PRE-PROPOSAL
Macondo 252 Oil Spill Impacts in Louisiana Coastal Wetlands: Effects on SoilMicrobial-Plant Systems
Principal Investigators: Irving A. Mendelssohn1, Aixin Hou2, Qianxin Lin1
1
Department of Oceanography and Coastal Science
2
Department of Environmental Sciences
School of the Coast and Environment, Louisiana State University
Baton Rouge, LA 70808
225 578-6425
imendel@lsu.edu
Background and Justification
The Macondo 252 oil spill resulting from the blowout of the Deepwater Horizon drilling
platform on April 20, 2010 is debatably the largest environmental disaster ever
experienced in the United States, and, without question, the largest oil spill. The release
of an estimated 4.9 million barrels of oil exposed the nation’s largest and most productive
wetland-estuarine environment to an unprecedented potential for environmental damage.
The coastal wetland system, which comprises almost 40% of all coastal wetlands of the
48 conterminous United States, is of special concern because of the suite of
environmentally and economically important services they provide, not only to the
northern Gulf of Mexico, but also to the nation. Most, if not all, of these ecosystem
services are dependent on a healthy, functioning soil-microbial-plant system, which
provides the base for such ecosystem services as hurricane and storm protection, water
quality enhancement, faunal support, sedimentation and carbon sequestration, and many
others. Hence, the critical importance of understanding to what extent the soil-microbialplant system, and dependent ecosystem services, has been impacted by the Macondo 252
oil spill is evident. Thus, our proposed research will address the question: Did the
Macondo 252 Oil Spill cause large-scale perturbations to the structure and function of
soil-microbial-plant ecosystems in the wetlands of the Northern Gulf of Mexico
(NoGM)?
Goals and Objectives:
The primary goal of the proposed research is to assess impact and recovery of the
soil-microbial-plant system to Macondo 252 oil in the realistic field environment and
under more controlled greenhouse conditions. This information will be essential for
estimating degree of damage to coastal ecosystems as well as the potential for
remediation.
Specifically, we shall answer the following questions:
1. What are the effects of the spilled oil on the ecological structure and function of
the soil-microbial-plant system of coastal salt marshes dominated by Spartina
alterniflora and Juncus roemerianus?
2. How do these effects on microbial and plant structure and function differ with
dominant plant species (Spartina or Juncus) and what factors determine any
differential response?
3. What is the relative sensitivity of dominant plant species to different degrees of
oiling and how does mode of oil-exposure (aboveground versus belowground)
control response?
Research Approach
We shall use both field and greenhouse studies to answer the above questions.
Field sites in northern Barataria Basin have already been identified. Field experiments
will employ replicated field sites which have received no to high oiling as determined
from available map data. Greenhouse treatments will include different degrees of oil
coverage of the vegetation and soil. We presently have the necessary oil to do the
greenhouse studies. We shall assess impacts to and recovery of (1) microbial structure
(genomic assessments [see below]) and function (functional genes, denitrification rates
and denitrifying bacteria quantification), (2) marsh vegetation structure (vegetation
species composition, species richness, cover and biomass) and function (above and
below-ground primary productivity, organic matter decomposition, sedimentation,
erosion, soil stability), and (3) soil physico-chemical variables (soil texture, organic
matter, dissolved organic carbon, redox potential, salinity, pH, sulfide, temperature, NH4,
NO3, P, K. Ca, Mg, Na, S, Fe, Mn, Cu, Zn) and oil concentration (TPH and limited GCMS) that will be used to help explain the microbial and plant responses. The above
microbial and vegetation responses will be measured in replicated field and greenhouse
studies. In the field, sites that received low/med, medium/high and no oiling have been
identified and will be used.
Microbial Component
The proposed research will combine field study with greenhouse mesocosm
experiments. Two powerful genomic tools (GeoChip 3.0 and 454 Pyrosequencing) are
now available for monitoring microbial community structure in environmental samples.
The GeoChip is specially designed to provide enhanced capability for studying
biogeochemical processes and functional activities of microbial communities. It is
particularly useful for providing direct linkages of microbial genes/populations to
ecosystem processes and functions. The new version 3.0 contains more than 50,000
probes from genes involved in C, N, S cycling, organic contaminant degradation, and
metal resistance. We will employ the GeoChip analysis to answer the following
questions: (1) what are the effects of the spilled oil on the composition of major
functional genes critical for biogeochemical cycling and natural bacterial processes in
coastal marshes, (2) what are the changes in distribution and diversity of genes that play
critical roles in alkane and PAH degradation (e.g., alkB, ndo, phe, others) in marsh soils
in response to the oil spill, and (3) what is the relative sensitivity of functional genes to
different oiling scenarios on the marsh.
Although understanding the response of the microbial structure to the Macondo oil is
essential, it is equally critical to quantify oil effects on microbial function. An important
microbial function in wetland soil ecosystems is microbial denitrification, the process by
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which nitrate is reduced to gaseous nitrogen forms. This process is important in lowering
plant-available nitrogen, and hence in promoting the ecosystem service of enhanced
water quality. Thus, in addition to the above general characterization of microbial
community structure and function, the proposed research will also determine
denitrification and denitrifying bacteria as impacted by the spilled oil. We will employ
the C2H2 block technique because it is still a widely used and suitable technique for
quantifying denitrification across a large number of sites for comparisons of sites and
experimental treatments. The high phylogenetic diversity among bacterial denitrifiers
makes the use of 16S rDNA-based approaches inappropriate for ecological study of this
group. Genes involved in the denitrification process, such as those coding for nitrite
reductase (nir) or nitrous oxide reductase (nosZ), are directly relevant. We will measure
denitrifying bacteria by quantifying denitrification genes nir and nosZ using quantitative
polymerase chain reaction (QPCR).
Vegetation Component
The vegetation component of the research will be conducted at the same locations
and within the same plots (field and greenhouse) as the microbial component.
Specifically, we shall measure the following vegetation responses to the various
oiling scenarios: plant photosynthetic rate, plant species cover, species composition and
richness, new and old plant stem density, plant canopy height, plant mortality rate, and
live and dead aboveground biomass. In addition, plant oil coverage index, soil physiochemical characteristics such as organic matter, interstitial inorganic elements (NH4,
NO3, P, K, Ca, Mg, Na, Fe, Mn, Cr, Ni, Cu, Pb, Zn, V, pH), salinity, Eh, conductivity,
pH, dissolved and particulate organic matter, soil texture and bulk density, total
petroleum hydrocarbons (TPH), n-alkanes and polycyclic aromatic hydrocarbons (PAHs)
in the composite sediment samples with gas chromatography/mass spectrometry
(GC/MS) will also be analyzed to determine their relationship to marsh structural and
functional responses.
Also, marsh functional processes, such as ecological resilience (a measure of the
rate at which a system recovers from disturbance, above and belowground productivity,
soil organic matter decomposition, sedimentation, soil stability and erosion, and soil
respiration will also be measured to determine their responses to the oil and recovery over
time.
Relevance to NGI General Themes
The proposed research addresses the "Observe" and "Understand" NGI general
themes. All of the experimental and observational data collected will be used to
understand how the oil impacts the soil-microbial-plant system.
Budget: $148,500
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