Research Article
Deep-Sea Benthic Footprint of the Deepwater Horizon Blowout
Paul A. Montagna mail, * E-mail: paul.montagna@tamucc.edu
Affiliation: Harte Research Institute for Gulf of Mexico Studies, Texas
A&M University-Corpus Christi, Corpus Christi, Texas, United States of
America
X Jeffrey G. Baguley, Affiliation: Department of Biology, University of
Nevada-Reno, Reno, Nevada, United States of America
X Cynthia Cooksey, Affiliation: National Centers for Coastal Ocean Science,
National Oceanic and Atmospheric Administration, Charleston, South Carolina,
United States of America
X Ian Hartwell, Affiliation: National Centers for Coastal Ocean Science,
National Oceanic and Atmospheric Administration, Silver Spring, Maryland, United
States of America
X Larry J. Hyde, Affiliation: Harte Research Institute for Gulf of Mexico
Studies, Texas A&M University-Corpus Christi, Corpus Christi, Texas, United
States of America
X Jeffrey L. Hyland, Affiliation: National Centers for Coastal Ocean
Science, National Oceanic and Atmospheric Administration, Charleston, South
Carolina, United States of America
X Richard D. Kalke, Affiliation: Harte Research Institute for Gulf of
Mexico Studies, Texas A&M University-Corpus Christi, Corpus Christi, Texas,
United States of America
X Laura M. Kracker, Affiliation: National Centers for Coastal Ocean
Science, National Oceanic and Atmospheric Administration, Charleston, South
Carolina, United States of America
X Michael Reuscher, Affiliation: Harte Research Institute for Gulf of
Mexico Studies, Texas A&M University-Corpus Christi, Corpus Christi, Texas,
United States of America
X Adelaide C. E. Rhodes Affiliation: Harte Research Institute for Gulf of
Mexico Studies, Texas A&M University-Corpus Christi, Corpus Christi, Texas,
United States of America
X
Abstract
The Deepwater Horizon (DWH) accident in the northern Gulf of
Mexico occurred on April 20, 2010 at a water depth of 1525 meters, and a
deep-sea plume was detected within one month. Oil contacted and persisted in
parts of the bottom of the deep-sea in the Gulf of Mexico. As part of the
response to the accident, monitoring cruises were deployed in fall 2010 to
measure potential impacts on the two main soft-bottom benthic invertebrate
groups: macrofauna and meiofauna. Sediment was collected using a multicorer so
that samples for chemical, physical and biological analyses could be taken
simultaneously and analyzed using multivariate methods. The footprint of the oil
spill was identified by creating a new variable with principal components
analysis where the first factor was indicative of the oil spill impacts and this
new variable mapped in a geographic information system to identify the area of
the oil spill footprint. The most severe relative reduction of faunal abundance
and diversity extended to 3 km from the wellhead in all directions covering an
area about 24 km2. Moderate impacts were observed up to 17 km towards the
southwest and 8.5 km towards the northeast of the wellhead, covering an area 148
km2. Benthic effects were correlated to total petroleum hydrocarbon, polycyclic
aromatic hydrocarbons and barium concentrations, and distance to the wellhead;
but not distance to hydrocarbon seeps. Thus, benthic effects are more likely due
to the oil spill, and not natural hydrocarbon seepage. Recovery rates in the
deep sea are likely to be slow, on the order of decades or longer.
Citation: Montagna PA, Baguley JG, Cooksey C, Hartwell I, Hyde LJ, et al.
(2013) Deep-Sea Benthic Footprint of the Deepwater Horizon Blowout. PLoS ONE
8(8): e70540. doi:10.1371/journal.pone.0070540
Editor: Fabiano Thompson, Universidade Federal do Rio de Janeiro, Brazil
Received: January 11, 2013; Accepted: June 20, 2013; Published: August 7,
2013
Copyright: © 2013 Montagna et al. This is an open-access article
distributed under the terms of the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided
the original author and source are credited.
