Andrei Rozanov

Influence of clay content on bioavailability of copper in the earthworm Eisenia fetida

We investigated the effect of clay content on the bioavailability of copper to the earthworm Eisenia fetida, in the laboratory for 28 days using OECD artificial soil adjusted to 5%, 20% and 40% clay. Mortality, growth, cocoon production and internal copper concentrations were assessed in worms, and total, DTPA and CaCl(2) extractable copper in the substrates were also determined. The results showed that with increased clay content, there was significant reduction in internal Cu concentration of worms as well as toxicity of copper as shown by data for growth and mortality. However, internal copper concentrations of worms could not explain fully the observed toxicity in this study probably because of Cu regulation. Among the three extraction methods, DTPA extraction revealed the strongest relationship between partitioning and toxicity of Cu in this study. DTPA extract is thus a promising surrogate measure of bioavailability of Cu to earthworms. It is concluded that clay content has significant influence on the bioavailability of copper to earthworms and other similar species.

Role of clay content in partitioning, uptake and toxicity of zinc in the earthworm Eisenia fetida☆

We studied the effect of clay content on the bioavailability of zinc to pre-clitellate earthworm, Eisenia fetida in the laboratory using OECD artificial soil adjusted to 5%, 20%, and 40% clay. Batches of worms were exposed to a wide range of zinc concentrations. Mortality, growth, maturation (% clitellate), cocoon production, and body zinc concentrations were assessed over and after a period of 4 weeks. Total, DTPA, and CaCl(2) extractable zinc in the substrates were also determined. The results of the biological responses showed that interaction of clay and zinc had a significant influence on mortality but not on the other biological parameters. None of the three extraction methods showed consistent and significant effect of clay content on zinc partitioning. Although total, DTPA, and CaCl(2) extracts of zinc correlated strongly with one another and were in similar relation with the observed biological responses, only the CaCl(2) extract revealed a time dependent availability of this metal. It is concluded that clay content had no significant influence on sub-lethal toxicity of zinc to this earthworm over the range of exposure concentrations.

Understanding the combined effect of soil properties on gully erosion using quantile regression

The individual effects of soil properties on soil erodibility are well understood. It is also known that various interactions between these properties exist, which creates the need for unique investigations into how soil properties influence soil stability. Quantile regression was used in this paper to determine which soil properties control gully erosion in a catchment in Lesotho. Samples of typical soil forms found in the catchment were analysed for properties related to soil erosion. Dispersion ratio had the best correlation with areas of severe gully erosion. No strong correlation was found for a single soil property with dispersion ratio. Quantile regression showed that a combination of effective cation exchange capacity (CEC), total carbon, exchangeable sodium percentage (ESP) and free iron influenced soil dispersion. When the aggregating agents (effective CEC, total carbon and free iron) are deficient in the soil sample, very small amounts of a dispersing agent (ESP > 0.67%) will lead to above-average dispersion. Soils with an increased amount of basaltic parent material tended to be more stable.

Generation and size distribution of sediment eroded in a small-scale catchment of the Western Cape (South Africa)

Rainfall, runoff (overland flow), total sediments mobilized and their size distribution were measured for a number of events over three years (from 2006 to 2008) in a small-scale catchment of the Berg River (Western Cape). The aim was to develop local-scale rainfall/runoff, sediment generation and particle size distribution relationships that could be incorporated into existing hydrological catchment models for predicting erosion, transport and deposition of sediments with sorbed contaminants. The results indicated that rainfall intensity was weakly correlated to rainfall amounts (R 2 = 0.54), whilst runoff (between 12.4% and 18.2% of rainfall) was weakly correlated to the product of rainfall amount and peak intensity at two sites with different soil properties and slopes (R 2 = 0.29 and 0.44), depending on antecedent moisture condition, land use and management practices. Sediment concentration was inversely correlated to runoff volume. However, more runoff produced larger total sediment loads. The bulk of sediment particles mobilized via runoff water had diameters in the range between 4.76 and 15.95 μm (measured with a Saturn DigiSizer 5200 particle size analyzer). Sediment size distribution was relatively uniform for all events recorded, did not depend on sediment concentration, runoff, rainfall amount and intensity, and it was similar to the texture of the soil A-horizons (source of sediments). Spatial information on soil A-horizon textural properties could therefore be used to infer the nature of sediments mobilized in the catchment.

Rheological parameters of some soil samples before and after H2O2 treatment

the effect of soil organic matter (som) on formation of inter-particle bonds was studied in soils with high organic and no mineral carbon content in the top (A1, Ap) layers of different origin and under various land uses. the first set of soil samples was collected in the Alekhin central chernozem reserve (kursk region, russia): under native steppe vegetation and under 67-yearold bare fallow. the second set of samples was sourced from the midlands of kwa-zulu natal, south Africa: under pine plantation and under long-term maize monoculture. soil organic matter was removed by of 30% hydrogen peroxide (H2o2) treatment for 20-40 days. the rheological behaviour of the capillary-wetted soil pastes was characterized by amplitude sweep test with the modular compact rheometer mcr-302 (Anton-Paar, Austria). the storage modulus in linear viscous-elasticity range (Lve-range) and crossover of storage modulus and loss modulus were determined. the samples treated with H2o2 in all cases except the Ferralsol under pine plantation, increased the storage modulus in the Lve-range. it shows more rigid particle interaction due to loss of som. the peculiarity of soil under pine plantation is very high resistance to stress in native state and loss of this resistance upon som oxidation or removal. We connect this with significant change in particle size distribution upon the H2o2 treatment. in contrast to other samples, this soil shows significant reduction in coarse silt fraction (from 44.5 to 23.2%) and an increase in clay content (from 10.8 to 36.5). We connect the observed differences to the type of organic matter inputs. unlike the herbaceous vegetation, pine plantations lead to significant accumulation of plant litter on the soil surface. the dissolved organic matter (Dom) is leached out of the litter layer by percolating water. the sorption of Dom (ligand exchange, cation bridges, hydrophobic interactions) on the mineral surfaces contributes to particle aggregation. keywords: soil, structure, organic matter, rheology, amplitude sweep test kulcsszavak: talaj, szerkezet, szervesanyag, reológia, változó frekvenciájú nyírásvizsgálat Dolgor khayDaPOVa Associate professor at the m. v. Lomonosov moscow state university, Department of soil science. specializes in the study of soil structure, soil physics, soil rheology. Evgeny MilanOVSkiy Leading researcher at m. v. Lomonosov moscow state university, Department of soil science. specializes in the study of soil organic matter, soil structure, soil physics. liesl WiESE Ph.D. student, stellenbosch university, Department of soil science. specializes in the study of soil organic matter. andrei rOzanOV senior lecturer, stellenbosch university, Department of soil science. specializes in the study of soil.