Report - ICP Forests

56 3. Intensive Monitoring
centrifugation of soil samples and saturation extraction had rarely been used for soil solution
collection.
Evaluation of soil solution data is based on single samplers that are of a defined type (i.e.
tension and zero tension lysimetry) and that sample soil solution in a defined layer and soil
depth. On each plot more than one sampler may exist in each sampling depth. Most countries
submit data for one ‘sampler’ per soil depth and plot. This ‘sampler’ can represent a mean of
different single measurements per soil depth and plot or one single measurement of a sample
that was pooled from different lysimeters in one soil depth of the same plot. If data for more
than one lysimeter per soil depth and plot were submitted, means were calculated for each
sampling depth and plot and evaluated as one ‘sampler’.
Data availability was best for the calculation and evaluation of (Ca+Mg+K)/Al ratio. Data were
available for 2054 samplers on 263 plots. From the total of these, only those samplers were
included in the analysis from which data were available for at least 6 months per year in 2006
and in at least three more previous, consecutive years, i.e. complete data availability in the years
2003 – 2006 was a criterion for plot selection. This resulted in 160 plots with 396 soil solution
samplers in different soil depths.
Mean sampler pH and trend of pH were calculated for all samplers that continuously provided
data from 2000 to 2006 with at least four measurements per monitoring year.
The calculation of trends of BC/Al ratio used all samplers that continuously provided data from
2000 – 2006 and at least six single measurements per monitoring year. Following these criteria,
linear trends for BC/Al were calculated for 111 samplers on 58 plots and for pH 166 samplers at
66 plots. From single measurements annual arithmetic means were calculated. Trends were
evaluated using regression coefficients and significance of linear regression analysis of
monitoring year and annual mean.
Soil solution has been sampled in different soil depths. The manual of ICP Forests (Submanual
on Soil Solution and Analysis, updates 6/2002) (ANONYMOUS, 2004) suggests sampling
depths for soil solution chemistry assessment of 10-20 cm (within the rooting zone) and 40-80
cm (below the rooting zone). Both suggested sampling depths are well represented; about 77%
of all samplers are located in the upper 20 cm and 17% below the rooting zone. About 10% of
the samplers had been located below 90 cm soil depth. Table 3.3.2.2-1 gives an overview on
data availability for all monitoring years of parameters that are mandatory or optional according
to the ICP Forests manual. Even though those parameters are mandatory to assess following the
current version of the ICP Forest manual they are not available from all plots.