Funding: Sample collection during cruises on board R/V Gyre and R/V Ocean
Veritas during the Response phase was funded by BP and NOAA as part of the DWH
Response effort through funds from BP under the direction of the DWH Unified
Area Command (UAC). Sample analysis and production of this paper was funded in
part by contract DG133C06NC1729 from the National Oceanic and Atmospheric
Administration (NOAA) via subcontract 1050-TAMUCC from Industrial Economics as
part of the Deepwater Horizon Oil Spill Natural Resource Damage Assessment
(NRDA). Christopher Lewis (Industrial Economics, Inc.) and Rob Ricker (NOAA)
reviewed and commented on earlier versions of the manuscript. The views
expressed herein are those of the authors and do not necessarily reflect the
views of NOAA or any of its personnel. The study design and scope of work for
the present deep-water/soft-bottom benthic study was approved jointly by
representatives of the DWH NRDA Trustees and BP; neither party had a role in the
corresponding sample processing, data analysis, decision to publish, or
preparation of the manuscript. Pre-approval to submit the manuscript for
publication was provided by representatives of the NRDA Trustees.
Competing interests: The authors have the following interests. Sample
collection during cruises on board R/V Gyre and R/V Ocean Veritas during the
Response phase was partly funded by BP as part of the DWH Response effort
through funds from BP under the direction of the DWH Unified Area Command (UAC).
Christopher Lewis (Industrial Economics, Inc.) reviewed and commented on earlier
versions of the manuscript. The study design and scope of work for the present
deep-water/soft-bottom benthic study was approved jointly by representatives of
the DWH NRDA Trustees and BP. There are no patents, products in development or
marketed products to declare. This does not alter the authors' adherence to all
the PLOS ONE policies on sharing data and materials, as detailed online in the
guide for authors.
snip...
Discussion Diversity and community structure are often used as
bioindicators of community integrity. Since its proposal [21], the N:C ratio has
been regarded as a useful indicator of organic enrichment and pollution. While
the N:C ratio may vary seasonally due to natural fluctuations in food
availability [22] and sediment granulometry [23], it has worked well to classify
impacts of pollution and organic enrichment in field and mesocosm studies [24],
[25], [26]. More recently, and arguably more relevant to the current study, the
N:C has worked well to classify impacts of drilling activities in the Gulf of
Mexico [16]. While natural seasonal pulses of surfaced-derived primary
production could elevate nematode dominance in deep-sea meiobenthic communities,
it is unlikely that seasonality enhanced N:C in the region of the MC252 wellhead
relative to more distant stations at the same depth and in the same general
region of the Gulf of Mexico. Sediment granulometry is nearly constant at all
stations investigated in the current study with >90% silt/clay, and therefore
granulometry is not likely to have an effect on N:C here. Finally, prior surveys
of the meiofauna community throughout the entire northern Gulf of Mexico deep
sea revealed a Gulf-wide N:C mean of 5.7±1.8 across 5 replicate core samples
taken from 51 stations ranging in depth from 200–3500 m [17], [27].
Strong positive correlations of N:C, PAH, TPH, and Ba indicate that
contaminants are correlated to benthic community change in soft-bottom benthos,
and this was reflected in positive scores on the PC1 axis (Fig. 1). The strong
inverse correlations between measures of contaminants and diversity (Mei_N1 and
Mac_N1) on PC1 provide additional evidence of such impacts. Together these
results indicate that PC1 can be used as a new variable to depict the footprint
of oil-spill impacts to the benthos and loss of ecological integrity. Thus PC1
defines the chemical and biological footprint of the oil spill.
The hydrocarbon flow rate from the DWH wellhead is estimated to have been
approximately 10.1±2.0×106 kg/day [3] and as much as 35% of released oil may
have entered the observed deep-sea plume. Model simulations of hydrocarbon
trajectories in the deep-sea indicate a potential for variable flow paths at
different depths [28]. However, direct tracking of the plume and observed oxygen
anomalies in the water column follow an overall trajectory to the southwest
[29], [30] at depths of 1100–1200 m, concordant with predominant deep-water
currents at that depth. The deep-sea oil plume was as much as 200 m thick and 2
km wide in some locations providing a potential mechanism for transfer of DWH
hydrocarbons to deep-sea communities [29].
Several studies have reported on the observed oxygen anomaly in the
deep-sea plume, and the data suggest hydrocarbon-mediated enrichment of
indigenous bacteria within the water column [30], [31], [32]. Similar increases
in bacterial abundance and gene expression have been observed in both deep-sea
plume and coastal marsh investigations [31], [33], [34]. Bacterial blooms may
have resulted in increased dissolved or particulate organic matter flux to
deep-sea sediments, which could possibly enrich benthic communities. While there
have been several coastal studies of benthic microbial dynamics [34], [35], we
are not aware of any deep-sea sediment microbial studies published to date. In
fact, it has already been pointed out that the initial round of studies of the
DWH incident were lacking in deep-sea studies [4].
