Long-Term Alterations to the Varna-Beloslav Lake Complex due to Human Activities (Bulgarian Black Sea Coast (original) (raw)
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Recent State of Beloslav Lake (Bulgaria)
The paper deals with the dynamic of hydrochemical parameters in Beloslav Lake-one of Bulgarian Black Sea coastal lakes. It is strongly affected by human activities. An estimation of water quality (WQ) and anthropogenic impact on the lake is of the first importance for a sustainable management in context of EU Water Framework Directive/60/2000. On the base of seasonal monitoring data for nutrients (nitrite, nitrate, phosphate), dissolved oxygen, BOD and oxidizability the lake could be considered as a high eutrophicated area. High polluted rivers discharge into the lake and cause negative changes of WQ, including hypoxia in the near bottom waters. The paper discusses different periods of anthropogenic influence depending on human activities and different kind of pollution sources. The comparison of the data after 2000 with the data from period of intensive eutrophication (80s) reveal a slight decreasing tendency of nutrients in relation of the collapse of the economy during the last 1...
2010
A revision of river and lake typology in Bulgaria has been done within the Ecoregion No. 12 Pontic province and Ecoregion No. 7 Eastern Balkans according to the Water Framework Directive 2000/60/EC. Certain geographic changes between the Ecoregion No. 12 and Ecoregion No. 7 have been proposed based on existing biogeographic data, at the beginning. The whole part of the Danube and Black Sea River Basin district have been associated to the Pontic Province (ER No. 12) as well as the rest part of the Southern Bulgaria (Maritsa river basin, Mesta RB and Struma RB) has been allied to the Eastern Balkan (ER No. 7). A serious reduction of the total number of river types (from 33 to 16 types) was justified using clear hydromorphological and biological criteria, e.g. ecoregion, vertical factors (4 altitude zones, main substratum characteristics, slope, and other supplementary factors such as fish and vegetation zonation, climate maps) and horizontal factors (calcareous geology, salinity, size category). Similar reduction of the number of lake types (from 33 to 17 types) was proposed in parallel with a significant modification of the lake typology method. Lake typology in Bulgaria was based on the obligatory factors (4 altitude zones, size typology based on surface area, depth, salinity and geology) and optional factors (residence time, mixing characteristics, e.g. monomictic, dimictic and polymictic, presence of profundal zone, reference trophic status). Seven lake types were identified as "reservoir types", which were only presented by heavily modified and artificial water bodies without any possibility for natural lake equivalent within the country or region. Four coastal lake types with various salinity (from freshwater <0.5 ‰ to hypersaline >40‰) have been reviewed as belonging to the category "transitional waters".
Palaeoecology and geoarchaeology of the Varna Lake, northern Bulgarian Black Sea coast
The coastal lakes are rich sources of biostratigraphic information that is very useful in palaeoecological reconstructions of climate changes and human impact on the natural vegetation. This information is of great importance for the archaeological descriptions of submerged praehistorical settlements found in the northern Bulgarian Black sea area. There are 4 archaeological sites in this area that have been palynologically studied for the last 30 years: the Durankulak Lake, the Shabla-Ezeretz Lake system, the Lake Bolata, as well as the Varna-Beloslav Lake system. Because of the lack of AMS radiocarbon dates for these sites, it was not possible to correlate adequately all palaeoenvironmental results with the available archaeological chronology.
Hydrobiologia, 2013
We applied a multi-proxy palaeolimnological approach to provide insights into the natural variability and human-mediated trends of two interconnected temperate large shallow lakes, Peipsi and Võrtsjärv, during the twentieth century. The history of the lakes was assessed on the basis of age-related changes in the sediment main constituents (water, organic matter and carbonate), sub-fossil pigments, diatom assemblages and organic matter dissolved in pore water. The temporal changes in the palaeodata indicate an increase of the in-lake biological production in both lakes from about the 1960s, suggesting enhanced nutrient inputs. In subsequent decades, the gradual increase of autochthonous organic matter becomes more obvious, indicating progressive eutrophication of the lakes. Palaeolimnological indicators from the sediment record of Lake Peipsi indicate a slight recession of the lake's eutrophication in the 1990s but not for Lake Võrtsjärv. The results of the study also suggest that after the lakes became eutrophied, the climatically induced water-level fluctuations ceased to be the main driver determining the abundance of phytoplankton. Responses of the lakes to human-induced impacts are better recorded in the sediments of Lake Peipsi than in those of Lake Võrtsjärv, which is shallower of the two and where the wave-induced resuspension of deposits markedly smooths or erases the signals of environmental changes. The results of the investigation expand the knowledge on how large shallow lakes respond to human-mediated and natural perturbations, including those in the lake catchment areas and the capability of the lakes to store the chronology and sequence of these changes.
