Kristina Pikelj

Eastern Adriatic Coast (EAC): Geomorphology and Coastal Vulnerability of a Karstic Coast

ABSTRACT Pikelj, K., and Juračić, M., 2013. Eastern Adriatic coast (EAC): Geomorphology and coastal vulnerability of a karstic coast. Coastal zones are one of the most rapidly changing environments on the global scale, mainly caused by anthropogenic activities (industry, urbanization, tourism, and food production). Coastal erosion is primarily a natural process, although human-induced coastal changes are becoming more and more present and are significant factors associated with the loss of beach capacity. The eastern Adriatic coast (EAC) is one of the most rapidly growing tourist markets within the Mediterranean, along which beaches still represent a leading component of the tourism resource. The objective of this paper is to provide an overview of natural geomorphologic features of the EAC as a starting point for further investigation and sustainable management of the coastal zone. The EAC is generally steep and rocky, mostly built up of karstified carbonates, and characterized, thus, by a variety of drowned karstic forms. Beaches in carbonates are mostly small, narrow, and scattered pocket gravel beaches. Coasts developed in the flysch and associated rocks are characterized by longer sandy and gravel beaches. The total beach length along the EAC presumably does not exceed 5%, and the small proportion of the beach length in relation to the rest of the EAC emphasizes their value in the tourist valorization, indicating the need for protection and sustainable management. Due to their geomorphologic diversities, fragmentation, different orientation, length, and sediment composition and budget, each beach should be studied separately and on a small scale. Detailed information on beach profiles, the nearshore geomorphology, and the beach processes needed to plan a sustainable coastal development is still mostly missing.

Early Miocene European loess: A new record of aridity in southern Europe

The intercalation of silty units and coarse-grained units represented by conglomerates and breccia characterizes a Lower Miocene terrestrial sedimentary sequence in the North Croatian Basin, a part of the southwestern Pannonian Basin system. These sediments were previously interpreted as alluvial sediments, where the silty units would reflect deposition on a floodplain. However, in this study, we show new results that support a different interpretation of the genesis of the silty units. The units, which vary in thickness between 6 and 180 cm, are mostly composed of structureless loose silt. They are brownish yellow to yellowish brown in color and do not contain fossils. Scanning electron microscopy indicated that quartz grains show fracture faces, conchoidal fractures, V-shaped percussion marks, linear steps, and conchoidal crushing features. Such microtextures together with the macroscopic characteristics of the silt units indicate that they were deposited by wind. Therefore, this study reports the first occurrence of Miocene loess outside of China. Silt-sized particles were probably produced by salt-weathering processes on salina-type lake flats during long arid periods. Alluvial deposition was controlled by a more humid climate, so the intercalation of eolian silty units with alluvial conglomerates and breccias reflects alternation of arid and more humid periods in the early Miocene. This agrees with regional paleoclimate studies that show cyclicity in the climate, with a dry cycle and orbital-scale climate variability controlling paleoenvironmental and sedimentary changes in the area during the early Miocene.

Origin and distribution of surface sediments in the Grgur Channel, Adriatic Sea, Croatia

Granulometrical, mineralogical and morphological investigation of the sea-bottom sediments in the Grgur Channel revealed five sediment types; the most frequent of them are muds containing some amount of coarse sediment fractions (sand and gravel). The coarsest fractions are prevalently composed of recent shell fragments. Unexpected well rounded carbonate gravel was found SE of the Prvic Island at 83 m of water depth. This gravel was presumably transported, shaped and deposited during a lowstanding sea-level by stream and/or in beach environment. Fine-grained fractions have siliciclastic composition and show a prevalenty terrigenous origin. One part of the fine-grained fraction originates from recent subaerial weathering of flysch outcrops and the other from subaerial erosion of presently submerged flysch outcrops active during a lower sea-level. Due to the rapid Late Pleistocene-Holocene transgression, the investigated sediments are now below the present wave-base. Due to the presumed very low or even negligible recent sedimentation in the study area, older sediments in the Grgur Channel remain uncovered and mixed by burrowing organisms. Therefore, analyzed surface sediments from the Grgur Channel are considered as a mixture of recent and subrecent deposits. By this investigation, a new seabed sediments map of the Grgur Channel was produced, as an improvement of the existing sedimentological map of the Kvarner area.

