Kenneth Mopper

Old Dominion University | ODU · Department of Chemistry and Biochemistry

This study reports the development of a new type of organic carbon (OC) analyzer that combines flow through analysis and ultraviolet‐wet chemical oxidation (UV‐WCO). Total or dissolved OC (TOC or DOC, respectively) is determined through detection of CO2 as the oxidation product using a vibration insensitive nondispersive infrared (NDIR) gas analyze...

Antioxidants are a class of molecules that provide a protective function against reactive oxygen species (ROS) in biological systems by out competing physiologically important molecules for ROS oxidation. In natural waters, the reactivity of antioxidants gives an estimate of oxidative stress, and may determine the reactivity and distribution of rea...

Based on reverse genomics and growth of cultured populations, it has been hypothesized that cyanate is utilized as a nitrogen source by ubiquitous groups of marine phytoplankton. Recently a nanomolar method was developed to measure cyanate concentrations in marine and estuarine waters. Here we report the first measurements of cyanate distributions,...

Light plays a critically important role in driving photo- and biogeochemistry of aquatic systems, and our ability to measure and model submarine light fields is fairly sophisticated. However, previous approaches have relied almost entirely upon Eulerian rather than Lagrangian measurements. Such approaches can provide good estimates of the instantan...

The iron-poor leachate from decaying wood can be an important source of colored dissolved organic matter (CDOM) in natural waters. In this study, we examined hydroxyl radical (•OH) formation with respect to photoreactivity of wood leachate DOM, the Fenton reaction, and photoflocculation. The relationship of •OH photoproduction rate and leachate opt...

Dissolved organic matter (DOM) is the strongest light-absorbing component of seawater, especially in coastal regions, and therefore it plays a dominant role in marine photochemical and photophysical processes in surface waters. This critical review focuses on the impact of DOM photochemistry on marine biogeochemical processes, highlighting and eval...

The hydroxyl radical (•OH) is the most reactive oxidant produced in natural waters. Photoproduction by chromophoric dissolved organic matter (CDOM) is one of its main sources, but the structures responsible for this production remain unknown. Here, a series of substituted phenol model compounds are examined to test whether these structures could ac...

Extracellular and intracellular dissolved organic matter (E-DOM and I-DOM, respectively) produced in axenic cultures by the cosmopolitan cyanobacteria Microcystis aeruginosa were characterized, and photoreactivity, bioreactivity, and the effects of phototransformations on bioavailability of E-DOM and I-DOM were assessed in laboratory experiments. C...

A simplified method to characterize the lignin phenolic composition of environmental samples using alkaline CuO oxidation, solid-phase extraction (SPE), and high performance liquid chromatography (HPLC) is described. Samples were oxidatively hydrolyzed in inexpensive, commercially available Teflon vials rather than expensive high-pressure Teflon-li...

Photochemical processing of dissolved organic matter (DOM) in natural waters can alter its composition and structure, supply particulate organic matter (POM) to sediments, and deliver modified terrestrial DOM to the ocean. Our studies show that terrestrial DOM exposed to simulated sunlight is altered to produce POM with a markedly different molecul...

Two water samples from the Great Dismal Swamp National Wildlife Refuge with high dissolved organic matter (DOM) concentrations (51 and 121 mg C L−1) were subjected to ultraviolet (UV) light for up to 110 days. During the course of the irradiations, 74–88 % of the original dissolved organic carbon was lost along with 95–99 % of the absorption at 300...

Wavelength and temperature-dependent apparent quantum yields (AQYs) were determined for the photochemical production of hydrogen peroxide using seawater obtained from coastal and oligotrophic stations in Antarctica, the Pacific Ocean at Station ALOHA, the Gulf of Mexico, and at several sites along the East Coast of the United States. For all sample...

In this study it was observed that, during long-term irradiations (>1 day) of natural waters, the methods for measuring hydroxyl radical (˙OH) formation rates based upon sequentially determined cumulative concentrations of photoproducts from probes significantly underestimate actual ˙OH formation rates. Performing a correction using the photodegrad...

Dissolved organic matter (DOM) rich water samples (Great Dismal Swamp, Virginia) were 0.1-μm filtered and UV-irradiated in a solar simulator for 30 days. During the irradiation, pH increased, particulate organic matter (POM) and particulate iron formed. After 30 days, 7% of the dissolved organic carbon (DOC) was converted to POC while 75% was remin...

Light is a critical parameter in aquatic ecosystems, affecting primary production and in situ photochemistry. However, measuring light exposure for suspended particles or dissolved components in a dynamic water column can be challenging with existing Eulerian approaches. Here, we assess the simultaneous deployment of two dyes differing in photolabi...

