Nearshore Zone Research Articles

Groundwater nutrient loading into the northern Indian River lagoon: measurements and modeling

The Indian River Lagoon System (IRLS) has been impacted by the surrounding development, leading to excessive nutrient loads that have resulted in frequent and prolonged phytoplankton blooms in the northern reaches. Our study focused on estimating terrestrial groundwater discharge (TGD) and associated nutrient loads by combining field measurements and hydrogeologic modeling at four transects: Eau Gallie (EGT), River Walk (RWT), Banana River (BRT), and Mosquito Lagoon (MLT) across the IRLS. Multiple monitoring stations were installed to collect groundwater and surface water levels, salinity, and nutrient concentrations during 2014-2015. Samples were analyzed for dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP). Numerical modeling was accomplished using SEAWAT to simulate TGD rates, whereas nutrient loads were calculated by multiplying simulated TGD by measured concentrations. TGD rates and nutrient loads were also estimated specifically for the “near-shore zone” along each transect. The effect of recharge from underlying Hawthorn Formation was also evaluated by incorporating estimated recharge rates into the models. Porewater and lagoon water samples showed that ammonium predominated over (NO2+NO3) and PO4 at all sites, resulting in DIN/DIP ratio surpassing the Redfield ratio. Low nitrite/nitrate, coupled with elevated ammonium concentrations at RWT, BRT, and MLT, may be attributed to biogeochemical transformations catalyzed by mangroves and wetlands. Simulated TGD showed mild temporal but significant spatial variation, especially between EGT and RWT compared to BRT and MLT. The highest average TGD of 0.73 and 0.77 m3/d.m occurred at RWT and EGT, respectively, whereas the lowest rates were predicted at BRT and MLT. The highest estimated average DIN loads of 507 and 428 g/yr.m were received at EGT and RWT, respectively, whereas MLT and BRT exhibited lower loads. The DIP loads were remarkably lower than the DIN loads and were significantly different in space and time between sites. Elevated DIN combined with reduced DIP resulted in DIN/DIP exceeding the Redfield ratio, thereby encouraging the blooming of harmful algae. Although the majority of seepage occurs through the near-shore zone, small amounts are received along the entire transect at all sites. The Hawthorn Formation does not contribute significant recharge to the aquifer at the transect locations.

Chemical elemental composition of Elodea canadensis Michx. 1791. and its use for the assessment of anthropogenic pollution of the littoral of Lake Baikal

The ICP-MS method was used to study chemical elemental composition of the invasive species Elodea canadensis Michx. at Lake Baikal littoral sites with different degree of anthropogenic load. It is found out that dominant macroelements in E. canadensis are K > Ca > Na > P > Mg > S > Cl, dominant microelements are Fe, Mn > Si, Sr > Al, Ba, Zn > Br, B. The content of Ca, Sr, Mg, B and Si in E. canadensis samples are characterized by the least variability, and Na, P, Cl, K, V, Ni, Cu, Zn, As, Se, Br, Rb, Cd, I, Pb contents are more variable. The maximal heterogeneity in distribution is characteristic for lithophilous elements (Be, Al, Ti, Cr, Mn, Y, Zr, Nb, REE (rare earth), Hf, Ta, W, Th) as well as for Fe, Co, Sn, Sb, Bi. Maximal contents of Na, Cl, K and P associated with income of household waste waters into the near-shore zone is found in Elodea samples collected in Frolikha vent and at littoral sites adjacent to such populated areas as Gremyachinsk, Maksimikha, Nizhneangarsk. The elevated level of Zn, Cd, Pb is characteristic as well for the samples collected at the littoral sites with a high anthropogenic charge (Listvyanka settl., Bugul’deyka, Nizhneangarsk, Maksimikha village and Gremyachinsk).

