14. The deposition of pollutants over forest land

Leszek Kluziński

The deposition of pollutants reaching forest ecosystems is largely shaped by the amount of atmospheric precipitation. In 2003, the distribution of precipitation was not different from the one in the previous year. The annual mean of precipitation was 80% of the 2002 mean. The month mean of precipitation for 2003 with the exception of April, July and December were lower than the means in respective month of the previous year. The highest monthly mean of precipitation was in July, the lowest - in February.

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 Fig. 17. The trends of changes over the last five years revealed lower values of deposition of alkalising ions in all natural-forest regions but with a rising tendency noted in the Silesian natural-forest region. The maximal values of deposition of those ions were found in southern Poland in winter, minimal - in the Mazury-Podlasie, Wielkopolska-Pomerania and Sudeten natural-forest regions. 

The deposition of acidifying ions (N-NO₃^-, S-So₄^2-, Cl^-) over the last five years was higher in southern Poland in the Małopolska and Carpathian natural-forest regions. In northern and central Poland high level of ion deposition occurred in the Baltic natural-forest region - Fig. 18. A clear tendency towards increase in the deposition of acidifying ions over the last five years was noted for the Silesian and Sudeten natural-forest regions while almost all natural-forest regions in northern and central Poland and the Małopolska natural-forest region saw a downward tendency. The lowest level of deposition of acidifying ions was found in the Mazowsze-Podlasie and Sudeten natural-forest regions. The Silesian natural-forest region was characterised by the even level of ion deposition.

The lowest concentrations of the acid-generating ions were noted in the Mazury-Podlasie and Sudeten natural-forest regions. In 2003, concentrations of these ions increased in both seasons in the majority of natural-forest regions when compared to the year 2002 with the exception to the Mazury-Podlasie natural-forest region where an increase in concentrations of acid-generating ions were noted during the winter and summer periods.

The deposition of metallic ions (Al³⁺, Fe²⁺, Mn²⁺, Zn²⁺, Cu²⁺) in 2003 was higher in the southern regions of Poland during the winter period. The maximal concentrations occurred during the winter period in the Małopolska, Carpathian and Silesian natural-forest regions and minimal in the Wielkopolska-Pomerania and Sudeten natural-forest regions. For metallic ions, the maximal concentrations in 2003 were higher than in 2002 in the majority of natural-forest regions irrespective of the season.

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 2002 in all natural-forest regions with the exception to the Mazowsze-Podlasie and Carpathian natural-forest regions where an increase in percentage share of acidifying ions was noted. There was a slight decrease in percentage share of the metallic ions in all natural-forest regions. The ratio of deposition of the discussed groups of ions remained at the previous year level in the Wielkopolska-Pomerania natural-forest region.

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 in the south of Poland in the Małopolska and Carpathian natural-forest regions. Since 2001, the trend of changes in the deposition of eutrophicating ions has been declining in all natural-forest regions on northern and central Poland and in the Małopolska region. The opposite tendency was observed in other natural-forest regions where the values of ion deposition has been rising since 2001 - Fig. 19.

The concentrations of ammonium ions (N-NH₄⁺) in 2003 showed higher values during the summer period in all but the Baltic and Mazowsze-Podlasie natural-forest regions. The highest mean concentrations were noted in the Wielkopolska-Pomerania natural-forest region during the summer and in the Mazowsze-Podlasie natural-forest region during the winter. The year 2003 saw an increase in concentrations of ammonium ions when compared to 2002 in all natural-forest regions during the winter period with the exception to the Sudeten natural-forest region and Mazowsze-Podlasie, which had lowered N-NH₄⁺ concentrations during the summer.

The values for sums of deposition of ammonium and nitrate ions ranged from 12.3 kg/(ha*year) in the Mazury-Podlasie natural-forest region to 23.1 kg/(ha*year) in the Carpathian natural-forest region. Thus, when compared to 2002, a slight increase is recorded in nitrogen minimal and maximal value of deposition and a change in the order of particular natural-forest regions based on increase in sum of nitrogen deposition. An increase in the sum of ammonium deposition occurred in six natural-forest regions while a decrease was noted in the Baltic and Wielkopolska-Pomerania natural-forest regions.

The share of ammonium form in the total nitrogen deposition plays an important role. The higher share of ammonium ions (N-NH₄⁺) over nitrate ions (N-NO₃) is thought to be a characteristic of lands intensively used for agriculture. This proportion is opposite for urbane environments [1]. In 2003, the ratio of ammonium ions to nitrate ions was high in the Wielkopolska-Pomerania natural-forest region and ranged from 68% of nitrogen deposition in the Sudeten natural-forest region to 77% in the Wielkopolska-Pomerania natural-forest region. The percentage share of both forms of nitrogen deposition was similar in all natural-forest regions and it increased in five natural-forest regions in comparison with the year 2002. It remained at the previous year level in the Wielkopolska-Pomerania natural-forest region, but it decreased in the Mazowsze-Podlasie natural-forest region.

