Varna Bay Research Articles

Influence of Some Environmental Factors on Summer Phytoplankton Community Structure in the Varna Bay, Black Sea (1992–2019)

During the last decades, a decrease in the nutrients and an increase in marine temperature on the surface of the Varna Bay of the Black Sea have been registered. The main aim of this study was to establish the influence of some environmental factors (SST, TP, DIN) on the structure of the phytoplankton and to define what part of these dynamics results from the changes in temperature. Bivariate correlation and Nonlinear regression analyses were used to establish the connection between factors of the environment and the quality parameters of different size and taxonomic groups of phytoplankton. The rising SST proved to statistically significantly influence the decrease in the abundance of nano-phytoplankton (50.9%), the abundance and biomass of micro-phytoplankton (53%; 33.2%), the Bacillariophyceae (49.5%; 35.6%), and the biomass of the species of group “Other” (51.4%). The decreasing TP has a significant influence on the decrease in the abundance and biomass of the diatoms and the biomass of group “Other”. The decreasing DIN significantly affects the decrease in the abundance and biomass of Dinophyceae. The analyses showed that rising temperatures had a leading role in the changes in the taxonomic and size structure of phytoplankton during the period 1992–2019.

Pollution of Varna Lake and possibilities of using the pollutants as resources

Varna Lake is of great social and economic importance for the city of Varna and the entire region. The urbanisation of the areas surrounding the Varna-Beloslav Lake complex and the accelerated industrialisation around the coastline of Varna Bay have significant anthropogenic pressure on the aquatic ecosystem. An essential aspect is that industrial development, maritime transport and urbanisation are substantial sources of large-scale inorganic and organic pollution with all the resulting negative consequences. Recent measurements show that the surface sediments, which are a source of nutrients for the water body of Varna Lake, are contaminated with heavy metals and oil products. In this paper, we present a quantitative assessment of the degree of contamination with heavy metals (Hg, As, Fe, Cu, Pb) and petroleum products in the upper sediments of Varna Lake and then discuss opportunities for using some of these pollutants as a resource. The exploitation of these resources would bring significant benefits for improving the ecological status of Varna Lake.

LIFEWAY INTERPRETATIONS FROM ANCIENT DIET IN THE VARNA CEMETERY

SummaryRescue excavations in the urbanized area of the Varna Bay in 2017 have brought to light 15 prehistoric burials whose grave goods and AMS dating have unequivocally related them to the famous Copper Age cemetery in Varna on the Bulgarian Black Sea coast. The newly excavated area was called Varna 3 and the ten AMS‐dated individuals from there and 19 individuals from the Varna 1 cemetery were subjected to FRUITS modelling for the purposes of dietary reconstruction. There is no link between diet and grave deposition but differentiation in diet does exist in terms of sex. The results showed overall isotopic consistency with a small group of five outliers, among whom is a five‐year‐old girl with steppe aDNA ancestry, who is considered to be a migrant to the Varna area. We discuss the social implications of the dietary and aDNA results that reveal a more complex pattern than had previously been considered.

Recent expansion of the alien invasive blue crab Callinectes sapidus (Rathbun, 1896) (Decapoda, Crustacea) along the Bulgarian coast of the Black Sea

Thirteen new records of the blue crab Callinectes sapidus (Rathbun, 1896) have been documented near the Bulgarian Black Sea coast since 2006. This is an evidence for a recent expansion of the species in this part of the Black Sea. This expansion could be explained by the existing of established population in the area and is confirmed by the capturing of an egg-bearing female in the Varna Bay in 2005.

Varna Bay (Bulgaria): research based on the water-related challenges.

