Here we demonstrate the application of 3-D NMR spectroscopy to structural studies of humic substances, the most abundant of organic compounds on earth. The increased spectral dispersion provided by ...the additional dimension is proven to be highly advantageous in separating the overlapping signals observed in 2-D spectra. Assignments of the major aliphatic structures and selected aromatic moieties are given as examples. We find that in a forest soil fulvic acid the major aliphatic materials are likely derived from leaf cuticles and further demonstrate that lignin signatures can be identified among the aromatic species. Once identified from the 3-D spectra, these structures can be assigned using the partial information available in 2-D, and in some cases, in the 1-D spectra. These signals are demonstrated to be characteristic to given samples of natural organic matter, and the case is made for their use as indicators of terrestrial biomarkers in mixtures of compounds with unknown origins.
Non-living natural organic matter (NOM) is ubiquitous in the oceans, atmosphere, sediments, and soils, and represents the most abundant organic carbon reserves on earth. However, a large proportion ...is considered to be "molecularly uncharacterized" because the inherent complexity of NOM is problematic when applying conventional analytical techniques. This manuscript presents initial applications of LC-NMR (1H) and LC-SPE-NMR (1H) to the studies of NOM isolated from water and soil. LC-NMR is applied to dissolved natural organic matter (DNOM) collected from freshwater environments, and both LC-NMR and LC-SPE-NMR are applied to an alkaline soil extract. The polar and complex nature of the DNOM samples limits conventional reversed phase separation, which can be partially overcome with the use of an ion pair reagent, although such an approach further complicates the NMR detection. LC-SPE-NMR of the soil alkaline extract was encouraging, and specific components in the mixture could be assigned. This work demonstrates that it is both possible to separate and concentrate specific components in NOM such that NMR detection is possible. As NMR information will be critical in unraveling the novel and/or complex structures in NOM this represents a key analytical hurdle in this area.
The substantial heterogeneity of dissolved organic matter (DOM) inhibits detailed chromatographic analysis with conventional detectors as little structural information can be obtained in the presence ...of extensive coelution. Here we examine the direct hyphenation of high-performance size exclusion chromatography (HPSEC) with nuclear magnetic resonance (NMR) spectroscopy to determine how size-distinguished fractions differ in composition. The results support the applicability of using HPSEC to generate more homogeneous fractions of DOM prior to NMR analysis and demonstrate that structure is significantly altered with size. The largest fractions are enriched in carbohydrate- and aromatic-type structures. The midsized material is substantial and is representative of carboxyl-rich alicyclic molecules (CRAMs). The smallest material has strong signatures of material derived from linear terpenoids (MDLT). Both CRAMs and MDLT have been recently hypothesized as major components of DOM, and detection by HPSEC−NMR confirms their existence as unique and separable entities. This preliminary work focuses on NMR hyphenation to HPSEC due to widespread use of HPSEC to characterize DOM. Online hyphenation is useful not only for time-efficient analysis of DOM but also for that of other highly complex samples such as those found in many environmental analyses.
Diffusion ordered spectroscopy (DOSY) was applied to two extracts of organic matter from the surface horizon of an oak forest soil. It was possible to identify and confirm the presence of numerous ...aliphatic, aromatic, sugar, and amino acid components that could be separated on the basis of diffusion in DMSO-d 6 and D2O. On average, sugar components were identified as the largest molecules in solution, with molecular masses up to ∼1500 Da followed by the aliphatic and aromatic components. Amino acids with a range of molecular weights were also identified in the mixture. The summation of the individual slices from the DOSY experiment closely resembles the conventional 1H spectra of the material, indicating that the components identified with DOSY represent all the components present in the mixture. The separation of components in the mixture in organic solvent supports new findings that fulvic and humic acids are not cross-linked, high molecular weight macromolecules but are instead aggregates composed of relatively simple molecules that take on colloidal properties in the presence of metal ions in aqueous solution. Using the knowledge that these organic mixtures are combinations of relatively simple entities with well-documented reactivities and behavior will improve our ability to predict and model their interactions and fate under natural conditions.
