A. D. Karathanasis

Water dispersible colloids and factors influencing their dispersibility from soil aggregates

Since water dispersible colloids (WDC) influence many aspects of soil processes, development of a better understanding and characterization of this soil fraction is necessary. This study involved the fractionation of WDC from 6 soil samples with diverse physicochemical and mineralogical composition and the evaluation of soil and colloidal properties affecting colloid dispersibility from soil aggregates. The percentage of the WDC fraction recovered from the samples ranged from 1.0 to 29.9%, depending on the soil properties and the mineralogical composition of the soil clay (< 2 μm) and WDC fractions. The kaolinite content in the soil clay or colloidal fraction, and the Fe, and Al content in the soil accounted for most of the variability in soil dispersibility. Total clay, cation exchange capacity (CEC), organic carbon (OC), exchangeable sodium percentage (ESP), sodium adsorption ratio (SAR), and ionic strength (1) in the ranges of thesoils studied, and mica, quartz and surface area (SA) of the clay or WDC fractions were not significant contributors. The most significant single-variable linear regression relationship (P≤ 0.01) was between log Al and WDC (R2 = 0.85). The highest correlation coefficient (r = − 0.87) through an exponential function was obtained between colloid kaolinite and WDC. The coefficient of determination (R2) was improved only slightly by combining the effects of kaolinite, Fe and Al in the multiple regression, apparently due to synergistic effects. Potentiometric titration data suggested that the dispersibility of colloids is controlled by their mineralogical composition and the magnitude of charges on particle surfaces. soils dominated by kaolinitic minerals due to low charge were less dispersed than those dominated by more reactive minerals.

Constructed wetlands treating highway runoff in the central Mediterranean region.

Two free water surface (FWS) and two subsurface flow (SSF) pilot-size constructed wetlands treating highway runoff (HRO) were monitored over a period of two years (September 2005-August 2007). One FWS and one SSF were designed with a hydraulic retention time (HRT) of 12h, named FWS12 and SSF12, respectively, with each one capable of treating a maximum HRO of 12.6 m(3) d(-1). The other couple, named FWS24 and SSF24, respectively, was designed with an HRT of 24h, with each receiving a maximum HRO of 6.3 m(3) d(-1). The influent flowed from a highway section with a total surface 2752 m(2) on the island of Crete, Greece, in the heart of the South-Central Mediterranean region. Influent and effluent were monitored for COD, TSS, total N (TN), NO(3)(-) and total P (TP) concentrations. Furthermore, removal efficiencies were examined for heavy metals (Cu, Ni, Pb, Zn) for both years, while polycyclic aromatic compounds (PAHs) were examined for the period between September 2006 and August 2007. The influent had a two-year average COD value of 101 mg l(-1), whereas the mean values for TSS, TN, N-NO(3)(-) and TP were 203, 4.30, 1.25 and 4.17 mg l(-1), respectively. For Cu, Ni, Pb and Zn the respective two-year mean influent concentrations were 56, 114, 49 and 250 microg l(-1). Mean concentration of total PAHs in runoff (summation operator PAHs, 16 compounds) were 12.01 microg l(-1). The performance among the four beds was not significantly different according to ANOVA analysis followed by Tukey test (at p<0.05) for almost all the above physicochemical parameters, suggesting that all systems performed in a similar way. All studied systems, achieved a mean of two-year removal efficiencies of 47% for COD, 89% for TSS, 49% for TN, 58% for N-NO(3)(-), 60% for TP, 47% for Cu, 23% for Ni, 33% for Pb, 61% for Zn and 59% for summation operator PAHs (16 compounds).

Characterization of iron-manganese concretions in Kentucky alfisols with perched water tables

Iron-manganese concretions are common in upper sola of Alfisols in the Inner Bluegrass Region of Kentucky. Their nature and quantities appear to be related to the fluctuation of seasonal perched water tables above clayey argillic horizons. This study was conducted to examine changes in the macro-and micromorphology, chemistry and mineralogy of concretions as a function of size, color and soil depth. Total Mn and Fe contents increased, while SiO2 decreased with concretion size. Black concretions contained higher Mn, while brown concretions were higher in Fe. Crystalline Mn- and Fe-oxides fractionated with a sequential extraction procedure increased, but amorphous Mn and Fe decreased with concretion size. Goethite was the only crystalline Fe oxide mineral identified by X-ray diffraction (XRD) analysis. Manganese oxide minerals were very difficult to detect due to the diffuse nature of their XRD peaks and poor crystallinity. Examination of soil thin sections showed concretions of soil horizons overlying restrictive clayey layers to exhibit differentiated fabrics, sharp external boundaries and generally spherical shapes. Concretions found within clayey restrictive layers or above lithic interfaces usually had less structural organization, softer matrices and diffuse external boundaries due to longer term saturated conditions. Scanning electron microscopy (SEM) examinations suggested that the concretionary matrix, in spite of its density, has numerous cavities and an extensive micropore system within which dissolved plasmic Fe and Mn can diffuse and precipitate.