Many factors influence bay waters, including greater concentration of people in cities, industrial production, how land is used, dynamics of flow in water systems, and climate change. Water management remains one of the greatest human challenges. Scientists continue to respond to water-related challenges through the research to improve both human and environmental health. Study in the Varna Bay, providing key knowledge on hydrological and hydrochemical characteristics, was done over 2015-2018. Unified methods for marine waters were used. An increase in SST was ascertained. The range of SSS monthly fluctuations increased almost twice compared to a long-term range. Nitrate nitrogen range was bigger than phosphate phosphorus range. A sharp increase in organic matter was ascertained but generally the range decreased compared to a long-term range.

Organization Of The Medical Aspect In Overcoming The Consequences During The First Training In Emergency Water Landing Of An Aircraft In The Varna Bay

All aircrafts fly over water areas, which makes the possibility of water landing great. Aviation accidents are a growing problem and some of them occur in coastal areas where there is a possibility for timely assistance. In Varna, a training program named Search and Rescue in Case of an Air Accident and Elimination of the Consequences was held. It covered actions of the constituent parts in the district of Varna on organization, management and interaction of the forces for search, rescue and liquidation of the consequences in case of an accident of an aircraft near a body of water. The search and rescue teams have the task of reaching the remains on land and water, rescuing people, evacuating victims and transporting to medical facilities, extinguishing the fire, limiting the access to the area and providing corridors connecting the scene with the services and medical facilities. The triage of the injured and the victims is carried out by medical professionals while the performing of first aid is being done by the Center for Emergency Medical Aid (CSMP) and the volunteers from the Bulgarian Red Cross (BRC). Through scientific sources and the approved plan for conducting the exercise, the medical aspects of overcoming the consequences of an emergency water landing of an aircraft in the Varna Bay have been analyzed. Of particular importance is the good cooperation between the medical, voluntary and rescue teams in order to be able to react quickly and efficiently. With the help of these exercises, Varna is better prepared to deal with any disaster or mass accident that may befall the region.

Influence Of Lake Inflow On The Benthic Communities Of Varna Bay

As a result of high urbanization and industrialization the Varna Bay is one of the most influenced by anthropogenic activity region of the Bulgarian Black Sea area. Simultaneously the Varna Lake nutrient-enriched inflow contributes additionally to the negative changes of the ecological situation, especially in summer. To establish the state of the benthic communities in contact with lake waters in 2019, samples of macrozoobenthos were collected. The quantitative parameters of macrozoobenthos in Varna Bay established: taxonomic structure dominated by Polychaeta , spring abundance 2.5 twice higher that in autumn, built mainly by Oligochaeta , known as indicators for eutrofication. During both seasons the biomass maintains low values, due to predominance of small-sized mollusks. According to statistical indices the ecosystem status is slightly or moderately disturbed, with better results for the North region. Cluster analysis clearly defines 2 groups, according to the bottom substrata, with stations along the way of lake inflow waters forming an independent cluster. In conclusion, despite the total state of the Varna Bay ecosystem, the most negatively influenced stations are along the lake inflow way.

Relationship Between Solar Energy And Sea Surface Temperature In The Varna Bay

Here we present a relationship between solar energy and sea surface temperature for the months from April to October in a 10-year period (2010-2019). The solar energy data is provided by the automatic weather station Vantage Pro2 located in the meteorological station in Varna and the sea surface temperature data is received from measurements in the Varna bay. A direct relationship between the two variables is found with the strongest correlation for two periods of time – for April-May and for September-October. During the months of June, July, and August, when the change in the amount of solar energy is with very small variations and trends, we suggest that the increase of the sea surface temperature is due to some of its physical characteristics, geographical location of the bay and/or the predominant wind direction, heat capacity, etc.

