Sea Inlet Research Articles

Relationships Between Land Use and Terrestrial Organic Matter Transfer to the Baltic Sea Over the Last 500 Years

AbstractTerrestrial organic matter (OM) plays a key role in coastal organic carbon burial. However, few studies focus on the relationship between land use in the watershed and the transport of terrestrial OM to coasts from a long‐term perspective. In this study, we compared terrestrial OM deposition between an inlet of the Baltic Sea and an upstream lake within the same watershed over the last 500 years, using lignin biomarkers in the sediments. In combination with pollen‐based quantitative land cover reconstruction, we assessed the impacts of semicentennial‐scale changes in land use on terrestrial OM export. The results indicated that the concentration, composition, and degradation state of the lignin‐derived OM differed substantially between the two sites. The lake received larger amounts of lignin‐derived OM during periods of intensified agriculture, but the coastal site did not. The composition of lignin in the coastal sediment did not directly reflect variations in vegetation cover in the watershed. The reason could be that the OM was settled in the upstream basins. Furthermore, the terrestrial OM that did reach the coastal sediments was modified through degradation during the transport, and only the refractory component was deposited at the coast in a relatively unaltered form.

Macrobenthos of the Tortolì Lagoon: A Peculiar Case of High Benthic Biodiversity among Mediterranean Lagoons

Coastal lagoons and brackish ponds are extremely dynamic and temporary ecosystems that follow natural changes throughout their geological history. The correct management of the lagoons ensures their integrity and proper functioning. For this reason, their ecological status should be surveyed for assessing the most appropriate strategies of use. In the present study, historical datasets collected in 2003–2004 are used to investigate the spatiotemporal variation in the species composition and community structure of the macrobenthos of the Tortolì Lagoon (Sardinia, Italy) and to assess their relationship with key environmental variables. Owing to the presence of a riverine runoff at a site and confined areas at some distance from the sea inlet, we hypothesize the marked spatiotemporal changes of the macrobenthic community consistent with the high environmental variability typical of coastal lagoons. The results show a surprisingly high benthic biodiversity for a medium-sized lagoon (250 ha), with 101 species unevenly distributed across the lagoon. The environmental variables did not explain the zonation of the macrobenthic community as that typically found along a lagoonal gradient, due to a marked marine influence. The sampling sites were in fact discriminated by the species distribution according to their ecological affinity; in particular, the most distinctive characteristics of the Tortolì Lagoon emerged from the strictly marine species that represented the most abundant group, consistently with the high marinization of the lagoon. Our results show that the Tortolì Lagoon constitutes a peculiar ecosystem within Mediterranean lagoons, departing from the classic confinement theory.

A Deep-Learning Based Pipeline for Estimating the Abundance and Size of Aquatic Organisms in an Unconstrained Underwater Environment from Continuously Captured Stereo Video

The utilization of stationary underwater cameras is a modern and well-adapted approach to provide a continuous and cost-effective long-term solution to monitor underwater habitats of particular interest. A common goal of such monitoring systems is to gain better insight into the dynamics and condition of populations of various marine organisms, such as migratory or commercially relevant fish taxa. This paper describes a complete processing pipeline to automatically determine the abundance, type and estimate the size of biological taxa from stereoscopic video data captured by the stereo camera of a stationary Underwater Fish Observatory (UFO). A calibration of the recording system was carried out in situ and, afterward, validated using the synchronously recorded sonar data. The video data were recorded continuously for nearly one year in the Kiel Fjord, an inlet of the Baltic Sea in northern Germany. It shows underwater organisms in their natural behavior, as passive low-light cameras were used instead of active lighting to dampen attraction effects and allow for the least invasive recording possible. The recorded raw data are pre-filtered by an adaptive background estimation to extract sequences with activity, which are then processed by a deep detection network, i.e., Yolov5. This provides the location and type of organisms detected in each video frame of both cameras, which are used to calculate stereo correspondences following a basic matching scheme. In a subsequent step, the size and distance of the depicted organisms are approximated using the corner coordinates of the matched bounding boxes. The Yolov5 model employed in this study was trained on a novel dataset comprising 73,144 images and 92,899 bounding box annotations for 10 categories of marine animals. The model achieved a mean detection accuracy of 92.4%, a mean average precision (mAP) of 94.8% and an F1 score of 93%.