Recent studies suggest that cyanate (OCN-) is a potentially important source of reduced nitrogen (N) available to support the growth of aquatic microbes and thus, may play a role in aquatic N cycling. However, aquatic OCN- distributions have not been previously described because of the lack of a suitable assay for measuring OCN- concentrations in n...

Congo River water was filtered and then irradiated for 57 d in a solar simulator, resulting in extensive photodegradation of dissolved organic matter (DOM). Whole-water (i.e., unfractionated) DOM was analyzed pre- and post-irradiation using ultrahigh resolution Fourier transform ion cyclotron mass spectrometry (FT-ICR MS), revealing the following t...

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June, 1973 The goal of this thesis is to examine the distribution and diagenesis of carbohydrates in aquatic environments. The following questions are studied: what is...

Photochemical mineralization of dissolved organic matter (DOM) plays an important role in the cycling of carbon in estuarine systems. A key to modeling this process is knowledge of apparent quantum yields (AQYs) for the photochemical products. Here we determined spectral AQYs for carbon dioxide (CO2) and carbon monoxide (CO), the main products of D...

Photochemical degradation of Congo River dissolved organic matter (DOM) was investigated to examine the fate of terrigenous DOM derived from tropical ecosystems. Tropical riverine DOM receives greater exposure to solar radiation, particularly in large river plumes discharging directly into the open ocean. Initial Congo River DOM exhibited dissolved...

We identified two regions (275-295 nm and 350-400 nm) within log-linearized absorption spectra of seawater that have distinct spectral slopes. We recently reported that the slope of the short wavelength region (275-295 nm), and the ratio of the slopes (Sr) of the two spectral regions, were related to DOM molecular weight (MW) and to photochemically...

A multi-method approach was applied to study changes in dissolved organic matter (DOM) at three estuarine sites with varying salinity, as well as changes resulting from experimental photodegradation. Following measurement of ultraviolet and visible absorption spectra of bulk samples, DOM was isolated using C18 solid phase extraction. The extract wa...

We evaluated the role of nitrate (NO3−) as a potential photosensitizer and the bacterial responses to dissolved organic matter (DOM) phototransformation from coastal waters in the northwestern Mediterranean Sea. In spring, without any addition of NO3−, the exposure of 0.2μm filtered seawater (DOM-solution) to natural solar radiation (i.e. Full Sun...

We evaluated the role of nitrate (NO3 −) as a potential photosensitizer and the bacterial responses to dissolved organic matter (DOM) phototransformation from coastal waters in the northwestern Mediterranean Sea. In spring, without any addition of NO3 −, the exposure of 0.2�m filtered seawater (DOM-solution) to natural solar radiation (i.e. Full Su...

The Congo River basin drains the second largest area of rainforest in the world and is also the second largest river in terms of catchment size (3,680,000 km2) and freshwater discharge (42,000 m3 s- 1). Congo riverine dissolved organic carbon (DOC) export is estimated at 12.4 Tg DOC yr -1 or approximately 5 % of global riverine DOC export to the oc...

An analytical system was developed to determine photochemically produced carbon dioxide in marine waters. Our system was designed to measure low levels of carbon dioxide by maintaining a closed system to prevent atmospheric contamination during sample preparation, irradiation, and analysis. To detect low levels of photoproduced carbon dioxide in se...

Aqueous solutions of humic substances (HSs) and pure monomeric aromatics were irradiated to investigate the chemical controls upon carbon monoxide (CO) photoproduction from dissolved organic matter (DOM). HSs were isolated from lakes, rivers, marsh, and ocean. Inclusion of humic, fulvic, hydrophobic organic, and hydrophilic organic acid fractions f...

Measuring oxygen to determine primary production (PP) is the oldest method still in common usage. However, the photochemical reaction of molecular oxygen with chromophoric dissolved organic matter (CDOM) represents a sink that can exceed microbial respiration in highly colored surface waters. This interference can be minimized by using containers o...

Direct temperature-resolved mass spectrometry (DT-MS) was used to evaluate the molecular-level photodegradation of dissolved organic matter (DOM) isolated from three sites in a Chesapeake Bay subestuary (swamp- and marsh-influenced up-river, midestuarine, and bay mouth). From each site, filtered (<0.1 or <0.2 μm) water samples were irradiated in so...

A new approach for parameterizing dissolved organic matter ( DOM) ultraviolet-visible absorption spectra is presented. Two distinct spectral slope regions ( 275-295 nm and 350-400 nm) within log-transformed absorption spectra were used to compare DOM from contrasting water types, ranging from wetlands (Great Dismal Swamp and Suwannee River) to phot...

