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UDC 551.444.3:556.3(497.561) Ognjen Bonacci, Maja Oštrić & Tanja Roje-Bonacci: Water resources analysis of the Rječina karst spring and river (Dinaric karst) The paper deals with complex hydrological/hydrogeological behaviour in the Rječina karst spring and river basin located in the north-western part of the deep and developed Croatian Dinaric karst. The Rječina Spring is one of the major karst springs in Croatia, used for water supply of Rijeka City and its surrounding area. Beside the use of Rječina spring for water supply, the development of the Rijeka hydroelectric power plant (HEPP) also changed hydrological and hydrogeological regime of the whole catchment. In order to analyse the anthropogenic influences in the system, hydrological analysis of the Rječina river and spring discharge was done, as well as the analysis of the available data of groundwater measurements. The analysis showed that, due to the increase of water caption and decrease of precipitation, the average annual spring discharge decreased for approximately 25% in the 1980-2016 period. Detailed analysis of groundwater measurements indicated aquifer behaviour and the need for additional measurements and catchment delineation. [ABSTRACT FROM AUTHOR]

Surface sediments (fraction <63 μm) from the source to the mouth of the Rječina, short (18.3 km) karst allogenic river in Croatia, which is an important source of drinking water, were studied to investigate their mineral (by XRD) and chemical (by ICP-MS) composition to check possible anthropogenic influence at the lower course due to paper industry and mills, and in the prodelta area from untreated municipal sewage and the large harbor of Rijeka town. In all analyzed sediment samples and in the sandstone source, rock quartz is a major mineral, while feldspar and mica group minerals are less abundant. Chlorite is a minor or trace mineral in all samples. Calcite and dolomite are abundant in the river prodelta, reflecting changes in bedrock lithology from flysch to carbonates. In river sediments, Fe is the most abundantly analyzed element, while Ca is the most abundant in prodelta sediments. Concentrations of Al, Mn, Ni, Cr, Co, La and Nd decrease downstream, while Mg, S, Na, B, Pb, Zn, As, Sn, U, Mo, Hg and Ag have relatively higher concentration in prodelta sediments. The results are compared with sediments of other rivers in the area: Raša, Rižana and Dragonja, as well as with those of the Rosandra Creek (Italy). Sediments in the Raša River showed similar behavior as those in the Rječina, as the highest concentration of metals was found in the restricted upper part of the estuary, characterized by rapid deposition of clay particles and terrestrial sedimentary organic matter. The comparison also showed that the most contaminated were the sediments from the Rižana, followed by those from the Rječina and Rosandra Creek, which had similar results. Among the studied elements, As was present in all sediment samples at concentrations >6 ppm that might have the lowest toxic effects. At the lower Rječina and in prodelta sediments, Pb was also present at slightly elevated concentrations (>31 ppm) that could cause such effects. Concentrations of Zn in the prodelta correspond to those occurring in moderately polluted sediments (90-200 ppm). In the prodelta sediments, Hg is slightly below toxicity threshold (1 ppm), while Ag is present at toxicity threshold (0.5 ppm) or close to it. Rječina River could act as a good illustrative example for behavior of toxic metals in allogenic karstic rivers, in which accumulation of anthropogenically introduced pollutants usually occurs in their estuaries, as a result of transport and deposition of fine particles. [ABSTRACT FROM AUTHOR]