Export of Terrestrial Dissolved Organic Matter Along a River to Ocean Transect of the Lower Chesapeake Bay Investigated by Advanced Analytical Techniques

Ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) has proved essential for the complete separation of the thousands of peaks present in natural organic matter (NOM), a complex assemblage of organic molecules present in water, soils, and sediments. An improved understanding of its composition is crucial to understand how pollutants interact with NOM and how NOM cycles through global carbon cycles. Optimizing the acquisition and handling of the FTICR mass spectra is the first step to obtaining high quality data. A simple method to internally calibrate the peaks in the complex spectra, using naturally present fatty acids, is demonstrated. Furthermore, a method was developed to directly analyze natural waters with low dissolved organic carbon (DOC), by utilizing sequential selective ion accumulation (SSIA), which decreases the baseline noise while increasing signal to noise ratios. Once optimization is achieved, ESI-FTICR-MS is applied to characterize dissolved organic matter (DOM) as it is transported along a river to ocean transect of the lower Chesapeake Bay. To evaluate the advantages of using direct analysis, a C18 extract of riverine water is compared to its whole, unfractionated water. Along this transect, the DOM tends to become more aliphatic and contain lower abundances of oxygen-rich molecules as one progresses from inshore to the offshore. Next, multivariate statistics, such as hierarchal cluster analysis (HCA) and principal component analysis (PCA), are utilized to explore the large datasets acquired from DOM mass spectra. PCA deciphers which of the thousands of formulas are significant to particular samples, and then van Krevelen diagrams highlight what types of compounds are molecular signatures to the samples. A considerable amount of formula overlap exists between samples along the transect, but having identical molecular formulas does not necessarily indicate the same molecular structure. Taking advantage of the tandem mass spectrometry (MS/MS capabilities, I isolate and fragment ions in the DOM. The MS/MS fragmentation pattern obtained for selected peaks are strikingly similar in the terrestrial and saline bay DOM, leading us to believe that the compounds have similar structural entities. Based on the functionalities lost during the fragmentation, a lignin-derived structure fits the molecular formulas best. Overall, ESI-FTICR-MS is a powerful technique for the investigation of DOM and has the ability to detect compositional variations along the river to ocean transect. Further use of ESI-FTICR-MS will clearly lead to additional future advancements in the areas of aquatic, soil, and analytical chemistry

The Application of Electrospray Ionization Coupled to Ultrahigh Resolution Mass Spectrometry for the Molecular Characterization of Natural Organic Matter

Mass spectrometry has recently played a key role in the understanding of natural organic matter (NOM) by providing molecular-level details about its composition. NOM, a complex assemblage of organic molecules present in natural waters and soils/sediments, has the ability to bind and transport anthropogenic materials. An improved understanding of its composition is crucial in order to understand how pollutants interact with NOM and how NOM cycles through global carbon cycles. In the past, low-resolution (\u3e 3000) mass analyzers have offered some insights into the structure of NOM, but emerging ultrahigh resolution (\u3e 200000) techniques such as electrospray ionization (ESI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) have significantly advanced our knowledge of NOM chemistry. Here, a review of the recent literature on the advancements of NOM characterization and the applications of mass spectrometry to this central task is presented. Various methods for the analysis and display of the extremely complex mass spectra, such as the van Krevelen diagram and Kendrick mass defect analysis, are discussed. We also review tandem mass spectrometry techniques employed to gain structural information about NOM components. Finally, we show how ESI-FT-ICR-MS has been applied to examine specific issues that are important to the NOM scientific community, such as NOM reactivity, transport and fate, degradation, and existence of components, which are indicators of NOM origin. In general, ultrahigh resolution provided by FT-ICR-MS is essential for the complete separation of the thousands of peaks present in the complex NOM mixture and will clearly lead to additional future advancements in the areas of aquatic, soil, and analytical chemistry. Copyright (c) 2007 John Wiley & Sons, Ltd

Compositional Features of Japanese Humic Substances Society Standard Soil Humic and Fulvic Acids by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and X-Ray Diffraction Profile Analysis