Greek Words in Maltese Harbour Toponymy

The study presents place names and site names (toponyms) found in the Maltese islands and which comprise Greek words or have origins in the Greek language. With a focus on maritime connections, it presents historic events which would have brought harbour communities in close encounter with the Greek language and culture. Through a multidisciplinary approach the study analyses placenames and site names still used or found in historical documents, backed by archaeological evidence, oral tradition, cartography, other knowledge, and studies. Findings show that in the Maltese islands, placenames mirroring or containing Greek words occur at sea inlets and creeks which could have served as harbours; however, the occurrence of both place names and site names is higher in the south of Malta and around its ancient harbour, witnessing to higher contacts between the two cultures. The study concludes that connections between the Maltese islands and the Greek cultures happened mostly in maritime harbours owing to events in history which gave importance to the use of the Greek language or Greek maritime terminology. Keywords: Greek, harbour, Malta, maritime, Mediterranean, toponyms

Boat-induced pressure does not influence breeding site selection of a vulnerable fish species in a highly anthropized coastal area

The brown meagre (Sciaena umbra) is a vulnerable vocal fish species that may be affected by boat noise. The breeding site distribution along the anthropized Venice sea inlets was investigated, by using the species' chorusing activity as a proxy of spawning. Passive acoustic campaigns were repeated at 40 listening points distributed within the three inlets during three-time windows in both summer 2019 and 2020. The role of temporal, morphological, and hydrodynamic variables explaining the observed distribution patterns was evaluated using a GLM approach, considering also human-induced pressures among the candidate predictors. The GLM analysis indicates a higher probability of recording S. umbra chorus after sunset in deeper areas of the inlets, characterized by low water current, while the underwater noise overlapping the species' hearing range and boat abundance did not play any role. This suggests that the species' breeding site choice in the inlets was not influences by boat-induced pressure.

Metal Bioaccumulation and Oxidative Stress in Ulva laetevirens in the Venice Lagoon: Early Warning Biomarker for Metal Bioaccumulation

Transitional water systems (TWSs) may be threatened by various metals originating from increased agricultural, industrial activities, or urban effluents. Macroalgae are one of the biological quality elements used to monitor and assess the health status of TWS due to their structural and functional key role in marine ecosystems. Here, metal accumulation from the macroalgae Ulva laetevirens Areschoug (1854) and oxidative stress by lipid peroxidation (LPO) biomarker were investigated during four sampling seasons from three sampling sites (SMM: Santa Maria del Mare; PM: Porto Marghera; SG: San Giuliano) of Venice Lagoon, affected by different anthropogenic stressors. The metal pollution index (MPI) scores for U. laetevirens increased in the order SMM < PM < SG (sea inlet < industrial area < Osellino River estuary), with average values per site of 2.99, 4.37, and 6.33, respectively. The level of LPO was statistically correlated with the concentration of toxic metal(loid)s (As, Pb, Hg) measured in macroalgae, and seasonality affected both levels of LPO and metal bioaccumulation, with peak values during spring and summer. These findings highlighted the efficiency and usefulness of the oxidative stress test (LPO) on the common macroalga U. laetevirens as an early warning signal for health assessment in aquatic ecosystems.

The Fahrdorf wreck: another large 12th-century cargo ship in the Schlei, northern Germany

In 2014 an accidentally raised construction timber turned out to be a part of a medieval shipwreck resting in the murky waters of the Schlei inlet of the Baltic Sea in northern Germany. The Study Group for Maritime and Limnic Archaeology (AMLA) of the Christian-Albrechts University (CAU) at Kiel has examined and documented the remains using computer vision photogrammetry over recent years. Based on these campaigns it has been possible to date the wreck and determine its function as a large cargo sailing vessel, which testifies to the importance of the Schlei as a trading route for the cities of Hedeby and Schleswig.