Impacts of tidal mixing on diurnal and intraseasonal air-sea interactions in the Maritime Continent

The Maritime Continent (MC) is a region with enhanced tidal mixing and ocean cooling, which influences regional-scale sea surface temperatures (SSTs). We examine the coupled impacts of tidal mixing on near-surface stratification, SST, and deep convection on diurnal and intraseasonal time-scales, using ensembles of high-resolution, coupled ocean-atmosphere regional model simulations, with and without tidal forcing. Results show that the area-averaged SST in the eastern MC is reduced by 0.20 °C due to tidal forcing, with cooling exceeding 1 °C in the nearshore zones of shallow and complex bathymetry. The reduced SSTs decrease surface heat fluxes, leading to tropospheric drying and reduced precipitation, which are most pronounced in the nearshore zones. The results show that the magnitude of tidally-induced SST cooling is phase-dependent during the passage of the Madden Julian Oscillation (MJO). Strong westerly winds enhance entrainment cooling through wind-driven mixing and upwelling during the active phase. Conversely, the upper-ocean stratification is enhanced during the suppressed phase, and SSTs are less sensitive to subsurface cooling. Such spatio-temporal variability in the SST response to tides is accompanied by consistent changes to deep convection and atmospheric circulation. On the diurnal time-scale, nearshore cooling weakens the early-morning convection when the land-based convection propagates offshore and interacts with the cooler SST. On intraseasonal time-scales, the coupling between SST and precipitation is strengthened because of the asymmetric impacts of tide-induced mixing on SST and MJO-induced winds. The robust SST and precipitation responses demonstrated in this study suggest the need for an accurate representation of tidal forcing and vertical mixing processes in local MJO prediction models for the MC.

The Interaction between Storm Surge and Concomitant Waves in Shandong Peninsula

Storm surge and concomitant waves induced by extreme weather systems can significantly modulate the marine dynamic environment. In this study, we used the Advanced Circulation-Simulating Waves Nearshore (ADCIRC-SWAN) coupled model to analyze spatiotemporal variation in dynamic processes during two types of weather systems, i.e., typhoons and extratropical storms, in the sea area near the Shandong Peninsula. The effects of waves on water level, water level change on wave height, and currents on wave height were investigated and quantified separately by performing sensitivity experiments. Our results showed that the interaction between water level change and waves occurred mainly in the nearshore zone. The wave-induced surge accounted for about 10–15% of the total storm surge. The water level change-induced significant wave height reached up to 0.9–1.3 m. Wave–current interaction occurred mainly in the offshore zone and was related to the relative angle between wave and current directions. The modulations of water level and wave height were strongly dependent on not only storm track and intensity but also topography and coastline shapes.

Functional non‐equivalence in ecosystem engineers? Different freshwater mussels (Bivalvia: Unionidae) are associated with different macroinvertebrate communities in a subtropical lake

Abstract Freshwater mussels (Bivalvia: Unionidae) are often described as ecosystem engineers, with the capacity to alter abiotic habitats; this can facilitate certain macroinvertebrate taxa, increasing biodiversity and potentially altering community composition. Mussel species are often implicitly considered to be broad ecological equivalents, with similar impacts on abiotic environments and benthic communities. This assumption of redundancy is important in conservation approaches that aim to preserve ecosystem functioning, rather than species identity. We tested this assumption of equivalence in two species of subtropical freshwater mussels, Lamellidens marginalis and Parreysia caerulea, studying the associations between these mussel species and macroinvertebrate communities. We measured mussel density and abundance of macroinvertebrates, identified to family level, at 50 sites within Dhanmondi Lake, a heavily polluted sub‐tropical urban lake in Dhaka, Bangladesh. We investigated the associations of mussel density on different macroinvertebrate families, which we further classified into functional feeding groups (predators, scrapers, collectors and shredders). We found that densities of the two mussel species were negatively correlated in the 1–3‐m nearshore zone; average density of Lamellidens was 46.4 ± SE 3.6 individuals/0.25 m2, and average density of Parreysia was 6.4 ± SE 1.4 individuals/0.25 m2. In total, 2319 Lamellidens and 320 Parreysia specimens were recorded. Sites containing higher densities of Lamellidens had greater similarity in macroinvertebrate community composition, while there was no effect for Parreysia. Particular macroinvertebrate families and functional feeding groups were also associated with mussels; the majority of significant associations were with Lamellidens but not Parreysia. The clearest associations were with predators and scrapers, which increased in abundance with Lamellidens density. This provides support for a possible role for mussels in structuring freshwater invertebrate communities and emphasises the importance of species identity in these effects, with one possible keystone species (Lamellidens) largely accounting for mussel–invertebrate associations. While microhabitat variables (shading and sediment type) were poor predictors of abundance in any invertebrate taxa (including mussels), manipulative studies are needed to disentangle the direct effects of mussels from the role of overlapping habitat preference between mussels and other invertebrates. Our results highlight the importance of species identity in patterns of community composition, particularly for ecosystem engineer species. We also reinforce the need to test the assumption of ecological redundancy within communities.

