Cheryl A. Page

Comparative toxicity of oil, dispersant, and oil plus dispersant to several marine species

Dispersants are a preapproved chemical response agent for oil spills off portions of the U.S. coastline, including the Texas-Louisiana coast. However, questions persist regarding potential environmental risks of dispersant applications in nearshore regions (within three nautical miles of the shoreline) that support dense populations of marine organisms and are prone to spills resulting from human activities. To address these questions, a study was conducted to evaluate the relative toxicity of test media prepared with dispersant, weathered crude oil, and weathered crude oil plus dispersant. Two fish species, Cyprinodon variegatus and Menidia beryllina, and one shrimp species, Americamysis bahia (formerly Mysidopsis bahia), were used to evaluate the relative toxicity of the different media under declining and continuous exposure regimes. Microbial toxicity was evaluated using the luminescent bacteria Vibrio fisheri. The data suggested that oil media prepared with a chemical dispersant was equal to or less toxic than the oil-only test medium. Data also indicated that continuous exposures to the test media were generally more toxic than declining exposures. The toxicity of unweathered crude oil with and without dispersant was also evaluated using Menidia beryllina under declining exposure conditions. Unweathered oil-only media were dominated by soluble hydrocarbon fractions and found to be more toxic than weathered oil-only media in which colloidal oil fractions dominated. Total concentrations of petroleum hydrocarbons in oil-plus-dispersant media prepared with weathered and unweathered crude oil were both dominated by colloidal oil and showed no significant difference in toxicity. Analysis of the toxicity data suggests that the observed toxicity was a function of the soluble crude oil components and not the colloidal oil.

Intrinsic bioremediation of a petroleum-impacted wetland

Following the 1994 San Jacinto River flood and oil spill in southeast Texas, a petroleum-contaminated wetland was reserved for a long-term research program to evaluate bioremediation as a viable spill response tool. The first phase of this program, presented in this paper, evaluated the intrinsic biodegradation of petroleum in the contaminated wetland. Sediment samples from six test plots were collected 11 times over an 11-month period to assess the temporal and spatial petroleum concentrations. Petroleum concentrations were evaluated using gas chromatography-mass spectrometer analyses of specific target compounds normalized to the conservative biological marker, C(30)17alpha,21beta(H)-hopane. The analyses of specific target compounds were able to characterize that significant petroleum biodegradation had occurred at the site over the one-year period. Total resolved saturate and total resolved aromatic hydrocarbon data indicated the petroleum was degraded more than 95%. In addition, first-order biodegradation rate constants were calculated for the hopane-normalized target compounds and supported expected biodegradation patterns. The rapid degradation rates of the petroleum hydrocarbons are attributed to conditions favorable to biodegradation. Elevated nutrient levels from the flood deposition and the unconsolidated nature of the freshly deposited sediment possibly provided a nutrient rich, oxic environment. Additionally, it is suggested that an active and capable microbial community was present due to prior exposure to petroleum. These factors provided an environment conducive for the rapid bioremediation of the petroleum in the contaminated wetland.

Behavior of a chemically-dispersed oil and a whole oil on a near-shore environment

Abstract To investigate the use of dispersants as an oil spill chemical countermeasure in the surf-zone, a simulated oil spill was conducted at the Shoreline Environmental Research Facility (SERF), formerly known as the Coastal OilSpill Simulation System (COSS), a wave tank facility in Corpus Christi, Texas. Sand was added to each tank to establish a beach with a prescribed slope of 10 degrees. Natural seawater flowed continually through the system to emulate alongshore currents. The replicated experimental treatments included pre-mixed oil plus dispersant (three tanks), oil only (three tanks), and unoiled controls (two tanks). Known amounts of either whole oil or dispersed oil were added to the respective tanks. Both the sediment and water column were periodically sampled during the 10-day experiment, and a materials balance on the oil was determined for both oil treatments. The environmental compartments where oil accumulated were sediments, water column, and non-aqueous-phase layer. The discharge from the tanks was presumed to be the primary sink, as water was drawn from the tanks at a known and constant flow rate. Tidal cycles were simulated by varying the computer-controlled influent rate. The oil mass (measured as total petroleum hydrocarbons) for each compartment/sink was calculated using data from four time points. At the experiment’s conclusion, approximately 49% of the applied oil for the oiled treatment remained in the tanks sorbed to sediments or other surfaces. The rest of the oil was removed via the effluent. In the chemically-dispersed oil treatment, all of the oil was flushed from the tanks; no oil (≪1%) remained on the sediments. These studies indicate that a timely dispersant application to spilled oil can reduce residual oil accumulation on beach substrates.

