John H. Pardue

Potential for Enhancement of Biodegradation of Crude Oil in Louisiana Salt Marshes using Nutrient Amendments

Salt marsh ecosystems in Louisiana are at high risk of an oil contamination event while remediation of these systems is mainly limited to intrinsic bioremediation due to the physical sensitivity of salt marshes. This study investigated both the intrinsic and nutrient enhanced rates of crude oil degradation both in microcosm and core studies. In addition, limiting elements, loading rates and optimum nitrogen forms (NH4+ or NO3-) were determined. Salt marshes have relatively low intrinsic degradation rates (0–3.9% day-1) of the alkane component (C11-C44) but high rates (8–16% day-1) of degradation of the polycyclic aromatic hydrocarbon (PAH) fraction (naphthalene, C1, and C2-Naphthalene and Phenanthrene, C1, and C2-Phenanthrene). Additions of nitrogen statistically enhanced degradation of many alkanes and total PAHs while naturally present phosphorous was found to be sufficient. Nitrogen was found to be most effective if applied as NH4+ in the range of 100-500-N mg kg-1 of soil producing a pore water range of 100-670-N mg L-1. Core studies indicate that similar trends are observed when applying fertilizers to intact portions of salt marsh.

Accretion and canal impacts in a rapidly subsiding wetland. I.137Cs and210Pb techniques

The influence of canals on vertical marsh accretion, including mineral sediment and organic matter accumulation, was evaluated at three locations along the Louisiana coast representing different geographic regions. The isotopes210Pb and157Cs were used to determine vertical accretion along transects representing a canal and a control site. Rapid rates of vertical accretion were measured at all sites and ranged from 0.47 cm yr−1 to 0.90 cm yr−1. Results indicated that there was no measurable effect of canals on marsh accretionary processes. In general, greater variation in vertical accretion, including mineral sediment deposition and organic matter accumulation, was observed between geographical regions than between canal and control sites within a region. Statistical analysis of data suggest that any difference between canal and control site would be less than 0.20 cm yr−1. Such a change in marsh surface-water level relationships as a result of any canal influence on marsh accretionary processes would be less than reported eustatic sea-level rise for the Gulf of Mexico. Results suggest that any change in the marsh surface-water level relationship could be the influence of canals on local hydrology, resulting in increased water level rather than any appreciable reduction in accretionary processes. Such changes in hydrology under certain conditions could stress vegetation, resulting in marsh deterioration.

Treatment of chlorinated volatile organic compounds in upflow wetland mesocosms

Sorption, biodegradation and hydraulic parameters were determined in the laboratory for two candidate soil substrate mixtures for construction of an upflow treatment wetland for volatile organic compounds (VOCs) at a Superfund site. The major parent contaminants in the groundwater at the Superfund site were cis-1,2-dichloroethene (cis-1,2-DCE) and 1,1,1-trichloroethane (1,1,1-TCA). The two mixtures; one a mixture of sand and peat, the other a mixture of sand, peat and Bion Soil, a product derived from agricultural wastes; were selected from ten possible mixtures based on the results of hydraulic and geotechnical testing. The sand and peat mixture had an average hydraulic conductivity of 4.95×10−4 cm/s with a critical flow of 39.5 gpm/acre (368 l/min/ha) without fluidization of the bed. The sand, peat and Bion Soil mixture had an average hydraulic conductivity of 3.02×10−4 cm/s with a critical flow of 36.8 gpm/acre (344 l/min/ha) without fluidization of the bed. Retardation coefficients ranged from 1 to 7.3 for target VOCs with higher coefficients observed in the mixture containing the Bion Soil. Consistently higher spatial and temporal first-order removal rate constants were observed in the sand, peat and Bion Soil mixture (cis-1,2-DCE, 0.84±0.36/day; 1,1,1-TCA, 6.52±3.12/day) than in the sand and peat mixture (cis-1,2-DCE, 0.37±0.13/day; 1,1,1-TCA, 1.48±0.42/day). Results from anaerobic microcosm studies confirmed that biodegradation was occurring in the columns and that the sand, peat and Bion Soil mixture had higher degradation rate than the sand and peat mixture. Vinyl chloride (VC) was identified as a ‘design’ contaminant since it is a proven carcinogen and had the lowest removal rate constant for both substrate mixtures. Effective wetland bed depths for VC removal of 900 and 210 cm will be required for peat and sand alone and sand, peat and Bion Soil mixtures, respectively.