Morphometric, quantitative and population characteristics oF Rapana venosa (Valenciennes, 1846) in front of Pasha Dere

A total of 468 individuals of the rapa whelk (Rapana venosa) were studied in terms of size, weight and sex in the sea area in front of Pasha dere (south of Varna Bay, Black Sea) in the summer of 2016. Sampling was performed by bottom trawling on three transects at different depths (from 9.0 m to 24.5 m) and different type of substrate (sand, sandy silt and silt). In the present study the average length was 6.36 cm and the absolute shell length ranged from a minimum of 3.24 cm to a maximum of 9.68 cm. The established average total weight was 47.31 g, its absolute value ranging from 9.98 g to 135.02 g. The average values of the shell length and total weight of the rapa whelk were the lowest on shallow sandy bottom (6.01 cm and 41.94 g, respectively) and the highest at 21 m depth on silty sediments (6.84 cm and 55.13 g, respectively). The size-weight relationship between all individuals was described by the formula W = 0.248L 2.797 (R 2 = 0.937), with the allometric coefficient (b) ranging from 2.817 to 3.066. On the sandy sediment, the male: female ratio was 2:1; in sandy silt, the percentages of male and female specimens were 55% and 45% respectively, and in silty sediment the sex ratio was 1:1. The male specimens were characterized by higher values of all morphometric parameters compared to the females. In the size distribution of sexes, the highest was the frequency of the males in size class of 6-7 cm, and the females with 5-6 cm shell length. In the weight distribution of the males, the individuals with total weight in the range 30-40 g dominated, while the prevailing female individuals weighed between 20 g and 30 g.

Risk assessment of some heavy metals in mussels (Mytilus galloprovincialis) and veined rapa whelks (Rapana venosa) for human health

The purpose of the present study was to analyze the concentrations of lead, cadmium and mercury in mussels (Mytilus galloprovincialis) and veined rapa whelks (Rapana venosa) caught in the Varna Bay of Black Sea and to evaluate the risk for human health from the presence of the three heavy metals. The highest average concentrations in mussels were those of cadmium (0.280 mg/kg), followed by lead (0.251 mg/kg) and mercury (0.017 mg/kg). Veined rapa whelks also showed highest levels of cadmium (1.113 mg/kg), followed by lead (0.045 mg/kg) and mercury (0.034 mg/kg). EDI values for adults consuming mussels and veined rapa whelks were below the published RfDo and PTWI values. All THQ and HI values were below 1. The consumption of M. galloprovincialis and R. venosa caught in the Varna Bay, Black Sea, did not pose any risk for the health of adult people as lead, cadmium and mercury were concerned.

A framework to include the (inter)dependencies of Disaster Risk Reduction measures in coastal risk assessment

Effective coastal risk management often involves the selection and appraisal of Disaster Risk Reduction (DRR) measures. Such measures, however, are rarely implemented in isolation and their (inter)dependencies need to be considered to assess the overall contribution to risk reduction. This paper presents a framework that utilises a pathway-based approach to consider such (inter)dependencies. The framework identifies measures that have the potential to directly influence risk reduction (primary measures) at the individual/household level and how these relate to the implementation of other measures (non-primary). These two types of measures are linked using intermediate pathway factors, which aggregate to the effective uptake and/or operation of primary measure(s) and subsequently represent the direct influence on risk reduction when included in a risk assessment.The approach is demonstrated utilising two coastal risk examples. The case of Varna Bay, Bulgaria highlights a pathway, which explores how developing a coastal Early Warning System (EWS), can enable assets to be moved and saved prior to an event. The Praia de Faro, Portuguese application provides an example of how local risk awareness meetings can support the uptake of property raising to protect against erosion. Past experience, poor trust in authorities, house type/feasibility, transient population and strong community networks are identified as key influencing variables across both cases.The process of considering the (inter)dependencies between measures has potential to lead to improved decision-making and strategy building. The framework developed is flexible in nature and can be applied in many different situations; however, it is one step towards accounting for these (inter)dependencies at the individual/household level. Ex-ante or ex-post survey data, expert judgement and literature have been used to estimate these factors. However, in many cases this good quality data is not available, and is something that national level monitoring strategies, along with the research community, must address.