Multi-Parameter Algorithms of Remote Sensing Reflectance, Absorption and Backscattering for Coastal Waters of the Southern Baltic Sea Applied to Pomeranian Lakes

The Pomeranian lakes in Northern Poland and the nearby coastal waters of the Baltic Sea belong to optically complex water bodies characterised by high eutrophication levels. These water types require a local approach when developing bio-optical algorithms that combine the inherent and the apparent properties of seawater. Well-established local algorithms are of great value for understanding and addressing rapid changes in water quality related mostly to human activities in coastal and near-shore zones, as well as in optically similar lakes. Our research analyses the possibility of using the multi-parameter algorithms of absorption a(λ), backscattering bb(λ) and remote sensing reflectance Rrs(λ), originally developed for the coastal waters of the Southern Baltic Sea, for three selected Pomeranian lakes. Our multi-parameter algorithms are based on the input concentrations of the biogeochemical components measured in the lake waters, i.e., chlorophyll a (Chl a), suspended particulate matter (SPM), inorganic suspended particulate matter (SPMinorg), the sum of the surface concentrations of accessory pigments (ΣC) and coloured dissolved organic matter with a wavelength of 400 nm (aCDOM(400)). Rrs(λ) and a(λ) output values were compared with independent measurements of these parameters conducted in the lake waters at 20 sampling stations. Our algorithm output values of bb(λ) were compared to the values obtained based on the algorithm provided by Ficek, previously developed and validated for Pomeranian lakes, at the same stations. The statistical analyses conducted afterwards showed that the multi-parameter algorithms of Rrs(λ) and a(λ) for the Southern Baltic Sea are sufficient to be used for the stations investigated in the aforementioned three lakes. Specifically, the correlations between the bb(λ) values obtained based on the Ficek algorithm and the bb(λ) values obtained using our multi-parameter algorithm reveal a statistical error rate of less than 20%.

Quantitative mapping of effective habitats for the White grouper Epinephelus aeneus (Geoffroy Saint–Hilaire, 1817) in North West Africa

Within the Mauritania–Senegal maritime zone, we have identified and mapped habitats of the white grouper (Epinephelus aeneus). To this end, data collected since the 1980s through scientific sampling surveys along the coastline and on the continental shelf in the study zone have been analysed. On the basis of data collected in shallow coastal and estuarine environments, it has been shown that only the juvenile fraction of the E. aeneus population lives in the diverse habitats (mangroves, sea grass beds, salt marshes, etc.) of both the Banc d’Arguin and the estuaries. On the continental slope, habitat suitability of both juvenile and adult was modelled, using descriptors relating to environment (bathymetry, sediment) and landscape (proximity of estuaries and the Banc d’Arguin). Bathymetry is a major factor driving these distribution patterns, while other environmental descriptors also have significant influence, though to a lesser degree: juveniles of E. Aeneus live in nearshore zones and their density is higher near the Banc d’Arguin and the estuaries, unlike the adult populations found further offshore. The density of both populations has varied over time, falling significantly in 1990, and partly recovering since 2010. These habitat maps tell us the importance of the coastal fringe as essential habitat for juvenile E. aeneus and the usefulness of space-based management measures to enhance the population and allow for sustainable fishing exploitation.