An oxidation-reduction buffer for evaluating the physiological response of plants to root oxygen stress

Abstract Zea mays and Spartina patens were grown in nutrient solution containing either an oxidized (+4) or a reduced (+3) form of titanium citrate. Low oxidation-reduction conditions in the nutrient solution as a result of titanium (+3) citrate reduced photosynthetic activity of Zea mays. Photosynthetic activity of flood-tolerant S. patens was initially reduced by the addition of titanium (+3) citrate but subsequently increased, indicating the existence of adaptation mechanisms in S. patens. Titanium citrate was non-toxic since titanium (+4) citrate (oxidized form) added to rooting medium resulted in no reduction in photosynthetic activity of either species. Titanium (+3) citrate may be an excellent non-toxic oxidation-reduction buffering system for evaluating wetland plant response to root oxygen stress.

Fate of petroleum hydrocarbons and toxic organics in Louisiana coastal environments

Numerous potentially toxic compounds are entering Louisiana’s inshore and nearshore coastal environments. To a large degree there is insufficient information for predicting the fate and effect of these materials in aquatic environments. Studies documenting the impact of petroleum hydrocarbons entering Louisiana coastal wetlands are summarized. Also included are research findings on factors affecting the persistence of petroleum hydrocarbons and other toxic organics (pentachlorophenol (PCP), 2,4-dichlorophenoxyacetic acid (2,4-D), creosote, etc.) in sediment-water systems. Sediment pH and redox conditions have been found to play an important role in the microbial degradation of toxic organics. Most of the hydrocarbons investigated degrade more rapidly under high redox (aerobic) conditions although there are exceptions (e.g., 1,1,1-trichloro-2,2-bis(4-chlorophenyl) (DDT) and polychlorobiphenyls (PCBs)). Some of these compounds, due to their slow degradation in anaerobic sediment, may persist in the system for decades.

The influence of soil oxygen deficiency on alcohol dehydrogenase activity, root porosity, ethylene production and photosynthesis in Spartina patens

Abstract Laboratory experiments evaluated root-shoot responses of Spartina patens (Ait) Muhl. to changes in soil redox potential ( Eh ). Three levels of soil redox potential, +460, +230 and −110 mV were imposed in microcosms where plants were grown. Leaf chlorophyll content, gas exchange, root aerenchyma formation, alcohol dehydrogenase (ADH) activity in the roots and ethylene production of leaf and roots in response to the redox treatments were measured. Root responses to hypoxia included a significantly increased porosity and greater ADH activity in hypoxic roots as compared to roots of control (aerated) plants. Ethylene production was significantly greater in leaves and roots of plants under hypoxic treatment compared to control plants. Leaf chlorophyll content was not affected by the treatments; however, stomatal conductance and net carbon assimilation were reduced significantly in response to hypoxia, by 46 and 18%, respectively. Results show a close relationship between root hypoxia, increase in ADH activity, ethylene production and aerenchyma tissue development in S. patens . The enhanced ADH activity and ethylene production found in plants subjected to hypoxia support the postulate that these metabolites have adaptive significance for plants under hypoxic conditions.

Biodegradation of MC252 oil in oil:sand aggregates in a coastal headland beach environment

Unique oil:sand aggregates, termed surface residue balls (SRBs), were formed on coastal headland beaches along the northern Gulf of Mexico as emulsified MC252 crude oil mixed with sand following the Deepwater Horizon spill event. The objective of this study is to assess the biodegradation potential of crude oil components in these aggregates using multiple lines of evidence on a heavily-impacted coastal headland beach in Louisiana, USA. SRBs were sampled over a 19-month period on the supratidal beach environment with reasonable control over and knowledge of the residence time of the aggregates on the beach surface. Polycyclic aromatic hydrocarbons (PAHs) and alkane concentration ratios were measured including PAH/C30-hopane, C2/C3 phenanthrenes, C2/C3 dibenzothiophenes and alkane/C30-hopane and demonstrated that biodegradation was occurring in SRBs in the supratidal. These biodegradation reactions occurred over time frames relevant to the coastal processes moving SRBs off the beach. In contrast, submerged oil mat samples from the intertidal did not demonstrate chemical changes consistent with biodegradation. Review and analysis of additional biogeochemical parameters suggested the existence of a moisture and nutrient-limited biodegradation regime on the supratidal beach environment. At this location, SRBs possess moisture contents <2% and molar C:N ratios from 131–323, well outside of optimal values for biodegradation in the literature. Despite these limitations, biodegradation of PAHs and alkanes proceeded at relevant rates (2–8 year−1) due in part to the presence of degrading populations, i.e., Mycobacterium sp., adapted to these conditions. For submerged oil mat samples in the intertidal, an oxygen and salinity-impacted regime is proposed that severely limits biodegradation of alkanes and PAHs in this environment. These results support the hypothesis that SRBs deposited at different locations on the beach have different biogeochemical characteristics (e.g., moisture, salinity, terminal electron acceptors, nutrient, and oil composition) due, in part, to their location on the landscape.

