Abstract. Palynological investigation and radiocarbon dating of a 6-m core from lake Durankulak, north-eastern Bulgaria, enables vegetation development and human occupation from ca. 5500-5300 cal. B.C. onwards to be traced. Steppe vegetation that included with groves of deciduous trees as Quercus, Ulmus, Carpinus betulus and Corylus changed to a forest-steppe after 4000 cal. B.C. The archaeopalynological record indicates three distinct phases of human activity as follows: (1) 5300- 4200 cal. B.C. (late Neolithic and Eneolithic) during which farming, that included a substantial arable component, was pursued, (2) 3500-3000 cal. B.C. (transition to early Bronze Age) when stock rearing appears to have dominated, and (3) after 1300 cal. B.C. (late Bronze Age) when arable farming again assumed importance. The palynological data correlate well with the rich archaeological record for human settlement that is available for the region from late Neolithic times onwards.

   Palynological investigations of lakes along the Bulgarian Black Sea coast have enabled the main phases of vegetation development and human impact for the last 8000 years to be traced. The pollen diagrams generally demonstrate a long period of uniformity in forest composition for the greater part of the Holocene. One of the main outstanding issues arises from the fact that, in the basal parts of some pollen sequences (cf. lake Durankulak and lake Shabla-Ezeretz), NAP values are comparatively high but radiocarbon dates older than 8000 B.P. are not available (Bozilova and Beug 1994).
    This paper presents results of further palynological research in the lake Durankulak area, northern Black Sea coastal region. A 6.2-m long profile from lake Durankulak (core Durankulak-1) has already been presented in a preliminary publication (Bozilova and Tonkov 1985). For that profile, only two ¹⁴C dates were available and these related to the upper part of the sequence, i.e. 1810±60 B.P. (cal. A.D. 131-324) and 2625±65 B.P. (826-770 cal. B.C.) at 140 cm and 180 cm depth, respectively. Unfortunately, it was not possible to attach a chronology to the middle and lowermost sections or to correlate these with sequences from other coastal lakes. The high NAP values of 80-90% in the lower part of the profile indicate a steppe environment in the early Holocene but precise spatial and temporal patterns could not be established. With a view to addressing these unresolved questions, a new core, Durankulak-2, has been investigated and a chronology constructed based on of ¹⁴C dates. On the basis of these results, a critical assessment of the age of the lake sediments is attempted and comparison is made with the chronological framework presented by Bozilova et al. (1996). The course of vegetation development and human impact is then reconstructed on the basis of the new results and also the palynological and archaeological data obtained during the course of research carried out in the northern coastal area during the last decade.

   The lake is separated from the Black Sea by a sand strip, 100-200 m wide. In stormy weather, water from the Black Sea penetrates the lake, the sand strip is occasionally washed away and subsequently forms again. The lake is essentially freshwater though slightly brackish (average salinity is 2%o; in summer, 4%o is attained), oligohalobic and eutrophic, rich in carbonates, with high pH (8-8.5) and does not experience oxygen deficits.

   Lake Durankulak belongs to the Dobrudza-Varna subregion of the Black Sea climatic region. The climate is determined by the north-eastern continental influence and partly by the Black Sea. Mean annual precipitation is 440 mm with 140-170 mm precipitation in late autumn and early winter, while in spring and in summer, rainfall is at 100 mm and 125-150 mm, respectively. The predominant winds in January and July are northerlies and westerlies, respectively. The strong winter winds blow away the thin snow cover and so contribute to freezing of the soil.
    The soils around the lake and near the sea are carbonate-rich and consist of eroded chernozems. Typical chernozems with medium water and nutrient-holding capacity are developed in the Dobrudza region and along the border with Romania. In these areas, they occupy a narrow strip and are a major determinant in the formation of a xerothermic vegetation type. Plant nomenclature follows Jordanov (1963-1995) (ed.).
    According to Bondev (1982, 1991), lake Durankulak is included in the Black Sea region of the Euxinian province of the European deciduous forest area. In southern Dobrudza and around the lake, xerothermic herb communities are developed with dominant grass species such as Chrysopogon gryllus, Andropogon ischaemum, Agropyrum brandzae, and also other xerophytes such as Artemisia pedemontana, Paeonia tenuifolia and Iris pumila. Ulmus minor, Pyrus pyraster, Fraxinus excelsior, Crataegus monogyna, Corylus avellana and Sambucus nigra grow as isolated specimens or in clusters on the lower terraces and in the ravines near the lake. Most of the former forest stands have been cleared for agriculture. To the west, in the area of the Ludogorie plateau and the Danube river, fragments of forests are preserved, composed mainly of Quercus pubescens, Q. cerris, Q. frainetto, Tilia argentea, F. excelsior, Acer campestre and Carpinus betulus.
    A reed formation dominated by Phragmites australis is developed mainly on the western and southern shores of the lake. The most important hydrophytes and hygrophytes are Zanichellia palustris, Wolffia arrhiza, Potamogeton crispus, Typha latifolia, T. angustifolia, Sparganium erectum, Bolbosehoenum maritimum, Schoenoplectus litoralis, Butomus umbellatus, Alisma plantago-aquatica, Solanum dulcamara, Calystegia sepium and Lycopus europaeus. Halophytes along the eastern shore include Puccinellia convoluta, Salicornia europaea, Limonium gmelinii and Aeluropus littoralis(Kotchev et al. 1983).