Efstathios Diamantopoulos

Lead removal from aqueous solutions by raw sawdust and magnesium pretreated biochar: Experimental investigations and numerical modelling

Lead removal from aqueous solutions by raw cypress (Cupressus sempervirens L.) sawdust (RCS) and its derivative magnesium pretreated biochar (Mg-B) was investigated under static and dynamic conditions through batch and column assays. The Hydrus-1D model was used to estimate the transport parameters of the lead measured breakthrough curves. The batch experiments results showed that Mg-B was very efficient in removing lead compared to RCS and several other previously tested natural and modified materials. The column experiments results indicated that for both RCS and Mg-B, lead breakthrough curves and the related removal efficiencies were mainly dependent on the used initial concentration and the adsorbents bed height. The use of Hydrus-1D showed that the two-site chemical non-equilibrium model describes better the experimental lead breakthrough curves for both RCS and Mg-B as the equilibrium model.

Hydraulic Properties and Non-equilibrium Water Flow in Soils

Accurate knowledge of hydraulic properties for unsaturated soils is critical in the estimation of soil water fluxes by simulation models that are based on the Richards equation. The purpose of this chapter is to review the characterization of unsaturated soil hydraulic properties for their applicability in models simulating unsaturated water transport. We start with a short review of the fundamentals that lead to the definition of the hydraulic functions in the framework of continuum hydromechanics. Next, we address problems of common parameterizations of hydraulic functions in the critical regions near and at saturation, towards dryness, and on hysteresis. We find that traditional approaches have deficiencies, but recent progress has been significant in particular with respect to including film and corner flow components in the hydraulic conductivity function. The chapter closes with a discussion of the phenomenon of dynamic non-equilibrium in soil water flow, which shows to our opinion toward the need for a paradigm change in the modeling of soil water transport.

Strong sesquiterpene emissions from Amazonian soils

The Amazon rainforest is the world’s largest source of reactive volatile isoprenoids to the atmosphere. It is generally assumed that these emissions are products of photosynthetically driven secondary metabolism and released from the rainforest canopy from where they influence the oxidative capacity of the atmosphere. However, recent measurements indicate that further sources of volatiles are present. Here we show that soil microorganisms are a strong, unaccounted source of highly reactive and previously unreported sesquiterpenes (C15H24; SQT). The emission rate and chemical speciation of soil SQTs were determined as a function of soil moisture, oxygen, and rRNA transcript abundance in the laboratory. Based on these results, a model was developed to predict soil–atmosphere SQT fluxes. It was found SQT emissions from a Terra Firme soil in the dry season were in comparable magnitude to current global model canopy emissions, establishing an important ecological connection between soil microbes and atmospherically relevant SQTs.Recent measurements in the Amazon rainforest indicate missing sources of volatile organic compounds (VOCs). Here the authors show that soil microorganisms are a strong, unaccounted source of highly reactive sesquiterpenes, a class of VOCs that can regulate ozone chemistry within the forest canopy.

Relationships between soil hydraulic parameters and induced polarization spectra

Spectral induced polarization is a promising method to estimate soil hydraulic properties relatively quickly without interfering with the subsurface. It is essential for the interpretation of the spectral induced polarization data to understand the relationships between soil hydraulic properties and the parameters obtained from spectral induced polarization measurements. Recent studies often relate to certain types of unconsolidated sediments, e.g., artificial mixtures of sand and clay, or refer to particular pairs of soil hydraulic and complex electrical parameters. In the present study, we investigated seven samples of natural soils and a pure sand sample in the laboratory by spectral induced polarization and soil hydraulic measurements. After examining single combinations of parameters that can be expected from theoretical considerations, we calculated the correlation coefficients for all available pairs of complex electrical and soil hydraulic parameters. Based on this, two new empirical relationships are proposed and discussed in more detail. First, a linear relationship between the van Genuchten–Mualem parameter α and the inverse of the normalized chargeability mn is described. Second, a power law was found to estimate the saturated hydraulic conductivity Ks from the DC resistivity ρ0, the normalized chargeability mn, and the fluid conductivity σw.

ESTIMATION OF VAN GENUCHTEN-MUALEM PARAMETERS AND THE SATURATED HYDRAULIC CONDUCTIVITY FROM SIP MEASUREMENTS

We performed laboratory measurements on samples of unconsolidated sediments with the method of spectral induced polarisation (SIP) and with hydrological experiments. We determined integrating parameters, e. g. the normalized chargeability , from the SIP spectra by application of the Debye decomposition (Nordsiek and Weller, 2008). The normalized chargeability, that is the ratio of the total chargeability to the DC resistivity, is a measure of the strength of the polarisation effect. In this study is the key parameter for the development of two empirical power laws to estimate parameters of the common hydrological model by Mualem (1976) and van Genuchten (1980).