The values for the annual influx of sulphate-sulphur ranged from 6.8 kg/(ha*year) in the Mazury-Podlasie natural-forest region to 22.4 kg/(ha*year) in the Carpathian natural-forest region. When compared to 2002, an increase in sulphate-sulphur deposition was noted in the majority of natural-forest region with the exception to Wielkopolska-Pomerania and Mazury-Podlasie natural-forest regions and it was particularly distinct in the Carpathian natural-forest region. The downward trend in the deposition of sulphur compounds in the precipitation during the recent years was reversed. In 2003, only the Sudeten natural-forest region exceeded the lower limit of the background deposition of sulphur compounds while it increased in other regions to approach the upper limit of deposition in the Carpathian natural-forest region. 

The mean monthly Ph of atmospheric precipitation ranged between 4.5-6.8 in northern and central Poland and between 4.1-6.7 in southern Poland. In 2003, the higher values for pH were noted in southern natural-forest regions. The seasonal variation in pH of atmospheric precipitation was characteristic of all natural-forest regions. The lowest values for pH of atmospheric precipitation were noted in the winter period (January-March and October-December). In 2003, like in the previous year, the highest pH values were noted between April and September, the lowest values - in the winter season (February, March and December) in southern regions of Poland. The country mean pH of atmospheric precipitation was the highest in the Sudeten natural-forest region (means pH=4.79) and the lowest in the Mazury-Podlasie natural-forest region (means pH=5.24) - Fig. 20. The country mean value for pH in 2003 was 4.9 and was lower than pH in 2002.

During the year 2003, the concentrations of heavy metals were measured monthly in atmospheric precipitation samples collected from 148 second-level POPs - Table 21. The highest concentrations of cadmium (Cd) were found in the Carpathian natural-forest region during the winter and summer seasons. The lowest mean concentration of cadmium was found in the Mazury-Podlasie natural-forest region in the summer. In all natural-forest regions, the concentrations of this element were higher in the winter the than in the summer with a single exception of the Mazury-Podlasie natural-forest region.

Sulphur dioxide (SO₂) and nitrogen oxides (NO_x) together with carbon dioxide play a major role in the acidification of atmospheric precipitation [13]. The concentrations of these compounds in the chemical composition of atmospheric precipitation directly 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 [8].

The NO₂ concentrations were higher than the values found in 2002 in all natural-forest regions but the Mazowsze-Podlasie and Małopolska natural-forest regions.

The lowest mean concentrations of NO₂ in the air was found in the Mazury-Podlasie natural-forest region (4.15 μg/m³) while the highest - in the Silesian natural-forest region (12.47 μg/m³) and was higher than in 2002.

The monthly means indicate a similar annual course of changes in of NO₂ concentration over all natural-forest regions with maximum in January or February and minimum from May to September.

In the last five years, high concentrations of NO₂ were noted in southern natural-forest regions. In northern Poland the highest concentrations of NO₂ in the air was found in the Wielkopolska-Pomerania natural-forest region, in southern Poland - in the Silesian and Małopolska natural-forest regions (Fig. 21). In the last five years, the lowest concentrations of NO₂ were noted in the Mazury-Podlasie natural-forest region. Since 2000, an increase in concentrations of NO₂ has been recorded in all natural-forest region of northern Poland. Since 2002, the low rate of this increase was noted in all natural-forest regions. While in northern regions this rate was low, in the south of Poland in the Małopolska and Carpathian natural-forest regions it was high.

The mean values of sulphur dioxide over the last twelve months were lower than those in 2002 in northern natural-forest regions but Mazowsze-Podlasie where an increase in concentrations of SO₂ was noted (Fig. 21). The higher concentrations of SO₂ than in the previous year were noted in southern regions of Poland with the exception to the Silesian natural-forest region which saw a decrease in concentrations of SO₂ in the air. The variation in concentrations from 1.98 mg/m³ in the Mazury-Podlasie natural-forest region to 5.63 mg/m³ in the Małopolska natural-forest region was higher than in 2002. An increase in the level of maximal concentrations was accompanied by a decrease in minimal concentrations. The monthly means indicate a similar annual course of changes in SO₂ concentration over all natural-forest regions with maximum in January or December and minimum in May, June and August.

The tendency to decrease in SO₂ concentrations was noted before 2001 in all natural-forest regions - stronger in southern regions of Poland. After that year, there was a noticeable tendency to increase in SO₂ concentrations (Mazowsze-Podlasie, Mazury-Podlasie and Carpathian natural-forest regions) or to level concentrations of SO₂ (other natural-forest regions). The lowest concentrations of sulphur dioxide over the last five years were found in the Mazury-Podlasie and Sudeten natural-forest regions.