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Measurement of the fluorescence properties of dissolved organic matter (DOM) provides a window into the biological, chemical and physical processes that affect this significant portion of the global carbon pool. Parameters such as fluorescence intensity, quantum yields, peak bandwidth and peak position provide the basis for interpretation of DOM ch...

The biogeochemical cycling of dissolved organic matter (DOM) in natural waters is affected by numerous processes, including photochemical alteration. Photochemical processes result in the net oxidation and mineralization of DOM concomitant with dissolved oxygen consumption and production of dissolved inorganic carbon (DIC; principally CO2). The pho...

The determination of total organic carbon and dissolved organic carbon (TOC and DOC) is one of the most important parameters in water quality and environmental analysis today. TOC is composed of particulate organic carbon, DOC and volatile organic carbon, (POC, DOC and VOC). In most waters, DOC is the dominant component of TOC. POC consists of livi...

We performed laboratory studies to determine the effects of salinity on the photodegradation of dissolved organic matter (DOM) from the Great Dismal Swamp, Virginia, an important source of terrestrial DOM to the lower Chesapeake Bay. Samples were created by mixing Great Dismal Swamp water (ionic strength ≈ 0 mol L_1) with modified artificial seawat...

Sunlight-initiated photolysis of chromophoric dissolved organic matter (CDOM) is the dominant source of carbon monoxide (CO) in the open-ocean. A modelling study was conducted to constrain this source. Spectral solar irradiance was obtained from two models (GCSOLAR and SMARTS2). Water-column CDOM and total light absorption were modelled using spect...

This study addresses how humic substance (HS) chemical composition and photoreactivity affect bacterial growth, respiration, and growth efficiency (BGE) in lake water. Aqueous solutions of HSs from diverse aquatic environments representing different dissolved organic matter sources (autochthonous and allochthonous) were exposed to artificial solar...

Hydrogen peroxide (H2O2) has been studied extensively in the atmosphere and natural waters employing numerous techniques based on absorbance, voltammetry, fluorescence or chemiluminescence. Here we compare the 10-methyl-9-(p-formylphenyl)-acridinium carboxylate trifluoromethanesulfonate chemiluminescent-based (AE-CL) flow-injection analysis (FIA) m...

Characterization of dissolved organic matter (DOM) from aquatic environments has always been constrained by the ability to obtain a representative fraction of the DOM pool for analysis. Ultrafiltration or extraction, commonly using XAD or C18 sorbents, is therefore generally used to concentrate and desalt DOM samples for further analyses. In this s...

Specific UV absorbance (SUVA) is defined as the UV absorbance of a water sample at a given wavelength normalized for dissolved organic carbon (DOC) concentration. Our data indicate that SUVA, determined at 254 nm, is strongly correlated with percent aromaticity as determined by 13C NMR for 13 organic matter isolates obtained from a variety of aquat...

This chapter presents a discussion on photochemistry and the cycling of carbon, sulfur, nitrogen, and Phosphorus. Dissolved organic matter (DOM) plays a dominant role in the absorption of ultraviolet (UV) and visible light in the open ocean. As DOM absorbance is regulated in part by photobleaching processes, light availability for photosynthesis an...

Photochemical production rates and steady-state concentrations of the highly reactive OH radical were determined in Antarctic seawater in the Weddell-Scotia Confluence during the austral spring of 1993 and along the Antarctic Peninsula during the austral summer of 1994. OH radical photoproduction rates were 30±2 nM/day and 46±2 nM/day in surface op...

Photochemical production rates of hydrogen peroxide (H2O2) were determined in Antarctic waters during two research cruises. The first cruise was from mid-October to mid-November, 1993, in the confluence of the Weddell and Scotia Seas, and the second cruise was in December, 1994, along the coast of the Antarctic Peninsula. During these cruises, midd...

A preliminary study was carried out toexamine the feasibility of measuring tropospherichydroxyl radicals (OH) by liquidphase scrubbing andhigh performance liquid chromatography (HPLC). Thepotential advantages of this approach are itssimplicity, portability, and low expense. Thesampling system employs glass bubblers to trapatmospheric OH into a buff...

Ultraviolet (UV) sunlight actinometers were developed based on the photolysis of nitrate and nitrite. Photon exposures (i.e. time-integrated irradiances) were quantified from the photochemical production of salicylic acid (SA) or p-hydroxybenzoic acid (pHBA) formed by the reaction of the hydroxyl radical with benzoic acid. The solar response bandwi...

This book, first published in 2000, provides a comprehensive review of UV radiation effects in the marine environment. A multidisciplinary approach is adopted to discuss all aspects from a physical, chemical and biological perspective. The book begins by describing the attenuation of UV radiation in the atmosphere and sea water, outlining the photo...

