Evaluating climate change at the Croatian Adriatic from observations and regional climate models’ simulations

The 2m temperature (T2m) and precipitation from five regional climate models (RCMs), which participated in the ENSEMBLES project and were integrated at a 25-km horizontal resolution, are compared with observed climatological data from 13 stations located in the Croatian coastal zone. The twentieth century climate was simulated by forcing RCMs with identical boundary conditions from the ERA-40 reanalysis and the ECHAM5/MPI-OM global climate model (GCM); climate change in the twenty-first century is based on the A1B scenario and assessed from the GCM-forced RCMs’ integrations. When forced by ERA-40, most RCMs exhibit cold bias in winter which contributes to an overestimation of the T2m annual cycle amplitude and the errors in interannual variability are in all RCMs smaller than those in the climatological mean. All models underestimate observed warming trends in the period 1951–2010. The largest precipitation biases coincide with locations/seasons with small observed amounts but large precipitation amounts near high orography are relatively well reproduced. When forced by the same GCM all RCMs exhibit a warming in the cold half-year and a cooling (or weak warming) in the warm period, implying a strong impact of GCM boundary forcing. The future eastern Adriatic climate is characterised by a warming, up to +5 °C towards the end of the twenty-first century; for precipitation, no clear signal is evident in the first half of the twenty-first century, but a reduction in precipitation during summer prevails in the second half. It is argued that land-sea contrast and complex coastal configuration of the Croatian coast, i.e. multitude of island and well indented coastline, have a major impact on small-scale variability. Orography plays important role only at small number of coastal locations. We hypothesise that the parameterisations related to land surface processes and soil hydrology have relatively stronger impact on variability than orography at those locations that include a relatively large fraction of land (most coastal stations), but affecting less strongly locations at the Adriatic islands.     

Sources,Distribution and Behavior of Major and Trace Elements in a Complex Karst Lake System

Sources and distribution of major and trace elements were investigated in the Plitvice Lakes, a pristine cascade hydrological system of sixteen karst lakes situated in a sparsely populated area of the central Croatia. Water and surface sediment samples from 17 locations, including springs, tributaries and lakes, were analyzed for the content of 22 elements by high-resolution inductively coupled mass spectrometry. Principal component analysis of the collected data set showed that different springs and tributaries displayed distinct multielemental compositions, reflecting primarily the differences in their corresponding geological backgrounds. It was shown that the springs situated in the Upper and Middle Jurassic dolomite bedrock represented the main source of several trace elements, including some toxic metals (Cd, Zn, Ni and Tl), to the Plitvice Lakes system. The concentrations of most of the trace elements (Mn, Fe, Al, Cd, Zn, Cu, Ni, Pb, Co, Cr and Tl) showed decreasing spatial trends in the downstream direction, from sources to the lakes. Such a distribution was interpreted to be a consequence of an efficient removal of the dissolved elements in the lentic parts of the system, mainly by co-precipitation with authigenic calcite and Mn oxides. Nevertheless, most of the elements in the lake sediments were highly correlated with Al, which indicated their prevalent association with terrigenic material. It was shown that the multicascade system of the Plitvice Lakes had an enhanced autopurification efficiency regarding the elimination of most of the trace metals from the aqueous phase.     

Modeling compositional compressible two-phase flow in porous media by the concept of the global pressure

We derive a new formulation for the compositional compressible two-phase flow in porous media. We consider a liquid–gas system with two components: water and hydrogen. The formulation considers gravity, capillary effects, and diffusivity of each component. The main feature of this formulation is the introduction of the global pressure variable that partially decouples the system equations. To formulate the final system, and in order to avoid primary unknowns changing between one-phase and two-phase zones, a second persistent variable is introduced: the total hydrogen mass density. The derived system is written in terms of the global pressure and the total hydrogen mass density. The system is capable of modeling the flows in both one and two-phase zones with no changes of the primary unknowns. The mathematical structure is well defined: the system consists of two nonlinear parabolic equations, the global pressure equation, and the total hydrogen mass density equation. The derived formulation is fully equivalent to the original one. Numerical simulations show ability of this new formulation to model efficiently the phase appearance and disappearance.     

The influence of building materials on salt formation in rural environments

Blocks of limestone and sandstone used in walls of the Manasija Monastery complex showed damage caused by the efflorescence and subflorescence of different salts in a low-pollution rural environment. In addition to common salts such as thenardite, thermonatrite, trona and gypsum, a small amount of eugsterite and darapskite was also present. Although these sodium and sodium–calcium salts formed where cement mortar was used for repairs, the lithological type and chemical composition of the substrate also had an influence on the development of distinct salts. The interaction between limestone and sandstone (substrates) and a solution rich in sodium (without calcium) was successfully simulated in the laboratory. The presence of gypsum and sodium–calcium sulphate, as experimental products, solely on the limestones indicated that, in addition to the cement-mortar solution, part of the calcium required for the formation of calcium and double sodium–calcium salts could occur from this substrate.     

Structure analysis of geopolymers synthesized from clay originated from Serbia

The paper presents chemical and structural analysis of geopolymer materials which are obtained by alkali-activated calcined clay (metakaolin) originated from Serbia under strictly defined conditions. Characterization of the metakaolin and geopolymers molecular structure has been done using X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The paper presents the possibility of obtaining geopolymer structure and differences in chemical and structural characterization of these materials taking into account the concentration of NaOH as a variable parameter. The results of MALDI analysis of metakaolin and synthesized geopolymer structures using various matrix system: 2,4,6 trihydroxyacetophenone (THAP), α-cyano-4-hydroxycinnamic, 2,6 dihydroxyacetophenone and laser desorption/ionization, have shown that THAP matrix is the most appropriate for analysing these aluminosilicate materials.     

Diagenesis of diatomite from the Kolubara Coal Basin,Baroševac,Serbia

Diatomite associated with the Kolubara Coal Basin was studied to better understand early stage silica diagenesis of shallow water deposits. The Kolubara Basin consists of Neogene siliciclastic rocks, diatomite, marlstone and rare carbonates. Palaeozoic metamorphic and Mesozoic sedimentary and igneous basement rocks are transgressively overlain by Upper Miocene sandstone, siltstone, shale and mudstone. This Upper Miocene section is transgressively overlain by the Pontian section, which contains diatomite and coal beds. White and grey diatomite forms beds 0.7-2.2 m thick that are continuous over an area of about 2 km². Siliceous rocks vary in composition from diatomite (81-89 per cent SiO₂) to diatom-bearing shale (58-60 per cent SiO₂). Siliceous deposits are laminated in places, with the laminae defined by variations in clay minerals, organic matter and diatoms. Diatomite shows only incipient diagenesis characterized by the fragmentation of diatom frustules, the minor to moderate corrosion of frustules and the formation of minor amounts of opal-A' (X-ray amorphous inorganic opal) cement. The low degree of diagenesis results from the young age of the deposits, low burial temperatures and possibly also from the presence of abundant organic matter and the dissolution of kaolinite. The presence of only weak diagenesis is also reflected by the characteristically poor consolidation of the rocks and low rank of the associated coal.