Potential for intrinsic and enhanced crude oil biodegradation in Louisiana's freshwater marshes.

This study determined the intrinsic rates of biodegradation of Louisiana “sweet” crude oil (LSCO) in aPanicum hemitomon freshwater marsh using kinetic microcosm studies and verified the results in a large intact core study. In addition, the potential to enhance biodegradation using inorganic nutrient additions was determined. These freshwater marsh soils have high intrinsic rates of degradation (2.0%/day) for the measured alkane fraction (C11–C66) and even higher rates (6.8%/day) for the measured polycyclic aromatic hydrocarbon (PAH) fraction (naphthalene, methylated naphthalenes, phenanthrene, and methylated phenanthrenes). However, there were compound-specific effects with intrinsic rates of degradation highest for the smaller alkanes (C<15) (8.5–2.1%/day), while rates for longer chain alkanes (C>15) were much lower (0.7–1.2%/day). Results from the intact core study indicate that these rates are similar to those experiencedin situ, with the exception of the PAH fraction, whose rate constants will be substantially lower than those determined in the kinetic study. Nitrogen (ammonium) was primarily the limiting nutrient and increased degradation rate constants (2–3 fold). Few differences were seen between different classes of alkanes after fertilization. Critical nitrogen loading rates (amount needed to produce significant degradation increases) were similar for both the microcosm and core study (2.2–8.8 mg NH4+-N/g oil), while maximum rates of degradation were observed at higher loading rates (22–44 mg NH4+-N/g oil). While crude oil degradation can be enhanced by fertilization, the benefits need to be weighed against the presence of high intrinsic biodegradation rates in these systems.

Nutrient enhanced biodegradation of crude oil in tropical salt marshes

Tropical salt marshes in Louisiana are at risks ofaccidental oil spills and remediation of these ecosystemsis mainly limited to natural biodegradation due tophysical sensitivity of the ecosystems. This studyinvestigated both intrinsic and nutrient enhanced ratesof crude oil degradation in core studies. In addition,loading rates of nitrogen and optimal porewater nitrogenconcentrations were determined. Nitrogen additionsincreased biodegradation rates of some alkanes andpolycyclic aromatic hydrocarbons (PAHs). Addition ofNH4+-N increased zero-order mineralizationconstants of labeled hexadecane and phenanthrene up to15.4–19.2% (Fourchon marsh) and 56.2% (Ugly Shack Bayoumarsh) and rates of total carbon dioxide production up to14.0–33.1% (Fourchon marsh) and 3.0% (Ugly Shack Bayoumarsh), respectively. Efficient biodegradation of crudeoil was achieved when NH4+ was applied at theloading rate of 28.3–56.6 g N m-2 producing porewaterconcentration at the level of 80–450 mg NH4+-N L-1. No significant lag time was observed indicating thatnitrogen application directly stimulates biodegradationof crude oil in tropical salt marshes in Louisiana.

Sediment addition enhances transpiration and growth of Spartina alterniflora in deteriorating Louisiana Gulf Coast salt marshes

Transpiration, leaf conductance, net photosynthesis, leaf growth, above-ground biomass and regeneration of new culms were studied in a rapidly subsiding Spartina alterniflora Lois. salt marsh following the addition at 47 and 94 Kg m−2 of new sediment. Plant growth was enhanced in response to sediment addition as was evident by a significant increase in leaf area, above-ground biomass production and regeneration of new culms (p ≤ 0.05). Leaf conductance and transpiration rates were significantly greater in sediment treated plants than in control plants (p ≤ 0.05). Enhanced production of culms per unit area of marsh resulted in increased leaf area which allowed a greater capacity for net photosynthesis and contributed to increases in above-ground biomass of sediment treated plots.