6. The deposition of pollutants over forest land (second-level POPs)

The deposition of pollutants reaching forest ecosystems is largely shaped by the amount of atmospheric precipitation. In 2002, the distribution of precipitation was not different from the one in the previous year. The highest monthly mean of precipitation was in October. During the period from March to October the precipitation level was very low. In July, usually abundant in precipitation, the monthly mean precipitation was lower than that in the previous year by almost 70 mm.

The deposition of alkalising ions (Ca2+, Mg2+,K+, Na+) over the last five years maintained on the high level in the Małopolska and Carpathian natural-forest regions and by 2000 was equally high in the Mazowsze-Podlasie natural-forest region - see Ryc. 8. In 2001-2002, a distinct decline in the deposition of alkalising ions was noted in the south of the country. The lower values of deposition of alkalising ions but with a rising tendency were noted in the Silesian natural-forest region, while definitely lower (the lowest in the country) deposition of these ions was found in the Sudeten natural-forest region - see Tab. 7.

In 2002, like in the previous years, the markedly higher level of concentrations was noted during the winter period. The exception was potassium (K+) showing even or slightly higher level of ion concentrations during the summer period. The maximal values were characteristic for the natural-forest region in southern Poland during the winter, while the minimal values occurred in the Sudeten natural-forest region during the summer. A relatively high level of Na+ concentrations was noted in the Baltic natural-forest region, which could be associated with the influence of aerosols flowing from the sea. This phenomenon might have explained a high level of the Cl+ ion concentration during the summer period in this natural-forest region.

The deposition of acidifying ions (N-NO3-, S-So42-, Cl-) over the last five years was higher in the southern Małopolska and Carpathian natural-forest regions - see Ryc. 9. High levels of ion deposition occurred in the Wielkopolska-Pomerania and Baltic natural-forest regions. A clear tendency to increase in the deposition of these ions was noted for the Baltic and Carpathian natural-forest regions, while the Wielkopolska-Pomerania and Mazowsze-Podlasie natural-forest regions saw a downward tendency. The lowest level of deposition of acidifying ions was found in the Sudeten and Mazowsze-Podlasie natural-forest regions. The Silesian natural-forest region was characterised by the even level of ion deposition.

The higher concentrations of the acid-generating ions were noted in the winter period, which were distinct in the natural-forest regions of southern Poland. In 2002, the maximal depositions of these ions were found in the Silesian and Małopolska natural-forest regions, while the lowest concentrations - in the Sudeten natural-forest region. The year 2002 saw a slight increase in concentrations of acid-generating ions during the winter and a decrease during the summer when compared to 2001.

The deposition of metallic ions (Al3+, Fe2+, Mn2+, Zn2+, Cu2+) in 2002 was higher in the southern regions of Poland during the winter period. The maximal concentrations occurred in the Silesian and Małopolska natural-forest regions during the winter period. For a majority of metallic ions, the maximal concentrations in 2002 were higher than in 2001. The minimal ion concentrations occurred in the Sudeten natural-forest region during the summer.

The percentage share of the acidifying, alkalising and metallic ions in the total annual influx of pollutants from atmospheric precipitation was estimated. The ratio of deposition of alkalising to acidifying ions was higher than that of 2001 in all natural-forest regions with the exception to the Sudeten natural-forest region where it remained at the previous year level. There was a slight decrease in percentage share of the metallic ions in all natural-forest regions.

The highest deposition of eutrophicating ions (N-NH4, N-NO3) over the last five years occurred in the north of Poland in the Wielkopolska-Pomerania and Mazowsze-Podlasie natural-forest regions and in the south of Poland in the Małopolska natural-forest region - see Ryc. 10. A decrease in the deposition of eutrophicating ions was noted across the country over the analysed period with a marked decrease in the Wielkopolska-Pomerania, Mazowsze-Podlasie and Silesian natural-forest regions. Lower values of ion deposition occurred in the Mazury-Podlasie and Sudeten natural-forest regions. The values for sums of deposition of ammonium and nitrate ions ranged from 10.7 kg/(ha*year) in Sudeten natural-forest region to 20.8 kg/(ha*year) in the Wielkopolska-Pomerania natural-forest region - see Tab. 7. Thus, when compared to 2001, the range of nitrogen deposition was similar. A decrease in sum of nitrogen deposition occurred in 5 natural-forest regions, while an increase was noted in the Silesian, Baltic and Wielkopolska-Pomerania natural-forest regions. The concentrations of ammonium ions (N-NH4+) showed higher values during the summer period in all but the Sudeten natural-forest region. The highest mean concentrations were noted in the Wielkopolska-Pomerania natural-forest region during the summer and in the Małopolska natural-forest region during the winter. The year 2000 saw an increase in concentrations of ammonium ions when compared to 2001 in the natural-forest regions of southern Poland during the winter period with the exception to the Sudeten natural-forest region, which had the lowest concentrations during the both periods.

The values for the annual influx of sulphate-sulphur ranged from 7.2 kg/(ha*year) in the Sudeten natural-forest region to 18.4 kg/(ha*year) in the Carpathian natural-forest region - see Tab. 7. When compared to 2001, a decrease in sulphate-sulphur deposition was noted in the majority of natural-forest region (the exception was the Baltic natural-forest region) and was particularly distinct in the Carpathian natural-forest region. The background deposition of sulphur, i.e. not affected by the anthropogenic sources reached a few kg/ha*year [6]. The literature data for sulphur deposition in southern Poland cover the range 13-26 kg/ha*year [4, 17] thus, the analysis of results of measurements taken within the network of forest monitoring points out to the marked decrease in the contents of sulphur in the precipitation during the recent years. In 2001 and 2002, only three natural-forest regions exceeded the lower limit of the background deposition of sulphur compounds while in the upper limit of deposition was not exceeded in any of the regions.

