My research Ph.D. project was entitled: Geochemical patterns in
the soils of Zeeland, natural variability versus anthropogenic
impact The research aimed at assessing patterns in geochemical soil composition and
distinguishing natural variability from anthropogenic impact. The variability
is assessed in geographical space and in attribute space. Patterns
from both spaces are related
to natural and human processes influencing the soil composition.
The research took place in 1999-2005 and the results were
published in a thesis in February 2005. This thesis was successfully
defended at February 17.
Soils can both be a sink and a source for many components influencing
our environment. These components may either be beneficial or damaging
and for assessing the current environmental condition knowledge about
the extent these components are present in the soils is necessary.
For the Netherlands the government demanded a nation wide inventory of
soil contamination by drafting so called soil pollution risk maps.
These maps pertain to levels of priority chemicals relative to their
legal thresholds in soil. However, I argue that using methods as used
in establishing geochemical baselines and deriving models to estimate
the anthropogenic enrichment based on these baselines provide much more
insight in the extent of the contamination, or enrichment, of the soils.
Therefore a large geochemical survey, using a consequent sampling
design and analytical methods, was done in Zeeland, south-west of
the Netherlands. The young Holocene marine clayey sediments in the
agricultural area were sampled at two depths in the profile, using the
deeper layer as a reference. A specific survey was used to estimate the
extent of spatial variability. The results indicated a distinct human
influence can be discerned and that elements like Cd, Cu, Sn, Sb, Pb,
Zn, As are enriched. These elements have also more variability, both
in spatial as in attribute space, than the non-anthropogenic influenced
elements. The result indicated also the the used legal threshold levels
are a overestimation of the natural soil background composition.
To assess the soil concentrations of DDT and its derivatives and
metabolites (sum DDT), the most troublesome organic components due
to exceedance of legal limits, likewise statistical methods as for the
inorganic assessment were used. The data was taken from local surveys
demanded by the authorities using national standards for sampling design
and analytical procedures. This research indicated that the sum DDT
values were highly variable, in general determined by small scale
variability, resulting in limited value of the data.