Molecular characterization of harmful algal blooms in the Bohai Sea using metabarcoding analysis

Although the occurrences of harmful algal blooms (HABs) have been intensifying, many HABs in coastal waters may have been neglected despite their damaging impact directly on ecology and indirectly on human and animal health. The current detection of HABs depends primarily on the water coloration, chlorophyll intensity, cell density, and mortality due to HAB toxicity. Such methods may not be adequately sensitive to detecting HABs that are relatively transient or small scale. The Bohai Sea is the largest inlet of the Yellow Sea located on the northeast coast of China and famous for shipping and marine aquacultures. HABs frequently occur in the Bohai Sea. In this study, we explored the composition, diversity, and distribution of HAB species using the metabarcoding approach. Through sequencing and the analyzing the 18S rDNA V4 region of 15 samples collected from spatially isolated sites in the Bohai Sea during an expedition in the summer of 2019, we identified 74 potential HAB species including 34 that had not been reported in the Bohai Sea in previous studies. This project provided a detailed analysis of phytoplankton composition, and molecular detection of HAB species in the Bohai Sea. In particular, these analyses revealed extremely high relative abundances of the ichthyotoxic phytoplankton species Vicicitus globosus (Dictyochophyceae) at multiple adjacent sampling sites in the Bohai Bay, which were close to the Yellow River Estuary during the expedition. The results revealed the occurrence of a potential HAB event that would be otherwise undetected using conventional methods, highlighting the sensitivity and power of metabarcoding analysis in detecting HABs and HAB species. This research suggested the value for routine and long-term monitoring of HAB species as an approach for monitoring HABs.

A Trophic Model for a Periodically Closed Coastal Lagoon System in the Southern Mexican Pacific

Carretas-Pereyra is an estuarine lagoon system located in the southern Mexican Pacific coast. Its connection to the sea is intermittent, because the mouth of the system closes seasonally under natural conditions, but it is often opened artificially for artisanal fishery purposes. In order to know the degree of development, structure, and functioning of this system, under intermittent communication with the sea, a trophic model was built using software Ecopath. The model was composed of 32 functional groups: one for birds, one for crocodylians, 18 for fishes, 9 invertebrates, 2 plankton, and detritus. The pedigree index of the model was 0.62, which mean it is an acceptable model. The results are consistent with findings for lagoon systems with permanent connection to the sea. Some of the ecosystemic mechanisms probably used to face the abrupt changes induced by the opening of a sea inlet are: system omnivory, elevated overhead, efficient metabolism in phytoplankton, species replacement, and species adaptability to dominant environmental conditions. These elements provide stability to the ecosystem and help in its recovery. Detritus, zooplankton, and phytoplankton were important components for the resiliency of the system. In spite of the biological and environmental changes induced by the intermittent opening of an inlet, Carretas-Pereyra has the necessary elements to absorb the impacts and function adequately.

Study on the Influence of Reservoir Dispatch of the Upper Yangtze River on the Runoff Control

The reservoir group focusing on the Three Georges reservoir has been established in the upper Yangtze River, with a total regulation capacity of 51.5 billion m3. The reservoir group dispatch plays an important role in regulating the runoff. Economic activity in the Yangtze River estuary poses high requirements for water resources security. The water quality of main water supply reservoirs is influenced by the saltwater intrusion. The upstream reservoir group dispatch can enhance sea inlet runoff and mitigate saltwater intrusion hazard. In order to clarify the upstream reservoir group’s influence on the sea inlet water quantity in the Yangtze River estuary, the author designed three typical reservoir group dispatch scenarios to analyze flow rate change and different dispatch scenarios of Datong section. According to the findings, the upstream reservoir group dispatch is important to secure water quantity in the dry season. Through normal dispatch, the Three Georges reservoir can cut the days with a flow rate less than 100 million m3/s from 50.6 days to 8.8 days. In the special dry year, the sole emergency water supplement by the Yangtze River reservoir to the estuary will exert influence on the reservoir power generation. The joint operation of upstream reservoir group can basically eliminate such influence.