St. Louis Bay, along with its two major tributaries, Wolf River and Jourdan River, are included in the Mississippi 1998 Section 303(d) List for violation of the designated water use of recreation and ...shellfish harvesting. Fecal coliform was identified as one of the pollutants that caused the water quality impairment. In order to facilitate the total maximum daily loads (TMDL) development, the fecal coliform dynamics was investigated under 2 flow scenarios with a calibrated and validated modeling framework by integration of Environmental Fluid Dynamic Code (EFDC) and Hydrological Simulation Program Fortran (HSPF). EFDC was used to model the hydrodymics and fecal coliform transportation in the Bay and the tributaries, whereas HSPF was applied to compute the flow and fecal coliform loadings from the watersheds. The total amount of precipitation in the dry year simulation corresponds to a 50-year return period of low flow condition, and a 10-year return period of high flow condition for wet weather simulation. For EFDC modeling, the fecal coliform sources considered were the contributions from the 2 upper watersheds (no tidal influence), the 28 small surrounding watershed, and 12 municipal, industrial, and domestic point sources. When simulating the fecal coliform loadings from the 2 upper watersheds using HSPF, the simulated non-point source loadings of fecal coliform included wildlife, land application of hog and cattle manure, land application of poultry litter, and grazing animals. The EFDC modeling results indicated that the wet weather exerted greater stress on fecal coliform water quality conditions. The number of exceedance of fecal coliform water quality standard in wet year simulation is much higher than that in dry year simulation. The impact of the upper rural watersheds loads on fecal coliform levels in the St. Louis Bay is much less significant than that from the surrounding urban runoff. Fecal coliform TMDL development should be based on high flow conditions since the decision makers are more concerned about worse scenarios. This fecal coliform modeling research would provide useful information of critical condition selection for TMDLs development in similar coastal areas.
ABSTRACT
Copper sulfate (CuSO4) is applied periodically to commercial channel catfish (Ictalurus punctatus) ponds as an algicide or parasiticide. Current understanding of the chemistry of copper in ...soil–water systems suggests that copper may accumulate in pond sediments, although the forms and potential bioavailability of copper in catfish pond sediments are not known. This study investigated the accumulation and distribution of copper in the sediment of catfish ponds receiving periodic additions of CuSO4 · 5H2O. All ponds were constructed in Sharkey (very‐fine, smectitic, thermic Chromic Epiaquert) soil. Nine 0.40‐ha ponds received 59 applications of 2.27 kg CuSO4 · 5H2O per application per pond over 3 yr; no CuSO4 · 5H2O applications were made to nine additional ponds. Total Cu concentration in the sediments of CuSO4 · 5H2O‐amended catfish ponds (172.5 mg kg−1) was four to five times higher than that in the sediments of nonamended ponds (36.1 mg kg−1). Copper accumulated in catfish pond sediments at a rate of 41 μg kg−1 dry sediment for each 1 kg ha−1 of CuSO4 · 5H2O applied to ponds. Copper in the sediments of amended ponds was mainly in the organic matter–bound (30.7%), carbonate‐bound (31.8%), and amorphous iron oxide–bound (22.1%) fractions with a considerable fraction (3.4%; 3 to 8 mg kg−1) in soluble and exchangeable fractions. This indicates that Cu accumulates differentially in various fractions, with proportionally greater initial accumulation in potentially bioavailable forms. However, toxicity bioassays with amphipods (Hyallela azteca) and common cattail (Typha latifolia L.) indicated that the effect of exposure to amended or nonamended pond sediments was not different.