Simulation of suitable habitats for typical vegetation in the Yellow River Estuary based on complex hydrodynamic processes

Estuarine ecosystems are influenced by the combination of freshwater runoff and ocean tides, and the natural environment is intricate and complex, with special natural environmental conditions and biological habitat characteristics. The Yellow River is characterized by high sediment-bearing water flow, and the estuary forms a unique clear and turbid confluence. The Water and Sand Regulation (WSRS) from the Xiaolangdi Reservoir to the estuary and nearshore has had significant impacts on the environmental conditions of water, sediment and nutrients, further affecting the growth and development of vegetation in the nearshore zone. In recent years, more studies have focused on the effects of climate change and ocean tides on vegetation in the Yellow River Estuary; however, few studies have been conducted on the effects of the WSRS on klysmoeionion. In this study, we investigated the influence of water flow, sediment and nutrients on klysmoeionion based on long-term field monitoring and indoor control experiments; constructed a three-dimensional hydrodynamic water quality model to simulate the hydrodynamic characteristics, sediment transport patterns and nutrient salt distribution in the Yellow River Estuary under the combined influence of tides and riverine water and sediment; and further combined the growth competition model of typical vegetation (including the native species Zostera japonica and invasive species Spartina alterniflora) to construct a suitable habitat simulation model for typical vegetation communities in the Yellow River Estuary. Habitat and biomass changes in Z. japonica and S. alterniflora in the Yellow River Estuary were simulated under the influence of the WSRS and climate change. The results showed that the distribution of suitable habitats for Z. japonica and S. alterniflora in the Yellow River Estuary and offshore was characterized by a zonal distribution along both sides of the estuary, with an increasing trend of suitable habitat area from the estuary to both sides of the estuary; due to environmental conditions and inter- and intra-species competition, the biomass of Z. japonica and S. alterniflora was mainly distributed in the estuary and near the northern and southern shores, with the southern shore have the most distribution. In contrast, S. alterniflora was mainly distributed in the northern shore away from the estuary and in Laizhou Bay. During the WSRS period, the suitable habitat area of Z. japonica decreased by 25%, and the biomass decreased by 50%, while the suitable habitat and biomass of S. alterniflora were not significantly affected. The growth of Z. japonica was severely affected by the dual effects of global warming and the WSRS, while the biomass of S. alterniflora showed an increasing trend. The WSRS can further consider the growth pattern of vegetation to protect the resources of Z. japonica and to curb the expansion of the invasive S. alterniflora.

Wave-driven sediment transport potential on a tropical coast: Implications for the northeastern Australian sediment budget

Coastal dynamics are governed by the interface of complex, multidimensional processes that result from the interaction between offshore wave climate and local geomorphology. Nearshore waves are usually the primary driver of sediment transport in the coastal zone. However, nearshore wave processes in sub-tropical to tropical regions are often poorly understood, since deep-water waves are often substantially transformed, via interaction with coral reefs, as they propagate towards the nearshore zone. Here, we produce a suite of nearshore wave conditions using a discrete set of representative deep-water wave parameters to determine the potential for large-scale, wave-driven longshore sediment transport along the sub-tropical to coral reef mediated tropical northeastern coast of Australia (15-28oS). Representative conditions at deep-water source points, determined using a Maximum Dissimilarity Algorithm (MDA), were used as boundary conditions for a coastal wave model. Potential longshore sediment transport is largely dependent on offshore wave direction and the presence (or lack thereof) of the Great Barrier Reef (GBR). There is a decrease in mean, wave-driven transport potential from >500,000 m3/year in southern Queensland to <50,000 m3/year north of Fraser Island and along the section of the coast regulated by wave transformation through the GBR. Seasonal changes in the deep-water wave regime control patterns of sediment transport along the entire coast, even in the low wave energy regions. We also show that there are complex sediment transport pathways on this tropical coast with large variability in both direction (up-coast vs. down-coast transport) and magnitude in the nearshore. Our results provide insights into the potential volumes, pathways, and complexity of sediment transport on tropical and sub-tropical coasts and a methodological approach that can be applied globally to efficiently construct wave-driven sediment flux estimates on tropical coastlines where coral reefs influence nearshore wave processes.

