Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS


ANTHROPOL . PROT Streszczenie raportu

Project ID: ICA2-CT-2002-10009
Źródło dofinansowania: FP5-INCO 2
Kraj: Croatia

Investigation of anthropogenic influence to Plitvice Lakes, Croatia

The Plitvice Lakes consist of a series of 16 lakes separated by tufa barriers and waterfalls. In this very complex aquatic system calcium carbonate precipitates intensively, forming tufa barriers in the presence of microphytes and macrophytes.

The area was proclaimed as a National Park almost 60 years ago and included into the UNESCO World Heritage List in 1979. In this WP we tried to identify the sources of eutrophication process in the Plitvice Lakes area to see whether it is a consequence of anthropogenic pollution or a natural process. The results of physico-chemical measurements of water at 15 sampling points along a flow distance of about 12 km, including sites with very intense CaCO3 precipitation, show that temperature, pH, alkalinity, and hence the saturation index of CaCO3, show significant change in downstream flow and also some seasonal variations.

The results show that the carbon exchange process plays an important role for tufa precipitation. Additionally, DOC values are also higher in some “clean” stream waters, where tufa does not precipitate in spite of otherwise favorable physico-chemical conditions for calcite precipitation, such as the high degree of supersaturation. In this case probably DIC inhibits tufa deposition. No systematic difference in concentration of these species between “clear” and eutrophicated waters was observed. d13C values of DIC in water of the Plitvice Lakes area steadily increase downstream from the karst springs (d13C= 12.5‰) to the river mouth (d13C= 10.0‰). Simultaneously, increase of 14C activity of DIC in downstream flow in the same area was observed as the consequence of the exchange process between the atmospheric CO2 and DIC in water at rapids and waterfalls. According to the chemical and isotopic measurement of water there is indication that the concentration of DIC is higher in the areas where the process of eutrophication is pronounced and that higher DOC concentration in water can inhibit the calcite precipitation in form of tufa.

These measurements do not indicate recent anthropogenic pollution of lake waters, and higher concentration of DOC in some sampling points can be a consequence of input of natural organic matter (humus) to the lake water. The chronology of the pollutant input was established by measuring activities of anthropogenic and natural radionuclides, which gave us the sediment accumulation rate and thus the age of specific sediment layers. For the smaller lakes higher sedimentation rates are obtained for the anthropogenic tracer 137Cs. In contrast sedimentation rates in the larger lakes give similar values for 137Cs and 210Pb. One possible explanation for the higher sedimentation rates in the smaller lakes is the higher water temperature during the warm months and accordingly quicker carbonates precipitation than in the bigger, colder lakes. By measurements of 14C in sediment cores we found the increased values of 14C at the depths between 5 and 10cm, which are the consequence of the bomb-produced 14C in the period 1949-1963 and they correspond to the peak values in 137Cs activity. The relative composition of minerals for each sediment core shows prevalent presence of calcite.

Also the content of organic matter is the highest in this core as the consequence of transport of terrestrial material. At the same location the concentration of most trace elements including phosphorus is the highest causing the high degree of the eutrophication process in this area. Trace elements and organic matter content decrease from the uppermost lake downstream to the lowest lake. This fact indicates that the most of trace elements in sediments could be of natural origin due to transport from the main springs and their steady deposition along downstream lakes. Content of trace elements along the 40 cm sediment cores from all sampling sites is much below maximum concentrations permitted for metals in soils in EU. There is no significant difference among the trace element concentration in the upper segment of all cores, corresponding to last 50 years when higher anthropogenic influence can be expected, and the lower part of the cores, corresponding to the period 100-200 years before present.

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