Implementation and validation of a multi-domain coastal hazard forecasting system in an open bay

European coasts are increasingly threatened by hazards related to low-probability and high-impact hydro-meteorological events. Uncertainties in hazard prediction and capabilities to cope with their impact lie in both future storm pattern and increasing coastal development. Therefore, adaptation to future conditions requires a re-evaluation of coastal Disaster Risk Reduction (DRR) strategies and introduction of a more efficient mix of prevention, mitigation and preparedness measures. The latter presumes that development of tools, which can manage the complex process of merging data and models and generate products on the current and expected hydro-and morpho-dynamic states of the coasts, such as forecasting system of flooding and erosion hazards at vulnerable coastal locations (hotspots), is of vital importance. Output of such system can be of an utmost value for coastal stakeholders and the entire coastal community. In response to these challenges, Delft-FEWS (Flood Early Warning System) provides a state-of-the-art framework for implementation of such system with vast capabilities to trigger the early warning process. In addition, this framework is highly customizable to the specific requirements of any individual coastal hotspot. Since its release, many Delft-FEWS based forecasting system related to inland flooding have been developed.In this paper, a set-up of Delft-FEWS based forecasting system for Varna Bay (Bulgaria) and a coastal hotspot, which includes a sandy beach and port infrastructure, is presented. The system output generated in hindcast mode is validated with available observations of surge levels, wave and morphodynamic parameters for a sequence of three short-duration and relatively weak storm events occurred during February 4–12, 2015. Generally, while a longer term system operation/validation is needed for the model skills to be affirmed, the results obtained indicate a reliable prediction of coastal hazards, thus giving a sound basis for estimation of hazard impact.

Seasonal Changes in Quality and Fatty Acid Composition of Black Mussel (Mytilus galloprovincialis)

ABSTRACTThe study was designed to assess the seasonal variations in the quality and lipid profile of mussel meat (Mytilus galloprovincialis) harvested along the Bulgarian coast of the Black Sea. The trial period lasted from June to October, and the sampling was carried out in the area of Varna Bay. Technological quality of the mussels was determined by measuring the water holding capacity (WHC) and cooking and roasting losses. Proximate composition, total aerobic plate count, and fatty acid analysis were carried out. Technological parameters and nutritional quality of the mussel meat were strongly affected by the season. During the summer, the mussels had higher mass, meat content, and meat yield (p < 0.001) compared to the early autumn, which corresponds to the lowest protein content during this season. Lipid profile showed seasonal variations in both individual and total fatty acid amounts (p < 0.001). Saturated fatty acids (SFA) had the highest content in summer, while monounsaturated fatty acids (MUFA) decreased gradually until the autumn. The content of polyunsaturated fatty acids (PUFA) reached its peak in October, contributing to the most favorable values of the nutritional indices of lipids in the early autumn.

Applicability of massively parallel sequencing on monitoring harmful algae at Varna Bay in the Black Sea

In this study the plankton diversity in 13 environmental samples from Varna Bay (in the western Black Sea) was analyzed using massively parallel sequencing (MPS). This preliminary study was undertaken to assess the potential of this technology for future implementation in monitoring programs in the Black Sea. Amplicon sequences of the 18S rRNA gene (V4-5 regions) were obtained using the Illumina MiSeq 250PE platform. A total of 1137 operational taxonomic units (OTUs) were obtained among which 242 OTUs with >0.990 BLAST top hit similarity (21.3% of all detected OTUs) closely related to sequences belonging to −protists. A large portion (175 OTUs=72.3%) was identified at the species levels, including species typical for the Bulgarian Black Sea plankton community, as well as many that haven’t been reported earlier in the Bulgarian Black Sea coast (124 OTUs=51.2%). Dinoflagellates were represented by the highest species number (77 OTUs comprising 31.8% of protist species), with dominant genera Gyrodinium and Heterocapsa. The present survey revealed the presence of 12 species listed as harmful, some of which have been previously overlooked, such as Cochlodinium polykrikoides, Karenia bicuneiformis, and Karlodinium veneficum. Species identification was possible for 10.3–36.0% of the detected OTUs in the six major supergroups. The frequency in Rhizaria was significantly lower than that in other major groups (p<0.05–0.01), implying difficulties in the classification from morphology-based observations. The metagenetic data had an insufficient resolution of the 18S rRNA gene for species identification in many genera. These issues may hamper the implementation of MPS-based surveys for plankton monitoring, especially for detecting harmful algal blooms (HAB). The sequencing technology is steadily improving and it is expected that sequence length and quality issues will be resolved in the near future. The ongoing efforts to register taxonomic information and quality controls in the international nucleotide sequence databases (INSDs) will be essential for improving taxonomic identification power.

