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Organic and inorganic soil C pools are major components of the global C budget, yet they are still poorly estimated and understood. This study ranked atmospheric wet Ca2+ deposition from 1994 to 2003 within the continental United States by soil order using spatial analysis of Ca2+ wet deposition data and a state soil geographic database. The total average annual atmospheric wet deposition (AAAWD) of Ca2+ within the continental United States was 8.6 x 108 kg, which would be equivalent to the theoretical formation of 2.6 x 108 kg C as soil inorganic C (SIC), barring losses from erosion and deep leaching. The soil orders receiving the highest area-normalized total AAAWD of Ca2+ were: (i) Alfisols (172 kg km-2 Ca2+), (ii) Mollisols (170 kg km-2 Ca2+), (iii) Histosols (168 kg km-2 Ca2+, and (iv) Vertisols (157 kg km-2 Ca2+). Barring losses from erosion and leaching, these Ca2+ wet deposition fluxes would equate to the theoretical formation of the following amounts of area-normalized total C equivalents in the pedon: (i) Alfisols, 52 kg C km-2 (ii) Mollisols, 51 kg C km-2 (iii) Histosols, 50 kg C km-2 and (iv) Vertisols, 47 kg C km-2. The sequestration of SIC has been shown to be important in soil orders of nonarid regions, particularly in Mollisols and Aluisols. [ABSTRACT FROM AUTHOR]

The impacts of land disturbance on streams have been studied extensively, but a quantitative mechanism of stream degradation is still lacking. Small changes in land use result in changes in physical and chemical characteristics in the stream, which significantly alter biotic integrity. The objective of this study was to quantify the mechanisms of aquatic ecosystem degradation in streams impacted by watershed urbanization. By quantifying the development level and the changes in the physical parameters of receiving streams, the effects of land use change can be illustrated in a conceptual model and evaluated using a traditional ecological risk assessment framework. Three 1st-order streams draining catchments undergoing varying stages of land development were examined in the upper Piedmont physiographic province of South Carolina, USA. A disturbance index was developed to quantify the changes in land use on a monthly basis. This normalized disturbance index (NDI) was quantitatively linked to an increase in the percentage of impervious cover, stormwater runoff, storm-event total suspended solid (TSS) concentrations, and the North Carolina biotic index (NCBI). The NDI was inversely related to a decline in habitat, median bed-sediment particle size, and benthic index of biotic integrity (BIBI). Unlike the percentage of impervious cover, the NDI facilitated the development of strategies for multiple scales of regulation. Predictive multivariate regressions were developed for storm-event TSS concentrations, the BIBI, and the NCBI. These regressions can be used to develop improved regulations for the effects of development and can lead to better implementation of best management practices, improved monitoring of land use change, and more sustainable development. [ABSTRACT FROM AUTHOR]

The main objectives of this research were to examine the effects of colloidal and particulate matter in freshwaters on dissolved organic carbon (DOC) and ultraviolet light absorbance at 254 nm (UV254) and to develop some guidelines for filtering freshwater samples with widely varying turbidities. More than 90% of the organic matter in the natural waters tested in this study was in the dissolved form, and filter cake formation did not have a significant impact on the DOC values of a sample. The experimental results showed that the level and characteristics of turbidity in a water sample, as well as the nature of pore structures and pore size distributions of a membrane filter selected for filtration, play important roles in UV254 and specific ultraviolet absorbance254 (SUVA254). Results indicated that when filtrate turbidities were below 0.3 ntu, filtration volume, filter cake formation, and pretreatment processes had no significant impact on DOC and UV254 determinations and thus on calculated SUVA254 values. When filtrate turbidities were >0.5 ntu, however, they increased the UV254 values (and also SUVA254) without causing an apparent impact on the DOC measurements. These findings suggest that a conservative criterion for the turbidity of a filtered UV254 sample, such as <0.3 ntu, should be adopted to minimize interferences on the results. [ABSTRACT FROM AUTHOR]

Investigates the ability of humic substance components to bind pyrene. Effects of different mineral characteristics; Validity of applying ideal mixture models to humic substance adsorption on minerals and subsequent pyrene binding; Alteration of effects of humic substance heterogeneity on hydrophobic organic contaminant sorption.

Describes potential cation-pi interactions between pi donors and exchangeable cations accumulated at mineral surfaces via both spectroscopic and batch sorption methods. Sorption of polycyclic aromatic hydrocarbons (PAH) to different minerals saturated with different cations; Molecular interactions of deuterated solutes with mineral surfaces; Sorption mechanism controlling PAH sorption to mineral surfaces.