The effect of in situ shading on a Posidonia oceanica meadow situated within a fish farm induced moderately nutrient enriched environment.

The aim of this research was to explore the possibility of a successful and balanced integration of fish farming installations into an ecosystem dominated by Posidonia oceanica (L.) Delile species. We selected light, temperature, seabed topography, sediment characteristics, meadow density, bottom coverage, maximum leaf length and lower depth limit as principle components in assessing the influence of the fish farm. All P. oceanica descriptors showed significant correlation with light deprivation effect while sediment organic matter content revealed slightly higher values than normal, increasing with distance from the cages. The results point to a conclusion that in such lightly nutrient enriched ecosystems, the seagrass growth and distribution are principally controlled by the shadow that cages cast on the seabed below, and that when carefully planned, fish farms do not necessarily degrade the health status of the surrounding area, but in fact facilitate a transition into a secondary stable state.

The performance, application and integration of various seabed classification systems suitable for mapping Posidonia oceanica (L.) Delile meadows

In the context of current global environmental changes, mapping and monitoring seagrass meadows have become highly important for management and preservation of coastal zone ecosystems. The purpose of this research was to determine the numerical precision of various cost-effective benthic habitat mapping techniques and their suitability for mapping and monitoring of Posidonia oceanica meadows in the Croatian Adriatic. We selected ultra-high resolution aerial imagery, single-beam echo sounder (SBES) seabed classification system from Quester Tangent Co. (QTC), and surface based underwater videography as affordable, non-destructive and simple to use systems for data acquisition. The ultra-high resolution digital imagery was capable of detecting P. oceanica meadows up to 4m depth with 94% accuracy, from 4m to 12.5m depth the accuracy dropped to app. 76%, and from 12.5 to 20 m the system was only capable of distinguishing seabed biota from substrata, though with 97% accuracy. The results of the QTC system showed over 90% detection accuracy for Cymodocea nodosa covered seabed, excellent separation capabilities (>92%) of different sediment types (slightly gravelly sand, gravelly muddy sand and slightly gravelly muddy sand) and reasonable accuracy for mapping underwater vegetation regardless of the bathymetric span. The system proved incapable of separating P. oceanica from dense macroalgae on the same type of substratum. Surface-based underwater videography demonstrated great potential for estimating P. oceanica cover in a sampled region using either a single human rater or a computer estimate. The consistency between two human scorers in evaluating P. oceanica bottom coverage was near perfect (>98%) and high between digital and human scorers (80%). The results indicate that although the selected systems are suitable for mapping seagrasses, they all display limitations in either detection accuracy or spatial coverage, which leads to a conclusion that suitable system integration is essential for producing high quality seagrass spatial distribution maps.

Application of empirical model to predict background metal concentration in mixed carbonate-alumosilicate sediment (Adriatic Sea, Croatia).

A 96m long sediment core (S10-33) from the Mali Ston Channel (Adriatic Sea) showed large natural variation in carbonate share (between 1% and 95%) and concentration of elements. These variations indicate rather significant changes in fine-grained sediment that was deposited in this area during Younger Pleistocene and Holocene. Unaffected by anthropogenic influence, sediment in the core was used to determine background concentration of trace elements in sediment with various carbonate content. Here we propose a method of the normalization of trace elements to carbonate share, in order to assess natural/background concentration of metals in sediments consisting of carbonates and alumosilicates in various proportions. Six characteristic metals (Co, Cr, Cu, Ni, Pb, and Zn) that were normalized to carbonate share showed very good correlation, with much higher background concentrations in alumosilicate than in carbonate end member. Simple formulas were proposed to easily determine background concentration of these elements, in coastal and shelf depositional environments with mixed carbonate-alumosilicate sediments.