field measurements of above-surface remote-sensing reflectance and the in situ CDOM absorption coefficient, from the coastal waters of Singapore. The leave-one-out cross-validation scheme was used to validate the model due to the small number of data points. The model is further tested with Sentinel-2 images of the same locations, not more than one day apart from the in situ measurements.

Particle Size Parameters of Particulate Matter Suspended in Coastal Waters and Their Use as Indicators of Typhoon Influence

The power law particle size distribution (PSD) slope parameter is commonly used to characterize sediment fluxes, resuspension, aggregates, and settling rates in coastal and estuarine waters. However, particle size distribution metrics are also very useful for understanding sediment source and dynamic processes. In this study, a method was proposed to employ the particle size parameters commonly used in sedimentary geology (average particle size (ø), sorting, skewness, and kurtosis) as indicators of changes in sediment dynamic processes, and MODIS images were used to estimate these parameters. The particle size parameters were estimated using a Mie scattering model, Quasi-Analytical Algorithm (QAA) analysis algorithm, and least squares QR decomposition (LSQR) solution method based on the relationship between the power law distribution of the suspended particles and their optical scattering properties. The estimates were verified by field measurements in the Yellow Sea and Bohai Sea regions of China. This method provided good estimates of the average particle size (ø), sorting, and kurtosis. A greater number of wavebands (39) was associated with more accurate particle size distribution curves. Furthermore, the method was used to monitor changes in suspended particulate matter in the vicinity of the Heini Bay of China before and after the passage of a strong storm in August 2011. The particle size parameters represented the influence of a strong typhoon on the distribution of the near-shore sediment and, together with the PSD slope, comprehensively reflected the changes in the near-shore suspended particulate matter. This method not only established the relationship between remote sensing monitoring and the historical sediment record, it also extends the power law model to the application of sediment source and dynamic processes in coastal waters.

Heterotrophic diazotrophs in a eutrophic temperate bay (Jiaozhou Bay) broadens the domain of N2 fixation in China's coastal waters

N2 fixation in coastal waters represents an overlooked process in the global marine nitrogen cycle, yet the mechanisms and controls are still poorly understood. This study first conducted simultaneous measurements of N2 fixation rates, primary production, chlorophyll a (Chl a) concentration, organic carbon concentration, and the composition of nitrogen-fixing genes (nifH) in a eutrophic temperate bay (Jiaozhou Bay, the western Yellow Sea) from 2015 to 2017. The activity of N2 fixation (not detected–1.53 nmol N L −1 h −1) were observed at most sampling stations, suggesting that the N-replete conditions in Jiaozhou Bay did not prevent N2 fixation. The major N2 fixers in JB were heterotrophic, while N2 fixation were mainly contributed by > 10 μm fraction, indicating the possible active N2 fixation of heterotrophic diazotrophs on large particles or planktonic aggregates. Positive correlations between N2 fixation and organic carbon concentration were observed in spring. Further estimates of the level of phytoplankton-derived organic carbon and its potential relationship with N2 fixation suggest that phytoplankton processes may stimulate N2 fixation in Jiaozhou Bay by increasing the bioavailability of organic carbon or/and providing suitable environmental conditions for N2 fixation. Our results first infer the co-regulation of physical factors and biological processes on N2 fixation. As Jiaozhou Bay has been subject to anthropogenic pollution of inorganic nutrients, our results provide insights into the dominant controls on N2 fixation and relevant biogeochemical processes in coastal waters under anthropogenic disturbance.

Spatiotemporal variability, size and photoreactivity of chromophoric dissolved organic matter in the Bohai Sea and the northern Yellow Sea