Metalloporphyrins are well known for their electron-transfer roles in many natural redox systems. In addition, several metalloporphyrins and related tetrapyrrole macrocycles complexed with various core metals have been shown to catalyze the reductive dechlorination of certain organic compounds, thus demonstrating the potential for using naturally occurring metallopor-phyrins to attenuate toxic and persistent chlorinated organic pollutants in the environment. However, despite the great interest in reductive dechlorination reactions and the wide variety of natural and synthetic porphyrins currently available, only soluble porphyrins, which comprise a small fraction of this particular family of organic macrocycles, have been used as electron-transfer shuttles in these reactions. Results from the present study clearly demonstrate that metalloporphyrin solubility is a key factor in their ability to catalyze the reductive dechlorination of tetrachloroethylene and its daughter compounds. Additionally, we show that certain insoluble and nonreactive metalloporphyrins can be activated as catalysts merely by changing solution conditions to bring about their dissolution. Furthermore, once a metalloporphyrin is fully dissolved and activated, tetrachloroethylene transformation proceeds rapidly, giving nonchlorinated and less toxic alkenes as the major reaction products. Results from the present study suggest that if the right environmental conditions exist or can be created, specific metalloporphyrins may provide a solution for cleaning up sites that are contaminated with chlorinated organic pollutants. [ABSTRACT FROM AUTHOR]

Examines the characterization of cation-π interactions in aqueous solution using deuterium nuclear magnetic resonance spectroscopy. Bond between silver and aromatic hydrocarbons; Indication of normal electrostatic interaction; Interaction between the π electrons of aromatic molecules and metal cations.

Spin-lattice relaxation times (T[sub 1]) and chemical shifts (δ) of perdeuterated pyridine (α, β, γ deuterium of d[sub 5]-pyridine) in aqueous solution (e.g., water, 0.001 M benzoic acid and phenol) are found to decrease with increasing pH values. This is because the concentration distribution of the two pyridine species, protonated and unprotonated, varies with solution pH. The T[sub 1] values of γ are lower than α and β deuterium in water and methanol compared with n-hexane, indicating more anisotropic molecular movements of pyridine resulting from interactions between amine and the polar solvent. Spin-spin relaxation times (T[sub 2]) and δ of d[sub 5]-pyridine in aqueous suspensions of water-dispersible clay (WDC) soil components are highly pH dependent. The lowest T[sub 2] and the most downfield-shifted δ compared with aqueous solution show that the strongest sorption occurs at the weak acidic condition (pH 6). The downfield shifts of δ observed in WDC suspensions are directly caused by the increased mole ratio of protonated pyridine through sorption. However, no significant changes in δ are observed for organic free minerals (H[sub 2]O[sub 2]-treated WDCs and a standard clay mineral) compared with aqueous solution, indicating interactions with mineral surfaces are negligible in pyridine sorption. A sorption mechanism of cation exchange between protonated pyridine and charged sites of soil organic matter (SOM) is inferred based on the measured δ values. [ABSTRACT FROM AUTHOR]

A promising approach to abiotically dechlorinate a variety of chlorinated organic contaminants under reducing conditions is to utilize porphyrins or other tetrapyrrole macrocycles as electron transfer mediators/shuttles for catalyzing their reduction. In this study, various experimental approaches were used to elucidate the role of porphyrin core metals in the reductive dechlorination of tetrachloroethylene (PCE). The importance of specific core metals for the reactivity of a porphyrin and its mediated reaction mechanisms was demonstrated by inserting different metals into metallo tetrakis (N-methyl-4-4 pyridiniumyl) porphyrin (TMPyP). No PCE dechlorination was observed when the free-base (i.e., no core metal) and iron core metal forms of TMPyP were utilized. When using nickel or cobalt TMPyP, reductive dechlorination of PCE occurred but appeared to follow different pathways for the two metals based on product analyses. Physical (e.g., steric) considerations suggest that direct contact between a porphyrin core metal and PCE may be limited and therefore that the entire metalloporphyrin molecule should be viewed as a functional system in which the organic macrocycle has an active part in reductive dechlorination reactions. This view is supported by the fact that slight changes in the functional groups on a porphyrin macrocycle, particularly those far removed from the core metal itself, greatly affected the reactivity and mechanism of the porphyrin. Solution conditions also had a major effect on porphyrin reactivities, to the extent that a nonreactive metalloporphyrin could be activated merely by adjusting the pH of the solution or by adding a small amount of cosolvent. The collective results of this study suggest that fine tuning of naturally occurring metalloporphyrin complexes and/or their environments can enhance the catalyzed detoxification of chlorinated contaminants in many natural and engineered environmental systems. [ABSTRACT FROM AUTHOR]

Evaluates several filter membranes for dissolved organic carbon (DOC) and ultraviolet (UV [sub254]) absorbance measurements in compliance with the U.S. Environmental Protection Agency's Disinfectants/Disinfection By-products Rule. Effects of dissolved and colloidal forms of natural organic matter (DOM) on water treatment; Components of DOM; Factors that can affect the results of DOC and UV[sub254] measurements.

Examines the molecular-level sorption behavior of monoaromatic compounds in suspensions of water-dispensable clay components. Measurement of the [sup2]H nuclear magnetic resonance spin-spin relaxation times; Indication of stronger solute-sorbent interactions; Increase in the sorption of solute.

Presents the results of a survey conducted to determine practices being utilized by drinking water practitioners and researchers to measure dissolved organic carbon concentrations and ultraviolet (UV) absorbances that are also used for specific UV-absorbance determinations. Filter brands used in dissolved organic carbon and UV measurements; Water sample collection and filtration; Time between sample preservation and sample analysis for dissolved organic carbon and UV measurements.