Forest Research Institute, Jastrebarsko, Croatia Tel/Fax: ++ 1 611 33 72 E-mails: firstname.lastname@example.org , email@example.com SUMMARY The following ions were monitored: Chloride (Cl-), sulphate (SO42--S), nitrate (NH4+-N), ammonium (NO3--N), sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+). Sampling on the plots was performed with funnels (bulks) and the amount of precipitation measured by plastic rain-gauges with opening surface of 60 cm2. 9 rain-gauges and funnels (bulks) were laid out in diagonal distribution on each plot of 30 X 30 m. On the control site, without the influence of vegetation, funnels (bulks) and rain-gauges were laid out at random or in circle. Lysimeters for collecting and measuring the quality of seepage water were set up in the soil at depth of 10 cm, or under the humus horizon. A filter consisted of 96% quartz sand in a plastic container for the purpose of purifying the liquid of soil particles. Lysimeters were set up on plots in the national parks on sites with fewer rocks and stones and on deeper soils. The method of ICP-Forest monitoring (International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests) is applied in Croatia for monitoring National Parks "Risnjak, "Paklenica", "Brijuni", "Mljet", "Plitvička jezera", "Sjeverni Velebit" and "Risnjak". The results obtained on experimental plots will be presented in this paper covering the regions of the National Parks of "Plitvice Lakes", "Northern Velebit" and "Risnjak". In the NP "Risnjak" dolomite was the dominant parental substrate on the plot, and the frequent soil type was luvisol typical (luvisol), and also in sink-holes. In the NP "North Velebit" the dominant parental substrate on the plot was limestone, and the most frequent was calcicambisol (cambisol). In the NP "Plitvice" the dominant parental substrate on the plot was limestone, and the soil was luvisol typical (luvisol), and also in the sink-holes with an additional non-calcareous loess. Soil reactions were very acid (very dystric) to acid (dystric), particularly in the surface horizons. Data show that the average annual intake of nitrogeneous compounds for the NP "Risnak" amounts to approximately 16-18 kgha-l, for NP "N. Velebit" approximately 11-14 kgha-l and for NP "Plitvice Lakes" from 13 to 16 kgha-1. Thus the investigated plot on NP "Risnajk" accumulated approx. 8 kgha-1 chloride and approx. 9 kgha-1 sulphur. The plot on NP "N. Velebit" collected approx. 6 kgha-1 chloride and approx. 8 kgha-1 sulphur and in the region of NP "Plitvice Lakes" approx. 5 kgha-1 chloride and approx. 6 kgha-1 sulphur. On average the lysimeters had a larger content of sedimentary material than the values registered in rain-gauges under tree crowns. This data indicates the reason for the lower pH values in the lysimetric samples. Accumulation of sedimentary material on the soil surface and further transportation through the soil profile into seepage water, is evident. Sedimentary materials effect the soil and quality of seepage water. The majority of pH values measured in the samples are acidic. By lysimetric pedology it is easy to establish the degree of soil acidification due to dry and wet sedimentation and to estimate their buffer capacity. Thus, the type of forest cover is an important factor.
Key words: monitoring, National Parks, precipitation, soil solution, acidification