Seasonal trends in marine heatwaves highlight vulnerable coastal ecoregions and historic change points in New Zealand

ABSTRACT Marine heatwaves (MHWs) have increased worldwide in intensity, frequency, and duration, often with severe impacts on ecologically and socio-economically important coastal habitats. Most MHW studies have focused on summer events in specific regions or global open-water analyses with little consideration to seasonality or spatial biogeography of the nearshore zone. We address this research gap by analysing changes to MHWs across seasons and ecoregions, within 12 nautical miles (NM) of New Zealand’s coastline, an area with high biodiversity and endemism. We used season-specific linear trend analysis with temporal breakpoints between 1982 and 2021 to identify the number of MHW events and MHW days, and mean, maximum, and cumulative intensity of MHWs for New Zealand coastal ecoregions. Across ecoregions, 69.5% of 200 trend analyses increased significantly whereas the remaining 30.5% were unaffected. For the significant increases, temporal breakpoints occurred between 1994 and 2012. We conclude that MHWs have become stronger, longer and more frequent across coastal New Zealand, but with some variability within and between regions. Our trend-analyses could enable retrospective analyses of biological tipping-points and inform management practices that may enhance the resilience of ecoregions yet to face MHW breakpoints or those in the initial stages of major climatic changes.

SPH modeling of dam-break bores on smooth and macro-roughness slopes

Understanding the kinematics and hydrodynamics of long waves in nearshore zones is currently one of the more pressing aims motivating research in the coastal engineering community. Owing to the simplicity of its setup, the dam-break mechanism is frequently adopted in laboratories to generate bores and model long-wave dynamics, kinematics, and runup processes in coastal regions. Numerical simulations have been used to replicate the results of laboratory experiments using a dam-break system. In this study, we aimed to evaluate the effect of different macro-roughness slopes owing to dam-break driven swash using an open-source particle-based program, DualSPHysics, based on smoothed particle hydrodynamics. To serve as a reference case, the swash flows of a dambreak-generated bore on a uniform slope were performed, and model–data comparisons were made for time-series analysis of the surface elevation, runup process and velocity profiles at selected points. Simulations of dam-break bores passing over slopes containing various configurations of macro-roughness elements were performed to replicate long waves impacting an array of structures in a waterfront area. Different configurations of slope roughness have varying effects on the flow hydrodynamics in the swash zone, which were examined in this study.

Numerical investigation on the mitigation of harbor oscillations by periodic undulating topography

Mitigation of harbor oscillations is a crucial concern in coastal engineering. It is more economical and accessible for an established harbor to reduce the intensity of oscillations by changing the incident wave conditions rather than modifying the harbor layout. Periodic sandbars and sand ripples, which are common in nearshore zones, can be modified into submerged breakwaters. When the wavelength of the bottom undulations is approximately half of the incident wavelength, the resonant reflection (i.e., Bragg reflection) appears, leading to significant enhancements in wave reflection, which further results in the reduction of the incident wave energy.The present study evaluates the effectiveness of Bragg reflection in inhibiting harbor oscillations using an extended mild-slope equation. The results show that undulating seabed topography outside the harbor can significantly weaken the intensity of the harbor oscillations. Subsequently, a possible mitigation mechanism is proposed. The influences of the bar wavelength, bar number, bar height, and the slope of seabed on the mitigation effect of harbor oscillations are studied. Furthermore, it is found that the optimal mitigation effect for different resonant modes is not constant, and the reason for this is explained.

Cold water pathways and regional flow patterns in the southwest Indian ocean associated with temperature anomalies on the Sodwana reef system, South Africa

