1. Introduction The concentration of heavy metals in the environment has increased due to, among other reasons, the influence of human activity. An increase in concentration is not at the same level for all metals and depends mainly on the amount and the way of transmission, as well as the source of pollution. VRBEK BORIS & PILAŠ IVAN Forestry Research Institute, Jastrebarsko Trnjanska 35, 10 000 Zagreb, CROATIA e-mails: borisv@sumins.hr Heavy Metals in Soil solution of lowland Oak Forest in Croatia Fig 1: Pedunculate oak and Common Hornbeam community Materials and Methods Monitoring of heavy metals (Pb, Cu, Zn and Cd) and the amount of seepage water was carried out at 9 experimental plots of Peduncled Oak and Common Hornbeam There were tree lysimeters on every plot installed at a depth of 20 cm, i.e. under the humic accumulative horizon. The second group of measuring instruments consisted of plastic funnels for collecting and measuring the amount of precipitation. Sets of nine funnels (throughfall) were installed on every plot, and on the control site tree plastic funnels (bulks) outside the influence of the forest (open space). Fig 2: Zero tension lysimeter beneth the humus layer Vegetation period PbCuZnCd μgL -1 Bulk Spring 2,4 ±0,09 3,1 ±0,05 19,3 ±4,8 0,21 ±0,07 Summer 1,0 ±0,6 2,0 ±0,7 9,2 ±4,4 0,08 ±0,05 Autumn 2,2 ±1,1 1,7 ±0,1 15,5 ±2,8 0,03 ±0,01 Throughfall Spring 2,9 ±2,1 4,3 ±2,5 20,2 ±7,5 0,24 ±0,12 Summer 2,9 ±2,9 5,2 ±3,1 20,3 ±18,6 0,13 ±0,12 Autumn 2,5 ±1,1 3,7 ±1,8 26,1 ±16,0 0,11 ±0,07 Lysimeters Spring 4,3 ±4,4 3,3 ±3,1 12,7 ±3,8 0,13 ±0,11 Summer 4,2 ±2,7 5,3 ±2,5 8,9 ±4,5 0,36 ±0,17 Autumn 5,1 ±3,1 4,6 ±3,2 17,6 ±9,5 0,37 ±0,19 Table 1: Average heavy metal contents in bulks, throughfall and lyzimeters seeped liquid (seepage) Results and Discussion In the lysimetric liquids a slightly increased amount of heavy metals was observed. The average content of cadmium in lysimeters (Spring, Summer and Autumn) was 0,13-0,36-0,37 μgL-1, lead 4,3-4,2-5,1 μgL-1, copper 3,3-5,3-4,6 μgL-1, zinc12,7- 8,9-17,6 μgL-1, respectively. There is an increased input of heavy metals into our forest ecosystems in all the monitored sites. At the control locations (bulks), where impact of vegetation is excluded, the amounts of heavy metals are always lower. On the basis of these investigations it can be concluded that problems of constant accumulation of heavy metals in soils are present in the region of lowland forests. In this process the types of soil play a significant role in buffering deposition substances which arrive by means of precipitation. References: Brechtel HM 1989 Monitoring wet deposition in forests; quantitative and qualitative aspects. In: Monitoring Air Pollution and Forest Ecosystem Research, Report No.21 in the Air Pollution Report Series of The Environmental Research Programme of the European Communities, Brussels, 39-63. Lindberg SE, Turner RR 1988 Factors influencing atmospheric deposition stream export, and landscape accumulation of trace metals in forested watersheds, Water Air and Soil Pollution 39, 123-156. Van Breemen N, Wisser, WFJ, Pape TH 1988 Biogeochemistry of an oak-woodland ecosystem in the Netherlands affected by acid atmospheric acid atmospheric deposition, Agricurtural Research Report 930, Pudoc, Wageningen.