Aral Sea: an environmental disaster in twentieth century in Central Asia

The Aral Sea catastrophe profoundly worsened the socio-economic, environmental and health conditions of the local communities in Central Asia. This research paper is based on quantitative approach. The three indicators of climate change temperature, relative humidity and precipitation were used to assess if climate change was one of the main contributors to the shrinkage of Aral Sea. The initial data were retrieved from Global Weather Data SWAT. The paper has analyzed the aforementioned indicators of climate change from January 01st, 1979 to July 05th, 2014 using Hydrologic Engineering Center-Hydrologic Modeling System model. The paper has found out that the discharge of Amu Darya River Basin at the inlet of Aral Sea Basin in Karakalpakstan, an autonomous Republic located in Uzbekistan, has sharply declined. A maximum peak flow happened at the inlet of Aral Sea in Karakalpakstan on May 25th, 1988. Since then, the inflow at the Aral Sea Basin in Karakalpakstan was sharply declined due to the drastic climate change in the region. The author believes that the outcome of the research paper will support policy makers of Central Asian states as well as other stakeholders to take measurable steps in addressing the issue of Aral Sea crisis.

COLREG-Compliant Collision Avoidance for Unmanned Surface Vehicle Using Deep Reinforcement Learning

Path Following and Collision Avoidance, be it for unmanned surface vessels or other autonomous vehicles, are two fundamental guidance problems in robotics. For many decades, they have been subject to academic study, leading to a vast number of proposed approaches. However, they have mostly been treated as separate problems, and have typically relied on non-linear first-principles models with parameters that can only be determined experimentally. The rise of deep reinforcement learning in recent years suggests an alternative approach: end-to-end learning of the optimal guidance policy from scratch by means of a trial-and-error based approach. In this article, we explore the potential of Proximal Policy Optimization, a deep reinforcement learning algorithm with demonstrated state-of-the-art performance on Continuous Control tasks, when applied to the dual-objective problem of controlling an autonomous surface vehicle in a COLREGs compliant manner such that it follows an a priori known desired path while avoiding collisions with other vessels along the way. Based on high-fidelity elevation and AIS tracking data from the Trondheim Fjord, an inlet of the Norwegian sea, we evaluate the trained agent's performance in challenging, dynamic real-world scenarios where the ultimate success of the agent rests upon its ability to navigate non-uniform marine terrain while handling challenging, but realistic vessel encounters.

Macrozoobenthos monitoring in relation to dredged sediment disposal: The case of the Marano and Grado Lagoon (northern Adriatic Sea, Italy)

Coastal lagoons often require direct human intervention, such as dredging and the disposal of dredged material, to maintain the safety and accessibility of navigation channels. Dredging may have short and long-term effects on macrozoobenthic communities. Because they respond relatively quickly to anthropic and natural stress, benthic invertebrates are considered a biological quality element sensu Water Framework Directive 2000/60/CE (WFD) used to assess the ecological status in transitional water such as coastal lagoons.The monitoring of dredged areas and the subsequent comparison to the ecological quality status (EcoQS) sensu WFD in the Marano and Grado Lagoon has revealed that macrozoobenthic communities are slightly unbalanced and tolerant species prevailed. In this naturally stressed environment, the recovery time after the disturbance caused by dredging was three to six months, and richness and diversity were mostly related to the salinity range and distance from sea inlets.

Fish assemblages of the Marchica lagoon (Mediterranean, Morocco): Spatial patterns and environmental drivers

The fish assemblages in the Marchica lagoon were studied in June 2015, by purse seine netting, according to a systematic sampling design of 32 stations covering the whole lagoon area. The fish community was analysed both in terms of its taxonomic and functional structure, and the spatial patterns in the community distribution analysed in relation to environmental gradients in the lagoon. A total of 25,674 individuals, belonging to 43 fish species and 20 families were recorded, consisting of 20 marine migrant, 12 marine straggler and 11 lagoon residents species. Numerically, the fish assemblage was largely dominated by pelagic marine planktivore species. A spatial gradient in the bentho-demersal component of the fish assemblage structure was observed, with more marine species occurring near sea inlet and more resident species in the lagoon inner margins. No clear spatial structure was identified for the pelagic fish component, which was homogeneously distributed within the lagoon. Depth was the most important abiotic factor affecting the abundance distribution of both bentho-demersal and pelagic species, along with other factors such as vegetation cover, pH, temperature, dissolved oxygen, salinity and suspended matter. To maintain high biodiversity and sustainable fishing in the lagoon, management measures based on the protection of shallow habitats are recommended.

