In Fig. 3, the effect of soil oven-drying on the total dissolved
trace metal concentrations in the soil solution extracts obtained
from the twelve soils used in the batch extractions is presented.
The data underlying this figure is included in Appendix C. Soil
oven-drying caused the Cu and Ni concentrations to increase
significantly by a factor of 1.6 and 1.1, respectively. No significant
changes were found for Cd and Cr while a small, but significant
decrease was found for Zn. Increases in total dissolved Cu levels
after soil drying have been found before (Klitzke and Lang, 2007).
Especially Cu is known to bind (much) more strongly to humic
substances than other metals (Temminghoff et al., 1997). Hence,
the increased total dissolved Cu and Ni concentrations seem to be
linked to the increased DOM levels as induced by soil oven-drying
(Fig. 2), which will be further discussed in Section 3.5. Interestingly,
soil oven-drying caused a significant decrease in the ratio
between the concentrations of total dissolved Cu and total DOC
(Appendix D). Apparently, the DOM released to the soil solution
extracts following soil oven-drying was less effective in binding Cu,
as found before by Amery et al. (2007). In Section 3.6, this will be
further discussed. The TDP concentration in the soil solution
extracts obtained from the four soils used in the DMT experiments
increased significantly by a factor of 1.7 (Pb0.001) (Appendix B),
which is rather similar to the increase of TDP in the batch extracts
(Fig. 1). Soil oven-drying caused both ortho-P and DOP to increase
significantly by a factor of 1.8 (P b0.01) and 1.5 (P b0.001),
respectively (Appendix B). However, ortho-P was mainly responsible
for the elevated TDP levels found after soil oven-drying. The
increase in ortho-P accounted for 66 to 70% of the increase in TDP,
while this percentage varied between 30 and 34% for DOP. The
elevated ortho-P levels can be attributed to increased competition
for a possibly reduced number of binding sites on metal oxides
between ortho-P and elevated FA levels leading to a higher ortho-P