Abstract We developed nitrate and nitrite actinometers to determine radiant fluxes from 290 to 410 nm. These actinometers are based on the reaction of the photochemically generated OH radical with benzoic acid to form salicylic acid (SA) and p-hydroxybenzoic acid (pHBA). Actinom-eter development included determination of the temperature and wavelen...

Experiments were performed to examine the role of surface-active polysaccharides in the formation of transparent exopolymer particles (TEP) by bubble adsorption in seawater. Filtered (1 .O pm, 0.45 pm) and ultrafiltered (0.1 pm, 100 kDa, and 10 kDa) seawater samples were bubbled in a glass foam tower. The neutral sugar composition, concentration of...

A free-floating drifter was designed to directly determine in situ photochemical production rates, photolysis rates, and light fluxes in seawater. This drifter consisted of six trays that were suspended in series from a single buoy line. The trays were constructed so that the attached quartz vessels, containing filtered seawater, were exposed to bo...

Coastal and oceanic surface microlayer samples were collected using a stainless steel screen, along with subsurface bulk seawater, and were analyzed for low-molecular-weight (LMW) carbonyl compounds, including formaldehyde, acetaldehyde, propanal, glyoxal, methylglyoxal, glyoxylic acid and pyruvic acid. The enrichment factor in surface microlayer c...

An intercomparison was conducted between 14 different cross-flow filtration (CFF) systems. Each CFF membrane had a 1000 nominal molecular weight cut-off, and five different manufacturers' membranes were tested. The goal of this exercise was to examine whether the different CFF systems were behaving in a well-defined and operationally reproducible m...

Colloid spectroscopic properties, contamination artifacts, and instrumental variability were evaluated during a cross-flow filtration (CFF) intercomparison exercise. Analyses were based on absorbance (at 337 nm), humic and protein fluorescence ( , respectively), absorption and fluorescence spectra, log-linearized and seawater-normalized absorbance...

A high-temperature combustion (HTC) total organic carbon analyzer, which has significant design improvements over existing systems, was developed. The new injection system directly connects a loop-type autoinjector to the head of the HTC column. This connection facilitates the coupling of an autosampler to the injection system. The entire injection...

The concentration of formaldehyde at Mauna Loa Observatory, Hawaii, was determined during four Mauna Loa Observatory Photochemistry Experiment 2 (MLOPEX 2) measurement intensives between September 1991 and August 1992. The observed diurnal variations, 200-900 parts per trillion by volume (pptv) during daytime and 60-200 pptv during nighttime, resul...

Five methods for the measurement of CH2O vapor were compared under remote tropospheric conditions. The techniques included an aqueous-scrubber enzyme fluorescence method (URIcoil), TDLAS (UNI), 2,4-dinitrophenylhydrazine (DNPH) impregnated-cartridges (BNL/WSUcart), an aqueous-scrubber DNPH method (BNL/WSUcoil), and an unpublished aqueous-scrubber i...

The overall goal of the project was to determine the importance of dissolved and colloidal exudates in flocculation of algae in the sea. Thus, during the course of algal blooms, we (1) studied bubble-generated, non-living background particles formed from surface active algal exudates, since these particles appear to play a key role in floc formatio...

A study was undertaken to evaluate the role of exocellular polysaccharides in the flocculation of a marine diatom bloom in a large tank mesocosm. Surface-active organic matter was extracted from 1.0 μ-filtered tank water by bubble adsorption each day for 7 days of the experiment. In agreement with past studies, particles (3–51 urn equivalent spheri...

Formaldehyde, acetaldehyde, acetone, and butanone were measured in 59 samples of marine air. Average clean air background concentrations were about 0.55, 0.50, 0.38, and 0.03 ppbv, respectively, in agreement with past measurements. The formaldehyde concentration is also in agreement with that predicted from photooxidation of methane and other local...

The technique of 3-D fluorescence contouring was applied to samples from the DOC (dissolved organic carbon) Intercalibration Experiment using two different instrument types: a SPEX Fluorolog 2 and a Hitachi F3010. A comparison of results from the two instruments is presented for humic-like and protein-like fluorescence signals. Distinct differences...

Key issues to emerge overall from the detailed discussions include, first of all, the uncertainty of the source and nature of the active oxidant, particularly in HTO methods. This major gap in our understanding of the oxidative processes and yields represents a substantial barrier to further systematic refinement of oxidative methods. A second issu...

Seawater samples from the Hawaiian HOTS station (used in the DOC/DON intercalibration exercise), and from a depth profile from the Sargasso Sea were studied by fluorescence spectroscopy using excitation-emission matrices based on corrected spectra. Our results suggest that marine dissolved organic matter (DOM) fluorescence can be categorized into t...