Lakes in coastal lowland areas represent a critically vulnerable environment as a transitional space between freshwater and seawater environments. The paleoenvironmental reconstruction and anthropogenic impact are assessed through the lake sediment cores from Velo, Malo, and Kolanjsko Blato using multi-proxy analyses (sedimentological, mineralogical, geochemical, 137Cs and ostracod analyses, and AMS 14C radiocarbon dating). The freshwater lake Velo Blato was formed at 8100 cal yr BP due to rising groundwater levels as a consequence of sea-level rise. The brackish conditions in Lake Velo Blato started at 7100 cal yr BP, giving the index point for the sea-level curve of 7-m lower than present. Lead concentrations showed slightly increased values in the last 1800 cal yr BP, while the spike in Malo Blato lake sediments probably derived from bird hunting with lead bullets. Kolanjsko Blato sediment core archives the sediment record of the last 2050 years, which represents a shallow brackish coastal wetland under marine influence. Enrichment factors showed the accumulation of Cu, Hg, P, Pb, S, and Zn in the sediments from Kolanjsko Blato in the last 650 cal yr BP, which coincides with the high organic carbon content, and in sediments from Malo Blato after the lake’s formation (from the depth of 20 cm upwards). Anthropogenic Cu introduced into the Kolanjsko Blato sediments is the highest in the surface sample. Surficial sediments from Velo Blato are characterized by the high organic carbon, S, P, and N content, indicating high productivity and eutrophication which led to occasional anoxic conditions on the lake bottom in the last 200 years.
Croatian bauxites are long known for their chemical and physical diversity arisen from their characteristic origin and emplacement within the area of the Adriatic–Dinaric carbonate platform (ADCP). They include eight horizons spanning the period between the Upper Triassic (Carnian) and the Miocene, formed on subaerially exposed platform paleoenvironments. The bauxite genesis is recorded in the bauxite geochemical composition as a unique signature of tectonostratigraphic evolution of the different parts of the Croatian Karst, including, for example, the forebulge unconformity typical for the Istrian area. In this work, an explanation of the typical patterns of bauxite formation is based on the construction of a discriminant function model (DFM) resulting from the compositional data (CoDa) analysis of bauxite geochemical data (major and trace elements). The model shows that the greatest part of the variation contained in the analyzed bauxite data (the first discriminant function, DF1) is associated with systematic alteration of geochemical composition in time, emphasizing characteristic decrease in clay component and gradual enrichment in heavy metals from oldest (Upper Triassic) to the youngest (Miocene) bauxites. In the general scheme, particular bauxite horizons represent standalone groups (Upper Triassic) while others form clusters showing increase and/or decrease of a particular set of elements signaling the changes in environmental conditions during the considered geological history of ADCP. Other discriminant functions (DF2 and DF3) also contribute to the all-inclusive distinction between the eight a priori defined bauxite groups discriminated by the characteristic set of geochemical variables where DF2 typically refers to the process of desilication, while DF3 to that of deferralitization.
<p>Lake Visovac is a tufa barrier lake on the Krka River between Ro&#353;ki slap (60 m asl) and Skradinski buk (46 m absl) waterfalls, included in the Krka national park as primarily unaltered area of exceptional natural value. Paleolimnological research was conceived to address a lake evolution and depositional environments through the geophysical survey and collection of the lake sediment cores. A high-resolution bathymetric map was obtained using a multibeam sonar. The average lake depth varies between 20 and 25 m. Sediment cores were investigated to extract physical properties, sedimentological, mineralogical, geochemical and paleoecological records constrained by the radiocarbon chronology, to understand what was happening to both the landscapes and lakescapes of Lake Visovac during the last 2.000 cal yr.</p><p>Significant findings of the project are geomorphological features on the lake bottom: submerged sinkholes of various sizes (up to 40 m deep); submerged tufa barriers in the area of Kali&#269;ki kuk (southern part of Lake Visovac) at the depths of 15 and 17 m, followed by a series of buried cascade tufa barriers at the depth of 25 m covered with up to 10 m of Holocene lake sediments; submerged vertical tufa barrier up to 32 m-high near the mouth of &#268;ikola River; submerged landslides, small (river) fan structures characterized by sediment waves. Ground-penetrating-radar (GPR) data have been acquired due to the presence of gas-saturated sediments over a large area of the lake, that limited the use of high-resolution acoustic profiling. A total thickness of sediments is up to 40 m. High resolution paleoenvironmental record through the Late Holocene gives evidence of high sedimentation rates in Lake Visovac, variable soil erosion impact on lake sediment composition and carbonate authigenic sedimentation. Higher organic carbon is observed in the last 50 years due to changes in land cover and reforestation. Pleistocene lake sediment outcrops occur up to 20 m above the present lake levels indicating higher lake levels as a consequence of higher elevation of tuffa barriers. Kali&#269;ki kuk, which lies up to 20 m above present lake level, is a remnant of these barriers which have been dated to MIS5. Results allow us to interpret the environmental and evolutionary dynamics of Lake Visovac in the following way: lake level more than 20 m higher than today in mid-Pleistocene with significantly larger lake volume in Lake Visovac, with active Kali&#269;ki kuk and Skradinski buk waterfalls; lower lake-level at the beginning of the Holocene when several small lakes existed in isolated basins in the area of Lake Visovac. The tufa barrier at Skradinski buk started to grow faster than the Kali&#269;ki kuk barriers and waterfalls resulting in their flooding and submergence during the Holocene. The tufa barrier at Skradinski buk has grown 15 m since then. This study demonstrates the role of geomorphological lakebed characteristics in reshaping our understanding of the environmental changes and the future of Lake Visovac.</p><p>The research was conducted as part of the project funded by the Krka National Park and CSF funded QMAD project (IP-04-2019-8505).</p>
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