The distribution, composition, and photoreactivity of chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) in the Bohai Sea (BS) and the northern Yellow Sea (NYS) were investigated during three cruises (summer 2017, winter 2017, and spring 2018) by combining size fractionation through a series of micro- and ultra-filtrations and irradiation experiments. A total of 484 excitation-emission matrix spectra were modeled by parallel factor analysis to yield four humic-like (C1–3 and C5) and three protein-like (C4 and C6–7) fluorescent components. CDOM in the BS and the NYS was primarily affected by terrestrial inputs. Microbial degradation processes and autochthonous production were considered to be important factors driving the dynamics of fluorescence components. A total of 73 triple CDOM absorption and fluorescence spectra (n = 219) from the study regions were measured on 0.2, 0.45, and 0.7 μm filters in winter; water samples were also collected from the Yellow River Estuary (YRE) to the NYS, which was further size fractionated through ultrafiltration membranes (10 kDa and 1 kDa) to investigate variability between spectra of different filter pore sizes. The significant mean difference of absorption coefficient and fluorescence spectra, and no consistent trend between spectral slope (S275–295, S350–400), slope ratio (SR) from these filtrates suggested that the choice of different filter pore sizes considerably influenced the CDOM optical assessment. Higher values of CDOM and FDOM in the particulate phases (0.2–0.7 μm) fraction were more distributed in the NYS where terrestrial inputs were less and DOM dynamics were more linked with phytoplankton production. As pore size decreased, the percentage of humic-like fluorescence increased suggesting that humic-like components of CDOM were more dominated by low-molecular-weight (LMW) materials compared with the protein-like components. Consistent with its higher terrestrial CDOM content, photodegradation resulted in losses of CDOM and FDOM and increasing of the spectral slope ratios (SR). These finding suggested that CDOM molecules were photochemically degraded to LMW substances. Our results indicated that the proportion of the LMW CDOM decreased from estuary to open sea, which likely resulted from high-molecular-weight (HMW) organic material produced during phytoplankton production in off-shore regions, and LMW substances produced during CDOM photochemical processes in coastal waters.

Impacts of ocean acidification on intertidal benthic foraminiferal growth and calcification.

Foraminifera are expected to be particularly susceptible to future changes in ocean carbonate chemistry as a function of increased atmospheric CO2. Studies in an experimental recirculating seawater system were performed with a dominant benthic foraminiferal species collected from intertidal mudflats. We investigated the experimental impacts of ocean acidification on survival, growth/calcification, morphology and the biometric features of a calcareous species Elphidium williamsoni. Foraminifera were exposed for 6 weeks to four different pH treatments that replicated future scenarios of a high CO2 atmosphere resulting in lower seawater pH. Results revealed that declining seawater pH caused a decline in foraminiferal survival rate and growth/calcification (mainly through test weight reduction). Scanning electron microscopy image analysis of live specimens at the end of the experimental period show changes in foraminiferal morphology with clear signs of corrosion and cracking on the test surface, septal bridges, sutures and feeding structures of specimens exposed to the lowest pH conditions. These findings suggest that the morphological changes observed in shell feeding structures may serve to alter: (1) foraminiferal feeding efficiency and their long-term ecological competitiveness, (2) the energy transferred within the benthic food web with a subsequent shift in benthic community structures and (3) carbon cycling and total CaCO3 production, both highly significant processes in coastal waters. These experimental results open-up the possibility of modelling future impacts of ocean acidification on both calcification and dissolution in benthic foraminifera within mid-latitude intertidal environments, with potential implications for understanding the changing marine carbon cycle.

Reevaluating the Role of Organic Matter Sources for Coastal Eutrophication, Oligotrophication, and Ecosystem Health

Organic matter (OM) in aquatic systems is either produced internally (autochthonous OM) or delivered from the terrestrial environment (ter-OM). For eutrophication (or the reverse – oligotrophication), the amount of autochthonous OM plays a key role for coastal ecosystem health. However, the influence of ter-OM on eutrophication or oligotrophication processes of coastal ecosystems is largely unclear. Therefore, ter-OM, or ter-OM proxies are currently not included in most policies or monitoring programs on eutrophication. Nevertheless, ter-OM is increasingly recognized as a strong driver of aquatic productivity: By influencing underwater light conditions and nutrient- and carbon availability, increased ter-OM input may shift systems from autotrophic towards heterotrophic production, but also alter the interactions between benthic and pelagic habitats. Thus, by changing baseline conditions in coastal zones, ongoing and predicted changes in inputs of ter-OM due to climate change (e.g. in precipitation) and anthropogenic activities (e.g. reduced sulfate deposition, damming, coastal erosion) may strongly modify eutrophication symptoms within affected ecosystems, but also hinder recovery from eutrophication following a reduction in nutrient loadings (i.e. oligotrophication). In this review, we aim to shed light upon the role of ter-OM for coastal eutrophication and oligotrophication processes and ecosystem health. Specifically, we (1) discuss the theoretical interactions between ter-OM and eutrophication and oligotrophication processes in coastal waters, (2) present global case studies where altered ter-OM supply to coastal ecosystems has shifted baseline conditions, with implications for eutrophication and oligotrophication processes, and (3) provide an outlook and recommendations for the future management of coastal zones given changes in ter-OM input. We conclude that it is essential to include and target all OM sources (i.e. also ter-OM) in monitoring programs to better understand the consequences of both eutrophication and oligotrophication processes on coastal ecosystems. Our review strongly urges to include ter-OM, or ter-OM proxies in eutrophication monitoring and policies to safeguard coastal ecosystem health also under changing climatic conditions and globally increasing anthropogenic perturbations of coastal ecosystems.

