Additional Chemical Properties Research Articles

Estimating WEPP Cropland Erodibility Values From Soil Properties

Highlights Very fine sand is the single most important variable for predicting rill and interrill erodibility values. Slope steepness is the most important property for predicting critical shear for rill erosion. Erodibility prediction equations with the best goodness-of-fits have both soil texture and mineralogy terms. Equations to predict erodibility from texture, organic carbon, cation exchange, slope, and taxonomy are proposed. Abstract. In the late 1980s, the USDA Agricultural Research Service, along with other federal agencies and multiple universities, collaborated to develop a new physically based soil erosion model, the Water Erosion Prediction Project (WEPP) Model. The WEPP model was intended to replace the Universal Soil Loss Equation and was to include estimates for upland runoff and erosion, sediment delivery to first order channels, and runoff and sediment routing through a downstream channel network. The WEPP technology estimated erosion from raindrop splash and sheet flow (interrill erosion) and concentrated channel flow (rill erosion). To make these erosion estimates, WEPP required new soil erodibility values for interrill erodibility (Ki). rill erodibility (Kr), and critical shear (𝜏c) for concentrated flow erosion. The WEPP Core team determined that they needed to estimate these three erodibility values from measurable soil properties for a wide range of soil conditions. To develop relationships between WEPP soil erodibility variables and other soil properties, a field study was carried out using rainfall and runoff simulation to measure the three erodibility values for 36 soils. Sites were identified on croplands from Washington to Georgia and Maine to California, USA for erodibility measurement. Concurrently, the USDA Soil Conservation Service (SCS) carried out detailed soil surveys and laboratory analyses for all sites to provide a large database of soil physical, chemical, and engineering properties. Correlation and regression analyses were carried out to develop relationships between SCS measurable soil properties and WEPP soil erodibility values. This article provides a summary of the field procedures, data analyses, and subsequent predictive equations that were developed. The predictive equations that were finalized in the WEPP User Summary used sand, very fine sand, clay, and organic carbon contents to predict cropland soil erodibility, but the Coefficient of Determination (r2) values were 0.55 or less. More complex predictive equations were developed with soil physical, chemical, mineralogical, and geomorphic properties, with r2 values up to 0.81. Most of the better predictive equations included terms for soil texture and clay mineralogy, often with additional chemical properties. A set of simplified erodibility equations using only the readily available properties of soil texture, organic carbon, cation exchange capacity, slope steepness, and taxonomic order were derived for use within the WEPP Model, with r2 values greater than 0.5 for all three equations for estimating soil erodibility from measurable soil properties. Keywords: Critical Shear, Interrill Erodibility, Rill Erodibility, Soil Properties, WEPP.

Multiple polar components in poorly-humified humic acids stabilizing free radicals: Carboxyl and nitrogen-containing carbons

To reveal the structural factors associated with free radicals in humic substances (HSs) with lower degrees of humification that are comparable to Type Rp, correlations between free radical content and chemical properties of 10 humic acids (HAs) and 2 fulvic acids (FAs) from different sources were investigated. Free radical contents of the HSs were analyzed using electron spin resonance spectroscopy (ESR) and ranged from 7.0 × 10 15–5.7 × 10 17spins g −1 carbon. The relative abundances for aromatic and/or olefin, alkyl, and carboxylic carbon species in the HSs were determined using solid state cross polarization magic angle spinning (CPMAS) 13C nuclear magnetic resonance spectroscopy (NMR). Aromaticity of the HSs estimated from 13C NMR varied slightly (30–40%) and no correlation was observed between aromaticity and free radical content. In contrast, a positive exponential relationship was observed between relative abundance of carboxyl groups and free radical content in HAs, while a negative exponential relationship was observed between relative abundance of alkyl carbon and free radical content. Two FAs were outliers in the correlations, probably due to the different chemical properties between HAs and FAs. Analysis of structural fragments using pyrolysis–gas chromatography–mass spectrometry (GC/MS) showed that additional chemical properties were also positively correlated with free radical content in HAs: two or more acidic functional groups-substituted phenolic compounds, short chain dicarboxylic acids, hydroxyacetic acid, nitrogen-containing compounds and heterocyclic carbonyl compounds. Possible semiquinone precursors, such as methoxyphenols, were not related to free radical content. These results show that free radicals are stabilized by combinations of multiple polar components such as carboxyl and nitrogen-containing carbons within HA structures during the early stages of humification.

Conductivity detection for conventional and miniaturised capillary electrophoresis systems

Since the introduction of capillary electrophoresis (CE), conductivity detection has been an attractive means of detection. No additional chemical properties are required for detection, and no loss in sensitivity is expected when miniaturising the detector to scale with narrow-bore capillaries or even to the microchip format. Integration of conductivity and CE, however, involves a challenging combination of engineering issues. In conductivity detection the resistance of the solution is most frequently measured in an alternating current (AC) circuit. The influence of capacitors both in series and in parallel with the solution resistance should be minimised during conductivity measurements. For contact conductivity measurements, the positioning and alignment of the detection electrodes is crucial. A contact conductivity detector for CE has been commercially available, but was withdrawn from the market. Microfabrication technology enables integration and precise alignment of electrodes, resulting in the popularity of conductivity detection in microfluidic devices. In contactless conductivity detection, the alignment of the electrodes with respect to the capillary is less crucial. Contactless conductivity detection (CCD) was introduced in capillary CE, and similar electronics have been applied for CCD using planar electrodes in microfluidic devices. A contactless conductivity detector for capillaries has been commercialised recently. In this review, different approaches towards conductivity detection in capillaries and chip-based CE are discussed. In contrast to previous reviews, the focus of the present review is on the technological developments and challenges in conductivity detection in CE.