Volume 10 (2023): Issue 1 (March 2023)

In this study we developed thermodynamic models for solid-liquid equilibrium for mixed systems HF-NaF-H₂O and HF-KF-H₂O up to 2 m HF at T = 25^oC. Models are developed on the basis of Pitzer ion interactions approach. The recommendations on mean activity coefficients (γ_±) have been used to construct the model for HF-H₂O system. The models for binary systems NaF-H₂O and KF-H₂O are taken from our previous study in the same journal [Donchev et al. ASN (2021) 8(2), 1-15]. To parameterize models for ternary systems we used the available solubility data, i.e. on the basis of solubility approach. The thermodynamic solubility products (as ln K^o_sp) of precipitating in mixed systems double salts [NaF.HF(cr), and KF.HF(cr)] have been determined on the basis of evaluated model ion interaction parameters and using experimental m(sat) solubility data. The model is in a good agreement with experimewnt solubility data in the systems HF–NaF–H₂O and HF–NaF–H₂O up to maximum HF molality of 2 mol·kg⁻¹. At higher acid molality the model predicts much higher solubility of double salts (NaF.HF(cr) and KF.HF(cr) for both mixed systems. It was concluded that not a correct raw data for binary HF–H₂O system used in parameterization are the main reason for concentration restriction of mixed HF models presented here.

The purpose of the present study was to gather information about the effects of the herb Levisticum officinale (lovage) and of its phenolic ingredients and to elucidate the potential health benefits of the plant in relation to its polyphenolic content. The study was performed by searching different internet-based databases (Google Scholar, ScienceDirect, PubMed, etc.).

Levisticum officinale (lovage) is a perennial aromatic plant from the Apiaceae family. This herb is rich in essential oil and is widely used as a seasoning for culinary purposes. Lovage contains up to 860 mg GAE/100 g fresh weight phenolic substances as well. Polyphenols in L. officinale belong to the classes of flavonoids (quercetin, rutin, kaempferol and anthocyanins) and phenolic acids (chlorogenic, neochlorogenic, ferulic, gallic, ellagic). They contribute to potent antioxidant properties of the plant. Anti-inflammatory, anticancer, neuroprotective, antidiabetic, antibacterial, hepatoprotective and other properties of L. officinale extracts have also been demonstrated. Phenolic substances abundant in lovage have shown to be protective in models of osteoporosis and different cardiovascular diseases as well.

The information confirms our assumption that Levisticum officinale is not only an useful and pleasant-tasting Mediterranean-cuisine seasoning but also a herb that can contribute to the healthy lifestyle.

Opuntia fragilis (Nutt.) Haw. (Cactaceae) is the smallest and most cold-hardy species of genus Opuntia in North America. In Bulgaria it is grown as an ornamental plant, but in 2019 a population of this species was discovered by other researchers in natural habitats in Lozenska Mt (Western Bulgaria) at 630–660 m a.s.l. on an area (extent of occurrence) of ca. 100 m². In July 2020, we established a population of this species on the Black Sea coast near the town of Primorsko (Eastern Bulgaria) at 5 m a.s.l. on an area of ca. 300 m². The distance between the two populations is 360 km in a straight line and their origins are independent of each other. The two localities of this species are so far the only ones described not only for the territory of Bulgaria, but also for Europe.

Data are given on the conditions characterizing each of the localities. The possible reasons for the appearance in natural habitats of this alien plant species for the Bulgarian flora are considered. The impacts and threats this species may have on biodiversity in natural habitats are indicated. Measures have been proposed to control the populations of the species.

The concept of sustainable development can play a key role for various knowledge-based sectors, a major factor in the educational system, focused on addressing the problems that exist and preventing new social, economic and environmental ones.

The article examines the definition of sustainability, the point of learning aimed at environmental sustainability. The new European Sustainability Competence Framework that outlines the competencies necessary for the ecological transition, including critical thinking, initiatives, conservation of nature and taking responsibility for the negative impact of everyday actions and decisions on the environment and climate worldwide, has been examined here.

Humanity continues to degrade natural capital, threatening its long-term sustainability. This more and more categorically imposes the need to create a specific green infrastructure - a response to the natural solutions to the accumulating problems (environmental pollution, floods, natural disasters and cataclysms). The failure of decisions to pay sufficient attention to ecological consequences and to apply systematic measures of high quality are among the main reasons for the current situation in most ecosystems. The fast-paced and highly mechanized way of life of modern man creates the illusion of remoteness from the natural world. Yet all human activity depends entirely on ecosystems and their functions and at the same time has (threatening) impacts on them. Therefore, the achievement of greater efficiency in the use of natural resources and the creation of suitable ecological living conditions are critically important goals both for Europe and for the whole world. Green Infrastructure (GI) is a successfully tested tool for providing environmental, economic and social benefits through environmentally sound solutions. Such a tool helps to understand the values provided by nature to human society and mobilizes investments for their maintenance and growth.

Bulgaria is a country with an extremely diverse nature. Unlike a number of European countries, Bulgarian nature is relatively well preserved. For the purposes of its protection, a network of protected areas was created, which occupy 5.3% of the country’s territory. Bulgaria also participates in a number of international initiatives, which put about 1/3 of the territory of Bulgaria under protection of the natural environment. According to the Protected areas Act in Bulgaria, 6 categories are distinguished - national parks, natural parks, reserves, maintained reserves, protected localities, natural attractions. Among them, important resources for the development of tourism are national parks, natural parks, protected localities and natural attractions. They represent unique sites for the development of alternative forms of tourism such as ecological, cultural-cognitive, route-cognitive tourism, etc. On the other hand, reserves and maintained reserves prohibit tourism activities. The network of protected areas is unevenly developed throughout the country. It is better represented in the mountainous areas, and in the plain parts of the country it is more limited due to the strong anthropogenic changes and the pressure from various human activities. In connection with the preserved nature, the mountains are preferred sites for tourism. The contribution of the protected areas in this regard is significant.

Stara planina tourist region is among the country’s tourist areas with well-defined mountainous characteristics. This is an important prerequisite both for the preservation of nature and for the formation of a suitable environment for recreation and tourism, and the mentioned directions are mutually bound.

The purpose of this article is to valorize the protected areas in Stara Planina tourist region and to highlight the possibilities for their current and future use for the development of tourism.

Tourism is one of the fastest growing industries of the new millennium. Bulgaria is a destination with an extremely large variety of natural and anthropogenic tourism resources and a relatively well-developed tourism sector of the economy, which brings significant income to the country’s economy. Varna tourist region is one of the leaders in the development of tourism, both for sea vacations and specialized types of tourism. Despite the great potential of the country and the researched tourist areas in particular, there are a number of problems related to uneven tourist development, seasonality, deteriorated tourist infrastructure and the quality of the services offered. The purpose of this paper is to study the current state of tourism and the opportunities for its development in the region.

The report reveals the impact of tourism on changing national identity. The interaction between tourism and cultural identity as social phenomena is noted. Globalization as a prerequisite for cultural disorientation is examined. The concept of anthropotok, as a mass self-sustaining process of identity change, is examined.