ГИДРОФИЗИЧЕСКИЕ ПРОЦЕССЫ В ПРИБРЕЖНЫХ ВОДАХ МОРСКОЙ АКВАТОРИИ АБХАЗИИ

ГИДРОФИЗИЧЕСКИЕ ПРОЦЕССЫ В ПРИБРЕЖНЫХ ВОДАХ МОРСКОЙ АКВАТОРИИ АБХАЗИИ

Physical-biogeochemical interactions and potential effects on phytoplankton and Ulva prolifera in the coastal waters off Qingdao (Yellow Sea, China)

In recent years, the spectacular massive green tide of Ulva prolifera has become a recurrent phenomenon appearing every summer in the coastal waters off Qingdao (Yellow Sea, China), attracting the attention of scientists and local government. Based on multidisciplinary data collected during summer and winter, this study focuses on the hydrological characteristics and regional biogeochemical processes in coastal waters off Qingdao. The results show that the boundary of the Yellow Sea Cold Water Mass (YSCWM) can reach the Qingdao coastal region in summer and is locally raised to the upper layers to form coastal upwelling beyond tidal mixing and favorable wind. The regional summer upwelling off the Qingdao coast effectively enriches the nutrient concentrations in the upper water column and thus promotes growth of phytoplankton but reduces the dissolved oxygen (DO) concentration and pH value in the bottom. The regional summer upwelling off Qingdao coast may facilitate the growth and regional blooming of the U. prolifera that migrate to this region with the southerly wind. Additionally, the effects of the front on the aggregation of U. prolifera may be significant. In winter, the Yellow Sea Warm Current (YSWC) extends and spreads along the offshore region off the Subei Shoal towards the Qingdao coastal sea. This tongue-shaped warm water meets the cold coastal water off Qingdao, which leads to the formation of a physical front. As a consequence, remarkable fronts of nutrient and chlorophyll a (Chl a) also form between the shoreward warm water and the cold coastal water. This study increases the understanding of the interactions between the regional physical, chemical, and biological processes off the Qingdao coast.

A Semi-Analytic Model for Estimating Total Suspended Sediment Concentration in Turbid Coastal Waters of Northern Western Australia Using MODIS-Aqua 250 m Data

Knowledge of the concentration of total suspended sediment (TSS) in coastal waters is of significance to marine environmental monitoring agencies to determine the turbidity of water that serve as a proxy to estimate the availability of light at depth for benthic habitats. TSS models applicable to data collected by satellite sensors can be used to determine TSS with reasonable accuracy and of adequate spatial and temporal resolution to be of use for coastal water quality monitoring. Thus, a study is presented here where we develop a semi-analytic sediment model (SASM) applicable to any sensor with red and near infrared (NIR) bands. The calibration and validation of the SASM using bootstrap and cross-validation methods showed that the SASM applied to Moderate Resolution Imaging Spectroradiometer (MODIS)-Aqua band 1 data retrieved TSS with a root mean square error (RMSE) and mean averaged relative error (MARE) of 5.75 mg/L and 33.33% respectively. The application of the SASM over our study region using MODIS-Aqua band 1 data showed that the SASM can be used to monitor the on-going, post and pre-dredging activities and identify daily TSS anomalies that are caused by natural and anthropogenic processes in coastal waters of northern Western Australia.