The composition of humic acids (HAs) and Fulvic Acids (FAs) from Inogashira (Umbric Andosol) and Dando (Dystric Cambisol) soils authorized as standard samples by the Japanese Humic Substances Society was characterized using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and X-ray diffraction (XRD) 11 band profile analysis. In FTICR-MS, the number of peaks that molecular formulas were assigned to was 2549-2913 for the FAs and 1943-2457 for the HAs. Molecular formulas with H/C and O/C ratios similar to condensed hydrocarbons were dominant in both the HAs, while those with H/C and O/C ratios similar to lignin were more abundant in the Dando HAs than in the Inogashira HAs. In both the FAs, molecular formulas having H/C and O/C ratios similar to lignin, condensed hydrocarbons, and tannins were dominant. The double bond equivalent (DBE), an index of the degree of unsaturation, was in the range of 0-30. However, larger DBE values of 26-30 were observed only in the Inogashira HAs with a larger degree of humification. The XRD results also showed that the Inogashira HAs contain larger amounts of condensed aromatic structures with a higher condensation degree. Relative content of carbon layer planes estimated from the peak area of the 11 band profile analysis, which could be estimated only for HAs, was 0.48-1.68 nm (4-37 rings) in the Inogashira HAs and 0.48-1.20 nm (4-19 rings) in the Dando HAs

Abiotic Stress Mitigation: A Case Study from 21 Trials Using a Natural Organic Matter Based Biostimulant Across Multiple Geographies

Crop productivity and yields can be greatly diminished by abiotic stress events including drought, extreme temperatures, excess moisture, and saline irrigation water. Multiple stressors occurring simultaneously can further exacerbate the strain on plants. Various types of biostimulants have been shown to mitigate abiotic stress and here, the results of 21 trials on corn, wheat, soybean, and various high-value crops are discussed in the context of the abiotic stress that either occurred naturally or was experimentally induced. Treatments in these trials included stressed and non-stressed plants, as well as either an untreated control or grower standard fertilizer applications alone and in combination with a natural organic matter (NOM)-based biostimulant. While stressed plants suffered compared with non-stressed plants, the stressed plants receiving the NOM-based biostimulant were healthier and larger, as indicated by whole, root, and shoot weights and yields at harvest. Plant response was stronger when stress existed, but the biostimulant also led to healthier plants when no stress occurred. Positive results occurred for 20 of the 21 trials, indicating that biostimulants can effectively mitigate abiotic stress events regardless of the plant species tested or the growing conditions encountered, by increasing sap Brix, enzymatic activity, and nutrient use efficiency

Naturally Present Fatty Acids as Internal Calibrants for Fourier Transform Mass Spectra of Dissolved Organic Matter

The analysis of dissolved organic matter ( DOM) by Fourier transform ion cyclotron resonance mass spectrometry ( FTICR- MS) has gained wide interest recently, driven primarily by its ultrahigh resolving power and mass accuracy. Accurate calibration of mass spectra is a key step to successfully decipher the DOM components. We propose a simple and accurate method to internally calibrate the peaks in the complex spectra without the need to add a calibrant. Mass spectra of DOM samples from the Dismal Swamp, Virginia, and the lower Chesapeake Bay display the presence of naturally occurring fatty acids which can be readily recognized and calibrated with accuracies \u3c 0.1 ppm. Once calibrated with fatty acids, approximately 80% of all peaks in the DOM mass spectra can be assigned unique molecular formulas with accuracies \u3c 0.4 ppm. Although the formula errors for the assigned molecular formulas do increase with increasing m/z, the dynamic range of the fatty acids used as calibrants is sufficient because high m/z values (\u3e 600) have formulas with an average error of \u3c 0.6 ppm. Because fatty acids are ubiquitous components of most DOM, this approach is applicable to a large variety of DOM samples. © 2008, by the American Society of Limnology and Oceanography, Inc

TEnvR: MATLAB-Based Toolbox for Environmental Research

With the advancements in science and technology, datasets become larger and more multivariate, which warrants the need for programming tools for fast data processing and multivariate statistical analysis. Here, the MATLAB-based Toolbox for Environmental Research TEnvR (pronounced ten-ver ) is introduced. This novel toolbox includes 44 open-source codes for automated data analysis from a multitude of techniques, such as ultraviolet-visible, fluorescence, and nuclear magnetic resonance spectroscopies, as well as from ultrahigh resolution mass spectrometry. Provided are codes for processing data (e.g., spectral corrections, formula assignment), visualization of figures, calculation of metrics, multivariate statistics, and automated work-up of large datasets. TEnvR allows for efficient data analysis with minimal by-hand manual work by the user, which allows scientists to do research more efficiently. This manuscript is supplemented with a detailed tutorial, example data, and screenshots, which collectively provide instructions on how to use all codes. TEnvR is novice-friendly and experience in programming with MATLAB is not required. TEnvR fulfills the need for a concise MATLAB-based toolbox for working with environmental data and will be updated annually to keep pace with the latest advances and needs for computational work in the environmental sciences

