Fjölrit RALA - 15.06.2004, Page 64

metals with short-range-order aluminosilicates and organo-mineral complexes. Cr(III)
isotherm adsorption curves obtained at pH 6 were adequately described by the Langmuir
equation and showed significative difference between control and flodded soils. High
adsorption capacity of Cr(III) ions from aqueous solutions on the control and flooded E3 soil
was observed. A significant presence of short-range ordered mineral phases, shown by
selective chemical extractons and by the x-ray diffractometry of the clay ffaction, was likely
involved in soil metal retention.
Total microbial biomass and fungal mycelium were generally higher in soil El. Similarly, in
this soil was observed the greatest bacterial diversity, as compared to soils E2 and E3. In
terms of bacteria community similarity (Sprensen index) the studied soils could be ranked as
follow: C = E1 = E2 = E3. Only some of the measured enzymatic activities (acid phosphatase,
arylsulphatase, P-glucosidase, dehydrogenase) decreased with the number of flooding events,
whereas others (urease and FDA hydrolase) were not changed or increased. In some cases the
control soil showed lower enzymatic activities than those of flooded soils. The high metal
content of soils did not appear to have a predominant influence on the studied biological and
biochemical parameters possibly as a result of both low metal mobility and high C content.
Infact, soil E4 sampled immediately after a new flooding event, although its high Cr content
(536 mg kg"1), had higher biological and biochemical activities. The large input of Cr from the
sediments (1012 mg kg ') was masked by their high levels of organic carbon (61 g kg"1).
Soil hydraulic properties and solute transport behaviour, determined by the Wind’s method
and by a miscible flow experiment on P1 and P2 profiles, confirmed the high Cr(III) retention
capacity of the soil with high values of dispersivity and showed occurrence of preferential
flow paths. The analysis of the soil water retention curves showed a decrease of large pores in
the flooded soil compared to control. Frequent occurrence of clay and silt coatings along
elongated pores in the surface and subsurface soil horizons was showed by optical microscopy
observations. This suggested a possible transfer of metal-rich sediments along the soil pore
network during water movement.
References
Adamo, P., M. Arienzo, M.R. Bianco, P. Violante. 2001. Impact of land use and urban runoff
on the contamination of the Samo river basin in Southwestem Italy. Water, Air and Soil
Pollution 131: 36-45.
Adamo, P., L. Denaix, F. Terribile, M. Zampella. 2003. Characterization of heavy metals in
contaminated volcanic soils of the Solofrana river valley (southem Italy). Geoderma 2027:
1-25
Soil Survey Staff. 1998. Keys to soil Taxonomy. United States Department of Agriculture
Natural Resources Conservation Service (USDA). Washington, pp. 22-23
47