Temporal variation and stoichiometric ratios of organic matter remineralization in bottom waters of the northern Gulf of Mexico during late spring and summer

AbstractAn improved extended optimum multiparameter (eOMP) analysis was applied to hydrographic (temperature and salinity), and water chemistry data, including dissolved oxygen (O2), nutrients (nitrate plus nitrite, phosphate, and silicate), dissolved inorganic carbon (DIC), and total alkalinity (TAlk) data collected during late spring and summer from 2006 to 2012 in bottom waters off the Louisiana coast, to explore the dynamics and stoichiometry of DIC production during the development and maintenance of summer hypoxia. Our analysis demonstrated that DIC in bottom water was relatively low from April to June, but increased significantly in July, peaked in August, and dropped slightly in September. Furthermore, DIC production resulted from both aerobic organic carbon (OC) respiration and denitrification, as well as substantial loss due to vertical mixing with surface water. The average summer gross OC respiration rate was estimated to be 0.19 g C m−2 d−1, with the highest values occurring in late summer when hypoxic conditions dominated. We also found that Corg/N/P/‐O2 remineralization ratios for aerobic respiration were generally consistent with the classic Redfield ratio (106/16/1/138) except individual C/N and C/P ratios were slightly lower, indicating that marine OC was the major source of the DIC production in the bottom water. This study quantified the role of temporal bottom‐water microbial respiration to seasonal DIC dynamics and provided a means for studying the stoichiometry of biogeochemical processes in coastal waters.

Effects of landscape configuration on the exchange of materials in seagrass ecosystems

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 532:89-100 (2015) - DOI: https://doi.org/10.3354/meps11384 Effects of landscape configuration on the exchange of materials in seagrass ecosystems Aurora M. Ricart*, Andreu Dalmau, Marta Pérez, Javier Romero Facultat de Biologia, Departament d’Ecologia, Universitat de Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain *Corresponding author: auroramartinez@ub.edu ABSTRACT: Landscape (or seascape) attributes play an important role in modulating the flow rates of materials between habitats in the coastal marine environment. Seagrass meadows are known to both export and import organic matter, thus establishing links with other habitats. Most of those links remain unexplored, and little is known about the relevance of landscape configuration on these flows. We studied the relationships between landscape configuration (continuous meadows, patchy meadows in a sand matrix and patchy meadows in a rock matrix) and the exchange and accumulation of detrital material. Moreover, we evaluated the impact of landscape configuration on (1) plant nutrient content and (2) the diet of a model deposit feeder (holothurians). We determined detritus stocks in seagrass meadows as well as the carbon and nitrogen elemental and isotopic composition of plants, detritus and other food sources (e.g. suspended organic matter). Based on this, we identified, by applying mixing models, the different contributions of these sources to the diets of deposit feeders. Our results showed that landscape configuration influences the exchange of materials across the coastal seascape. Less accumulation of detrital seagrass leaves was found in patchy meadows, although no effects were found for allochthonous materials. In addition, patchy seagrass meadows showed significantly lower nitrogen concentrations in leaves compared to continuous meadows. Landscape configuration had no effect on the diet of the deposit feeder studied. These findings highlight the importance of landscape-level processes in coastal waters and specifically warn of the possible effects of changes in meadow size on seagrass performance. KEY WORDS: Coastal seascape · Habitat linkages · Spatial subsidy · Deposit feeder diets · Stable isotopes · Holothuria Full text in pdf format Supplementary material PreviousNextCite this article as: Ricart AM, Dalmau A, Pérez M, Romero J (2015) Effects of landscape configuration on the exchange of materials in seagrass ecosystems. Mar Ecol Prog Ser 532:89-100. https://doi.org/10.3354/meps11384 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 532. Online publication date: July 21, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Selective transport of microplastics and mesoplastics by drifting in coastal waters

The quantity and size distributions of small plastic fragments in the Seto Inland Sea, Japan were investigated using field surveys and a numerical particle-tracking model. The model was used to interpret the distributions of small plastic fragments and the possible transport processes in coastal waters. Of note, the size and quantity of mesoplastics (approximately >5mm) gradually increased close to the coast irrespective of the existence of river mouths, which probably act as a major source of anthropogenic marine debris. Additionally, microplastics were more dominant as we moved further offshore. The numerical model reproduced the near-shore trapping of mesoplastics, suggesting that mesoplastics are selectively conveyed onshore by a combination of Stokes drift and terminal velocity, dependent on fragment sizes. It is suggested that mesoplastics washed ashore on beaches degrade into microplastics, and that the microplastics, which are free from near-shore trapping, are thereafter spread offshore in coastal waters.

