Late Holocene Changes in Vegetation of the Mrągowo Lakeland (NE Poland) as Registered in the Pollen Record from Lake Salęt
Abstract Pollen analysis of sediments from the upper part of bottom deposits from Lake Salęt allowed reconstruction of main stages of the Late Holocene vegetation transformation in the Mrągowo Lake District (from ca. 3600 cal. years BC) and to correlate some of these changes with immigration and economic activity of local human groups. Significant spreading of secondary semi-natural birch forest, development of horn beam forest and increasing importance of anthropogenic open communities were the most characteristic features of vegetation evolution. A definite break down of elm took place between 2900 and 2500 cal. years BC, slightly after increased contribution of birch in wood lands. Disappearance of hazel around 1200 cal. years BC, accompanied by expansion of horn beam has been observed and should be linked with activity of the Ząbie-Szestno type culture and the Lusatian culture tribes during the Bronze Age, but not with a climate change. Considerable intensification of settlement processes recorded in the younger part of the Subatlantic chronozone was one of the important reasons that were responsible for quick changes in forest structure. Strong and continued deforestation started as early as the end of the 10th century AD and was substantially intensified in the first half of the 13th century.
Towards a dystrophic lake: The history of Smolak Lake (northern Poland) on the basis of geochemical and biological data
Abstract This study presents a multi-proxy reconstruction of the evolution of Smolak Lake from harmonic to dystrophic conditions. The lake’s history and environmental conditions, such as zooplankton and vegetation compositions, trophic state, water temperature and water level fluctuations, are discussed. Smolak Lake is located in the southern part of the Masurian Lakeland, northern Poland. A 350 cm core comprising thick sediments (Sm profile) are mainly composed of homogenous organic gyttja and dy was taken from the lake and analysed for geochemical and biological (cladoceran and pollen) proxies. Radiocarbon data show that the sediments accumulated from the Late Glacial (Younger Dryas period) to recent times. Based on the results of pollen data, six local pollen assemblage zones were recognized. The subfossil cladoceran fauna in the sediments are represented by 25 species belonging to four families. Five zones of Cladocera development were distinguished. The Cladocera species indicate the initial oligotrophic status of the lake and its subsequent slight increase in trophic status. From ~9000 yr cal BP (at the beginning of the Atlantic period), Smolak Lake began a fast transition to a dystrophic state. At this time, the amount of total organic carbon (TOC) in the sediments significantly increased to above 50%, and deposits containing more than 97% water were transformed into dy. The sedimentation rate was extremely low, i.e., 0.08–0.2 mm/yr. Dystrophic conditions are also reflected in the Cladocera and pollen found in the core during this period: Cladocera composition was dominated by species very resistant to acid conditions (e.g., Alonella excisa); the abundance of green algae was at its lowest level and dominated by only one genus (Botryococcus); no hydrophytes were found; and rush vegetation disappeared. Currently, Smolak Lake is a shallow, humic lake characterized by brown water and the presence of floating mats. This study shows that it’s current status is a result of it’s small, relatively undisturbed catchment, which should be protected in order to maintain this unique dystrophic habitat.
Natural Radioactivity of Intrusive-Metamorphic and Sedimentary Rocks of the Balkan Mountain Range (Serbia, Stara Planina)
Stara Planina (also known as the Balkan mountain range) is known for numerous occurrences and deposits of uranium and associated radionuclides. It is also famous for its geodiversity. The geologic framework is highly complex. The mountain is situated between the latitudes of 43° and 44° N and the longitudes from 22°16′ to 23°00′ E. Uranium exploration and radioactivity testing on Stara Planina began back in 1948. Uranium has also been mined in the zone of Kalna, within the Janja granite intrusive. The naturally radioactive geologic units of Stara Planina are presented in detail in this paper. The main sources of radioactivity on Stara Planina can be classified as: 1. Granitic endogenous—syngenetic–epigenetic deposits and occurrences; 2. Metamorphogenic—syngenetic; and 3. Sedimentary, including occurrences of uranium deposition and fluctuation caused by water in different types of sedimentary rocks formed in a continental setting, which could be classified under epigenetic types. The area of Stara Planina with increased radioactivity (higher than 200 cps), measured by airborne gamma spectrometry, is about 380 square kilometers. The highest values of measured radioactivity and uranium grade were obtained from a sample taken from the Mezdreja uranium mine tailing dump, where 226Ra measures 2600 ± 100 Bq/kg and the uranium grade is from 76.54 to 77.65 ppm U. The highest uranium (and lead) concentration, among all samples, is measured in graphitic schist with high concentrations of organic (graphitic) material from the Inovska Series—99.47 ppm U and 107.69 ppm Pb. Thorium related radioactivity is the highest in granite samples from the Janja granite in the vicinity of the Mezdreja granite mine and the Gabrovnica granite mine tailing dump, and it is the same—250 ± 10 Bq/kg for 232Th, while the thorium grade varies from 30.82 to 60.27 ppm Th. In gray siltstones with a small amount of organic material, the highest radioactivity is related to potassium—2080 ± 90 Bq/kg for 40K.