Coral reefs around the world are under increasing threat to global climate change and coral bleaching events that can result in severe damage and mortality to the reef systems. Some coral reefs are situated in areas where the complex ocean flow patterns and their interaction with topographical features around the reefs provide certain refuges to the rising ocean temperatures and coral bleaching. The Sodwana reef system experiences cold water temperature anomalies that cause short-term temperature fluctuations on the reefs. It is suggested that these temperature anomalies provide relief from bleaching and are an integral part of the coral’s survival at Sodwana. Previous studies have shown that the temperature anomalies are linked to regional scale hydrodynamic features surrounding Sodwana. We investigated the cold water pathways and regional flow patterns associated with the temperature anomaly events between 1994 and 2015 using data from the global reanalysed NEMO ocean model output. A comparison between temperature measurements taken on the Sodwana reefs and temperature data extracted from the model near Sodwana shows a good agreement and that the model replicates the temperature anomalies. This indicates that the temperature anomalies are associated with the regional hydrodynamic flow structures replicated in the NEMO model. We used a Lagrangian particle backtracking model and the hydrodynamic data from the NEMO model to delineate the pathways associated with the 63 temperature anomalies observed between 1994 and 2015. The pathways delineated from the Lagrangian particle backtracking model originate to the northeast of Sodwana within the Delagoa Bight region, indicating that hydrodynamics around the Delagoa Bight is linked to the cold water temperature anomalies observed at Sodwana. A statistical analysis of the modelled regional Eulerian flow fields showed that two representative regional flow fields are associated with the anomalies and representative pathways. The first representative flow field features a high-speed concentrated southward stream that separates from the Delagoa Bight peninsula and flows along the seaward edge of the Delagoa shelf and a cyclonic eddy structure within the Delagoa Bight. The second representative flow field features the southward stream that separates from the Delagoa Bight peninsula and flows directly to the Sodwana region with a significantly smaller separation zone within the Delagoa Bight. The second representative flow field shows no observable cyclonic eddy structure. The southward stream observed in all representative flow fields reattaches to the South African coastline near the Sodwana region. We also show through the mean particle vertical displacement and temperature change along the anomaly pathways that the nearshore zone within 50 km of Sodwana is a region of enhanced upwelling and mixing during the anomaly periods.

Environmental drivers of spatial and temporal water quality variability in four coastal wetlands of Lake Ontario

Great Lakes coastal wetlands serve as mediation zones between the land and the lake, regulating the fate of materials received from tributaries prior to discharge to the lake nearshore zone. To improve our understanding of water quality processing and nutrient fate in coastal wetlands, we evaluated within- and across-wetland water quality as a function of environmental drivers over a decade (2009–2018) in three drowned river mouth (Carruthers, Duffin’s, and Rouge) and one barrier lagoon (Frenchman’s Bay) wetlands on the north shore of Lake Ontario. Overall, land-use had a weak relative association with most water quality parameters, reflecting no appreciable changes in land-use across the study years. The barrier lagoon wetland Frenchman’s Bay had a distinctly different water quality pattern from the drowned river mouth wetlands, where water quality followed a high to low concentration gradient from near the tributary confluences (high) to the lake-wetland confluence (low) (permutational analysis of variance p-value < 0.001). Notably, we observed significant differences among celled (i.e., natural ponds in wetlands) and non-celled sites in Duffin’s and Rouge marshes, primarily attributed to strong covariation among phosphorus, phosphate, and organic nitrogen concentrations (permutational analysis of variance p-value < 0.001). This water-quality signature seemed to be driven by solar radiation and lake level variability (i.e., seiche inundation), inferring that wetlands may be important sites for the mobilization of legacy phosphorus in sediments under certain climatic conditions, and following seiche events.

Estimation of the main parameters of wave action on the gentle slopes of the banks of large water bodies

When designing coastal protection measures, special attention is paid to the creation and expansion of a natural beach slope on the coast of a water body. To assign geometric dimensions to relatively stable beach slopes, it is necessary to evaluate the relationship of waves, taking into account the level regime characteristic of a given section of the coast. The aim of the research is to explore the features of the transformation of the wave profile in shallow water and to conduct a comparative analysis of theory and experiment. The studies were carried out in a wave tray, where the waves were reproduced by a swinging shield. The features of the transformation of the wave profile at decreasing depths of the shallow water of a large water body are considered. An assessment is given of the change in the kinematic characteristics of a wave incident in a shallow water zone on an unfortified beach slope with a depth of 10, 20 and 30. The results of experimental studies are presented and analyzed, as a result of which the influence of the wave steepness on the kinematic characteristics and features of wave transformation in shallow water is revealed. A comparative analysis of theoretical solutions and experimental data with an assessment of the area of their applicability is carried out. On the whole, the wave profile and the horizontal component of the orbital velocity during the passage of the wave crest are in satisfactory agreement with the calculations according to the Stokes theory at relative depths of more than 0.07. It has been established that for shallow water conditions the relative height of the wave crest affecting the beach slope of the near-shore zone of the coast of a large water body is most noticeably affected by the slope, with an increase from 10 to 30 the magnitude of the wave steepness can increase by 1.2 times.