Solubility of petroleum hydrocarbons in oil/water systems

Abstract To elucidate mechanisms, two laboratory-scale experiments were correlated to understand and quantify how oil partitions into the aqueous phase. In the two experiments, free-phase petroleum was exposed to water in an effort to determine aqueous concentrations of various oil components. In the first investigation, an oil/water system was allowed to equilibrate for 16 days. The water column in the system was periodically sampled, and sample analysis was performed by GC-MS. After analyzing for naphthalene and various alkyl-substituted naphthalene compounds, the data was modeled and rate coefficients and the saturation concentrations were predicted. For naphthalene, the modeled saturation concentration was 1.4×10 −6 mol/l , the rate coefficient was 0.239 h −1 and the predicted time to reach equilibrium was 19.3 h. For the alkyl-substituted compounds, there was an inverse correlation between both the rate coefficients and saturation concentrations and the degree of alkyl-substitution. In the second investigation, oil/water systems were allowed to equilibrate for 36 h. Various oil loadings (mass of oil/volume of water) were investigated. The mixing energy was twice that of the first experiment. After the 36 h, the water column was sampled and analyzed by GC-MS. There was a direct correlation between the measured total petroleum hydrocarbon (TPH) concentrations in the water and the oil loading. However, there was no such correlation between the naphthalenes and oil loading. It was concluded that the first experiment was a solubility phenomenon while the second experiment also included a colloidal phenomenon.

Multi-parameter Instrument Array and Control System (MPIACS): a software interface implementation of real-time data acquisition and visualization for environmental monitoring

Recent developments in sensor technology over the past decade have shifted the paradigm in environmental as well as oceanographic sampling and monitoring. The environmental and oceanographic scientific communities continue to deploy more and more in situ sensors either as single-unit deployments for generation of time-series and vertical profiles or as a towed-array for mapping environmental variables in surface waters in multidimensional space. Emergency response activities are also enhanced by way of real-time geo-referenced data acquisition using mobile in situ sensor arrays. Against this backdrop, we developed a software interface for real-time acquisition, analysis and visualization from a towed-array of sensors. This is the Multi-parameter Instrument Array and Control System (MPIACS) described in this paper and was used in the fall of 2002 during a mock oil-spill exercise in Corpus Christi Bay, Texas under he auspices of the Texas General Land Office (TGLO). The interface is designed for correlative visualization along the transect between as many as six state variables or environmental indicators allowing the implementation of adaptive sampling schemes. The software can also be used for scheduled sampling of water quality parameters in surface waters.

A mobile monitoring system to understand the processes controlling episodic events in Corpus Christi Bay

Corpus Christi Bay (TX, USA) is a shallow wind-driven bay and thereby, can be characterized as a highly pulsed system. It cycles through various episodic events such as hypoxia, water column stratification, sediment resuspension, flooding, etc. Understanding of the processes that control these events requires an efficient observation system that can measure various hydrodynamic and water quality parameters at the multitude of spatial and temporal scales of interest. As part of our effort to implement an efficient observation system for Corpus Christi Bay, a mobile monitoring system was developed that can acquire and visualize data measured by various submersible sensors on an undulating tow-body deployed behind a research vessel. Along with this system, we have installed a downward-looking Acoustic Doppler Current Profiler to measure the vertical profile of water currents. Real-time display of each measured parameter intensity (measured value relative to a pre-set peak value) guides in selecting the transect route to capture the event of interest. In addition, large synchronized datasets measured by this system provide an opportunity to understand the processes that control various episodic events in the bay. To illustrate the capability of this system, datasets from two research cruises are presented in this paper that help to clarify processes inducing an inverse estuary condition at the mouth of the ship channel and hypoxia at the bottom of the bay. These measured datasets can also be used to drive numerical models to understand various environmental phenomena that control the water quality of the bay.