A comparison of distributions of ions by seasons revealed that a majority of ions reached their higher concentrations during the winter period with an exception to N-NH4+ and K+, which showed the opposite tendency. For majority of ions, the higher level of concentrations is repeatedly noted in southern Poland during the winter period. During the summer period, the differences between northern and southern Poland were not so much distinct.

The period 1998-2002 saw a marked increase in the mean pH of atmospheric precipitation both in individual natural-forest region and throughout the country - see Ryc. 11. The higher values for pH were noted in northern Poland, while in the southern natural-forest regions the values for pH were below the country mean. In 2002, the seasonal variation in pH of atmospheric precipitation was characteristic of both the northern and southern natural-forest regions. The highest values for pH of atmospheric precipitation were noted from April to September, while the lowest values for pH were noted in the winter period (January, November and December). The higher values for precipitation pH were noted in southern Poland. The mean monthly values for precipitation pH ranged from 4.45 to 6.50 for northern and central Poland and from 4.30 to 5.88 for southern Poland. The lowest annual values for pH of atmospheric precipitation were noted in the Małopolska natural-forest region (mean pH=4.90), and the highest one - in the Mazury-Podlasie natural-forest region (medium pH=5.22). Information that the natural reaction of precipitation in Poland resulting from the presence of CO2 in the atmosphere (concentration 320 ppm and temperature 15oC) is 5.65 can be the explanation of the results [18].

Plate 11. SHIMADZU ion chromatograph system with conductivity detector - photo by Józef Wójcik

2001/2002 saw the first measurements of concentrations of heavy metals in atmospherics precipitation. The highest concentrations of cadmium (Cd) were found in the Silesian and Małopolska natural-forest regions during the winter period. In all natural-forest regions, the concentrations of this element were higher in the winter the than in the summer. The minimal annual mean concentrations of cadmium were found in the Mazowsze-Podlasie natural-forest region. The maximal values for sums of cadmium deposition (0.0035 kg/ha*year) in atmospheric precipitation were noted in the south of Poland in the Małopolska and Carpathian natural-forest regions, and minimal values (0.0015 kg/ha*year) - in the Mazowsze-Podlasie natural-forest region - see Tab. 8. The concentrations of lead (Pb) were generally higher during the summer period and this period noted the highest mean in the Carpathian natural-forest region. The Małopolska and Sudeten natural-forest regions were characterised by higher concentrations of lead ions in the winter than in the summer. The lowest mean value noted for lead was in the Baltic natural-forest region during the winter period. The low values for annual sums of lead deposition in atmospheric precipitation were noted in the south of the country (below 0.0200 kg/ha*year), higher in the central and south-western part of Poland (from 0.0205 to 0.0232 kg/ha*year) and highest in the south-eastern regions (from 0.0318 to 0.0506 kg/ha*year). The minimal level of the annual mean deposition of lead was found in the Sudeten natural-forest region reaching 0.0118 kg/ha*year - see Tab. 8.

Sulphur dioxide (SO2) and nitrogen oxides (NOx) together with carbon dioxide play a major role in the acidification of atmospheric precipitation. The concentrations of these compounds in the chemical composition of atmospheric precipitation negatively affect the assimilatory apparatus of trees. Besides, the throughfall waters reaching the soil result in an increase in the acidity of the soil environment, especially poor soils and those under spruce stands causing mobilisation of toxic ions of aluminium and heavy metals.

The higher concen-trations of SO2 in the air over the last five years prevailed in the natural-forest regions (Silesian and Małopolska) of southern Poland. In northern and central Poland, high concentrations of SO2 were noted in the Wielkopolska-Pomerania and Mazowsze-Podlasie natural-forest regions. A noticeable tendency to increase in SO2 concentrations was noted in all natural-forest regions over the analysed period. The 2002 mean annual values for concentrations of SO2 were lower than those in 2001 in all but Mazury-Podlasie natural-forest regions. The Mazury-Podlasie together with the Carpathian and Sudeten natural-forest regions exhibited the lowest concentrations of sulphur dioxide. In 2002, SO2 concentrations ranged from 2.29 ľg/m3 in the Mazury-Podlasie natural-forest region to 5.42 ľg/m3 in the Silesian natural-forest region - Ryc. 12. The monthly means indicate a similar annual course of changes in of SO2 concentration over all natural-forest regions with maximum in January or December and minimum from May, June and July. In 2002, the concentrations of sulphur dioxide and nitrogen dioxide over the forested areas stayed within the 50% of the norm for Poland [16].

In the last five years, high concentrations of NO2 were noted in the Wielkopolska-Pomerania, Silesian and Małopolska natural-forest region, and the lowest ones in the lowest Mazowsze-Podlasie, Sudeten and Carpathian natural-forest regions. Since 2000, an increase in concentrations of NO2 has been recorded in all natural-forest region of southern Poland. The high rate of this increase was noted in the Małopolska and Carpathian natural-forest regions. The 2000 saw a decrease in NO2concentrations. In 2002, a noticeable tendency to increase in the mean NO2 concentration was observed countrywide. The NO2 concentrations were higher than the values found in 2001 in all but the Baltic and Wielkopolska-Pomerania natural-forest regions. The lowest mean concentrations of NO2 in the air were found in the Mazury-Podlasie natural-forest region (3.91 ľg/m3) while the highest - in the Małopolska natural-forest region (13.76 ľg/m3) - see Ryc. 12. The monthly means indicate a similar annual course of changes in of NO2 concentration over all natural-forest regions with maximum in January or December and minimum from May to September.