Studies on the vegetation history of Lake Varna region, northern Black Sea coastal area of Bulgaria
Vegetation History and Archaeobotany, 1994
On the basis of pollen analytical investigations of two cores from Lake Varna and Lake Beloslav, the vegetation history of the Lake Varna region is traced back to the beginning of the 6th millennium B.C. A twofold zoning system is used whereby the pollen diagrams are divided into pollen zones, based on tree migration patterns, and settlement periods. Pollen zone 1 is characterised by the absence of Carpinus betulus and Fagus sylvatica. The spread of hornbeam started at ca. 6500 B.C. (pollen zone 2) and beech at ca. 6200 B.C. (pollen zone 3), the latter being the last tree to spread into the region and considerably enrich the forests of the study area. Of the many pollen taxa representing plants that are favoured by open habitats and hence potentially indicative of human impact, only a few taxa are regarded as reliable indicators of human activity. These include above all Triticura-type, and also Secale and to a certain extent Plantago lanceolata, Rumex and Polygonum aviculare. The spatial pattern of settlements is somewhat different in the areas represented by the two profiles. At both sites the first period of settlement occurred during the 6th millennium B.C. (early Neolithic). After the Neolithic period, the main settlement periods of the Eneolithic and the Early and Middle Bronze Age are recorded. On the other hand, land-use history during the Greek and Roman periods is poorly recorded. Studies on the stratigraphy, diatoms and molluscs indicate that the sixth Black Sea transgression (6500-5800 B.C.), which reached -10 m, had considerable influence on the limnological environment.
Long-Term Coastal Changes Of Varna Bay Caused By Anthropogenic Influence
2011
Abstract. This research aims to explore coastline alterations and changes to the beaches of Varna Bay, North Bulgarian Black Sea coast, between 1908 and 2007. A large number of different types of port and coast-protection structures have been constructed along the coast of the study area, over a 100-year period. As a result of human activities i.e. building of harbour, navigational channels, coastal dike and solid groin system, the coastline of study area and adjacent beaches have been significantly modified. Various sources of shoreline position data were used to detect long-term coastal changes: the historical map of Varna Bay at a scale of 1:10 000, from 1908; and the modern satellite image from 2007. Data processing and analysis were performed in GIS environment, as both map and satellite image were preliminary geo-referenced. An indicative segmentation by landform units (beaches/cliffs) and technogenous units (port/coast-protection structures) of both historical and current coa...
Lake Evolution in the Żnin Region in the Years 1912– 1960 (Central Poland)
Quaestiones Geographicae, 2013
The evolution of lakes, which, in the final stage, leads to their disappearance, is mainly based on the analysis of surface area change. However, there is one more, frequently overlooked process, which determines lake disappearance -namely the lake shallowing. The present paper presents the direction and rate of such evolution, taking both these processes into account. It is a comparative analysis of 9 lakes in the Żnin regionwhich has the greatest water deficit in the whole of Poland. Based on bathymetric plans from two periods (early 20 th century and early 60's of the 20 th century), the author was able not only to evaluate the scale of surface area change but also to determine the value of lake basins volume change. Both these values were negative and amounted 9.1% and 14.9% respectively. Assuming that the said processes are invariable, the prospective period of lake functioning is about 500 years when taking into consideration surface area change only, and is 150 years shorter when allowing for aquatic resources change. The presented approach to lake disappearance analysis, which treats this phenomenon as a decline in aquatic resources rather than a simple decrease in surface area, is more reliable and therefore, scientific works in this field should take the results of lake shallowing into consideration.
Palaeoecology and Geoarchaeology of Varna Lake, Northeastern Bulgaria
Proceeding of the Bulgarian Academy of Sciences, 2013
Palaeoenvironmental data from the high-resolution spore-pollen analysis of laminated sediments from newly-taken Core 3 -Varna Lake were combined with analyses of dinoflagellate cysts, acritarchs and other non-pollen palynomorphs (NPP), including fossil algal and fungal remains. The location of the core is close to submerged prehistorical sites and permits the palaeoenvironmental correlations of obtained results with available archaeological and geochronological data. The established Age Model shows that the accumulation of lake sediments started after 7870 cal. BP and is connected with a rise of the Black Sea level. One-hundred-ninety-cm-long molluskan shell hash layer of Mytilus galloprovincialis covers the interval from 7776 to 6183 cal. BP. The mixed oak and hornbeam forests dominated the vegetation cover during the Atlantic, Subboreal and Subatlantic chronozones of the Holocene. An important change in the forest composition occurred at ca 5598 cal. BP, when Carpinus betulus increased its spreading due to climatic changes. The high-resolution reconstruction of palaeovegetation also reveals the extent of anthropogenic influence in Varna Lake area. Two periods of significant presence of pollen from cultivated cereals, weeds and ruderals were identified. According to the available AMS-radiocarbon data, these periods are attributed to the Late Eneolithic and Early Bronze Age. The anthropogenic impact on the natural vegetation has been identified by deforestation and agricultural practice. The Transitional period without human activities between these two periods lasted ca 319 years