A mechanistic dissolved oxygen model of Corpus Christi Bay to understand critical processes causing hypoxia

Corpus Christi Bay (TX, USA) is a shallow wind-driven bay which experiences hypoxia (dissolved oxygen<2 mg/L) during the summer months in the southeast region of the bay. We have developed and installed real-time monitoring systems in the bay to measure various water quality, meteorological and hydrodynamic parameters. These systems can aid in determining the extent and frequency of hypoxic events in this energetic bay. A three-dimensional mechanistic dissolved oxygen model has been developed in this study to investigate the key processes that induce hypoxia in Corpus Christi (CC) Bay. This model includes variable advection and dispersion coefficients so that it can be driven by real-time monitoring hydrodynamic data. The results from model simulations indicate that hypoxia may occur at the lower depths of the bay when both stratification and higher biological activity conditions exist. The water column in the south-east part of the bay becomes stratified during calm wind conditions when there is inflow of hyper-saline water from the neighboring Laguna Madre waterbody. This condition, when combined with higher biological activity during the summer months, induces hypoxia at the lower depths of the bay. The simulation results also point out that physical transport processes have more pronounced effect on the DO distribution within the water column than the effects of biological activity. Therefore, it is necessary to develop suitable sampling strategies that will measure hydrodynamic data at greater spatial and temporal resolution. The integration of this data with our developed model will provide a useful tool to the stakeholders to assess the water quality of the bay in real time.

Sensing the coastal environment

Abstract The spatial and temporal dynamics of near-shore ecosystems are being studied by the Conrad Blucher Institute for Surveying and Science at Texas A&M University-Corpus Christi with special consideration of episodic events associated with anthropogenic activity. Our growing array of estuarine and coastal monitoring stations in the Corpus Christi region supplies real-time, continuous input from a broad array of sensors (physical, chemical and biological) to feed comprehensive converged data sets that in turn foster, in a new context, the interpretation and evaluation of environmental perturba- tions (episodic events) and their ecological effects.

Estimating Colloidal Concentration Using Acoustic Backscatter

Interest has grown for using acoustic Doppler current profilers (ADCPs) to measure suspended solids concentrations (SSC) in aqueous environments because of the ability to make simultaneous unobtrusive long-term multipoint measurements with high spatial and temporal resolutions. The acoustic backscatter intensity (ABS) measured by ADCPs is a function of the particle size distribution, concentration, and incident acoustic signal strength and thus provides the theoretical basis for measuring SSC. The applicability of using ABS from a 2400-kHz ADCP to estimate SSC in units of volume concentration over variable particle size distributions is evaluated in a controlled laboratory study. Results from this research show a log-linear relationship between ABS and volume concentrations over variable size distributions. Volume concentrations predicted from the sonar equation using measured ABS and empirically derived response coefficients compare well with the measured concentrations over the full range of concentrations and particle size distributions tested. The ABS response is shown to be linear with the theoretical Rayleigh scattering target strength, calculated from the empirical particle size distribution, and thus explains the observed linearity over a variable particle size distribution. These results indicate that ABS can be used to provide meaningful volume concentration estimates for characteristically variable colloidal suspensions.

REALTIME GEO-REFERENCED DETECTION OF DISPERSED OIL PLUMES

The current SMART protocol used by the U.S. Coast Guard relies on traditional ex-situ fluorometers that require physical transport of the sample from the water column to the instruments. While samp...