Paul Kepkay

Application of ultraviolet fluorometry and excitation–emission matrix spectroscopy (EEMS) to fingerprint oil and chemically dispersed oil in seawater

Excitation-emission matrix spectroscopy (EEMS) was used to characterize the ultra violet fluorescence fingerprints of eight crude oils (with a 14,470-fold range of dynamic viscosity) in seawater. When the chemical dispersant Corexit 9500 was mixed with the oils prior to their dispersion in seawater, the fingerprints of each oil changed primarily as an increase in fluorescence over an emission band centered on 445 nm. In order to simplify the wealth of information available in the excitation-emission matrix spectra (EEMs), two ratios were calculated. A 66-90% decrease in the slope ratio was observed with the addition of Corexit. When the slope ratios were reduced in complexity to intensity ratios, similar trends were apparent. As a result either of the ratios could be used as a simple and rapid means of identifying and monitoring chemically dispersed oil in the open ocean.

Colloid transport and bacterial utilization of oceanic DOC

Abstract A substantial amount of dissolved organic carbon (DOC) may exist as biologically-labile colloids in seawater, but the way in which bacteria gain access to this globally-significant reservoir of carbon remains unknown. Models of collision efficiency and the transport of colloids to bacteria by Brownian motion, turbulent shear and bacterial swimming suggest that a significant fraction of this carbon could escape degradation by virtue of its particle size characteristics. Collisions between bacteria and colloid-sized particles are influenced primarily by short-range surface and hydrodynamic forces, and bacterial cells are transported least efficiently to particles of their own diameter (≈ 1 gmm). When the models are modified to admit the possibility that bacteria have developed specific strategies to enhance their collision with particles, the transport minimum is forced by bacterial swimming to smaller colloid sizes (between 0.1 and 0.3 μm in diameter). A comparison of modelled transport rates to those derived from respiration measurements suggests that, in natural seawater, the collision efficiency ( E ) between bacteria and colloid-sized particles falls between an upper limit, when E is equal to a maximum of one, and a lower limit, when E is controlled by short-range surface and hydrodynamic forces. This comparison highlights the importance of coagulation and the formation of bacterial-colloid aggregates before larger colloids can be utilized efficiently by the bacteria and recycled to CO 2 by their respiration.

Application of Ultraviolet Fluorescence Spectroscopy to Monitor Oil–Mineral Aggregate Formation

Abstract At an excitation wavelength of 320 nm, the ultraviolet fluorescence (UVF) spectra emitted by reference oils dispersed in seawater with mineral fines yielded two important results: (1) Resuspended negatively-buoyant oil–mineral aggregates (OMAs) exhibited maximum fluorescence at an emission wavelength of 450 nm and, (2) the hydrocarbons dispersed and/or dissolved in the seawater that remained after the aggregates had settled out exhibited maximum fluorescence at 355 nm. Data from UVF analysis (450 nm emission) and microscopical observations of seven reference oils suggest that higher-viscosity oils are less likely to form aggregates with mineral fines. This decline in OMA formation with increased oil viscosity could be predicted from a decrease in the ratio of emission at 450–355 nm. The data suggest that direct UVF spectroscopy of dispersed/dissolved oil and OMAs in seawater can be used to predict and verify the extent of OMA formation.

Colloids and the Ocean Carbon Cycle

Colloidal organic carbon (COC) is a globally significant fraction of dissolved organic carbon (DOC) in the surface ocean. As a non-living but reactive reservoir of carbon, COC outweighs the living carbon stored in marine biomass by a wide margin. Aggregation, respiration and photooxidation are all involved in the removal of COC from surface waters. Despite these removal mechanisms, bioreactive COC can still build up. The end result of the incorporation of this COC into the repeated diurnal cycling of carbon is the accumulation of old, low molecular weight organic carbon (LMWOC) at the expense of younger, more reactive COC. With respect to the sequestration of carbon in deep water, COC is either caught up into aggregates that can sediment out to fuel the deep ocean ecosystem or is converted to less reactive LMWOC that can accumulate prior to deep transport by winter mixing. An understanding of the degree to which aggregation or accumulation is coupled to the net production of DOC is a key requirement for any quantitative description of the ocean carbon cycle.