Benefits of fully focused SAR altimetry to coastal wave height estimates: A case study in the North Sea

Estimating the three geophysical variables significant wave height (SWH), sea surface height, and wind speed from satellite altimetry continues to be challenging in the coastal zone because the received radar echoes exhibit significant interference from strongly reflective targets such as sandbanks, sheltered bays, ships etc. Fully focused SAR (FF-SAR) processing exhibits a theoretical along-track resolution of up to less than half a metre. This suggests that the application of FF-SAR altimetry might give potential gains over unfocused SAR (UF-SAR) altimetry to resolve and mitigate small-scale interferers in the along-track direction to improve the accuracy and precision of the geophysical estimates.The objective of this study is to assess the applicability of FF-SAR-processed Sentinel-6 Michael Freilich (S6-MF) coastal altimetry data to obtain SWH estimates as close as possible to the coast.We have developed a multi-mission FF-SAR processor and applied the coastal retracking algorithm CORALv2 to estimate SWH. We assess different FF-SAR and UF-SAR processing configurations, as well as the baseline Level-2 product from EUMETSAT, by comparison with the coastal, high-resolution SWAN-Kuststrook wave model from the Deltares RWsOS North Sea operational forecasting system. This includes the evaluation of the correlation, the median offset, and the percentage of cycles with high correlation as a function of distance to the nearest coastline. Moreover, we analyse the number of valid records and the L2 noise of the records. The case study comprises five coastal crossings of S6-MF that are located along the Dutch coast and the German coast along the East Frisian Islands in the North Sea.We observe that accurate and precise SWH records can be estimated in the nearshore zone within 1–3 km from the coast using satellite SAR altimetry. We find that the FF-SAR-processed dataset with a Level-1b posting rate of 140 Hz shows the greatest similarity with the wave model. We achieve a correlation of ∼0.8 at 80% of valid records and a gain in precision of up to 29% of FF-SAR vs UF-SAR for 1–3 km from the coast. FF-SAR shows, for all cycles, a high correlation of greater than or equal to 0.8 for 1–3 km from the coast. We estimate the decay of SWH from offshore at 30 km to up to 1 km from the coast to amount to 26.4% ± 3.1%.

Distribution of the Mass Species of Benthic Crustacean on Nearshore Slope the Ladoga Lake

The species list and distribution of crustacean of a nearshore zone of the Valaam Island (Ladoga Lake) have been investigated by sampler-syringe, dredge and video records. On the depth 1–25 m the five species of crustacean: Asellus aquaticus (Linnaeus, 1758), Monoporeia affinis (Lindström, 1855), Pallaseopsis quadrispinosa (G.O. Sars, 1867), Gmelinoides fasciatus (Stebbing, 1899), Mysis relicta Lovén, 1862 were described. For the first time the vertical distribution of naturalized Baikal amphipods G. fasciatus were inventoried and their features of joint residence with local species were characterized. The distribution of the alien species reliably connected with wave intensity, types of grounds and depth range. The most numerous local species P. quadrispinosa distribution affects by depth range. The types of grounds do not influence on the quantity of all indigenous crustacean in the nearshore zone. In all condition the local species successfully compete with G. fasciatus. All these species inhabit of littoral have higher resistance for wave action as compared with non-indigenous species. It guarantees existence of refuges which can safe diversity of the indigenous species. The obtained data on the spatial distribution of crustaceans make possible to characterize the benthic communities of the little-studied parts of the littoral and sublittoral and, as a result, the food base of bentophagous fishes.

