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In Memoriam Professor Vasile Pleniceanu – life and activity

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Climate aridity in southern Bulgaria for the period 1961-2015

Abstract: The climate change on a global, regional and local scale is one of the largest problems indicated by the 21st century studies. Some of the major climate changes on the Balkan Peninsula, and in particular in Bulgaria, are related to rising temperatures and decreasing precipitation, which leads to drought and climate aridity. The present study focuses on the investigation of the climate aridity in the non-mountainous part of Southern Bulgaria in order to assess the aridity condition in temporal and spatial scale. The main investigated period is 1961-2015 and the reference periods are 1961-1990 and 1986-2015. The aridity is analysed on the basis of monthly data for air temperatures and precipitation from eight meteorological stations by calculation of De Martonne aridity index and Emberger Index. The survey shows that in all the analysed meteorological stations in Southern Bulgaria there are periods which display characteristics of the semiarid or arid climate. The aridity is well-expressed in the southwest part of Bulgaria (station Sandanski) and the western part of the Thracian lowland (station Plovdiv). Despite the aridity conditions established in the investigated region the tendencies in multiannual variability of De Martonne and Emberger indices show decreasing of aridity during the last 30 years (1986-2015) of the investigated period.

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The occurrence of the armored mud balls during the flash flood phases of the streams from the Meledic Plateau – the Curvature Subcarpathians, Romania

Abstract: Armored mud balls that form in fluvial environments were observed on the river bed of two small streams from South-East Subcarpathians Bend, in the area of Miocene deposits with salt dia-pirs. Pieces of well-rounded clay mate-rial but with coarse surface were found on the gravel banks as well as partially submerged into stream channel and embedded in soft sediments of stream banks. The surfaces of mud balls, nearly spherical and ranging from 5 cm to 17 cm in diameter, were studded with sand grains and gravel that collected during flash floods as a result of bedload transport. The main source material of the armored mud balls consists of dark clay material detached from the cap rock of the salt massif that is crossed by the two streams. The newly formed armored mud balls, which were found among the gravels on the stream bed following the summer flash flood event from June 2019, supports the fact that these particular sedimentary features form during exceptional floods when pieces of clay material are rolled by the high-energy water flow, which results in acquiring of their spherical shape and the pebble shell. This paper represents the first report on the occurrence of modern armored mud balls formed in a fluvial environment, located in the Curvature Subcarpathians, Romania.

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Gross chemical analysis of the turf and podzolic soils on glacial deposits, laid by dense carbonate rocks

Abstract: Gross analysis allows us to reveal issues concerning the genesis of soils and to identify the peculiarities of elementary soil processes. The article summarizes the results of the study of gross chemical analysis of the turf and podzolic soils on alluvial and glacial deposits, laid by dense carbonate rocks. Features and relationships of oxides content in soils and soil-forming rocks are considered, that will make possible to justify important issues of the nature of these soils and to study the dependence of their natural properties with dense carbonate rocks.
It is established that oxides of silicon, ferum, aluminum and calcium form the basis of gross chemical composition of the turf and podzolic soils on alluvial and glacial deposits, laid by dense carbonate rocks. The maximum content of the first component is observed in the upper humus-eluvial horizon (90–94%), aluminum and ferum oxides – in iluvial accumulative horizons, where their content in total is 7–15%. Calcium oxide content in soil profile of studied soils, naturally increases from 0.36% in the upper horizons to 0.95% in the transitional, and in the laid carbonate rocks its content can reach up to 35%. This confirms the fact that laid carbonate rocks have a significant influence on the flow of all soil elementary processes, and gross analysis confirmed the presence of carbonates in the entire soil profile, which could not be determined during field or macromorphological studies. Oxides of alkaline-earth metals are mainly accumulated in the upper humus horizons of all soils, their content decreases down the profile. Potassium and phosphorus oxides, although pliable to washing, however are delayed in the soil and included in the biological cycle and partially fixed in secondary minerals. The content of biologically important components such as P2O5, MnO, S, N in the upper horizons of the studied soils is closely related to the accumulation of humus.

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On the linear trends of a water discharge data under temporal variation. Case study: the upper sector of the Buzău river (Romania)

Abstract: The aim of this paper is to provide a statistic overview of the hydrological impact of the Siriu Dam on the Buzau River (Romania), taking into account the temporal variations. Our case study uses the daily mean discharges of the Buzau River (1st of January 1955 to 31st of December 2010), registered at Nehoiu hydrometric station. The building of the Siriu Dam in 1984 required the division of the study interval into two sub-periods, each being analyzed annually and seasonally, on the series themselves or on the pre-whitened ones when prior required. The existence of a linear trend on different periods and sub-periods has been studied by using the Mann-Kendall and Seasonal Mann-Kendall tests. In the case of the existence of a linear trend, the slopes have been calculated with Sen’s Slope Estimator. The stationarity has been studied by using the Dickey-Fuller and Kwiatkowski–Phillips–Schmidt–Shin tests. According to our preliminary results, the stationarity in trend after the dam’s construction, respectively increasing linear trends for almost all the data series and subseries was observed. The trend and stationarity outcomes proved that the Siriu Reservoir has a good impact on the homogeneity of the Buzau River’s discharge and the increasing trends are related to human activity impact coupled with climate change/variability.