The influence of montmorillonite intercalated with representatives of three major classes of biological molecules L-lysine (amino acid), α-D-glucose (carbohydrate) and rhamnolipid (lipid) on the ...catalytic activity of acid phosphatase was investigated. In comparison to pure clay, the presence of the organic intercalates preserves residual activity at extreme pH values of 3 and 11 and temperatures as low as$10 \textdegree C.$Thermodynamic parameters of free energy, enthalpy and entropy, suggest that catalytic activity on the lysine and rhamnolipid intercalated surfaces is more spontaneous and favorable than that of pure clay. Michaelis-constants (Kmvalues) and maximum reaction velocities (Vmaxvalues) were determined and confirmed the enhancement of activity on the organo-mineral surfaces. The catalytic reaction product was measured as a function of time and the data fitted to equations describing the behavior of first and second order rates of reaction. All processes apart from the glucose-intercalated clay (second order) could be described by first order reactions. Catalytic activity was generally less on the glucose-mineral surface compared to the other organo-mineral surfaces and the pure clay. However, when all surfaces were saturated with acid phosphatase the glucose complex exhibited the highest level of catalytic activity.
Soil sorption and dissipation of fluometuron (FLM) and three metabolites, desmethyl fluometuron (DMF), trifluoromethyl phenyl urea (TFMPU), and trifluoromethyl aniline (TFMA), were assessed in ...conservation tillage soils. In study I, surface Dundee silt loam soils from no-tillage (NT) and reduced-tillage (RT) areas were treated with 14C ring-labeled FLM or TFMA or unlabeled DMF, incubated for 34−42 days, extracted, and analyzed. Mineralization and volatilization of 14C-labeled FLM or TFMA were monitored. In study II, batch sorption assays (solute concentrations 2−50 μmol L-1; 2:1 solution:soil; 18 h) were conducted using various soils from reduced- (RT) and conventional-tillage (CT) areas to determine the relative affinity of FLM and metabolites for soils with differing characteristics. Mineralization of FLM (3%, day 42) or TFMA (4%, day 34) and FLM volatilization (∼2%) were low for both soils. FLM and DMF dissipated more rapidly in RT soil than in NT soil. In FLM-treated RT soil, DMF and TFMPU accumulated more rapidly than in NT as FLM degraded. TFMA dissipated rapidly, primarily as nonextractable residues (∼70%, day 42) and volatilization (∼16%). For all respective soils in study II, sorption of all four compounds was higher for organic C-enriched RT soils than for CT soils, indicating strong relationships between organic C and FLM and metabolite sorption. For either tillage treatment, the percentage sorption was greater for metabolites (e.g., at lowest initial dosing concentration, TFMPU range, 45−91%; DMF range, 45−90%; and TFMA range, 45−98%) than for FLM (RT soils range, 19−65%). Nonsubstituted amino groups likely facilitated sorption to organic C, with nonsubstituted aniline in TFMA having the greatest affinity. NMR spectra of humic acid extracts from NT and CT Dundee soils indicated similar patterns of humic acid functional groups, but the potential capacity for sorption was greater in NT than in CT. The greater capacity for FLM and metabolite sorption in NT soil helps explain their longer persistence. Keywords: Tillage; herbicide; sorption; dissipation; fluometuron; metabolite
St. Louis Bay estuary is a vital water body in the Mississippi Gulf Coast Region and greatly affects the water quality in the Mississippi Sound. As the first step of total maximum daily load (TMDL) ...study, a hydrodynamics model was developed by integrating Hydrological Simulation Program Fortran (HSPF) and Environmental Fluid Dynamics Code (EFDC). In this application the EFDC model was configured to simulate time-varying surface water elevation, velocity, salinity, and water temperature. The HSPF was applied to compute the fresh water discharge from the upstream watersheds. The model reasonably simulated the tidal range and phase. The simulated water temperature and salinity showed good and fairly good agreement with observations. The calculated correlation coefficients between computed and observed velocity were lower compared with those for water level, temperature, and salinity, but the magnitudes of simulated velocity were found to be in the range of observed data. The wind data was found to have strong impacts on velocity simulation by modeling verification tests. Near the study area, there is wind data available only at one station, which has been applied to the entire modeling domain. The lack of high-resolution wind data makes it very difficult to simulate the velocity distribution well. It is anticipated and recommended that the development of this model be continued to synthesize additional field data into the modeling process.