Characterization of Terrestrial Dissolved Organic Matter Fractionated by pH and Polarity and Their Biological Effects on Plant Growth

Background: Humic substances are ubiquitous in the environment, complex mixtures, and known to be beneficial to plant growth. To better understand and identify components responsible for plant growth stimulation, a terrestrial aquatic DOM sample was fractionated according to pH and polarity, obtaining acid-soluble and acid-insoluble portions, as well as acid-soluble hydrophobic and hydrophilic fractions using C18. The various fractions were characterized then evaluated for their biological effects on plant growth using bioassays with corn at two carbon rates. Results: Approximately 43% and 57% of the carbon, and 31% and 69% of the iron, was found in the acid-insoluble and acid-soluble fractions, respectively. Upon separating the acid-soluble portion using C18 extraction, about 64% and 36% of the carbon (and 96% and 4% of the iron) was present in the hydrophilic and hydrophobic fractions, respectively. The acid-insoluble portion was more aromatic and less oxygenated than the acid-soluble fraction. The hydrophilic filtrate was oxygen-rich and contained mostly tannin-like molecules, while the hydrophobic retentate was more aromatic and lignin-like. During bioassay testing, it was found that more hydrophilic samples (those that are more oxygenated) yielded the highest response for shoot measurements. For root measurements, the lower DOC rate (0.01 mg/L C) gave better results than the higher DOC rate (0.1 mg/L C). Also, the hydrophobic, less oxygenated acid-insoluble sample performed better than the more hydrophilic acid-soluble portion. The polarity fractions at the lower carbon application showed that larger root systems occurred when there was more hydrophobic C18 retentate material present. The opposite was true for the root system at the higher carbon application, where larger roots existed when more hydrophilic C18 filtrate material was present. Conclusions: Compositional differences were found when comparing the acid-soluble versus acid-insoluble portions and the hydrophobic versus hydrophilic C18 fractions, and activity with respect to plant stimulation was discerned. While a carbon rate affect was observed during foliar application to corn plants (with the lower carbon rate generally yielding the best biological stimulation), the various observed trends indicate that plant response is due to not only the amount of carbon present but also the type of carbon

A coupled geochemical and biogeochemical approach to characterize the bioreactivity of dissolved organic matter from a headwater stream

The bioreactivity or susceptibility of dissolved organic matter (DOM) to microbial degradation in streams and rivers is of critical importance to global change studies, but a comprehensive understanding of DOM bioreactivity has been elusive due, in part, to the stunningly diverse assemblages of organic molecules within DOM. We approach this problem by employing a range of techniques to characterize DOM as it flows through biofilm reactors: dissolved organic carbon (DOC) concentrations, excitation emission matrix spectroscopy (EEMs), and ultrahigh resolution mass spectrometry. The EEMs and mass spectral data were analyzed using a combination of multivariate statistical approaches. We found that 45% of stream water DOC was biodegraded by microorganisms, including 31–45% of the humic DOC. This bioreactive DOM separated into two different groups: (1) H/C centered at 1.5 with O/C 0.1–0.5 or (2) low H/C of 0.5–1.0 spanning O/C 0.2–0.7 that were positively correlated (Spearman ranking) with chromophoric and fluorescent DOM (CDOM and FDOM, respectively). DOM that was more recalcitrant and resistant to microbial degradation aligned tightly in the center of the van Krevelen space (H/C 1.0–1.5, O/C 0.25–0.6) and negatively correlated (Spearman ranking) with CDOM and FDOM. These findings were supported further by principal component analysis and 2‐D correlation analysis of the relative magnitudes of the mass spectral peaks assigned to molecular formulas. This study demonstrates that our approach of processing stream water through bioreactors followed by EEMs and FTICR‐MS analyses, in combination with multivariate statistical analysis, allows for precise, robust characterization of compound bioreactivity and associated molecular level composition. Key Points Humic DOM is susceptible to microbial degradation along with peptide‐like DOM Labile DOM can be distinguished from recalcitrant DOM in van Krevelen space EEMs and FTICR‐MS chemically characterize bioreactive and recalcitrant DOMPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108612/1/jgrg20256.pd