Co, Hf, Ce, Cr, Th, and REE systematics of modern bottom sediments of the Barents sea

The Co, Hf, Ce, Cr, Th, and REE systematics are analyzed for modern sediments collected by a bottom grab during the 67th and 68th cruises of R/V “Akademik Mstislav Keldysh” and samples taken in the Barents Sea bays and inlets. Our results indicate that most modern bottom sediments are composed of fine silicoclastic material enhanced with a suspended matter of the North Cape current, which erodes the western coast of Scandinavia, and due to bottom erosion of some marine areas, as well as erosion of rock complexes of the Kola Peninsula, Novaya Zemlya, and Franz Josef Land (local provenances). Material from Spitsbergen also probably played a certain role. In the southern part of the Barents Sea, clastic material is supplied by the Pechora River.

Time-varying storm surges on Lorentz\u2019s Wadden Sea networks

We present an idealized network model for storm surges in the Wadden Sea, specifically including a time-dependent wind forcing (wind speed and direction). This extends the classical work by H.A. Lorentz who only considered the equilibrium response to a steady wind forcing. The solutions obtained in the frequency domain for the linearized shallow-water equations in a channel are combined in an algebraic system for the network. The velocity scale that is used for the linearized friction coefficient is determined iteratively. The hindcast of the storm surge of 5 December 2013 produces credible time-varying results. The effects of storm and basin parameters on the peak surge elevation are the subject of a sensitivity analysis. The formulation in the frequency domain reveals which modes in the external forcing lead to the largest surge response at coastal stations. There appears to be a minimum storm duration, of about 3–4 h, that is required for a surge to attain its maximum elevation. The influence of the water levels at the North Sea inlets on the Wadden Sea surges decreases towards the shore. In contrast, the wind shearing generates its largest response near the shore, where the fetch length is at its maximum.

An ultra‐high‐resolution 3D marine seismic system for detailed site investigation

ABSTRACTCurrently, marine ultra‐high‐resolution 3D surveys tend to be characterized by signal frequency ranges of 0–600 Hz and bin sizes of the order of 3 to 6 metres. This may be acceptable in industry geohazard studies for top‐hole well drilling, but it does not have sufficient resolution for the very detailed information required by geotechnical engineers for the design and positioning of the turbine foundations in offshore wind farms.We present a newly developed ultra‐high‐resolution 3D system, which takes the 3D‐resolution and 3D‐imaging one step further: to frequency ranges up to 2.5 kHz and 1‐m bin sizes. This system is based on an ultra‐high‐resolution sparker source utilising negative discharge technology, thus guaranteeing a stable and repeatable source signature. The high‐fidelity multi‐channel recording system is composed of four 24‐trace streamers with GPS positioning on both sources and receivers. Sophisticated navigation processing guarantees decimetre precision and the resultant 1‐m bin sizes. In addition, slant streamer technology is applied to ensure a broadband seismic response. Processing techniques, including critical corrections for wave motion and tides, have been developed.Trial surveys were conducted in Thailand to validate the method and later in Croatia to study the shallow geology for the foundations of a 2.5‐km bridge across a sea inlet. The resultant 3D cubes gave very detailed views of the subsurface allowing the imaging of stratigraphic structures and small‐scale features, such as individual boulders in a boulder bed, that had hitherto not been identified.

Windsurfing in Mute Swans (Cygnus olor)

ABSTRACT Mute Swans (Cygnus olor) were observed using tailwind as a support for high-speed water transportation on three different occasions in three different locations in Sweden. With the wings arched over the back, they traveled ∼100 m in an inlet of the Baltic Sea in Stockholm, several hundred meters in Lake Hjalstaviken in Enkoping, and ∼350 m in Lake Krankesjon in Lund. The speed of the movement was estimated to be much higher than normally seen for swimming swans. The first observation included two Mute Swans traveling one after another in the same direction, the second observation was of one single individual traveling towards a group of conspecifics, and the third observation was of a single individual traveling by itself. This behavior may serve as a means of medium-distance water transportation in this heavy bird species.