CALCULATION OF MAXIMUM WAVE RUN-UP AND EROSION AT VARNA REGIONAL COAST (WESTERN BLACK SEA) USING EMPIRICAL MODELS

European coasts suffer significantly from hazards caused by low-probability and high-impact hydro-meteorological events. The aim of the study is to assess in probabilistic terms the magnitude of storm‐induced flooding and erosion hazards along Varna regional coast (Bulgaria, western Black Sea). The study is performed employing the Coastal Risk Assessment Framework (CRAF) developed within EU FP7 RISC-KIT project. It constitutes a screening process that allows estimation of relevant hazard intensities and extents within predefined sectors. Since total water level was the chief property considered for determination of coastal flooding hazard, the accurate calculation of maximum wave induced run-up is of utter importance. Therefore, a central part of the study is testing the applicability and validation of three empirical models – from which the Holman model was preferred to be applied on sandy beaches, as well as EurOtop formulation for artificial or rocky slopes. As for erosion hazard, the performance of the convolution model was assessed and subsequently employed for evaluation of shoreline retreat. Quantification of hazard intensities allowed hinterland extent to be roughly delineated. As a final result of the study, hazard indicators were obtained for both flooding and erosion, which were subsequently mapped and used for identification of the most susceptible sectors along the regional coast. It was found that their concentration is highest in Varna Bay.

ASSESSMENT OF COASTAL RECEPTORS’ EXPOSURE VULNERABILITY TO FLOOD HAZARD ALONG VARNA REGIONAL COAST

Storms and related disasters are phenomena producing coastal hazards and endangering human life and occupation. The study evaluates coastal receptors’ exposure and their vulnerability to storm-induced flooding hazard along Varna regional coast in Western Black Sea, Bulgaria. The assessment is performed employing the Coastal Risk Assessment Framework (CRAF) developed within EU FP7 RISC-KIT project. It constitutes a screening process that allows determination of susceptible alongshore sectors (hotspots) by assessing relevant hazard intensities, hazard extents and potential receptors’ exposure vulnerability within them by means of coastal indices approach. The ultimate goal is to evaluate potential risk posed by flooding in support to coastal managers, decision and policy makers. Assessment of coastal receptors’ exposure vulnerability is done by exposure indicators approach, using hazard intensities and flooding extents relevant to return period of 100 years. The approach consists of combining several indicators into a single index, thereby allowing a rapid comparison of coastal sectors. Five types of receptors are considered to formulate the relevant exposure indicators: Land Use, Population, Transport, Utilities and Business, which subsequently are combined into an Overall Exposure Indicator to evaluate potential direct and indirect impacts. Results show that the most vulnerable to coastal flooding in terms of exposure are coastal sectors located within Varna Bay, comprising port and industry facilities with regional, national and international significance.

APPLICATION OF BAYESIAN NETWORK AS A TOOL FOR COASTAL FLOODING IMPACT PREDICTION AT VARNA BAY (BULGARIA, WESTERN BLACK SEA)

