Geochemical and sedimentological characteristics, the sedimentation rate (by 137Cs dating) and the history of the accumulation of trace metals (Cd, Pb, Cu and Zn) in sediments from anoxic, marine water of the Rogoznica Lake, Croatia, have been studied. The sediment is a fine-grained silt throughout the profile, characterized as an authigenic carbonate sediment of mainly biogenic origin, belonging to the anoxic-sulfidic sedimentation environment. The relatively high sedimentation rate (0.093 g/cm2 per year) in the Rogoznica Lake, in comparison with the nearby coastal area, and the Krka River Estuary can be explained by higher primary biological production in the upper, oxic water layer, as well as the absence of sediment resuspension. The Rogoznica Lake behaves as a ‘sediment trap’ because of its small dimensions and sheltered position. The concentrations of trace metals in sediments are in the range usual for unpolluted marine carbonate sediments. Nevertheless, concentrations of Pb, Cu and Zn, in the uppercore profile of recent and sub-recent (up to the past 40 years) sediments, reflect anthropogenic influences. Leaded gasoline seems to be the principal anthropogenic source of Pb enrichment, while for Zn and Cu it may be of a communal origin, possibly due to recent tourist activity in this area.
"nd clay silt . Authigenic carbonates of mainly biogenic origin are the most important component . Major mineral is calcite ( 65% – 92% ) followed by aragonite , quartz , dolomite and pyrite ( Table I ) . The accumulation rate , calculated by using the 137 Cs method is relatively high ( 0 . 45 cm / year ) at site A , the deepest point , Figure 1b ( Mihelčić et al . , 1996 ) . This implies that the 25 cm of deposition at A required about 50 years ."
[Show abstract][Hide abstract] ABSTRACT: Rogoznica Lake is highly eutrophic marine system located on the Eastern Adriatic coast (43°32′N, 15°58′E). Because of the relatively small size (10,276 m2) and depth (15 m) it experiences strong natural and indirect anthropogenic influences.
Continental Shelf Research 05/2015; DOI:10.1016/j.csr.2015.05.007 · 1.89 Impact Factor
"Cs appeared in the environment since the early 1950s following the first nuclear weapon testing. Two maxima can be identified, the first about 1965 caused by nuclear weapon testing, and the second corresponding to the Chernobyl accident in 1986 (Mihelčić et al., 1996; Appleby, 2008). The aim of this work is to determine the age and the accumulation rates of the sediment layers in the lake Qattinah. "
[Show abstract][Hide abstract] ABSTRACT: The constant rate of supply (CRS) of excess 210Pb model was successfully applied to assess 210Pb data of two sediment cores from the lake Qattinah, Syria. Gamma spectrometry was used to determine 137Cs and 210Pb activity concentrations. The bottom of the cores was 210Pb-dated to years 1907 and 1893. The accumulation rates were determined using 210Pb method and found to vary similarly in both cores from 0.10 ± 0.01 to 3.78 ± 0.57 kg m−2 y−1 during the past century. 137Cs was used as an in-dependent chronometer. The two distinct peaks observed on the 137Cs record of both cores, corresponding to 1965 and 1986, have allowed a successful validation of the CRS model.
"The surface of the narrow peninsula surrounding it consists of a carbonate pavement covered by sparse soil and vegetation. Its sediments are almost entirely biogenic, consisting primarily of calcite, aragonite, amorphous silica and organic matter (Mihelčić et al., 1996); the sediments can be classified as sapropels because the organic carbon content is 2 to 7%. Minor dolomite and 2000 1500 1000 "
[Show abstract][Hide abstract] ABSTRACT: Rogoznica Lake, on the Adriatic coast of Croatia, undergoes vertical mixing in autumn, but quickly restratifies and becomes intensely sulfidic during the succeeding 11 months. Autumn's vertically homogeneous dissolved Mo concentrations quickly revert to a summer profile in which Mo concentrations are lower by an order of magnitude in the sulfidic layer than in the oxic layer. Other redox sensitive elements (As, U and V) are much less affected on this time scale. Below the depth where sulfidic waters become saturated with iron monosulfide, Mo concentrations become nearly constant. A similar pattern can be recognized in other euxinic basins and seems inconsistent with Mo removal by sorption on sinking particles. Precipitation of a previously unrecognized, probably nanoscale Fe(II)-Mo(VI) sulfide mineral is postulated to explain this phenomenon. By fitting the Rogoznica data, a provisional composition and solubility product constant for this material are derived. The mineral's formula approximates Fe(5)Mo(3)S(14). Its Mo content is similar to that of a synthetic precipitate previously shown by X-ray spectroscopy to resemble molybdenum's host phase in black shales. Assuming saturation with this mineral, dissolved Mo in the deep water column of a number of other euxinic basins can be predicted in most cases to within a factor of three. The model has important implications for Mo behavior in euxinic basins. For example, the model attributes the near-total Mo removal from deep Black Sea waters to a serendipitous combination of pH and H(2)S concentration, implying that such removal would not be a general property of euxinic basins. This is a key point with regard to Mo isotope systematics. Contrary to previous views, the model assigns a critical role to pH in controlling the efficiency of Mo removal from euxinic basins.
Chemical Geology 05/2011; 284(3-4):323-332. DOI:10.1016/j.chemgeo.2011.03.012 · 3.52 Impact Factor
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