Increased N:C ratios at stations inside of 15 km from the wellhead indicate
that meiofauna communities exhibited disproportionately high nematode abundance
and dominance in comparison to more distant stations, which is consistent with
an organic enrichment hypothesis. It is not likely that total organic carbon
(TOC) is the enrichment driver because it does not vary much among the stations
and did not explain variance when added to the PCA. The increase in nematode
abundance relative to harpacticoid abundance may be the first evidence for a
community-level trophic response to the possibility that the DWH spill enriched
indigenous bacteria, which would then be available as food for deep-sea infauna.
However, the total number of harpacticoids decreased where nematodes increased,
and while we did not measure sedimentation, it is possible that some infauna was
smothered or covered by spilled oil as well.
It is apparent that the Deepwater Horizon blow out and subsequent oil spill
did adversely affect deep-sea soft-sediment benthos. How long will community
recovery take? Little is known about deep-sea infaunal community recruitment
rates or succession following a disturbance, especially one with lingering
contamination of the substrate. In situ experiments indicate that deep-sea
communities are slow to recolonize clean azoic sediments, taking on the order of
years or longer [36]. Full recovery at impacted stations will require
degradation or burial of DWH-derived contaminants in combination with naturally
slow successional processes. Oil degradation in the marine environment is
limited by temperature, nutrient availability (especially nitrogen and
phosphorous), biodegradability of the petroleum hydrocarbons, presence of
organic carbon, and the presence of microorganisms with oil degrading enzymes
[37], [38]. Recovery of soft-bottom benthos after previous shallow-water oil
spills has been documented to take years to decades [39], [40]. In the deep-sea,
temperature is uniformly around 4°C, and TOC and nutrient concentrations are
low, so it is likely that hydrocarbons in sediments will degrade more slowly
than in the water column or at the surface. Also, metabolic rates of benthos in
the deep-sea are very slow and turnover times are very long [41], [42]. Given
deep-sea conditions, it is possible that recovery of deep-sea soft-bottom
habitat and the associated communities in the vicinity of the DWH blowout will
take decades or longer.
Supporting Information
Gulf Oil Spill Recovery Could Take Decades For Deep-Sea Ecosystem, Study
Finds
Reuters | Posted: 09/24/2013 5:09 pm EDT
WASHINGTON, Sept 24 (Reuters) - The muddy deep-sea ecosystem around the
massive 2010 Gulf of Mexico oil spill could take decades to recover from the
effects of the disaster, researchers reported on Tuesday.
The oil spill from BP Plc's Macondo well had its most severe impact on the
ecosystem in an area about nine square miles (24 square km) around the wellhead,
the report in the online scientific journal PLoS One said.
Moderate effects were seen at 57 square miles (148 square km). The sea
bottom's rich biodiversity was greatly reduced by the oil plume, which was up to
200 yards (183 meters) thick and 1.2 miles (1.9 km) wide, it said.
"Given deep-sea conditions, it is possible that recovery of deep-sea
soft-bottom habitat and the associated communities in the vicinity of the DWH
blowout will take decades or longer," the report concluded.
The April 20, 2010 disaster aboard the Deepwater Horizon drilling rig
killed 11 workers and ruptured the Macondo well, triggering the worst offshore
oil spill in U.S. history.
The research was carried out for the National Oceanic and Atmospheric
Administration. Paul Montagna, an ecosystems professor at Texas A&M
University, said on NOAA's website that normally pollution was found within 300
to 600 yards (meters) of an offshore well.
In the Macondo case, it was found nearly two miles (3.2 km) from the well,
he said.
Jeff Baguley, an expert on tiny marine and freshwater invertebrates from
the University of Nevada, said on the NOAA website that the samples showed that
the dominant group in affected areas had become nematode worms.
The research team included members from University of Nevada-Reno, Texas
A&M, NOAA's National Centers for Coastal Ocean Science and representatives
from BP.
BP should be banned from working in North America, and around the globe, in
my opinion, for gross negligence. after polluting the gulf of Mexico, for 40
days and 40 nights BP spewed benzene into the air we breath where I live,
without even a word to the public, until they got caught. ...
Tuesday, May 14, 2013
Report challenges state pollutant de-listing effort in Texas City
TSS