Storms and related disasters are one of the most important phenomena producing coastal hazards and endangering human life and occupation. While coastal response to extreme forcing conditions can be evaluated using numerical models, there is increasing need for less computationally expensive probability tools that can quickly produce results thus contributing to more effective coastal risk management. A possible response to this demand is a Bayesian Network, which relates near-shore storm conditions to their onshore flood potential and ultimately translates them to relevant impact (consequences) expressed as damage to various receptor groups. Bayesian Network can constitute a module in an early warning system or can be used as a planning tool to evaluate the long-term vulnerability due to multiple coastal hazards, under various climate-related scenarios. The present study describes the application of a Bayesian Network for Varna Bay building on developments made in the framework of the RISC-KIT (Resilience-Increasing Strategies for Coasts – toolKIT) project. Moreover, several alternatives involving disaster risk reduction measures were examined both in present and future climate conditions. It was found that the analysis of results through the prism of the Bayesian Network provides a useful insight of the problems at the study site making it a reliable coastal impact prediction tool.

The impact of Shokarski stormwater canal on the quality of the Bulgarian Black Sea bathing waters in the area of discharge

The impact of Shokarski stormwater canal on the bathing waters quality of Varna Bay located in the northern Bulgarian Black Sea was investigated during 2007–2014. A total of five monitoring stations were selected: three city beaches near the area of discharge of the stormwater canal and two nearby resorts beaches. The water quality was assessed following the requirements of the old EU Bathing Water Directive (BWD) 76/160/EEC and the new BWD 2006/7/EC. The resort beaches exhibited excellent water quality through the whole period. The situation at the city beaches was worst. The “Officers Beach” situated exactly at the area of discharge of Shokarski stormwater canal exhibited concentrations of ammonium and nitrates significantly above the guide value in most of the cases, the lowest compliance with the total coliforms and faecal coliforms guide values and the highest concentrations of Escherichia coli and intestinal enterococci.

Development and blooms of Peridinea &lt;i&gt;Akashivo sanguinea&lt;/i&gt; in the Bulgarian marine aquatories

The article presents results of empirical field research on the development and distribution of the ''unarmoured'' peridinea Akashivo sanguinea in the Bulgarian marine aquatories during the period 1995-2015. The analysis has established that A. sanguinea is a phytoplankton species relatively rarely met in the water in front of the Bulgarian coast. The development and blooms of the species have been identified both in the surface water layer and up to 25 m (layer above the thermocline). It developed mainly in water areas rich in nutrients (Varna Bay, Burgas Bay, Balchik), but also in open sea areas (10-30 miles offshore), probably under the influence of the Danube inflow. Basically the blooms of the species were recorded in the mid-90s and at the beginning of the new century (2001). After this period the concentrations of A. sanguinea were minimal. A constant trend of reducing the size of the cells of the species has been registered. The purpose of this study was to describe, track and analyze the patterns in the development and distribution of the phytoplankton species A. sanguinea in the Bulgarian marine aquatories during that 20 year period.

Assessment of vulnerability to storm induced flood hazard along diverse coastline settings

European coasts suffer notably from hazards caused by low-probability and high-impact hydrometeorological events. The aim of the study is to assess in probabilistic terms the magnitude of storm‐induced flooding hazard along Varna regional coast (Bulgaria, western Black Sea) and to identify susceptible coastal sectors (hotspots). The study is performed employing the Coastal Risk Assessment Framework (CRAF) developed within EU FP7 RISC-KIT project. It constitutes a screening process that allows estimation of relevant hazard intensities, extents and potential receptors’ exposure vulnerability within predefined sectors. Total water level was the chief property considered for calculation of coastal flooding hazard. It was estimated using Holman model (for sandy beaches) and EurOtop formulation (for artificial or rocky slopes). Resulting values were subjected to Extreme Value Analysis to establish that the best fitting distribution corresponds to Generalized Extreme Value distribution. Furthermore, hazard extents were modelled by means of bathtubbing or overwash estimation in order to form the flooding hazard indicator. Land use, social vulnerability, transport systems, utilities and business settings were considered as exposure indicators. Finally, potential risk was assessed by coastal indices following an index-based methodology, which combines hazard and exposure indicators into a single index, thereby providing base for comparison of coastal sectors’ vulnerability. The study found that the concentration of hotspots is highest in Varna Bay.