Metals from mine waste as potential cause of oxidative stress in burrowing crab Neohelice granulata from San Antonio bay

The Natural Protected Area San Antonio bay is of particular importance for its congregation of migratory shorebirds and it has been declared one of the Western Hemisphere Shorebird Reserve Network International site (WHSRN). Present study represents the first assessment of variation on oxidative stress biomarkers in male crab Neohelice granulata from San Antonio bay (Río Negro, Argentina) under field conditions, associated mainly to metal contamination coming from passive mining wastes. Three sites were sampled once every three months from November 2012 to August 2013 within this sea inlet (Pile, Fishery and Port) and a control site at the southeast of the bay (Punta Perdices). Accumulation of Ni, Zn, Cr and Al varied only with seasons although without a constant trend, meanwhile Cd, Cu and Pb also varied among sites being highest in Pile and Port. Biochemical results indicated that variations in catalase activity was only site specific being maximum in Pile; meanwhile lipid radical, α-tocopherol and metallothioneins were only seasonal specific being higher in autumn and winter. Seasonal variation was also found for total thioles, being the content higher in summer and autumn than in winter. Correlation analysis revealed that malondialdehyde and α-tocopherol have a positive association with Al and negative with Ni, meanwhile GST has a positive association with Fe. Crabs from the closest area to the waste pile did not exhibit a differentiated oxidative pressure despite the higher accumulation of metals. It is possible that crabs from contaminated areas have developed a tolerance to metals, indicating a strong ecotoxicological selective pressure. More studies are needed to assess whether there is a transfer of metals through the food chain.

Evolving coastal character of a Baltic Sea inlet during the Holocene shoreline regression: impact on coastal zone hypoxia

Although bottom water hypoxia (O2 < 2 mg L−1) is presently widespread in the Baltic Sea coastal zone, there is a lack of insight into past changes in bottom water oxygen in these areas on timescales of millennia, and the possible driving factors. Here, we present a sediment-based environmental reconstruction of surface water productivity, salinity and bottom water oxygen for the past 5400 years at Gasfjarden, a coastal site in SE Sweden. As proxies, we use dinoflagellate cysts, benthic foraminifera, organic carbon (Corg), biogenic silica (BSi), Corg/Ntot, Corg/Ptot, Ti/Al, K/Al and grain size distribution. The chronology of the sediment sequence is well constrained, based on 210Pb, 137Cs and AMS 14C dates. Between 3400 and 2100 BCE, isostatic conditions favored enhanced deep water exchange between Gasfjarden and the open Baltic Sea. At that time, Gasfjarden was characterized by relatively high productivity and salinity, as well as frequently occurring hypoxic-anoxic bottom water, despite the relatively large connection with the Baltic Sea. The most severe interval of oxygen depletion is recorded between 2400 and 2100 BCE, and appears to coincide with a similar hypoxic event in the Gotland Basin in the open Baltic Sea. As regional climate became wetter and colder between 2100 BCE and 700 BCE, salinity declined and bottom water oxygen conditions improved. Throughout the record, grain size, Ti/Al and K/Al data indicate an evolution towards a more enclosed coastal system, as suggested by reconstructions of the post-glacial shoreline regression. Gasfjarden shifted to close to modern conditions after 700 BCE, and was characterized by less hypoxia and lower salinity compared with 3400–700 BCE. The timing of the shift corresponds with the Sub-Boreal/Sub-Atlantic transition in Europe. Human-induced erosion in the catchment is observed as early as 600 CE, and is particularly prominent since regional copper mining activity increased around 1700 CE. A sharp increase in sediment Corg concentration is recorded since the 1950s, indicating significant anthropogenic impact on biogeochemical cycles in the coastal zone, as observed elsewhere in the Baltic Sea.