SOIL CARBON AND MICROBIAL COMMUNITIES AT MITIGATED AND LATE SUCCESSIONAL BOTTOMLAND FOREST WETLANDS

The practice of wetland mitigation has come into question during the past decade because the relative capacity of the mitigated wetlands to perform normal wetland functions is mostly unknown. In this study, we wanted to determine whether soil microbial communities were significantly different in early successional mitigated wetlands (<10 years) (ES) compared to late successional bottomland hardwood forest wetlands (LS) due to differences in soil properties, such as carbon quality and storage and water-holding capacity. Carbon storage in litter and soil was 1.5 times greater in LS wetlands than ES wetlands. Soil water-holding capacity was significantly greater in LS wetlands and was related to soil organic C content (r2=0.87, p-value=0.0007). Gravimetric water content was a moderately strong predictor of microbial respiration (r2=0.55-0.61, p-value=0.001-0.0004) and microbial biomass (r2=0.70, p-value=0.0019). Anaerobic microbial groups were enriched in soils from LS wetlands in both the dry and wet seasons, which suggested that LS soils were wetter for longer periods of the year than ES soils. The capacity of these wetlands to support anaerobic microbial processes depends on soil water retention characteristics, which were dictated by organic matter content. As an integrator of microbial growth conditions in soils, determination of microbial community composition by phospholipid fatty acid (PLFA) analysis may be an important new tool for monitoring successional development of compensatory mitigation wetlands.

Evaluation of parent material uniformity criteria in loess-influenced soils of west-central Kentucky☆

Abstract Parent material relations in loess-influenced soils of west-central Kentucky were studied to better understand the nature of the loess and its impact on the soils of that area. Twenty-one stable landscape positions were sampled on two adjoining transects trending northwest to southeast from the Ohio River to the Tennessee border. Profiles were described in the field, and samples were collected for particle size, mineralogical, and other laboratory analyses. The soils consisted of a variable-thickness loess mantle overlying residuum-derived materials weathered from sandstone, siltstone, shale, and limestone. Diffuse lithologic discontinuities, indicating a gradual change from loessial to residual materials, were observed in both field and laboratory data. In most cases, the laboratory data supported the presence and position of lithologic discontinuities identified by field morphology. Loessial and residual materials were best differentiated by clay-free particle size distribution, and %K 2 O in the coarse silt fraction. Soil derived from loess and residuum was mixed at the interface of those materials. The mixing was more intense where loess was thin. A simple index was used to identify relative influence from each parent material type in the mixed zones.

Some physical and chemical factors contributing to fragipan strength in Kentucky soils

Abstract Sixteen pedons developed in various parent materials in Kentucky were studied in order to quantify fragipan strength and expression. The contribution to soil strength by clay, bulk density and amorphous or poorly crystalline chemical constituents in the soil fraction were also examined. The triple beam balance apparatus was successfully used to calculate strength of undisturbed, moist clods. Most argillic horizons were found to have strengths less than 40 Mg m−2, while most fragipan horizons had strengths exceeding 60 Mg m−2. Results using this simple technique corresponded favorably to those achieved by more sophisticated geotechnical equipment for unconfined compression tests. The contribution to strength by clay and bulk density decreased as peds became less plastic and more brittle. Amorphous materials were extracted by a selective sequential procedure using acid ammonium oxalate (in the dark), citrate-dithionite-bicarbonate, and alternating acid (6 N HCl)-alkali (KOH) treatments. Additional strength in fragipan horizons appeared to be related to an amorphous “binding” phase with a 0.5 Si (Al + Si) molar ratio, suggesting that the strength of fragipans is more than a “clay-bridging” or density phenomenon.

Treatment of metal-chloride-enriched wastewater by simulated constructed wetlands.

The ability of surface flow and subsurface flow simulated wetlands to remove heavy metals from a NaCI-enriched wastewater was examined, employing bulrush (Scirpus validus) and cattail (Typha angustifolia) plants, and two organically amended substrates (mixtures of mushroom compost and leaf litter,with topsoil) with a limestone liner. A simulated wastewater solution containing Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn as chloride salts was added to the wetlands at a rate of 0.3 l h−1. During 12 weeks of surface flow, Fe was retained most efficiently (74%), and Mn the least (24%). Most metal retention occurred in residual forms, primarily in the upper 5 cm of the substrate. A subsequent 10 week subsurface flow treatment exhibited greater removal efficiencies for all metals, probably due to increased contact with the highly buffered lower substrate. During both treatments, bioaccumulation occurred in plants, but accounted for a very small portion of the total metal removal. Plant species did not significantly influence wetland performance with respect to metal retention. Substrate type did not affect removal efficiency for most metals, but did influence the forms of the metals retained in the wetland.