A Method for Assessing Environmental Risks of Oil-Mineral-Aggregate to Benthic Organisms

ABSTRACT Previous studies have shown that Oil-Mineral-Aggregate (OMA) formation enhances the dispersion of marine oil spills, but the potential impacts of settled OMAs on benthic organisms are not well known. A comprehensive numerical approach is proposed here to model the transport of OMAs and assesses their potential risks. The predicted environmental concentrations (PEC) of settled oil in OMAs was calculated using a random walk particle tracking model and the benchmark concentrations (BCs) of individual hydrocarbon groups were computed based on a equilibrium partitioning (EqP) approach. The likely of risks in terms of Hazard Quotient (HQ) were then determined using a Monte Carlo simulation method. HQ for both aliphatic and aromatic hydrocarbon groups were calculated for OMAs formed with two sediments, Mississippi River Delta (MRD) and Standard Reference Material (SRM). Mean total HQs were also determined by a simple sum of individual HQ. The predicted results from a case study based on a spill of 1000 tons of South Louisiana crude oil in the Gulf of St. Lawrence with a water depth of 80 m show that the SRM is unlikely to cause adverse impacts but this may not be the case for MRD. Furthermore, it has been found that the application of chemical dispersant (CD) increased the risks of MRD but it had little effects on SRM.

Apparent calcite supersaturation at the ocean surface: Why the present solubility product of pure calcite in seawater does not predict the correct solubility of the salt in nature

It is generally accepted that seawaters near the ocean surface are supersaturated with calcite and that increasing atmospheric CO2 will not overcome this condition until late in the 21st century. These expectations are based on comparisons of the ion activity products (IAPs) of various seawaters to the solubility product (K) of seawater saturated with pure calcite at 1 atm and a given temperature. It has been shown in recent papers, however, that calcites in contact with natural seawater in the surface oceans are not pure, but are magnesian calcite compositions. As a result, the presently accepted values of the solubility product of calcite in seawater cannot be used to obtain a correct, or even a reasonable estimate of the saturation state of sea water relative to either pure or magnesian calcite. Data are presented demonstrating that use of the currently accepted solubility product of calcite in seawater to determine seawaters relative calcite saturation leads to gross overestimates of its extent.

Field Trials of in-situ Oil Spill Countermeasures in Ice-Infested Waters

An oil spill response technique in ice-infested waters based on the application of fine minerals in a slurry with mixing by propeller-wash to promote the formation of oilmineral aggregates (OMA) has been proposed. This process promotes the physical dispersion of mineral-fine stabilized oil droplets into the water column that support higher rates of oil degradation by natural bacteria. To validate the operational effectiveness of this technique a controlled oil spill experiment was conducted from a Canadian Coast Guard ice-breaker in the St. Lawrence Estuary (offshore of Matane, Quebec, Canada). Following the release of the test crude oil and the application of experimental treatments, time-series changes in oil concentrations were monitored to quantify dispersion effectiveness. Field samples were also recovered for laboratory microcosm studies on the biodegradation of petroleum hydrocarbons by monitoring CO2 production and the depletion of specific hydrocarbon components. Detailed chemical analysis (GC/MS with hopane normalization) from these studies showed that more than 60% of the total petroleum hydrocarbon, 75-88% of total alkanes, and 55-65% total PAHs, were degraded after 56 days of incubation at 0.5 o C. The alkylated PAH was degraded to a greater extent following the addition of mineral fines. This technique offers several operational advantages as a spill countermeasure for use under Arctic conditions such as reduced numbers of personnel required for its application, no need for waste disposal sites, and cost effectiveness.

Microbial binding of trace metals and radionuclides in sediments: Results from an in situ dialysis technique

Abstract The microbial oxidation of Mn and the microbial binding of 241 Am to a lacustrine sediment were five times greater than the binding effects of abiotic adsorption. In contrast, the microbial enhancement of Cu and 137 Cs binding were far less pronounced, resulting in only a doubling of the effects of adsorption. The microbial binding of trace metals or radionuclides could not be adequately expressed in terms of adsorption coefficients. Instead, binding rates were determined as a more accurate index of short-term processes at work in the sediment.

Microbial manganese oxidation and nitrification in relation to the occurrence of macrophyte roots in a lacustrine sediment

Aquatic macrophytes in the Concretion Cove area of Lake Charlotte, Nova Scotia, Canada appear to restrict microbial manganese oxidation to the production of dispersed, microscopic oxides within sediments. When macrophyte roots are not present in the sediments, large ferromanganese concretions are found at the sediment surface. Macrophyte roots and the manganese oxidizers may have also played a role in the restriction of nitrification to deeper in the sediments.

EFFECTS OF CHEMICAL DISPERSANTS AND MINERAL FINES ON PARTITIONING OF PETROLEUM HYDROCARBONS IN NATURAL SEAWATER

ABSTRACT The interaction of chemical dispersants and suspended sediments with crude oil influences the fate and transport of oil spills in coastal waters. Recent wave tank studies have shown that d...