An ensemble of models for identifying climate change scenarios in the Gulf of Gabes, Tunisia

Climate change is likely to increase the pressure on the environment and on human systems that are requiring new assessment tools aimed at supporting decision-makers and stakeholders towards a more sustainable and effective management of the coastal environment and its resources. This research appraises an ensemble of models that integrates complex interactions of climate and anthropogenic impacts on vulnerable Mediterranean coastal areas with application to the Gulf of Gabes, Tunisia. Starting from Global and Regional Circulation Models, the models’ ensemble includes simulations of marine and atmospheric dynamics and biogeochemical processes in coastal waters under expected anthropogenic forcings, with a spatial domain ranging from subnational to local. In the case study area, the simulations showed that atmospheric temperature increase is likely to be around 4 °C in the summer months of 2100, relative to 1961–1990. In order to obtain the most reliable estimate of sea-level rate variations, satellite altimetry data have been processed over a period of 15 years (1993–2007) showing that sea-level changes on the Tunisian shelf were of the order of 2 mm/year. This value was considered as a reference for the sea-level change scenarios. As far as the water quality is concerned, the areas most impacted by pollution are located near major towns and human infrastructures, such as harbours. The set of results obtained by the proposed models’ ensemble may be suitable for supporting a scientific dialogue with stakeholders and for the implementation of exposure scenarios supporting a regional risk assessment approach to the entire Gulf of Gabes area.

A physical–biogeochemical coupling scheme for modeling marine coastal ecosystems

Ecological modeling of dynamic systems such as marine environments may require detailed spatial resolution when the modeled area is greatly influenced by complex physical circulation. Therefore, the simulation of a marine ecosystem must be underlain by a physical model. However, coupling hydrodynamic and biogeochemical models is not straightforward. This paper presents a modeling technique that can be used to build generic and flexible fully-spatial physical–biogeochemical models to study coastal marine ecosystems using a visual modeling environment (VME). The model core is constructed in Simile, a VME that has the capacity to create multiple instances of submodels that can be interconnected, producing a fully-spatial simulation. The core is designed to assimilate a choice of different hydrodynamic models by means of matrices, enhancing its compatibility with different software. The biogeochemical model can be modified by means of a graphical interface, which facilitates sharing within the scientific community. This paper demonstrates the application of the coupling scheme to mussel aquaculture in Tracadie Bay (PEI, Eastern Canada). The model was run for two different years, 1998 and 1999, and indicated that mussel biomass exerts a top-down control of phytoplankton populations, causing a maximum chlorophyll depletion of 61.0% and 80.3% for 1998 and 1999 respectively. The difference between both years highlights the importance of inter-annual variability, which is significant from an ecosystem-level perspective because it reveals the relevance of applying a precautionary policy in the management of aquaculture activity. Therefore, the proposed core developed in Simile is a generic and flexible tool for modeling long-term processes in coastal waters, which is able to assimilate a choice of hydrodynamic models, constituting a novel approach for generating fully-spatial models using visual modeling environments.

Interaction of Wind-Waves and Currents in the Ems-Dollard Estuary

Physical processes in coastal waters and estuaries extend their influences on many economic and ecological processes in the coastal regions and affect the safety of the coastal defences. In a context with the global climate change, these physical processes underlie also inherent modifications. In order to win an impression of such future changes and of the probability of their occurrence, physically consistent simulations of these processes are used to describe how wind-waves and currents interact. This paper presents an offline-coupled simulation using the models HAMSOM (HAMburg Shelf Ocean Model) and SWAN (Simulating Waves Nearshore). These state-of-the-art models excel by high computing speed, so that they offer an opportunity to simulate hydrological conditions and physical processes over longer time periods, e.g. decades. For the influence of currents on the waves, we estimate less influence on tidal flats, but stronger influence in the tidal channels. Improvements in parameter estimation that were achieved by the interaction of currents and waves are described and discussed; we estimate new drag-coefficients for the hydrodynamic simulation. Because long-term simulations need to be simplified, a method is examined and presented that by-passes the direct online-coupling of models. For the aim of long term simulation improvements of the surface drag coefficient are useful, because online-coupled wind-wave models overcome the available machine time for climate runs. Our method yields an optimization regarding computing economy and physical consistency of simulations.