Report - ICP Forests

62 3. Intensive Monitoring
3.3.3.3 Temporal trends of BC/Al ratio and pH 2000 – 2006
For the majority of lysimeters no significant trends were detected for the BC/Al ratio and pH
(Figures 3.3.3.3-1 to 3.3.3.3-8). But both parameters decreased for 13 to 30% of all samplers
included in the analysis. For both parameters, the share of plots with a significant decrease was
larger as compared to the share of plots with an increase. The only exception was the BC/AL
ratio below 80 cm soil depth were the share of plots with a decrease was equal to the share with
an increase and the trend of pH between 40 and 80 cm soil depth were the share of plots with an
increase was slightly higher as compared to the share of plots with a decrease. BC/Al and pH
trends did not show distinct spatial patterns.
Figures 3.3.3.3-9 – 3.3.3.3-12 show that the relative frequency of the BC/Al ratio below 1,
which often is used as a general critical limit, did not follow a temporal trend in any of the
different soil depth classes but in general increased with increasing depth. Figures 3.3.3.3-13 –
3.3.3.3-15 show that the topsoil (0 – 20 cm) and also the main rooting zone (20 – 40 cm) are
subject to more acid conditions than the lower parts of the profile. Relative frequencies of soil
pH did not change during the specified evaluation period.