Colloid-mediated transport of Pb through soil porous media

Intact soil column leaching experiments were used to assess the role of water dispersible soil colloids with diverse physicochemical and mineralogical composition in co‐transporting Pb in subsurface soil environments. There was essentially no elution of Pb (0 to < 1%) in 10mg/L control Pb solutions, suggesting a near complete attenuation by the soil column matrix. When the control Pb solutions were mixed with 300mg/L soil colloid suspensions, Pb transport increased by 10–3,000 times over that of control solutions. The presence of colloids increased the transport of both, the colloid bound and the soluble Pb fraction. Colloid‐induced transport was enhanced by increasing colloid surface charge, pH, organic carbon, and soil macroporosity and inhibited by increasing colloid size, Al, Fe, and quartz content. However, increased soil organic carbon content appeared to compensate for some of these limitations. Colloid binding and co‐transport appeared to be the dominant mechanism for increases in Pb transportability, but physical exclusion of soluble Pb species from matrix exchange sites blocked by colloids, competitive sorption, and organic complexation were also important. These findings suggest that the colloids play a dual role as Pb‐carriers and facilitators in the migration process and could have important ramifications on contaminant transport prediction and remediation applications.

Colloid-facilitated transport of metolachlor through intact soil columns

This study evaluated the role of water dispersible colloids with diverse physicochemical and mineralogical characteristics in facilitating the transport of metolachlor through macropores of intact soil columns. The soil columns represented upper solum horizons of an Alfisol in the Bluegrass region of Kentucky. Three different colloid suspensions tagged with metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)N-(2-methoxy-1-methylethyl)acetamide] were introduced at a constant flux into undisturbed soil columns. The eluents were collected and analyzed periodically for colloid and metolachlor concentrations. Colloid recovery in the eluents ranged from 54 to 90 %. The presence of colloids enhanced the transport of metolachlor by 22 to 70 % depending on the colloid type and mobility. Colloids with higher pH, organic carbon, cation exchange capacity (CEC), total exchangeable bases (TEB), surface area (SA), and electrophoretic mobility (EM), showed better mobility, greater affinity for interaction with the herbicide and, thus, greater potential to co-transport metolachlor. In contrast, increased level of kaolinite, Fe, and Al inhibited metolachlor adsorption and transport. In spite of the increased transportability of metolachlor by the presence of soil colloids, the colloid bound herbicide portion accounted for a very small part of the observed increase. This suggests that surface site exclusion mechanisms and preferential sorption induced by the presence of colloids are more important than ion exchange phenomena in promoting herbicide mobility in subsurface environments.

HYDROLOGIC AND EDAPHIC CHARACTERISTICS OF THREE MOUNTAIN WETLANDS IN SOUTHEASTERN KENTUCKY, USA

Hydrologic patterns and soil characteristics were investigated at three high-elevation wetlands in southeastern Kentucky, Martins Fork, Kentenia, and Four Level. Despite below-normal precipitation, water tables at all sites remained within 35 cm of the surface and fluctuated seasonally with peak heights during early spring. Seasonal precipitation contributed substantially to Martins Fork hydrology, while ground water was the primary hydrologic source for Kentenia and Four Level. Vertical hydraulic gradients varied among the sites. Martins Fork was distinguished by strong seasonal downwelling, while Kentenia and Four Level exhibited upwelling and downwelling patterns. All sites exhibited prominent soil hydromorphic features immediately below the surface horizon, moderate organic carbon content (<6.5%), and a pH range between 4.4 and 6.2 according to the buffering capacities of local lithologies. The sites were dominated by sandy loam texture and siliceous mineralogy, reflecting the influence of sandstone parent materials prevalent in the area. Radiocarbon dating established that soil surface layers (≤30 cm) dated less than 250 years B.P., while soil horizons at 100-cm depths varied from 770–1,870 years B.P. Mean C sequestration rates ranged from 0.025 kg C m−2 at Four Level to 0.043 kg C m−2 for Martins Fork and Kentenia, with C accumulation in the upper 100 cm in the range of 19.5–36.7 kg C m−2. Each wetland exhibited distinctive hydrologic and soil properties derived from geologic, geomorphic, and vegetative influences.