Free Long-Wave Transformation in the Nearshore Zone through Partial Reflections

Abstract Long waves play an important role in coastal inundation and shoreline and dune erosion, requiring a detailed understanding of their evolution in nearshore regions and interaction with shorelines. While their generation and dissipation mechanisms are relatively well understood, there are fewer studies describing how reflection processes govern their propagation in the nearshore. We propose a new approach, accounting for partial reflections, which leads to an analytical solution to the free wave linear shallow-water equations at the wave-group scale over general varying bathymetry. The approach, supported by numerical modeling, agrees with the classic Bessel standing solution for a plane sloping beach but extends the solution to arbitrary alongshore uniform bathymetry profiles and decomposes it into incoming and outgoing wave components, which are a combination of successively partially reflected waves lagging each other. The phase lags introduced by partial reflections modify the wave amplitude and explain why Green’s law, which describes the wave growth of free waves with decreasing depth, breaks down in very shallow water. This reveals that the wave amplitude at the shoreline is highly dependent on partial reflections. Consistent with laboratory and field observations, our analytical model predicts a reflection coefficient that increases and is highly correlated with the normalized bed slope (bed slope relative to wave frequency). Our approach shows that partial reflections occurring due to depth variations in the nearshore are responsible for the relationship between the normalized bed slope and the amplitude of long waves in the nearshore, with direct implications for determining long-wave amplitudes at the shoreline and wave runup.

The importance of resolving nearshore currents in coastal dispersal models

Biophysical models often require shelf-scale domains to map larval dispersal over several weeks, presenting a computational challenge. This can be overcome by decreasing model spatial resolution; however, nearshore processes, which potentially play a significant role in larval dispersal, will inevitably be unresolved. Here, we evaluate how simulated larval dispersal in the nearshore is sensitive to model spatial resolution. We use an unstructured, finite element, hydrodynamic model of a topographically-complex coastline in North Wales, UK (which includes headlands, bays and channels) at four different spatial scales (50, 100, 250, 500 m) to compare the influence of spatial resolution on transport and dispersal patterns of particles released within the nearshore region (within 1 km of the shore). In the higher resolution (50 and 100 m) simulations, particles generally travelled offshore more quickly and further (∼18%) than in the coarser (250 and 500 m) simulations. This had important implications for potential connectivity along the coast: for the lower resolution simulations, retention of particles near source sites was increased by ∼50% and, whilst the magnitude of connectivity among discrete regions along the coast was also increased (by ∼27%), the number of connected regions was reduced (by ∼9%), compared with the higher resolution simulations. Our results, based on a case study in a highly energetic and topographically complex region, suggest that model spatial resolution of ≤100 m should be used for dispersal studies in the nearshore zone. These findings add to growing evidence of the importance of using appropriately scaled models when simulating the transport of material within – and out of – the coastal zone, with many applications, such as marine ecology, marine biosecurity, marine spatial planning and marine pollution.

Modelling the influence of seiche-events on phosphorous-loading dynamics in three Lake Ontario coastal wetlands

Coastal Wetlands (CWs) provide critical ecosystem services that maintain biogeochemical processes and habitats in the coastal zone of the Great Lakes. When nutrient-laden surface waters flow into CWs from their watersheds, internal physical, chemical, and biological processes can alter the final nutrient loadings to the lake. However, CWs can periodically be inundated with lake water from seiche events, and little is known about the impacts of seiches on nutrient processing and loadings from CWs. To evaluate the influence of lake seiches on CW phosphorous-loading dynamics, we built a multi group structural equation model (SEM) using climatic and wave data, and interannual (2009–2018) estimated sediment and phosphorous loadings from three CWs on the north-shore of central Lake Ontario (Rouge Marsh, Duffin’s Marsh, and Carruthers Marsh). Wind speeds, lake levels, and an increased peak period of wave spectra were significant explanatory variables of seiche events (p-value < 0.001). We identified that seiche events caused significant sediment resuspension (p-value < 0.001) in CWs, which contributed to a significant increase of phosphorous loading to the coastal zone of Lake Ontario (p-value < 0.001). Our results indicate that lake-seiche events can influence CW phosphorous-loadings to Lake Ontario, and should be considered when modelling water quality in the nearshore zone.